A physical and engineering breakthrough offers a more effective method than the currently existing techniques for reducing the phenomenon of light reflection
When a light beam passes from one medium to another, even if both are transparent (such as from air to glass), part of the light intensity is reflected and part passes through. This phenomenon, which is expressed for example in the reflection we see when looking outside in the hours of darkness from a lighted room through the window, is a general phenomenon of wave propagation and also exists in radio waves, microwaves, sound waves, pressure waves, and even in the wave functions that describe quantum particles.
"The partial reflection phenomenon is due to the fact that different mediators have different optical properties," explains Prof. Kobi Shuyer. "For example, the partial reflection from the window glass is due to the fact that the speed of light in the air and in the glass are different - the light moves slower through the glass. The echo phenomenon we hear near cliffs stems from a similar reason - sound waves can easily move through solid materials, at a higher speed than their speed in air. The difference between the speed of sound in the air and in the rock causes a partial reflection of the sound waves and is what creates the echo."
A new study offers an innovative method for eliminating the reflection of light waves from surfaces, which prevents the reflection of a wide range of wavelengths or frequencies. The research was conducted under the leadership of Prof. Kobi Shoyer and Prof. Pavel Ginzburg From the School of Electrical Engineering at the Ivy and Alder Fleishman Faculty of Engineering, in collaboration with Dr. Dmitry Filonov from the Institute of Physics and Technology in Moscow, and was recently published in the prestigious journal Optics Express.
neutralize the interfering factor
In many cases, the researchers point out, the partial return phenomenon is a disturbing factor. In complex observation and optics systems such as a microscope, the partial reflection phenomenon can cause a dramatic reduction in the light intensity reaching the human eye or the detector, thus significantly impairing the system's performance. To provide a solution to the partial return phenomenon over a wide frequency range, the researchers approached the problem from a completely different direction.
Prof. Shoyer elaborates: "In general, in order to reduce the phenomenon of partial reflection, an 'anti-reflection coating' can be used. This coating functions as a resonator that causes constructive interference of the light in the forward direction and destructive interference in the backward direction, and thus the degree of reflection decreases. Coatings of this type can be found in a wide variety of optical and acoustic systems, and even in eyeglasses. The main disadvantage of the method is its limited efficiency, which is suitable for a single frequency, this is the resonance frequency."
In systems required to handle a range of wavelengths or frequencies, for example eyeglasses or a microscope, the existing method does not completely eliminate the partial reflection of light. In principle, the method can be extended to treat a range of wavelengths or frequencies, by assembling a coating that includes several layers of different materials and thicknesses, but in practice it is very difficult to design multi-layer coatings because a complicated optimization of the thickness of the layers and their properties is required.
Nice to meet you: "White Light Resonator"
In order to overcome the efficiency limitation of the existing methods, the researchers developed a device known as a "white light resonator". According to Prof. Shoyer, "Unlike normal resonators, which are characterized by a specific and limited number of resonant frequencies, the new resonator is able to respond to a continuous range of frequencies." The idea behind the new method is to use the unique properties of the resonator with white light in order to create a destructive interference of the reflected waves over the entire resonance range of the resonator and in this way cancel them. The realization of the special resonator is made possible thanks to the combination of several layers with different optical properties, but unlike the conventional approach, the design is simple and does not require complicated computer optimization."
The researchers verified the validity of the idea by realizing a structure that eliminates repetitions in a wide frequency range in the microwave field. To this end, they assembled two waveguides with different characteristics and showed that it is possible to eliminate the partial reflection that occurs normally, when microwave waves pass from one waveguide to the other, by implementing a white light resonator consisting of segments of waveguides with characteristics chosen accordingly. To control the properties of the segments that make up the resonator, the researchers filled them with metamaterials realized through XNUMXD printing.
Prof. Shoyer concludes optimistically: "The white light resonator concept is universal and can be implemented for all types of waves and in all frequency ranges. The ability to cancel echoes over a wide frequency range may have far-reaching consequences and many applications such as better observation and imaging systems, communication systems with improved range and information rate, as well as the development of stealth technologies."
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