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  • richardmitnick 10:26 am on January 21, 2023 Permalink | Reply
    Tags: "Floquet engineering": one technique to manipulate the properties of materials using lasers., , "The Floquet engineering of quantum materials", A class of materials that was found to be particularly promising for studying some of these states are monolayer transition metal dichalcogenides., , HHG-high harmonic generation, , Monolayer transition metal dichalcogenides: 2D materials in single layers of atoms from a transition metal (tungsten or molybdenum) and a chalcogen (sulfur or selenium) arranged into a crystal lattice, , Quantum materials are materials with unique electronic and magnetic or optical properties which are underpinned by the behavior of electrons at a quantum mechanical level., Stanford scientists are revealing the virtual quantum states formed in novel two-dimensional materials subjected to intense laser pulses., , ,   

    From The DOE’s SLAC National Accelerator Laboratory And Stanford University And The University of Rochester Via “phys.org” : “The Floquet engineering of quantum materials” 

    From The DOE’s SLAC National Accelerator Laboratory

    And

    Stanford University Name

    Stanford University

    And

    The University of Rochester

    Via

    “phys.org”

    1.20.23

    1
    Stanford scientists are revealing the virtual quantum states formed in novel two-dimensional materials subjected to intense laser pulses. In the experiments, mid-infrared laser beam is focused to monolayers of tungsten disulfide, where the strong electric field of the laser interacts with excitons—electron-hole pairs therein. Credit: Yuki Kobayashi.

    Quantum materials are materials with unique electronic, magnetic or optical properties, which are underpinned by the behavior of electrons at a quantum mechanical level. Studies have showed that interactions between these materials and strong laser fields can elicit exotic electronic states.

    In recent years, many physicists have been trying to elicit and better understand these exotic states, using different material platforms. A class of materials that was found to be particularly promising for studying some of these states are monolayer transition metal dichalcogenides.

    Monolayer transition metal dichalcogenides are 2D materials that consist in single layers of atoms from a transition metal (e.g., tungsten or molybdenum) and a chalcogen (e.g., sulfur or selenium), which are arranged into a crystal lattice. These materials have been found to offer exciting opportunities for Floquet engineering (a technique to manipulate the properties of materials using lasers) of excitons (quasiparticle electron-hole correlated states).

    Researchers at the SLAC National Accelerator Laboratory, Stanford University and University of Rochester have recently demonstrated the Floquet engineering of excitons driven by strong fields in a monolayer transition metal dichalcogenide. Their findings, presented in a paper in Nature Physics [below], could open new possibilities for the study of excitonic phenomena.

    “Our group has been studying strong-field driven processes such as high-harmonic generation (HHG) in 2D-crystals subjected to intense mid-infrared laser fields,” [Nature Physics (below)] Shambhu Ghimire, one of the researchers who carried out the study, told Phys.org.

    “We are very interested to understand the detailed mechanism of the HHG process, and 2D-crystals seem to be a fascinating platform for this, as they are something in between isolated atoms in the gas phase and the bulk crystals. In the gas phase, the process is understood by considering the dynamics of the laser field ionized electron and its recombination to the parent ion [Physical Review Letters (below)].”

    When exposed to strong laser fields, 2D crystals can host strongly-driven excitons. In their previous research, Ghimire and his colleagues explored whether driving these quasiparticles with strong laser fields and measuring high harmonics would allow them to better understand the solid-state HHG process.

    “While this previous work was the inspiration for our study, we also started measuring the change in absorption on these driven systems and learned more about the non-equilibrium state of the material itself,” Ghimire explained. “Indeed, we find that there are previously not observed absorption features that can be linked to what’s known in the literature as the Floquet states of the materials subjected to strong periodic drives.”

    In their experiments, the researchers used high-power ultrafast laser pulses in the mid-infrared wavelength range to monolayer tungsten disulfide (TMDs). The use of these ultrafast pulses allowed them to avoid the sample damage that typically results from strong light-matter interactions.

    More specifically, the photon energy of mid-infrared laser pulses is around 0.31 eV, which is significantly below the optical bandgap of monolayer TMDs (~2 eV). Therefore, the team did not expect to observe a particularly sizable generation of charge carriers.

    “At the same time, the photon energy in our set up is tunable and can be resonant to exciton energies of the monolayer,” Ghimire said. “To fabricate our material samples, we collaborated with the team of Prof. Fang Liu at Stanford Chemistry. This group has pioneered a new approach [Progress in Surface Science (below)] to fabricate millimeter scale monolayer samples, which was also a key to the success of these experiments.”

    Yuki Kobayashi, a postdoctoral scholar, who is the lead author of the paper said that they unveiled two new mechanisms for creating quantum virtual states in monolayer TMDs. The first of these involves Floquet states, which are attained by mixing the quantum states of materials with external photons, while the second involves the so-called Franz-Keldvsh effect.

    “We found that an originally dark exciton state can be optically bright by mixing with single photon, being manifested as a separate absorption signal below the optical bandgap,” Kobayahsi said. “The second mechanism we unveiled is the dynamic Franz-Keldysh effect. This is caused by the external laser field triggering momentum kick to the excitons, leading to universal blue shift of the spectral features. This effect was observed because we applied a high-field laser pulse (~0.3 V/nm) that is strong enough to break apart the electron-hole pair.”

    Combining the two mechanisms they unveiled, Kobayashi and his colleagues were able to achieve an energy tuning over 100 meV in their sample of monolayer TMDs. These notable results highlight the huge potential of this monolayer transition metal dichalcogenide as a platform to realize strong-field excitonic phenomena.

    “One of the unanswered questions in our work is the real-time response of strong-field excitonic phenomena: how fast can we turn on and off the virtual quantum states?” Ghimire added. “We expect that, by going beyond the perturbative domain, it will be possible to imprint the oscillation patterns of laser carrier waves in the virtual quantum states, approaching the sub-petahertz regime of optical property control.”

    Nature Physics Current
    Nature Physics 2016
    See the above science paper for instructive material with images.
    Physical Review Letters 1993
    Progress in Surface Science 2021

    See the full article here .

    Comments are invited and will be appreciated, especially if the reader finds any errors which I can correct. Use “Reply”.


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    University of Rochester campus

    The University of Rochester is a private research university in Rochester, New York. The university grants undergraduate and graduate degrees, including doctoral and professional degrees.

    The University of Rochester enrolls approximately 6,800 undergraduates and 5,000 graduate students. Its 158 buildings house over 200 academic majors. According to the National Science Foundation , The University of Rochester spent $370 million on research and development in 2018, ranking it 68th in the nation. The University of Rochester is the 7th largest employer in the Finger lakes region of New York.

    The College of Arts, Sciences, and Engineering is home to departments and divisions of note. The Institute of Optics was founded in 1929 through a grant from Eastman Kodak and Bausch and Lomb as the first educational program in the US devoted exclusively to Optics and awards approximately half of all Optics degrees nationwide and is widely regarded as the premier Optics program in the nation and among the best in the world.

    The Departments of Political Science and Economics have made a significant and consistent impact on positivist social science since the 1960s and historically rank in the top 5 in their fields. The Department of Chemistry is noted for its contributions to synthetic Organic Chemistry, including the first lab-based synthesis of morphine. The Rossell Hope Robbins Library serves as The University of Rochester’s resource for Old and Middle English texts and expertise. The university is also home to Rochester’s Laboratory for Laser Energetics, a Department of Energy supported national laboratory.

    The University of Rochester Laboratory for Laser Energetics.

    The University of Rochester’s Eastman School of Music ranks first among undergraduate music schools in the U.S. The Sibley Music Library at Eastman is the largest academic music library in North America and holds the third largest collection in the United States.

    In its history The University of Rochester alumni and faculty have earned 13 Nobel Prizes; 13 Pulitzer Prizes; 45 Grammy Awards; 20 Guggenheim Awards; 5 National Academy of Sciences; 4 National Academy of Engineering; 3 Rhodes Scholarships; 3 National Academy of Inventors; and 1 National Academy of Inventors Hall of Fame.

    History

    Early history

    The University of Rochester traces its origins to The First Baptist Church of Hamilton (New York) which was founded in 1796. The church established the Baptist Education Society of the State of New York later renamed the Hamilton Literary and Theological Institution in 1817. This institution gave birth to both Colgate University and the University of Rochester. Its function was to train clergy in the Baptist tradition. When it aspired to grant higher degrees it created a collegiate division separate from the theological division.

    The collegiate division was granted a charter by the State of New York in 1846 after which its name was changed to Madison University. John Wilder and the Baptist Education Society urged that the new university be moved to Rochester, New York. However, legal action prevented the move. In response, dissenting faculty, students, and trustees defected and departed for Rochester, where they sought a new charter for a new university.

    Madison University was eventually renamed as Colgate University.

    Founding

    Asahel C. Kendrick- professor of Greek- was among the faculty that departed Madison University for The University of Rochester. Kendrick served as acting president while a national search was conducted. He reprised this role until 1853 when Martin Brewer Anderson of the Newton Theological Seminary in Massachusetts was selected to fill the inaugural posting.

    The University of Rochester’s new charter was awarded by the Regents of the State of New York on January 31, 1850. The charter stipulated that The University of Rochester have $100,000 in endowment within five years upon which the charter would be reaffirmed. An initial gift of $10,000 was pledged by John Wilder which helped catalyze significant gifts from individuals and institutions.

    Classes began that November with approximately 60 students enrolled including 28 transfers from Madison. From 1850 to 1862 the university was housed in the old United States Hotel in downtown Rochester on Buffalo Street near Elizabeth Street- today West Main Street near the I-490 overpass. On a February 1851 visit Ralph Waldo Emerson said of the university:

    “They had bought a hotel, once a railroad terminus depot, for $8,500, turned the dining room into a chapel by putting up a pulpit on one side, made the barroom into a Pythologian Society’s Hall, & the chambers into Recitation rooms, Libraries, & professors’ apartments, all for $700 a year. They had brought an omnibus load of professors down from Madison bag and baggage… called in a painter and sent him up the ladder to paint the title “University of Rochester” on the wall, and they had runners on the road to catch students. And they are confident of graduating a class of ten by the time green peas are ripe.”

    For the next 10 years The University of Rochester expanded its scope and secured its future through an expanding endowment; student body; and faculty. In parallel a gift of 8 acres of farmland from local businessman and Congressman Azariah Boody secured the first campus of The University of Rochester upon which Anderson Hall was constructed and dedicated in 1862. Over the next sixty years this Prince Street Campus grew by a further 17 acres and was developed to include fraternity houses; dormitories; and academic buildings including Anderson Hall; Sibley Library; Eastman and Carnegie Laboratories the Memorial Art Gallery and Cutler Union.

    Twentieth century

    Coeducation

    The first female students were admitted in 1900- the result of an effort led by Susan B. Anthony and Helen Barrett Montgomery. During the 1890s a number of women took classes and labs at The University of Rochester as “visitors” but were not officially enrolled nor were their records included in the college register. President David Jayne Hill allowed the first woman- Helen E. Wilkinson- to enroll as a normal student although she was not allowed to matriculate or to pursue a degree. Thirty-three women enrolled among the first class in 1900 and Ella S. Wilcoxen was the first to receive a degree in 1901. The first female member of the faculty was Elizabeth Denio who retired as Professor Emeritus in 1917. Male students moved to River Campus upon its completion in 1930 while the female students remained on the Prince Street campus until 1955.

    Expansion

    Major growth occurred under the leadership of Benjamin Rush Rhees over his 1900-1935 tenure. During this period George Eastman became a major donor giving more than $50 million to the university during his life. Under the patronage of Eastman the Eastman School of Music was created in 1921. In 1925 at the behest of the General Education Board and with significant support for John D. Rockefeller George Eastman and Henry A. Strong’s family medical and dental schools were created. The university award its first Ph.D that same year.

    During World War II The University of Rochester was one of 131 colleges and universities nationally that took part in the V-12 Navy College Training Program which offered students a path to a Navy commission. In 1942, The University of Rochester was invited to join the Association of American Universities as an affiliate member and it was made a full member by 1944. Between 1946 and 1947 in infamous uranium experiments researchers at the university injected uranium-234 and uranium-235 into six people to study how much uranium their kidneys could tolerate before becoming damaged.

    In 1955 the separate colleges for men and women were merged into The College on the River Campus. In 1958 three new schools were created in engineering, business administration and education. The Graduate School of Management was named after William E. Simon- former Secretary of the Treasury in 1986. He committed significant funds to the school because of his belief in the school’s free market philosophy and grounding in economic analysis.

    Financial decline and name change controversy

    Following the princely gifts given throughout his life George Eastman left the entirety of his estate to The University of Rochester after his death by suicide. The total of these gifts surpassed $100 million before inflation and as such The University of Rochester enjoyed a privileged position amongst the most well endowed universities. During the expansion years between 1936 and 1976 The University of Rochester’s financial position ranked third, near Harvard University’s endowment and the University of Texas System’s Permanent University Fund . Due to a decline in the value of large investments and a lack of portfolio diversity The University of Rochester ‘s place dropped to the top 25 by the end of the 1980s. At the same time the preeminence of the city of Rochester’s major employers began to decline.

    In response The University of Rochester commissioned a study to determine if the name of the institution should be changed to “Eastman University” or “Eastman Rochester University”. The study concluded a name change could be beneficial because the use of a place name in the title led respondents to incorrectly believe it was a public university, and because the name “Rochester” connoted a “cold and distant outpost.” Reports of the latter conclusion led to controversy and criticism in the Rochester community. Ultimately, the name “The University of Rochester” was retained.

    Renaissance Plan
    In 1995 The University of Rochester president Thomas H. Jackson announced the launch of a “Renaissance Plan” for The University of Rochester that reduced enrollment from 4,500 to 3,600 creating a more selective admissions process. The plan also revised the undergraduate curriculum significantly creating the current system with only one required course and only a few distribution requirements known as clusters. Part of this plan called for the end of graduate doctoral studies in Chemical Engineering; comparative literature; linguistics; and Mathematics, the last of which was met by national outcry. The plan was largely scrapped and Mathematics exists as a graduate course of study to this day.

    Twenty-first century

    Meliora Challenge

    Shortly after taking office university president Joel Seligman commenced the private phase of the “Meliora Challenge”- a $1.2 billion capital campaign- in 2005. The campaign reached its goal in 2015- a year before the campaign was slated to conclude. In 2016, The University of Rochester announced the Meliora Challenge had exceeded its goal and surpassed $1.36 billion. These funds were allocated to support over 100 new endowed faculty positions and nearly 400 new scholarships.

    The Mangelsdorf Years

    On December 17, 2018 The University of Rochester announced that Sarah C. Mangelsdorf would succeed Richard Feldman as President of the University. Her term started in July 2019 with a formal inauguration following in October during Meliora Weekend. Mangelsdorf is the first woman to serve as President of the University and the first person with a degree in psychology to be appointed to Rochester’s highest office.

    In 2019 students from China mobilized by the Chinese Students and Scholars Association (CSSA) defaced murals in the University’s access tunnels which had expressed support for the 2019 Hong Kong Protests, condemned the oppression of the Uighurs, and advocated for Taiwanese independence. The act was widely seen as a continuation of overseas censorship of Chinese issues. In response a large group of students recreated the original murals. There have also been calls for Chinese government run CSSA to be banned from campus.

    Research

    The University of Rochester is a member of the Association of American Universities and is classified among “R1: Doctoral Universities – Very High Research Activity”.

    The University of Rochester had a research expenditure of $370 million in 2018.

    In 2008 The University of Rochester ranked 44th nationally in research spending but this ranking has declined gradually to 68 in 2018.

    Some of the major research centers include the Laboratory for Laser Energetics, a laser-based nuclear fusion facility, and the extensive research facilities at the University of Rochester Medical Center.

    Recently The University of Rochester has also engaged in a series of new initiatives to expand its programs in Biomedical Engineering and Optics including the construction of the new $37 million Robert B. Goergen Hall for Biomedical Engineering and Optics on the River Campus.

    Other new research initiatives include a cancer stem cell program and a Clinical and Translational Sciences Institute. The University of Rochester also has the ninth highest technology revenue among U.S. higher education institutions with $46 million being paid for commercial rights to university technology and research in 2009. Notable patents include Zoloft and Gardasil. WeBWorK, a web-based system for checking homework and providing immediate feedback for students was developed by The University of Rochester professors Gage and Pizer. The system is now in use at over 800 universities and colleges as well as several secondary and primary schools. The University of Rochester scientists work in diverse areas. For example, physicists developed a technique for etching metal surfaces such as platinum; titanium; and brass with powerful lasers enabling self-cleaning surfaces that repel water droplets and will not rust if tilted at a 4 degree angle; and medical researchers are exploring how brains rid themselves of toxic waste during sleep.

    DOE’s SLAC National Accelerator Laboratory campus

    The DOE’s SLAC National Accelerator Laboratory originally named Stanford Linear Accelerator Center, is a Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the Department of Energy Office of Science and located in Menlo Park, California. It is the site of the Stanford Linear Accelerator, a 3.2 kilometer (2-mile) linear accelerator constructed in 1966 and shut down in the 2000s, which could accelerate electrons to energies of 50 GeV.
    Today SLAC research centers on a broad program in atomic and solid-state physics, chemistry, biology, and medicine using X-rays from synchrotron radiation and a free-electron laser as well as experimental and theoretical research in elementary particle physics, astroparticle physics, and cosmology.

    Founded in 1962 as the Stanford Linear Accelerator Center, the facility is located on 172 hectares (426 acres) of Stanford University-owned land on Sand Hill Road in Menlo Park, California—just west of the University’s main campus. The main accelerator is 3.2 kilometers (2 mi) long—the longest linear accelerator in the world—and has been operational since 1966.

    Research at SLAC has produced three Nobel Prizes in Physics

    1976: The charm quark—see J/ψ meson
    1990: Quark structure inside protons and neutrons
    1995: The tau lepton

    SLAC’s meeting facilities also provided a venue for the Homebrew Computer Club and other pioneers of the home computer revolution of the late 1970s and early 1980s.

    In 1984 the laboratory was named an ASME National Historic Engineering Landmark and an IEEE Milestone.

    SLAC developed and, in December 1991, began hosting the first World Wide Web server outside of Europe.

    In the early-to-mid 1990s, the Stanford Linear Collider (SLC) investigated the properties of the Z boson using the Stanford Large Detector [below].

    As of 2005, SLAC employed over 1,000 people, some 150 of whom were physicists with doctorate degrees, and served over 3,000 visiting researchers yearly, operating particle accelerators for high-energy physics and the Stanford Synchrotron Radiation Laboratory (SSRL) [below] for synchrotron light radiation research, which was “indispensable” in the research leading to the 2006 Nobel Prize in Chemistry awarded to Stanford Professor Roger D. Kornberg.

    In October 2008, the Department of Energy announced that the center’s name would be changed to SLAC National Accelerator Laboratory. The reasons given include a better representation of the new direction of the lab and the ability to trademark the laboratory’s name. Stanford University had legally opposed the Department of Energy’s attempt to trademark “Stanford Linear Accelerator Center”.

    In March 2009, it was announced that the SLAC National Accelerator Laboratory was to receive $68.3 million in Recovery Act Funding to be disbursed by Department of Energy’s Office of Science.

    In October 2016, Bits and Watts launched as a collaboration between SLAC and Stanford University to design “better, greener electric grids”. SLAC later pulled out over concerns about an industry partner, the state-owned Chinese electric utility.

    Accelerator

    The main accelerator was an RF linear accelerator that accelerated electrons and positrons up to 50 GeV. At 3.2 km (2.0 mi) long, the accelerator was the longest linear accelerator in the world, and was claimed to be “the world’s most straight object.” until 2017 when the European x-ray free electron laser opened. The main accelerator is buried 9 m (30 ft) below ground and passes underneath Interstate Highway 280. The above-ground klystron gallery atop the beamline, was the longest building in the United States until the LIGO project’s twin interferometers were completed in 1999. It is easily distinguishable from the air and is marked as a visual waypoint on aeronautical charts.

    A portion of the original linear accelerator is now part of the Linac Coherent Light Source [below].

    Stanford Linear Collider

    The Stanford Linear Collider was a linear accelerator that collided electrons and positrons at SLAC. The center of mass energy was about 90 GeV, equal to the mass of the Z boson, which the accelerator was designed to study. Grad student Barrett D. Milliken discovered the first Z event on 12 April 1989 while poring over the previous day’s computer data from the Mark II detector. The bulk of the data was collected by the SLAC Large Detector, which came online in 1991. Although largely overshadowed by the Large Electron–Positron Collider at CERN, which began running in 1989, the highly polarized electron beam at SLC (close to 80%) made certain unique measurements possible, such as parity violation in Z Boson-b quark coupling.


    Presently no beam enters the south and north arcs in the machine, which leads to the Final Focus, therefore this section is mothballed to run beam into the PEP2 section from the beam switchyard.

    The SLAC Large Detector (SLD) was the main detector for the Stanford Linear Collider. It was designed primarily to detect Z bosons produced by the accelerator’s electron-positron collisions. Built in 1991, the SLD operated from 1992 to 1998.

    SLAC National Accelerator Laboratory Large Detector

    PEP

    PEP (Positron-Electron Project) began operation in 1980, with center-of-mass energies up to 29 GeV. At its apex, PEP had five large particle detectors in operation, as well as a sixth smaller detector. About 300 researchers made used of PEP. PEP stopped operating in 1990, and PEP-II began construction in 1994.

    PEP-II

    From 1999 to 2008, the main purpose of the linear accelerator was to inject electrons and positrons into the PEP-II accelerator, an electron-positron collider with a pair of storage rings 2.2 km (1.4 mi) in circumference. PEP-II was host to the BaBar experiment, one of the so-called B-Factory experiments studying charge-parity symmetry.

    SLAC National Accelerator Laboratory BaBar

    SLAC National Accelerator Laboratory SSRL

    Fermi Gamma-ray Space Telescope

    SLAC plays a primary role in the mission and operation of the Fermi Gamma-ray Space Telescope, launched in August 2008. The principal scientific objectives of this mission are:

    To understand the mechanisms of particle acceleration in AGNs, pulsars, and SNRs.
    To resolve the gamma-ray sky: unidentified sources and diffuse emission.
    To determine the high-energy behavior of gamma-ray bursts and transients.
    To probe dark matter and fundamental physics.

    National Aeronautics and Space Administration Fermi Large Area Telescope

    National Aeronautics and Space Administration Fermi Gamma Ray Space Telescope.

    KIPAC


    KIPAC campus

    The Stanford PULSE Institute (PULSE) is a Stanford Independent Laboratory located in the Central Laboratory at SLAC. PULSE was created by Stanford in 2005 to help Stanford faculty and SLAC scientists develop ultrafast x-ray research at LCLS.

    The Linac Coherent Light Source (LCLS)[below] is a free electron laser facility located at SLAC. The LCLS is partially a reconstruction of the last 1/3 of the original linear accelerator at SLAC, and can deliver extremely intense x-ray radiation for research in a number of areas. It achieved first lasing in April 2009.

    The laser produces hard X-rays, 10^9 times the relative brightness of traditional synchrotron sources and is the most powerful x-ray source in the world. LCLS enables a variety of new experiments and provides enhancements for existing experimental methods. Often, x-rays are used to take “snapshots” of objects at the atomic level before obliterating samples. The laser’s wavelength, ranging from 6.2 to 0.13 nm (200 to 9500 electron volts (eV)) is similar to the width of an atom, providing extremely detailed information that was previously unattainable. Additionally, the laser is capable of capturing images with a “shutter speed” measured in femtoseconds, or million-billionths of a second, necessary because the intensity of the beam is often high enough so that the sample explodes on the femtosecond timescale.

    The LCLS-II [below] project is to provide a major upgrade to LCLS by adding two new X-ray laser beams. The new system will utilize the 500 m (1,600 ft) of existing tunnel to add a new superconducting accelerator at 4 GeV and two new sets of undulators that will increase the available energy range of LCLS. The advancement from the discoveries using these new capabilities may include new drugs, next-generation computers, and new materials.

    FACET

    In 2012, the first two-thirds (~2 km) of the original SLAC LINAC were recommissioned for a new user facility, the Facility for Advanced Accelerator Experimental Tests (FACET). This facility was capable of delivering 20 GeV, 3 nC electron (and positron) beams with short bunch lengths and small spot sizes, ideal for beam-driven plasma acceleration studies. The facility ended operations in 2016 for the constructions of LCLS-II which will occupy the first third of the SLAC LINAC. The FACET-II project will re-establish electron and positron beams in the middle third of the LINAC for the continuation of beam-driven plasma acceleration studies in 2019.

    SLAC National Accelerator Laboratory FACET

    SLAC National Accelerator Laboratory FACET-II upgrading its Facility for Advanced Accelerator Experimental Tests (FACET) – a test bed for new technologies that could revolutionize the way we build particle accelerators.

    The Next Linear Collider Test Accelerator (NLCTA) is a 60-120 MeV high-brightness electron beam linear accelerator used for experiments on advanced beam manipulation and acceleration techniques. It is located at SLAC’s end station B

    SLAC National Accelerator Laboratory Next Linear Collider Test Accelerator (NLCTA)

    SLAC National Accelerator LaboratoryLCLS

    SLAC National Accelerator LaboratoryLCLS II projected view

    Magnets called undulators stretch roughly 100 meters down a tunnel at SLAC National Accelerator Laboratory, with one side (right) producing hard x-rays and the other soft x-rays.

    SSRL and LCLS are DOE Office of Science user facilities.

    Stanford University campus

    Leland and Jane Stanford founded Stanford University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members.

    Stanford University, officially Leland Stanford Junior University, is a private research university located in Stanford, California. Stanford was founded in 1885 by Leland and Jane Stanford in memory of their only child, Leland Stanford Jr., who had died of typhoid fever at age 15 the previous year. Stanford is consistently ranked as among the most prestigious and top universities in the world by major education publications. It is also one of the top fundraising institutions in the country, becoming the first school to raise more than a billion dollars in a year.

    Leland Stanford was a U.S. senator and former governor of California who made his fortune as a railroad tycoon. The school admitted its first students on October 1, 1891, as a coeducational and non-denominational institution. Stanford University struggled financially after the death of Leland Stanford in 1893 and again after much of the campus was damaged by the 1906 San Francisco earthquake. Following World War II, provost Frederick Terman supported faculty and graduates’ entrepreneurialism to build self-sufficient local industry in what would later be known as Silicon Valley.

    The university is organized around seven schools: three schools consisting of 40 academic departments at the undergraduate level as well as four professional schools that focus on graduate programs in law, medicine, education, and business. All schools are on the same campus. Students compete in 36 varsity sports, and the university is one of two private institutions in the Division I FBS Pac-12 Conference. It has gained 126 NCAA team championships, and Stanford has won the NACDA Directors’ Cup for 24 consecutive years, beginning in 1994–1995. In addition, Stanford students and alumni have won 270 Olympic medals including 139 gold medals.

    As of October 2020, 84 Nobel laureates, 28 Turing Award laureates, and eight Fields Medalists have been affiliated with Stanford as students, alumni, faculty, or staff. In addition, Stanford is particularly noted for its entrepreneurship and is one of the most successful universities in attracting funding for start-ups. Stanford alumni have founded numerous companies, which combined produce more than $2.7 trillion in annual revenue, roughly equivalent to the 7th largest economy in the world (as of 2020). Stanford is the alma mater of one president of the United States (Herbert Hoover), 74 living billionaires, and 17 astronauts. It is also one of the leading producers of Fulbright Scholars, Marshall Scholars, Rhodes Scholars, and members of the United States Congress.

    Stanford University was founded in 1885 by Leland and Jane Stanford, dedicated to Leland Stanford Jr, their only child. The institution opened in 1891 on Stanford’s previous Palo Alto farm.

    Jane and Leland Stanford modeled their university after the great eastern universities, most specifically Cornell University. Stanford opened being called the “Cornell of the West” in 1891 due to faculty being former Cornell affiliates (either professors, alumni, or both) including its first president, David Starr Jordan, and second president, John Casper Branner. Both Cornell and Stanford were among the first to have higher education be accessible, nonsectarian, and open to women as well as to men. Cornell is credited as one of the first American universities to adopt this radical departure from traditional education, and Stanford became an early adopter as well.

    Despite being impacted by earthquakes in both 1906 and 1989, the campus was rebuilt each time. In 1919, The Hoover Institution on War, Revolution and Peace was started by Herbert Hoover to preserve artifacts related to World War I. The Stanford Medical Center, completed in 1959, is a teaching hospital with over 800 beds. The DOE’s SLAC National Accelerator Laboratory (originally named the Stanford Linear Accelerator Center), established in 1962, performs research in particle physics.

    Land

    Most of Stanford is on an 8,180-acre (12.8 sq mi; 33.1 km^2) campus, one of the largest in the United States. It is located on the San Francisco Peninsula, in the northwest part of the Santa Clara Valley (Silicon Valley) approximately 37 miles (60 km) southeast of San Francisco and approximately 20 miles (30 km) northwest of San Jose. In 2008, 60% of this land remained undeveloped.

    Stanford’s main campus includes a census-designated place within unincorporated Santa Clara County, although some of the university land (such as the Stanford Shopping Center and the Stanford Research Park) is within the city limits of Palo Alto. The campus also includes much land in unincorporated San Mateo County (including the SLAC National Accelerator Laboratory and the Jasper Ridge Biological Preserve), as well as in the city limits of Menlo Park (Stanford Hills neighborhood), Woodside, and Portola Valley.

    Non-central campus

    Stanford currently operates in various locations outside of its central campus.

    On the founding grant:

    Jasper Ridge Biological Preserve is a 1,200-acre (490 ha) natural reserve south of the central campus owned by the university and used by wildlife biologists for research.

    SLAC National Accelerator Laboratory is a facility west of the central campus operated by the university for the Department of Energy. It contains the longest linear particle accelerator in the world, 2 miles (3.2 km) on 426 acres (172 ha) of land. Golf course and a seasonal lake: The university also has its own golf course and a seasonal lake (Lake Lagunita, actually an irrigation reservoir), both home to the vulnerable California tiger salamander. As of 2012 Lake Lagunita was often dry and the university had no plans to artificially fill it.

    Off the founding grant:

    Hopkins Marine Station, in Pacific Grove, California, is a marine biology research center owned by the university since 1892., in Pacific Grove, California, is a marine biology research center owned by the university since 1892.
    Study abroad locations: unlike typical study abroad programs, Stanford itself operates in several locations around the world; thus, each location has Stanford faculty-in-residence and staff in addition to students, creating a “mini-Stanford”.

    Redwood City campus for many of the university’s administrative offices located in Redwood City, California, a few miles north of the main campus. In 2005, the university purchased a small, 35-acre (14 ha) campus in Midpoint Technology Park intended for staff offices; development was delayed by The Great Recession. In 2015 the university announced a development plan and the Redwood City campus opened in March 2019.

    The Bass Center in Washington, DC provides a base, including housing, for the Stanford in Washington program for undergraduates. It includes a small art gallery open to the public.

    China: Stanford Center at Peking University, housed in the Lee Jung Sen Building, is a small center for researchers and students in collaboration with Beijing University [北京大学](CN) (Kavli Institute for Astronomy and Astrophysics at Peking University(CN) (KIAA-PKU).

    Administration and organization

    Stanford is a private, non-profit university that is administered as a corporate trust governed by a privately appointed board of trustees with a maximum membership of 38. Trustees serve five-year terms (not more than two consecutive terms) and meet five times annually.[83] A new trustee is chosen by the current trustees by ballot. The Stanford trustees also oversee the Stanford Research Park, the Stanford Shopping Center, the Cantor Center for Visual Arts, Stanford University Medical Center, and many associated medical facilities (including the Lucile Packard Children’s Hospital).

    The board appoints a president to serve as the chief executive officer of the university, to prescribe the duties of professors and course of study, to manage financial and business affairs, and to appoint nine vice presidents. The provost is the chief academic and budget officer, to whom the deans of each of the seven schools report. Persis Drell became the 13th provost in February 2017.

    As of 2018, the university was organized into seven academic schools. The schools of Humanities and Sciences (27 departments), Engineering (nine departments), and Earth, Energy & Environmental Sciences (four departments) have both graduate and undergraduate programs while the Schools of Law, Medicine, Education and Business have graduate programs only. The powers and authority of the faculty are vested in the Academic Council, which is made up of tenure and non-tenure line faculty, research faculty, senior fellows in some policy centers and institutes, the president of the university, and some other academic administrators, but most matters are handled by the Faculty Senate, made up of 55 elected representatives of the faculty.

    The Associated Students of Stanford University (ASSU) is the student government for Stanford and all registered students are members. Its elected leadership consists of the Undergraduate Senate elected by the undergraduate students, the Graduate Student Council elected by the graduate students, and the President and Vice President elected as a ticket by the entire student body.

    Stanford is the beneficiary of a special clause in the California Constitution, which explicitly exempts Stanford property from taxation so long as the property is used for educational purposes.

    Endowment and donations

    The university’s endowment, managed by the Stanford Management Company, was valued at $27.7 billion as of August 31, 2019. Payouts from the Stanford endowment covered approximately 21.8% of university expenses in the 2019 fiscal year. In the 2018 NACUBO-TIAA survey of colleges and universities in the United States and Canada, only Harvard University, the University of Texas System, and Yale University had larger endowments than Stanford.

    In 2006, President John L. Hennessy launched a five-year campaign called the Stanford Challenge, which reached its $4.3 billion fundraising goal in 2009, two years ahead of time, but continued fundraising for the duration of the campaign. It concluded on December 31, 2011, having raised a total of $6.23 billion and breaking the previous campaign fundraising record of $3.88 billion held by Yale. Specifically, the campaign raised $253.7 million for undergraduate financial aid, as well as $2.33 billion for its initiative in “Seeking Solutions” to global problems, $1.61 billion for “Educating Leaders” by improving K-12 education, and $2.11 billion for “Foundation of Excellence” aimed at providing academic support for Stanford students and faculty. Funds supported 366 new fellowships for graduate students, 139 new endowed chairs for faculty, and 38 new or renovated buildings. The new funding also enabled the construction of a facility for stem cell research; a new campus for the business school; an expansion of the law school; a new Engineering Quad; a new art and art history building; an on-campus concert hall; a new art museum; and a planned expansion of the medical school, among other things. In 2012, the university raised $1.035 billion, becoming the first school to raise more than a billion dollars in a year.

    Research centers and institutes

    DOE’s SLAC National Accelerator Laboratory
    Stanford Research Institute, a center of innovation to support economic development in the region.
    Hoover Institution, a conservative American public policy institution and research institution that promotes personal and economic liberty, free enterprise, and limited government.
    Hasso Plattner Institute of Design, a multidisciplinary design school in cooperation with the Hasso Plattner Institute of University of Potsdam [Universität Potsdam](DE) that integrates product design, engineering, and business management education).
    Martin Luther King Jr. Research and Education Institute, which grew out of and still contains the Martin Luther King Jr. Papers Project.
    John S. Knight Fellowship for Professional Journalists
    Center for Ocean Solutions
    Together with UC Berkeley and UC San Francisco, Stanford is part of the Biohub, a new medical science research center founded in 2016 by a $600 million commitment from Facebook CEO and founder Mark Zuckerberg and pediatrician Priscilla Chan.

    Discoveries and innovation

    Natural sciences

    Biological synthesis of deoxyribonucleic acid (DNA) – Arthur Kornberg synthesized DNA material and won the Nobel Prize in Physiology or Medicine 1959 for his work at Stanford.
    First Transgenic organism – Stanley Cohen and Herbert Boyer were the first scientists to transplant genes from one living organism to another, a fundamental discovery for genetic engineering. Thousands of products have been developed on the basis of their work, including human growth hormone and hepatitis B vaccine.
    Laser – Arthur Leonard Schawlow shared the 1981 Nobel Prize in Physics with Nicolaas Bloembergen and Kai Siegbahn for his work on lasers.
    Nuclear magnetic resonance – Felix Bloch developed new methods for nuclear magnetic precision measurements, which are the underlying principles of the MRI.

    Computer and applied sciences

    ARPANETStanford Research Institute, formerly part of Stanford but on a separate campus, was the site of one of the four original ARPANET nodes.

    Internet—Stanford was the site where the original design of the Internet was undertaken. Vint Cerf led a research group to elaborate the design of the Transmission Control Protocol (TCP/IP) that he originally co-created with Robert E. Kahn (Bob Kahn) in 1973 and which formed the basis for the architecture of the Internet.

    Frequency modulation synthesis – John Chowning of the Music department invented the FM music synthesis algorithm in 1967, and Stanford later licensed it to Yamaha Corporation.

    Google – Google began in January 1996 as a research project by Larry Page and Sergey Brin when they were both PhD students at Stanford. They were working on the Stanford Digital Library Project (SDLP). The SDLP’s goal was “to develop the enabling technologies for a single, integrated and universal digital library” and it was funded through the National Science Foundation, among other federal agencies.

    Klystron tube – invented by the brothers Russell and Sigurd Varian at Stanford. Their prototype was completed and demonstrated successfully on August 30, 1937. Upon publication in 1939, news of the klystron immediately influenced the work of U.S. and UK researchers working on radar equipment.

    RISCARPA funded VLSI project of microprocessor design. Stanford and University of California- Berkeley are most associated with the popularization of this concept. The Stanford MIPS would go on to be commercialized as the successful MIPS architecture, while Berkeley RISC gave its name to the entire concept, commercialized as the SPARC. Another success from this era were IBM’s efforts that eventually led to the IBM POWER instruction set architecture, PowerPC, and Power ISA. As these projects matured, a wide variety of similar designs flourished in the late 1980s and especially the early 1990s, representing a major force in the Unix workstation market as well as embedded processors in laser printers, routers and similar products.
    SUN workstation – Andy Bechtolsheim designed the SUN workstation for the Stanford University Network communications project as a personal CAD workstation, which led to Sun Microsystems.

    Businesses and entrepreneurship

    Stanford is one of the most successful universities in creating companies and licensing its inventions to existing companies; it is often held up as a model for technology transfer. Stanford’s Office of Technology Licensing is responsible for commercializing university research, intellectual property, and university-developed projects.

    The university is described as having a strong venture culture in which students are encouraged, and often funded, to launch their own companies.

    Companies founded by Stanford alumni generate more than $2.7 trillion in annual revenue, equivalent to the 10th-largest economy in the world.

    Some companies closely associated with Stanford and their connections include:

    Hewlett-Packard, 1939, co-founders William R. Hewlett (B.S, PhD) and David Packard (M.S).
    Silicon Graphics, 1981, co-founders James H. Clark (Associate Professor) and several of his grad students.
    Sun Microsystems, 1982, co-founders Vinod Khosla (M.B.A), Andy Bechtolsheim (PhD) and Scott McNealy (M.B.A).
    Cisco, 1984, founders Leonard Bosack (M.S) and Sandy Lerner (M.S) who were in charge of Stanford Computer Science and Graduate School of Business computer operations groups respectively when the hardware was developed.[163]
    Yahoo!, 1994, co-founders Jerry Yang (B.S, M.S) and David Filo (M.S).
    Google, 1998, co-founders Larry Page (M.S) and Sergey Brin (M.S).
    LinkedIn, 2002, co-founders Reid Hoffman (B.S), Konstantin Guericke (B.S, M.S), Eric Lee (B.S), and Alan Liu (B.S).
    Instagram, 2010, co-founders Kevin Systrom (B.S) and Mike Krieger (B.S).
    Snapchat, 2011, co-founders Evan Spiegel and Bobby Murphy (B.S).
    Coursera, 2012, co-founders Andrew Ng (Associate Professor) and Daphne Koller (Professor, PhD).

    Student body

    Stanford enrolled 6,996 undergraduate and 10,253 graduate students as of the 2019–2020 school year. Women comprised 50.4% of undergraduates and 41.5% of graduate students. In the same academic year, the freshman retention rate was 99%.

    Stanford awarded 1,819 undergraduate degrees, 2,393 master’s degrees, 770 doctoral degrees, and 3270 professional degrees in the 2018–2019 school year. The four-year graduation rate for the class of 2017 cohort was 72.9%, and the six-year rate was 94.4%. The relatively low four-year graduation rate is a function of the university’s coterminal degree (or “coterm”) program, which allows students to earn a master’s degree as a 1-to-2-year extension of their undergraduate program.

    As of 2010, fifteen percent of undergraduates were first-generation students.

    Athletics

    As of 2016 Stanford had 16 male varsity sports and 20 female varsity sports, 19 club sports and about 27 intramural sports. In 1930, following a unanimous vote by the Executive Committee for the Associated Students, the athletic department adopted the mascot “Indian.” The Indian symbol and name were dropped by President Richard Lyman in 1972, after objections from Native American students and a vote by the student senate. The sports teams are now officially referred to as the “Stanford Cardinal,” referring to the deep red color, not the cardinal bird. Stanford is a member of the Pac-12 Conference in most sports, the Mountain Pacific Sports Federation in several other sports, and the America East Conference in field hockey with the participation in the inter-collegiate NCAA’s Division I FBS.

    Its traditional sports rival is the University of California, Berkeley, the neighbor to the north in the East Bay. The winner of the annual “Big Game” between the Cal and Cardinal football teams gains custody of the Stanford Axe.

    Stanford has had at least one NCAA team champion every year since the 1976–77 school year and has earned 126 NCAA national team titles since its establishment, the most among universities, and Stanford has won 522 individual national championships, the most by any university. Stanford has won the award for the top-ranked Division 1 athletic program—the NACDA Directors’ Cup, formerly known as the Sears Cup—annually for the past twenty-four straight years. Stanford athletes have won medals in every Olympic Games since 1912, winning 270 Olympic medals total, 139 of them gold. In the 2008 Summer Olympics, and 2016 Summer Olympics, Stanford won more Olympic medals than any other university in the United States. Stanford athletes won 16 medals at the 2012 Summer Olympics (12 gold, two silver and two bronze), and 27 medals at the 2016 Summer Olympics.

    Traditions

    The unofficial motto of Stanford, selected by President Jordan, is Die Luft der Freiheit weht. Translated from the German language, this quotation from Ulrich von Hutten means, “The wind of freedom blows.” The motto was controversial during World War I, when anything in German was suspect; at that time the university disavowed that this motto was official.
    Hail, Stanford, Hail! is the Stanford Hymn sometimes sung at ceremonies or adapted by the various University singing groups. It was written in 1892 by mechanical engineering professor Albert W. Smith and his wife, Mary Roberts Smith (in 1896 she earned the first Stanford doctorate in Economics and later became associate professor of Sociology), but was not officially adopted until after a performance on campus in March 1902 by the Mormon Tabernacle Choir.
    “Uncommon Man/Uncommon Woman”: Stanford does not award honorary degrees, but in 1953 the degree of “Uncommon Man/Uncommon Woman” was created to recognize individuals who give rare and extraordinary service to the University. Technically, this degree is awarded by the Stanford Associates, a voluntary group that is part of the university’s alumni association. As Stanford’s highest honor, it is not conferred at prescribed intervals, but only when appropriate to recognize extraordinary service. Recipients include Herbert Hoover, Bill Hewlett, Dave Packard, Lucile Packard, and John Gardner.
    Big Game events: The events in the week leading up to the Big Game vs. UC Berkeley, including Gaieties (a musical written, composed, produced, and performed by the students of Ram’s Head Theatrical Society).
    “Viennese Ball”: a formal ball with waltzes that was initially started in the 1970s by students returning from the now-closed Stanford in Vienna overseas program. It is now open to all students.
    “Full Moon on the Quad”: An annual event at Main Quad, where students gather to kiss one another starting at midnight. Typically organized by the Junior class cabinet, the festivities include live entertainment, such as music and dance performances.
    “Band Run”: An annual festivity at the beginning of the school year, where the band picks up freshmen from dorms across campus while stopping to perform at each location, culminating in a finale performance at Main Quad.
    “Mausoleum Party”: An annual Halloween Party at the Stanford Mausoleum, the final resting place of Leland Stanford Jr. and his parents. A 20-year tradition, the “Mausoleum Party” was on hiatus from 2002 to 2005 due to a lack of funding, but was revived in 2006. In 2008, it was hosted in Old Union rather than at the actual Mausoleum, because rain prohibited generators from being rented. In 2009, after fundraising efforts by the Junior Class Presidents and the ASSU Executive, the event was able to return to the Mausoleum despite facing budget cuts earlier in the year.
    Former campus traditions include the “Big Game bonfire” on Lake Lagunita (a seasonal lake usually dry in the fall), which was formally ended in 1997 because of the presence of endangered salamanders in the lake bed.

    Award laureates and scholars

    Stanford’s current community of scholars includes:

    19 Nobel Prize laureates (as of October 2020, 85 affiliates in total)
    171 members of the National Academy of Sciences
    109 members of National Academy of Engineering
    76 members of National Academy of Medicine
    288 members of the American Academy of Arts and Sciences
    19 recipients of the National Medal of Science
    1 recipient of the National Medal of Technology
    4 recipients of the National Humanities Medal
    49 members of American Philosophical Society
    56 fellows of the American Physics Society (since 1995)
    4 Pulitzer Prize winners
    31 MacArthur Fellows
    4 Wolf Foundation Prize winners
    2 ACL Lifetime Achievement Award winners
    14 AAAI fellows
    2 Presidential Medal of Freedom winners

     
  • richardmitnick 10:30 pm on December 5, 2022 Permalink | Reply
    Tags: "Measuring times in billionths of a billionth of a second", A novel interferometric technique capable of measuring time delays with zeptosecond (a trillionth of a billionth of a second) resolution, , , HHG occurs when an electron is removed from a molecule by a strong laser field; is accelerated by the same field and recombines with the ion giving up energy in the form of ultraviolet (XUV) radiation, HHG-high harmonic generation, , , The "Gouy phase": when phase of a light wave is shifted a certain way while going through a focus.   

    From Griffith University (AU): “Measuring times in billionths of a billionth of a second” 

    Griffith U bloc

    From Griffith University (AU)

    12.5.22

    1
    Prof Igor Litvinyuk and Prof Robert Sang.

    How fast do electrons inside a molecule move? Well, it is so fast that it takes them just few attoseconds (1 as = 10^-18 s or one billionth of billionth of a second) to jump from one atom to another. Blink and you missed it – millions of billions of times. So measuring such ultrafast processes is a daunting task.

    Scientists at the Australian Attosecond Science Facility and the Centre for Quantum Dynamics of Griffith University in Brisbane Australia, led by Professor Robert Sang and Professor Igor Litvinyuk have developed a novel interferometric technique capable of measuring time delays with zeptosecond (a trillionth of a billionth of a second) resolution.

    They have used this technique to measure the time delay between extreme ultraviolet light pulses emitted by two different isotopes of hydrogen molecules – H2 and D2 – interacting with intense infrared laser pulses.

    This delay was found to be less than three attoseconds (one quintillionth of a second long) and is caused by slightly different motions of the lighter and heavier nuclei.

    This study has been published in Ultrafast Science [below], a new Science Partner Journal.

    The light waves themselves were generated by molecules exposed to intense laser pulses in the process called high harmonic generation (HHG).

    HHG occurs when an electron is removed from a molecule by a strong laser field, is accelerated by the same field and then recombines with the ion giving up the energy in the form of extreme ultraviolet (XUV) radiation. Both intensity and phase of that XUV HHG radiation are sensitive to exact dynamics of the electron wavefunctions involved in this process – all different atoms and molecules emit HHG radiation differently.

    While it is relatively straightforward to measure spectral intensity of HHG – a simple grating spectrometer can do that – measuring HHG phase is a far more difficult task. And the phase contains the most relevant information about the timing of various steps in the emission process.

    Figure 1
    2
    Three-step model of HHG with the potential energy surfaces of and , and schematics of the Gouy phase interferometric technique. (a) Tunneling ionization launches an electron wave packet together with a nuclear vibrational wave packet. The ionized electron is driven by the laser electric field, and it returns to the parent ion at a certain recollision time. Simultaneously, the nuclear wave packet evolves on the potential energy surface 1 sσg of the ground state of . Upon electron recombination, a photon is emitted with an amplitude and phase dependent on the correlated electron-nuclear dynamics. (b) Two gas jets are placed sequentially with a separation in a single laser focus. Two coherent high-harmonic pulses are generated simultaneously from the top () and bottom () gas jets. A phase difference between the two pulses includes contributions from the Gouy phase shift of the driving laser field at the two jet positions and the intrinsic phase difference between the two species. By measuring HHG yields for different gas configurations and jet separations, these two contributions can be disentangled. The XUV radiation from the first jet has negligible effect on the phase of HHG emission in the second jet as was demonstrated in [23, 24] by measuring dependence of HHG yield on separation between the jets containing the same gas.

    To measure this phase, it is usual to perform a so-called interferometric measurement when two replicas of the wave with finely controlled delay are made to overlap (or interfere) with each other. They can interfere constructively or destructively depending on the delay and relative phase difference between them.

    Such measurement is performed by a device called an interferometer. It is very difficult to build an interferometer for XUV light, in particular to produce and maintain a stable, known and finely tuneable delay between two XUV pulses.

    The Griffith researchers solved this problem by taking advantage of the phenomenon known as the "Gouy phase": when phase of a light wave is shifted a certain way while going through a focus.

    For their experiments the researchers used two different isotopes of molecular hydrogen – the simplest molecule in nature. The isotopes – light (H2) and heavy (D2) hydrogen – differ only in mass of nuclei – protons in H2 and deuterons in D2. Everything else including the electronic structure and energies are identical.

    Due to their larger mass the nuclei in D2 move slightly slower then those in H2. Because nuclear and electronic motions in molecules are coupled, nuclear motion affects the dynamics of the electron wavefunctions during the HHG process resulting in a small phase shift ΔφH2-D2 between the two isotopes.

    3
    Interferomic measurement is at the crux of this research.

    This phase shift is equivalent to a time delay Δt = ΔφH2-D2 /ω where ω is the frequency of the XUV wave. The Griffith scientists measured this emission time delay for all the harmonics observed in the HHG spectrum – it was nearly constant and slightly below 3 attoseconds.

    To understand their result the Griffith researchers were supported by theorists at Shanghai Jiao Tong University in Shanghai, China, led by Professor Feng He.

    The SJTU scientists used the most advanced theoretical methods to comprehensively model the HHG process in the two isotopes of molecular hydrogen including all degrees of freedom for nuclear and electronic motion at various levels of approximation.

    Their simulation reproduced experimental results well, and this agreement between theory and experiment gave the team confidence that the model captured the most essential features of the underlying physical process, so adjusting the model’s parameters and levels of approximation can determine the relative importance of various effects.

    While the actual dynamics is quite complex, it was found that two-centre interference during the electron recombination step is the dominant effect.

    “In the future, this technique can be used to measure ultrafast dynamics of various light-induced processes in atoms and molecules with unprecedented time resolution.”

    Science paper:
    Ultrafast Science

    See the full article here .

    Comments are invited and will be appreciated, especially if the reader finds any errors which I can correct. Use “Reply”.

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Griffith U Campus

    In 1971, Griffith University (AU) was created to be a new kind of university—one that offered new degrees in progressive fields such as Asian studies and environmental science. At the time, these study areas were revolutionary—today, they’re more important than ever.

    Since then, we’ve grown into a comprehensive, research-intensive university, ranking in the top 5% of universities worldwide. Our teaching and research spans five campuses in South East Queensland and all disciplines, while our network of more than 120,000 graduates extends around the world.

    Griffith continues the progressive traditions of its namesake, Sir Samuel Walker Griffith, who was twice the Premier of Queensland, the first Chief Justice of the High Court of Australia, and the principal author of the Australian Constitution.

    Research

    Griffith researchers work in 38 centres and institutes, investigating areas such as water science, climate change adaptation, criminology and crime prevention, sustainable tourism and health and chronic disease.

    The University’s major research institutes include:

    Advanced Design and Prototyping Technologies Institute (ADaPT)
    Australian Rivers Institute
    Cities Research Institute
    Environmental Futures Research Institute
    Griffith Asia Institute
    Griffith Criminology Institute
    Griffith Institute for Educational Research
    Griffith Institute for Tourism
    Institute for Glycomics
    Institute for Integrated and Intelligent Systems
    Menzies Health Institute Queensland (formerly the Griffith Health Institute)
    Griffith Institute for Drug Discovery (GRIDD)

    Additionally, Griffith hosts several externally supported centres and facilities, including:

    Australian Institute for Suicide Research and Prevention
    National Climate Change Adaptation Research Facility
    Smart Water Research Centre
    NHMRC Centre of Research Excellence in Nursing

    Research commercialization

    Griffith offers research commercialization and services for business, industry and government through Griffith Enterprise.

    Other centres

    As well as research centres and institutes, Griffith has a number of cultural and community focused organisations. These include the EcoCentre, which provides a space for environmental education activities, exhibitions, seminars and workshops; and the Centre for Interfaith & Cultural Dialogue (formerly the Multi-Faith Centre).

     
  • richardmitnick 9:34 am on February 3, 2021 Permalink | Reply
    Tags: "A new hands-off probe uses light to explore the subtleties of electron behavior in a topological insulator", , , HHG-high harmonic generation, , ,   

    From DOE’s SLAC National Accelerator Laboratory and : “A new hands-off probe uses light to explore the subtleties of electron behavior in a topological insulator” 

    From DOE’s SLAC National Accelerator Laboratory

    and

    Stanford University Name

    From Stanford University

    February 2, 2021
    Glennda Chui

    Just as pressing a guitar string produces a higher pitch, sending laser light through a material can shift it to higher energies and higher frequencies. Now scientists have discovered how to use this phenomenon to explore quantum materials in a new and much more detailed way.

    1
    Researchers at SLAC National Accelerator Laboratory and Stanford University discovered that focusing intense, circularly polarized laser light on a topological insulator generates harmonics that can be used to probe electron behavior in the material’s topological surface, a sort of electron superhighway where electrons flow with no loss. The technique should be applicable to a wide range of quantum materials. Credit: Greg Stewart/SLAC.

    2
    Laser light is usually linearly polarized, meaning that its waves oscillate in only one direction – up and down, in the example at left. But it can also be circularly polarized, at right, so its waves spiral like a corkscrew around the direction the light is traveling. A new study from SLAC and Stanford predicts that this circularly polarized light can be used to explore quantum materials in ways that were not possible before. Cedit: Greg Stewart/SLAC.

    Topological insulators are one of the most puzzling quantum materials – a class of materials whose electrons cooperate in surprising ways to produce unexpected properties. The edges of a TI are electron superhighways where electrons flow with no loss, ignoring any impurities or other obstacles in their path, while the bulk of the material blocks electron flow.

    Scientists have studied these puzzling materials since their discovery just over a decade ago with an eye to harnessing them for things like quantum computing and information processing.

    Now researchers at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have invented a new, hands-off way to probe the fastest and most ephemeral phenomena within a TI and clearly distinguish what its electrons are doing on the superhighway edges from what they’re doing everywhere else.

    The technique takes advantage of a phenomenon called high harmonic generation, or HHG, which shifts laser light to higher energies and higher frequencies – much like pressing a guitar string produces a higher note – by shining it through a material. ­­By varying the polarization of laser light going into a TI and analyzing the shifted light coming out, researchers got strong and separate signals that told them what was happening in each of the material’s two contrasting domains.

    “What we found out is that the light coming out gives us information about the properties of the superhighway surfaces,” said Shambhu Ghimire, a principal investigator with the Stanford PULSE Institute at SLAC, where the work was carried out.

    “This signal is quite remarkable, and its dependence on the polarization of the laser light is dramatically different from what we see in conventional materials. We think we have a potentially novel approach for initiating and probing quantum behaviors that are supposed to be present in a broad range of quantum materials.”

    The research team reported the results today in Physical Review A.

    Light in, light out

    Starting in 2010, a series of experiments led by Ghimire and PULSE Director David Reis showed HHG can be produced in ways that were previously thought unlikely or even impossible: by beaming laser light into a crystal, a frozen argon gas or an atomically thin semiconductor material. Another study described how to use HHG to generate attosecond laser pulses, which can be used to observe and control the movements of electrons, by shining a laser through ordinary glass.

    In 2018, Denitsa Baykusheva, a Swiss National Science Foundation Fellow with a background in HHG research, joined the PULSE group as a postdoctoral researcher. Her goal was to study the potential for generating HHG in topological insulators – the first such study in a quantum material. “We wanted to see what happens to the intense laser pulse used to generate HHG,” she said. “No one had actually focused such a strong laser light on these materials before.”

    But midway through those experiments, the COVID-19 pandemic hit and the lab shut down in March 2020 for all but essential research. So the team had to think of other ways to make progress, Baykusheva said.

    “In a new area of research like this one, theory and experiment have to go hand in hand,” she explained. “Theory is essential for explaining experimental results and also predicting the most promising avenues for future experiments. So we all turned ourselves into theorists” – first working with pen and paper and then writing code and doing calculations to feed into computer models.

    An illuminating result

    To their surprise, the results predicted that circularly polarized laser light, whose waves spiral around the beam like a corkscrew, could be used to trigger HHG in topological insulators [above].

    “One of the interesting things we observed is that circularly polarized laser light is very efficient at generating harmonics from the superhighway surfaces of the topological insulator, but not from the rest of it,” Baykusheva said. “This is something very unique and specific to this type of material. It can be used to get information about electrons that travel the superhighways and those that don’t, and it can also be used to explore other types of materials that can’t be probed with linearly polarized light.”

    The results lay out a recipe for continuing to explore HHG in quantum materials, said Reis, who is a co-author of the study.

    “It’s remarkable that a technique that generates strong and potentially disruptive fields, which takes electrons in the material and jostles them around and uses them to probe the properties of the material itself, can give you such a clear and robust signal about the material’s topological states,” he said.

    “The fact that we can see anything at all is amazing, not to mention the fact that we could potentially use that same light to change the material’s topological properties.”

    Experiments at SLAC have resumed on a limited basis, Reis added, and the results of the theoretical work have given the team new confidence that they know exactly what they are looking for.

    Researchers from the Max Planck POSTECH/KOREA Research Initiative also contributed to this report. Major funding for the study came from the DOE Office of Science and the Swiss National Science Foundation.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    Stanford University campus. No image credit

    Stanford University

    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

    Stanford University Seal

    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

    SLAC National Accelerator Lab


    SLAC/LCLS


    SLAC/LCLS II projected view

    SLAC LCLS-II Undulators The Linac Coherent Light Source’s new undulators each use an intricately tuned series of magnets to convert electron energy into intense bursts of X-rays. The “soft” X-ray undulator stretches for 100 meters on the left side of this hall, with the “hard” x-ray undulator on the right. Credit: Alberto Gamazo/SLAC National Accelerator Laboratory.

    SSRL and LCLS are DOE Office of Science user facilities.

    3

     
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