Physics/7. Optics

Doctor of Sc. Rena J. Kasumova

Physics Department, Baku State University, Azerbaijan, rkasumova@azdata.net

Parametric generation in Zn0.75Mg0.25Se crystal

Abstract

         In the present work investigation is carried out of parametric intracavity interaction with account for phase change of interacting waves of pump, signal and idler waves in the materials for IR range of spectrum on case of Zn1-xMgxSe crystal. In work there has been made an analysis of threshold character of parametric generation in crystal of IR range Zn0.75Mg0.25Se. Increase in efficiency of intracavity conversion is possible at high entry values of pumping intensity.

Keywords: intracavity parametric interaction, middle IR, constant - intensity approximation.

         Recent years there are intensively investigated the new lasers of IR range. Thus, we can note solid-state lasers of IR range on the basis of Cr2+:ZnMgSe and Fe2+:ZnSe. These tunable compact quantum generators work with pumping in the region of generation of ions Cr2+ and Fe2+ respectively in the chalcogenide matrix [1-4]. Two versions of conversion of energy of coherent optical radiation into energy of parametric waves are possible: intracavity conversion and conversion outside of laser resonator [5].

         As is known, parametric generation of light waves has threshold character, which is determined by losses in a medium and resonator. At exceeding effort over losses parametric generation is realized. Therefore, high intensities of pumping are required to start this process. In the constant–intensity approximation [6] we determine threshold value of pump wave amplitude. At greater powers of pumping and lengths of interaction the threshold amplitude of pumping looks as () [7].

 

                                   (1)

         From the expression (1) it is seen that with increasing losses, condition of parametric gain, i.e.

                                                        (2)

is fulfilled at greater values of pumping amplitude.

 

Fig. 1. Dependencies of threshold pump intensity on linear losses  () in the crystal at phase matching condition D=0 for crystal length of =0.5 cm [1].

         For investigation of threshold intensity of pumping in case of mixed crystal Zn0.75Mg0.25Se well make numerical calculation using analytical expression for complex amplitude of signal wave, obtained in the constant-intensity approximation [8]. With this, we choose the task parameters according to conditions of existing experiment [1].

         In Fig. 1 there are offered dependences of parametric strengthening of signal wave  on losses. As it was expected with an increase of losses the minimum value of pump intensity, determining the threshold character of the process, according to (1), increases. In conditions of phase matching, from the numerical analysis (1) it is followed that in Zn0.75Mg0.25Se crystal the threshold intensity of pumping at  cm-1 is equal to  mJ, at  cm-1 is equal to  mJ, and at  cm-1 makes up value to  mJ. Note that in [1] in Zn0.75Mg0.25Se crystal there has been experimentally obtained threshold energy of pumping equal to 3 mJ (the thickness of the sample was 5 mm). From comparison of the results we may estimate that in the experimental sample losses make up a value  cm-1.

 

Fig. 2. Dependences of gain coefficient of signal wave in Zn0.52Mg0.48Se crystal  as a function of the reduced length  calculated in the constant-intensity approximation for =1 cm-1, =0.5, R2s=55% [1] at pump intensity of Ipo=40 kW/cm2 (curve 4), 30 kW/cm2 (curve 3), 20 kW/cm2 (curve 2), 10 kW/cm2 [1] (curve 1).

         Dynamics of parametric conversion after two passages of crystal Zn0.75Mg0.25Se is cited in Fig. 2 for case of nonzero phase mismatch in dissipative medium of crystal. With the increase in pumping intensity conversion efficiency nonlinearity increases. So, increase in pumping  two times leads to more than double fold (2.12 times) increasing efficiency .

         Thus, in work there has been made an analysis of threshold character of parametric generation in crystal of IR range Zn0.75Mg0.25Se. Increase in efficiency of intracavity conversion is possible at high entry values of pumping intensity.

 

         References

1.     M.E. Doroshenko, H. Jelikova, P. Koranda, J. Sulc, T.T. Basiev, V.V. Osiko, V.K. Komar, A.S. Gerasimenko, V.M. Puzikov, V.V. Badikov, and D.V. Badikov. Tunable mid-infrared laser properties of Cr2+:ZnMgSe and Fe2+:ZnSe crystals. Laser Phys. Lett., 7 (2010) 38-45.

2.     V.A. Akimov, V.I. Kozlovskii, Yu.V. Korostelin, A.I. Landman, Yu.P. Podmarkov, M.P. Frolov. Spectral dynamics of intracavity absorption in a pulsed Cr2+:ZnSe laser. Quantum Electronics, 35 (2005) 425-428.

3.     N. Kovalenko. Zn1-xMgxSe: A promising material for non-linear optics. J. of Nonlinear Optical Physics and Materials, 20 (2011) 123-127.

4.     Yu. A. Zagoruiko, N.O. Kovalenko, V.M. Puzikov, O.A. Fedorenko, T.T. Basiev, M.E. Doroshenko, V.V. Osiko, H. Jelikova, P. Koranda. Functional materials, 16 (2009) 329-331.

5.     V.G. Dmitriev, and L.V. Tarasov, Prikladnaya Nelineynaya Optika [Applied Nonlinear Optics] (Radio I Svyaz, Moscow, 1982).

6.     Z.H. Tagiev, and A. S. Chirkin. Fixed intensity approximation in the theory of nonlinear waves, Zh. Eksp. Teor. Fiz. 73 (1977) 1271-1282.

7.     Z.A. Tagiev, Sh.Sh. Amirov. On the efficiency of the optical parametric oscillation in the prescribed intensity approximation, Soviet Journal of Quantum Electronics 16 (1989) 2243-2247.

8.     R.J. Kasumova. Optical parametric interaction in infrared region crystals, Journal of Nonlinear Optical Physics and Materials 22, No. 3 (2013) 1350033-1- 1350033-9.