**Author details**

where *ν<sup>r</sup>* <sup>=</sup> \_\_\_\_\_\_ *πΔnT*

At the above *ξ*<sup>r</sup>

0.02°, respectively.

**9. Conclusions**

the mid‐IR spectral range.

**Acknowledgements**

them, ITMO University).

who was an active participant of this study.

*λ* sin *θ*<sup>0</sup>

430 Holographic Materials and Optical Systems

misalignment parameter *ξ*<sup>r</sup>

mm. Absorption in such sample does not exceed 3%.

from its magnitude of 90°; at the latter, DE ≅ 0 and the *ξ*<sup>r</sup>

*δλ* <sup>=</sup> <sup>−</sup> *<sup>ξ</sup><sup>r</sup> <sup>λ</sup>*<sup>2</sup>

are connected through a relation as follows:

. The *ξ*<sup>r</sup>

. For *δn* = 6.82 × 10-4, the thickness of a hologram with DE = 100% equals to 6

value of 3.5 corresponds to the deviation of pitch angle *θ*<sup>0</sup>

(2*πnT* sin *<sup>θ</sup>*0) (14)

parameter and the spectral selectivity

samples, Tatiana S.

The spectral and angular selectivity of the reflection hologram can be expressed through the

These estimates demonstrate the possibility of using the holographic elements based on CaF<sup>2</sup> crystals with color centers as the volume narrow‐band transmission and reflection filters for

The fluorite crystal with color centers is a promising holographic medium. The technology of its preparation allows for producing reproducibly large‐size samples and enables the modification of color center concentration in a wide range. There exists the set of color centers whose absorption bands overlap with each other, thus covering the entire transparency region of fluorite. The photochromism of color centers enables hologram recording in the fluorite crystals. The diffusion‐drift mechanism of recording that causes not only the color center transformation but also their redistribution over the crystal bulk determines the holographic features of this medium such as (i) the nonsinusoidal hologram profile, (ii) a high hologram stability with respect to temperature and optical radiation, and (iii) an opportunity to change the type of readout hologram (amplitude, amplitude‐phase, or phase) using postexposure incoherent radiation. The highly stable volume holograms with high angular and spectral selectivities can be used as metrological elements and narrow‐band transmission and reflection filters for the mid‐IR spectral range.

Semenova, Lyudmila F. Koriakina, and Marina A. Petrova for additive coloring the samples, and also Evgenii B. Verkhovskii and Anatolii K. Kupchikov for a technical assistance (all of

The paper is dedicated to the memory of our colleague, Aleksandr S. Shcheulin (1955–2016),

Research was funded by Russian Science Foundation (Agreement #14‐23‐00136).

The authors are grateful to Yurii I. Terekhin for preparing all CaF<sup>2</sup>

\_\_\_\_\_\_\_\_\_\_

value, the spectral |*δλ*| and angular *δϕ* selectivities are equal to 1.3 nm and

Aleksandr I. Ryskin, Aleksandr E. Angervaks\* and Andrei V. Veniaminov

\*Address all correspondence to: angervax@mail.ru

ITMO University, St. Petersburg, Russian Federation
