In the long term the alternative highly anisotropic materials will provide more flexibility in developing absorbers and sensors working within infrared range.
Scientists from Russia (the Moscow Institute for Physics and Technology) and the USA have shown the possibility of full absorption of electromagnetic radiation with the use of an anisotropic crystal. The observations are of fundamental importance for electrodynamics and provide researchers with an essentially new approach to absorption of the electromagnetic waves energy, the Moscow Institute for Physics and Technology reported to TASS. The work has been published in the journal Physical Review B.

The Way of Absorbing Electromagnetic Radiation
A classical example of an electromagnetic absorber is usual black paint known to everyone. It looks black just because a considerable part of incident light is absorbed in the paint coat and cannot reach the observer. And yet black paint is still a poor absorber – some part of incident light energy (about several percent) is nevertheless reflected environment. The interference phenomenon has to be involved in order to absorb the incident radiation completely. When incoming on an absorbing two-layer system, provided the covering parameters are properly matched, the reflected waves compensate each other and thus reflected radiation vanishes and perfect absorption is attained. Such interference is called destructive interference.
Researchers from Russia and the USA showed in their work that destructive interference is not an obligatory requirement for ideal absorption. They suggested anisotropic crystal – hexagonal boron nitride - as a particular absorbing system. The incident infrared radiation of a certain wavelength goes into such crystal without reflection and is completely absorbed inside. Thus there is no need for any antireflection layer or substrate to gain destructive interference — there is just no back-scattered radiation, unlike in isotropic absorbing medium.
So far the approach suggested by researchers provides full absorption only for a fixed value of wavelength and angle of incidence, which are determined with electronic properties of a material, whereas for practical use the opportunity to absorb energy in a wide range of wavelength and angle is of much greater value. However, the use of alternative highly anisotropic materials, such as, for example, the biaxial absorbing media, will probably help bypass these limitations and make this approach more flexible.

Why it is Necessary
Nevertheless, the experiment is of great interest from the fundamental point of view. It shows the possibility of complete absorption of radiation without involving destructive interference. Such effect gives a new method of controlling electromagnetic absorption. In the long term such materials will provide better flexibility in development of absorbers and sensors working within infrared range. 

Effective absorption of electromagnetic radiation energy is the cornerstone of a wide range of practical tasks. First of all, absorption of electromagnetic energy in the visible spectrum is important for transforming sunlight into electric energy. Absorbing materials in the microwave range of frequencies solve a problem that is no less important – they make it possible to reduce radar visibility of aircrafts. Besides, effective absorption of electromagnetic waves is of practical importance in the field of sensors, nanochemistry, and photodynamic therapy.