**7. Conclusions**

source falls on the recorded hologram that creates an image of the recorded mark in the image plane. The high transparency of PTR glass in the visible range (above 90% without AR coating)

**Figure 25.** Holographic sight (a) is the basic scheme of the sight and (b) is the observable image of a mark recorded on

**Figure 26.** Laser action of Nd3+ heavily doped (NNd = 2.5 × 1020) PTR glass measured for mirrors with the reflection of

The application of PTR glass can solve the problem of image stabilization, which is necessary due to the instability of laser diode source used in such sights. To date, this problem is solved by adding, into the optical scheme, the achromatizing diffraction elements such as thin

opens up this field of applications.

456 Holographic Materials and Optical Systems

1% (red curve) and 5% (black curve) [34].

PTR glass.

Recent achievements of ITMO University (St. Petersburg, Russia) in developing new holographic media such as fluoride, chloride, and bromide photo-thermo-refractive (PTR) glasses are demonstrated. PTR glasses change their refractive index after an exposure to the near-UV radiation followed by thermal treatment at temperatures close to the glass transition one. In the case of fluoride PTR glass, the increment of the refractive index is negative and its magnitude reaches 1.5 × 10−3 ppm. In the case of chloride and bromide PTR glasses, the increment of the refractive index is positive and its magnitudes reach 1.0 × 10−3 and 0.8 × 10−3 ppm, respectively. Thus, the fluoride, chloride, and bromide PTR glasses are very promising photosensitive materials for recording the 3D-phase holographic optical elements. Some examples of holographic optical elements based on PTR glasses are demonstrated such as the supernarrowband spectral filter for laser diodes, laser beam combiners, the holographic marker for the collimating sight, and lasers with Bragg and distributed feedback.
