## Focus on New Generation Holographic Materials  
[PERSON]  
Doctor of Sciences, Professor, ITMO University, Saint-Petersburg, Russia  
[PERSON] assigned a special role to optical materials, in particular, materials for holography. I met [PERSON] at the HOLOEXPO conference 7 years ago. At this meeting, [PERSON] expressed a simple but profound idea that the development of new photosensitive (holographic) materials will in the future determine the development and progress not only in the field of holography, but also in optical instrument-making industry and laser technology. In other words, without new holographic materials, it is impossible to create devices and photonic devices of a new generation with a fundamentally new functionality. The work of ITMO University in the field of developing new photosensitive materials over the past 10-15 years was of great interest to [PERSON], and he proposed close cooperation between his holographic group from Bauman University and the materials science group from ITMO University. The holographic material that attracted [PERSON]'s special attention was a silicate photo-thermo-refractive (PTR) glass, which was developed in our group more than 10 years ago. Holograms recording in PTR glass is based on the process of photo-thermo-induced crystallization, in which, after UV irradiation and subsequent heat treatment, nanocrystals grow in the irradiated area of the glass, the refractive index of which differs from that of non-irradiated glass. Compared to well-known holographic materials (silver halide emulsions, dichromated gelatin, photopolymers, chalcogenide glasses, etc. ), PTR glass has the following competitive advantages: high mechanical, thermal and optical strength, high chemical resistance, moisture resistance and abrasion resistance (these characteristics are close to well-known optical glass BK7), unlimited storage period of recorded information. These properties make it possible to create holographic optical elements with unique characteristics that are in high demand in the photonics market. For example, the following holographic optical elements have been created on the basis of PTR glass: ultra-narrowband filters for lasers, holographic prisms for calibrating angle-measuring and angle-setting navigation devices, high-power laser beams combiners, chirped gratings for light pulse compression, marks for holographic collimating laser sights, etc. [PERSON] expanded the fields of application of PTR glass. He suggested using PTR glass for the displays and eyeglasses of augmented reality. An important feature was that he proposed a new ideology for creating such devices--a monolithic integration of holograms (Bragg gratings) and a waveguide on a single substrate, i.e., when both the Bragg gratings for input-output of an optical image and the waveguide itself, which communicates between them, are made on the same material--PTR glass. Prior to this approach, the technology of a hybrid integration of optical elements on a single substrate was being developed in the world, i.e., when the input-output Bragg gratings and the waveguide were made of different materials (the gratings were made on a photopolymer, and the waveguide on glass). The use of dissimilar materials with different coefficients of thermal expansion in hybrid integration led to distortion of the transmitted image. The use of PTR glass for augmented reality displays and eyeglasses offers huge advantages over photopolymers. These are, first of all, the high-performance characteristics of PTR glass, which are extremely attractive for civil and military applications. Thus, displays and eyeglasses based on PTR glass can be used in a wide temperature range (from \(-60\)\({}^{\circ}\)C to \(+200\)\({}^{\circ}\)C) in any weather. The devices are not afraid of moisture, dirt and the impact of mechanical objects (sand, dust), because after the formation of surface scratches and defects, the glass surface can always be repolised again without changing the functionality of the displays and eyeglasses.