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Small-scale production (growing) and the implementation of the crystals ZnGeP2



1. DESIGNATION

Optical elements of the single compound diphosphide zinc-germanium (ZnGeP2) are designed for conversion of radiation frequency mid-IR lasers (1.7 - 11 microns) on the basis of nonlinear effects arising from the interaction of electromagnetic radiation of high intensity and substance.·
Optical elements of ZnGeP2 can be used in a threshold scheme for generating coherent radiation (receiving harmonics, sum and difference frequencies), and in the systems of parametric generation of optical radiation, allowing for pumping lasers with a wavelength near 2 microns to obtain tunable wavelength output radiation in a broad spectral range covers the range 3 - 10 microns.

2. PHYSICOCHEMICAL AND MECHANICAL PROPERTIES

Material - a single crystal ZnGeP2
Composition, chemical formula - ZnGeP2, nominally stoichiometry
Crystal structure - tetragonal, chalcopyrite
Point group symmetry - ¯ 42m
Lattice parameters: a = b = 5,467 Å; c = 10,710 Å
Melting point [1, 2] - 1027 ± 3 ˚ C
Density [1] - 4.158 g/cm3
Microhardness [2] - 980 ± 80 kg/mm2
Hardness by Moss [3] - 5.5

3. THERMOPHYSICAL PROPERTIES

Thermal conductivity [2] - 0.18 W / (cm * K)
Specific heat [4] - 0.392 J / (g * K)
The relative coefficients of thermal expansion [5], K-1 -
α = 2,4 • 10 -6, α = 3,7 • 10 -6




 


4. OPTICAL PROPERTIES·

ZnGeP2 refers to the positively birefringent (ne> no) uniaxial crystals.
Useful transparency range 2 - 12 microns.

4.1. Refractive index (Formula Selmeyera)
In the area of transparency ZnGeP2 refractive indices of ordinary and extraordinary rays, measured by different authors differ from each other only in the third decimal place. In the literature, several approximations of the experimental data formulas Selmeyera: n2 = A + B *
λ2 / (λ2 - C) + D * λ2 / (λ2-E), but the best agreement between calculated and experimental values of phase-matching angles for the crystals is performed at using the approximation of Barnes [6], the constants of which are listed in the table below:


Константы
аппроксимации

Обыкновенный луч

Необыкновенный луч

A

4,64467

4,71539

B

5,10087

5,26358

C

0,13656

0,14386

D

4,27777

2,3761

E

1653,89

1000,82

4.2. Birefringence ZnGeP2 - 0,04

4.3. Second-order nonlinear susceptibility [7,8] - d36 = 75 ± 8 pm / V
4.4 The effective nonlinear susceptibility for the three-frequency parametric interaction [3]:
Type I (ee → 0, 0 → ee) = d36 * sin 2θ * cos2φ
Type II (e0 → 0, 0 → 0e) = d36 * sin θ * sin 2φ

4.5. Typical data known from the literature on the optical breakdown threshold depending on the duration τ pulse CO2 laser is shown in Figure



The main performance characteristics ZnGeP2 include the following:
- High optical breakdown threshold, allowing to work with the pump pulse sources of high intensity;
- Good thermal conductivity, capable of operating at high power levels of radiation passing through the crystal, and crystal stability to thermal cycling;
- Large values of temperature, angular and spectral widths of synchronism, ensure easy configuration of converters based on single ZnGeP2 on matching and alignment of optical system as a whole;
- Mechanical strength, which allows firm to work in conditions of vibration;
- Resistance of crystals to conditions of high humidity and even to aggressive environments.
The totality of these characteristics represents a unique set of qualities that make the non-linear optical converters of single ZnGeP2 attractive for inclusion in many optical devices and systems for various purposes.


REFERENCES


1. Полупроводники А2В4С52 – под ред. Н.А. Горюновой, Ю.А. Валова – М., Сов. Радио, 1974
2. J.L.Shay and J.H. Wernick  - Ternary chalcopyrite Semiconductors: Growth, Electronic properties and Applications – ed/ by B.R. Pamplin, Pergamon Press, NY, 1975
3. V.G. Dmitriev, G.G. Gurzadyan and Nikogosyan “Handbook of nonlinear Optical Crystals”, 2-nd edition, Springer-Verlag, Berlin, 1995
4. Рекламный проспект INRAD Ltd. (USA)
5. Кожина И.И. – Тепловое расширение ряда соединений  А2В4С52 – Материалы Всесоюзной конференции «Тройные полупроводники и их применение» - Кишинев, Штиинца, 1976, с. 20-21
6. N.P. Barnes et. all – J.Opt.Soc.Am , 1998, v. B15, p. 232
7.  К.Л. Водопьянов, В.Г. Воеводин, А.И. Грибенюков, Л.А. Кулевский – Квантовая электроника, 1987, т. 14, № 9, с. 1815- 1818
8.  P.D.Mason, D.J.Jackson and E.K.Gordon, Optics Comm., v. 110, 163 (1994)