From The Chinese Academy of Sciences [中国科学院](CN)
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January 4, 2022
Schematics of surface Dyakonov-Čerenkov radiation. b, Field pattern of Čerenkov radiation with Dyakonov surface waves. c-d, Field patterns of Čerenkov radiation without Dyakonov surface waves. Credit: Hao, Hu, Lin, Yu Luo.
Recently, the research team led by Prof. Yu Luo from the school of Electrical and Electronic Engineering, The Nanyang Technological University [நன்யாங் தொழில்நுட்ப](SG), discovered surface Dyakonov-Čerenkov radiation. This new type of Čerenkov radiation not only presages the next generation of miniaturized Čerenkov detectors, but also provides an indispensable route to detect particle trajectory. Moreover, this work offers a feasible route to excite Dyakonov surface waves, opening a new area of research in Dyakonov surface optics.
Čerenkov radiation refers to the photon emission from the swift charged particle moves with the velocity greater than the phase velocity of light in the surrounding materials. Ever since its experimental observation by a Soviet physicist P.A. Čerenkov in 1934, Čerenkov radiation has been widely explored and applied in many research fields ranging from cosmology and information, to medical and life sciences. Among all these applications, the detection of high-energy particles (i.e., identifying the type of detected particles from the direction of the photon emission) is the most important one. With the help of Čerenkov radiation, scientists discovered many elementary particles including anti-proton and J-particle. Owing to its impacts on both the fundamental research and practical applications, Čerenkov radiation and its related applications were awarded at least six Nobel Prizes in Physics (in 1958, 1959, 1988, 1995, 2002 and 2015, respectively).
Although Čerenkov detectors are widely used in the high-energy and particle physics, their bulky sizes hinder their applications to emerging research fields such as particle detection on chip. Thus, achieving miniaturized particle detectors could potentially broadens the applications of Čerenkov detection. Surface waves propagating at the interface of two different materials provide a possible solution towards this goal.
Generally speaking, there are two major branches of surface waves in nature: surface plasmons propagating along the metallodielectric interface; and Dyakonov surface waves propagating along the surface of a birefringent material.
Since the 1950s, surface plasmons have been widely applied to surface-enhanced Raman spectroscopy, surface-enhanced sensing, and surface-enhanced fluorescence, etc. Recently, surface plasmons were deployed to enhance Čerenkov radiation and achieve integrated Čerenkov light sources (Nature Photonics). Nevertheless, the implementation of a miniaturized Čerenkov detector with surface plasmons is still challenging, mainly for two reasons: (1) The significant metallic dissipation hinders the detection of Čerenkov signals in the far field; (2) The strong chromatic dispersion of plasmons presents an inherent limit on the working bandwidth of the detector. On the contrary, Dyakonov surface waves can be excited in an all-dielectric platform with negligible dissipation loss and weak chromatic dispersion. Despite these advantages, applications of Dyakonov surface waves have been thus far quite limited due to the lack of an efficient excitation mechanism.
This research team led by Prof. Yu Luo from Nanyang Technological University has uncovered a new type of free-electron radiations, namely surface Dyakonov-Čerenkov radiation. It is achieved by exploring the interaction between the free charged particle and Dyakonov surface waves. Such a discovery not only facilitates the development of miniaturized Čerenkov detectors, but may also inspires future explorations of Dyakonov surface waves.
The research team investigated the emission behaviors of a swift charged particle moving atop the surface of a birefringent crystal. They found that when the particle velocity and trajectory fulfill a specific condition, the swift charged particle allows for efficient photon emission in terms of Dyakonov surface waves.
Surface Dyakonov-Čerenkov radiation is one of the best candidates for achieving miniaturized particle detectors on a chip. First, Dyakonov surface waves can significantly enhance the photon emission, offering a feasible route to reduce the interaction length of the swift charged particle and matter. Second, due to the negligible dissipation loss and weak chromatic dispersion of Dyakonov surface waves, the emitted photons can be readily collected in the far field.
Remarkably, the research team also found that the excitation of surface Dyakonov-Čerenkov radiation is highly sensitive to both the particle trajectory and velocity value. Only when the particle trajectory falls within the vicinity of a particular direction, the surface Dyakonov-Čerenkov radiation is allowed. Such a unique property results from the directional nature of Dyakonov surface waves. It allows the surface Dyakonov-Čerenkov radiation to detect the particle trajectory, with the accuracy up to 10 mrad.
The surface Dyakonov-Čerenkov radiation studied in this work also bridges the research gap between Čerenkov radiation and Dyakonov surface waves, and may produce far-reaching impacts on both areas. In the realm of Čerenkov radiation, this work not only facilitates the development of next-generation miniaturized Čerenkov detectors, but also offers a unique technique to track and collimate the particle beams, which is highly desired in nonlinear, ultrafast and quantum optics. In the realm of Dyakonov surface waves, the efficient excitation mechanism revealed in this work may open a new research area of Dyakonov surface optics.
Science paper:
Light: Science & Applications
See the full article here .
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The Chinese Academy of Sciences [中国科学院](CN) is the national academy for the natural sciences of the People’s Republic of China [中华人民共和国Zhōnghuá rénmín gònghéguó]. It has historical origins in the Academia Sinica during the Republican era and was formerly also known by that name. Collectively known as the “Two Academies (两院)” along with the Chinese Academy of Engineering, it functions as the national scientific think tank and academic governing body, providing advisory and appraisal services on issues stemming from the national economy, social development, and science and technology progress. It is headquartered in Xicheng District, Beijing with branch institutes all over mainland China. It has also created hundreds of commercial enterprises, Lenovo being one of the most famous.
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