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  • richardmitnick 10:43 pm on June 6, 2017 Permalink | Reply
    Tags: Anderson localization, Index of refraction, Nanometric disorder, , , Sensing the Nanoscale with Visible Light, , Wave localization   

    From Technion: “Sensing the Nanoscale with Visible Light” 

    Technion bloc

    Israel Institute of Technology

    06/06/2017
    No writer credit found

    1
    (Comparison) – scale of magnitude: two nearly-identical structures and a Flu virus.

    Sensing the nanoscale with visible light, and the fundamentals of disordered waves

    A general rule in optics is that light is insensitive to features which are much smaller than the optical wavelength. In fact, the whole concept of “index of refraction” arises from the fact that light experiences a medium as a whole, not responding to the individual atoms. However, a new experiment at the Technion-Israel Institute of Technology shows that even features that are more than 100 times smaller than the wavelength can still be sensed by light.

    Published last Thursday in Science, the work – conducted by Hanan Herzig Sheinfux and Dr. Yaakov Lumer from the group of Distinguished Professor Mordechai (Moti) Segev from the Technion, in collaboration with Dr. Guy Ankonina and Prof. Guy Bartal (Technion), and Prof. Azriel Genack (City University of New York), examines a stack of nanometrically thin layers – each layer is on average 20,000 times thinner than a sheet of paper. The exact thickness of the layers is purposely random. Ordinarily, this nanometric disorder should bear no physical importance: light just experiences the average properties, as if this were a homogeneous medium. But, in this experiment, a 2nm (~6 atoms) thickness increase to one single layer somewhere inside the structure is enough to change the amount of light reflected at a specific angle of incidence. Furthermore, the combined effect of all the random variations in all the layers manifests an important physical phenomenon called Anderson localization, but in a regime where it was believed to have vanishingly small effects.

    Wave localization was first discovered in 1958 by Philip W. Anderson, who was awarded the Nobel Prize for it in 1977. Anderson localization is a notoriously difficult effect to demonstrate in the lab. In particular, when the random features of a sample are much smaller than the wavelength, Anderson localization has practically no effect. Indeed, the random arrangement of the atoms in a material such as glass is not observable with visible light: the glass looks completely homogeneous, even under the best optical microscope. But the localization effect seen in this recent experiment is surprisingly potent.

    How is this possible? Imagine being pushed by a mosquito. Normally, mosquitos are too weak to push anything as heavy as a grown person. However, if you happen to be walking on a tightrope, even a relatively small shove can have a large effect – all the other forces are balanced and the effect of the mosquito is still effectively amplified (technically, a mosquito’s shove is so weak, that this amplification would likely be ineffective, but the principle remains). In a crude analogue, while nanometric disorder is very weak, this experiment was conducted near the threshold of total internal reflection – a point of fragile stability, analogous to standing on the tight-rope – and the influence of disorder was effectively amplified.

    These findings are a proof-of-concept which may pave the way for major new applications in sensing. This approach may allow the use of optical methods to make measurements of nanometric defects in computer chips and photonic devices. Since such an optical approach is expected to be faster and less expensive than measurements using electrons or X-rays, these results have a significant potential impact for manufacturing technology and basic science.

    See the full article here .

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    Technion Campus

    A science and technology research university, among the world’s top ten,
    dedicated to the creation of knowledge and the development of human capital and leadership,
    for the advancement of the State of Israel and all humanity.

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  • richardmitnick 4:39 pm on June 4, 2017 Permalink | Reply
    Tags: Anderson localization, Angle of incidence, , CUNY, Discovery of electron localization in 1958, Disorder turns a system from a conductor to an insulator, Features that are even 100 times smaller than the wavelength can still be sensed by light, , , Science Daily, Sensing the nanoscale with visible light and the fundamentals of disordered waves,   

    From Technion via Science Daily: “Sensing the nanoscale with visible light, and the fundamentals of disordered waves” 

    Technion bloc

    Technion

    1

    Science Daily

    2
    The multilayer stack is grown on a prism and covered with an absorbing Pt layer. A laser beam is incident at angle q on the prism, and the output reflection is measured by a charge-coupled device. Credit: Azriel Genack

    June 1, 2017
    No writer credit found

    We cannot see atoms with the naked eye because they are so small relative to the wavelength of light. This is an instance of a general rule in optics — light is insensitive to features which are much smaller than the optical wavelength. However, a new experiment appearing in Science shows that features that are even 100 times smaller than the wavelength can still be sensed by light.

    Features that are even 100 times smaller than the wavelength can still be sensed by light, a new experiment shows.

    Hanan Sheinfux and Dr. Yaakov Lumer, from the group of Prof. Moti Segev at the Technion -Technical Institute of Israel, carried out this study in collaboration with Dr. Guy Ankonina and Prof. Guy Bartal (Technion) and Prof. Azriel Genack (City University of New York).

    Their work examines a stack of nanometrically thin layers — each layer is on average 20,000 times thinner than a sheet of paper. The exact thickness of the layers is purposely random, and ordinarily this nanometric disorder should bear no physical importance. But this experiment shows that even a 2nm (~6 atoms) thickness increase to one single layer somewhere inside the structure can be sensed if light illuminates the structure at a very specific angle of incidence. Furthermore, the combined effect of all the random variations in all of the layers manifests an important physical phenomenon called Anderson localization, but in a regime where it was believed to have vanishingly small effects.

    “This work demonstrates that light can be trapped in structures much thinner than the wavelength of light and that minute changes in this structure are observable,” said Dr. Genack. “This makes the structure highly sensitive to the environment.”

    The discovery of electron localization in 1958, for which Anderson was awarded the Nobel Prize in 1977, is the phenomenon where disorder turns a system from a conductor to an insulator. The phenomenon has been shown to be a general wave phenomenon and to apply to light and sound as well as to electrons. Anderson localization is a notoriously difficult effect to demonstrate in the lab. Generally, localization has practically no effect when random features of a sample are much smaller than the wavelength. Indeed, the random arrangement of the atoms in a disordered medium such as glass is not observable with visible light: the glass looks completely homogeneous, even under the best optical microscope. However, the localization effect seen in this recent experiment is surprisingly potent.

    As a crude analogue to the physics enabling these results, try speaking to a friend in the same room with a loud engine. One way to be heard is to raise your voice above the sound of the engine. But it might also be possible to speak if you can find a quiet spot in the noise, where the engine’s sound is relatively weak. The engine’s sound is analogue to the “average” influence of the layers and raising your voice is the same as using “strong” disorder with wavelength-sized components. However, this experiment has demonstrated such structures exhibit an “exceptional point” which is equivalent to the quiet spot in the room. It is a point where, even if the disorder is weak (nanometric), the average effect of the structure is even weaker. The parts of the experiment performed in the vicinity of this point therefore show an enhanced sensitivity to disorder and exhibit Anderson localization.

    These findings are a proof-of-concept which may pave the way for major new applications in sensing. This approach may allow the use of optical methods to make high-speed measurements of nanometric defects in computer chips and photonic devices.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Technion Campus

    A science and technology research university, among the world’s top ten,
    dedicated to the creation of knowledge and the development of human capital and leadership,
    for the advancement of the State of Israel and all humanity.

     
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