Prof. Nirit Dudovich's lab reveals how strong light rapidly changes the properties of matter, breaking new ground for ultra-fast computing and communication capabilities.
Instantly transforming a material from opaque to transparent or from conductive to insulating is no longer science fiction – using a powerful, focused beam of light (laser), it has been possible in recent years to rapidly change the properties of the material. Because these changes occur on timescales of attoseconds – billionths of a billionth of a second – they are very difficult to track and understand step by step how they occur. In a new study Published in the magazine Nature photonics Presented by Prof.'s group Nirit Dudovich The Weizmann Institute of Science has developed an innovative method that allows us to track these rapid changes in matter. This development in the study of attosecond processes could lead to various future applications and pave the way for extremely fast communications and calculations.
Anyone who has ever seen a rainbow has actually observed the way light slows down and refracts as it passes through a material (raindrops). Since a ray of sunlight is made up of many light waves of different colors, each of which slows down to a different extent, the hues separate from each other to create a spectacular rainbow. We are used to thinking that a material like glass or water refracts light in a fixed pattern. However, in the new study, Prof. Dudovich's lab noticed that a powerful laser can rapidly change the refractive properties of the material, that is, change the degree to which light passing through it will slow down. The scientists hypothesized that if they could measure the extremely subtle changes in the degree of slowing down, they would be able to learn about the way a powerful laser rapidly changes the properties of the material.
The new method that made the measurement possible was developed under the leadership of research students Omer Kenler, Chen Mor and Noa Yaffe, all from Prof. Dudovich's group in the Department of Physics of Complex Systems at the Weizmann Institute of Science. The measurement is based on two laser beams: one is powerful, consisting of relatively long flashes, whose function is to cause a change in the material; and the other flashes in extremely short flashes of attoseconds and serves as a kind of high-resolution "video camera." After the fast flashes of light pass through the material and slow down, they are brought together with flashes whose properties are known. The scientists analyze the wave obtained from the combination of the two and are able to reconstruct exactly how the degree of deceleration of the light changed as it passed through the material.
Quantum "Wise" and a fast computer
In quantum mechanics, the properties of matter are determined by the energy levels it contains. Electrons, electrically charged particles in matter, can move between the energy levels if they gain or lose just the right amount of energy. A powerful laser changes the properties of matter because it changes the position of the levels on the scale—it can cause two levels to coalesce into one, a single level to split into two, and so on.
Just as navigation applications like "Waze" can estimate how long it will take to travel from one point to another along a route, the new method allows the electron's "travel plan" between energy levels in a material to be reconstructed from the delay time of light. From the electron's journey, scientists learn how the energy levels in the material changed in response to the powerful laser. The scientists initially applied this method to study how the laser beam changes the properties of individual atoms. However, they also present theoretical calculations in the study that show that the method can be used to learn about encounters between light and more complex materials.
"Once we know how to trace the 'journey' of individual electrons between energy levels in a material," says Prof. Dudovich. "We can use light and the knowledge we have gained about its effects to deliberately and precisely change the properties of the material within hundreds or tens of attoseconds. Based on this ability, the fastest processors that can be produced may be developed, which will accelerate by orders of magnitude the rate at which information is transmitted or processed. The new method also has important significance at the level of basic research - we hope that it will help us produce snapshots of electrons as they move, thereby observing a variety of quantum phenomena that were hidden until now."
Also participating in the study were Nikolai D. Klimkin, Prof. Olga Smirnova, Dr. Sergey Pechkovsky and Prof. Mikhail Ivanov from the Max Born Institute in Berlin; Dr. Michael Kruger from the Technion in Haifa; Dr. Doron Azouri from MIT, Cambridge, Massachusetts; Dr. Ayelet G. Ozen-Nerovlansky from Princeton University in New Jersey; Yotam Federman and Dr. Barry D. Brunner from the Department of Physics of Complex Systems at the Institute; Dr. Deborah Rajek and Prof. Yann Myers from the University of Bordeaux in France.
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