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Dependence of nonlinear refractive index of ZnSe on Be and Mg content

Derkowska B., Firszt F., Marasek A., Sahraoui B.

Opto-Electronics Review

2010

Vol. 18, No. 4

384-387

The values of the nonlinear refractive index n₂ and the two-photon absorption coefficient ß of ternary and quaternary ZnSe-based mixed crystals were extracted from the standard backward degenerate four wave mixing (DFWM) and nonlinear transmission measurements at 532 nm, respectively. Studied crystals were grown by the modified high-pressure Bridgman method. We found that the value of the nonlinear refractive index n2 for Zn0.79Be0.21Se is higher than that for Zn0.80Mg0.20Se. However, the opposite behaviour was found in the case of two-photon absorption coefficient ß for these compounds. We also found that the values of the nonlinear refractive index n2 and the two-photon absorption coefficient ß for Zn0.83Be0.04Mg0.13Se are about five times lower and three times higher than that for Zn0.80Mg0.13Se, respectively. In the case of ternary ZnSe-based crystals we noticed that the value of the nonlinear refractive index n2 decreases with increasing Mg or Be content. However, the value of the two-photon absorption coefficient ß increases with increasing Mg or Be content.

Study of the third order nonlinear optical properties of Zn1-xMgxSe and Cd1-xMgxSe crystals

Derkowska B., Firszt F., Sahraoui B., Marasek A., Kujawa M.

Opto-Electronics Review

2008

Vol. 16, No. 1

8-11

Third order nonlinear optical susceptibilities χ³ of ternary Zn₁-xMgxSe and Cd₁-xMgxSe crystals have been measured using standard degenerate four-wave mixing (DFWM) method at 532 nm. The nonlinear transmission technique has been applied to check if our crystals exhibit two-photon absorption. The studied Zn₁-xMgxSe and Cd₁-xMgxSe solid solutions were grown from the melt by the modified high-pressure Bridgman method. For both crystals the energy gap increases with increasing Mg content. In the case of Zn₁-xMgxSe, it was found that the value of third order nonlinear optical susceptibility χ³ decreases with increasing Mg content. An explanation of this behaviour results from the dependence of optical nonlinearities on the energy band gap Eg of the studied crystals. In the case of Cd₁₋xMgxSe with low content of Mg, no response was observed for the studied wavelength since the energy gap in such crystals is smaller than the photon energy of the used laser radiation. It was also found that the value of third order nonlinear optical susceptibility χ³ for Cd₀.₇₀Mg₀.₃₃ is higher than for Zn₀.₆₇Mg₀.₃₃Se. This behaviour can be understood if one take into consideration that the free carrier concentration in Cd₁₋xMgxSe samples is about four orders of magnitude higher than that in Zn₁₋x MgxSe ones with comparable Mg content respectively. It is commonly known that when the electric conductivity increases, the values of nonlinear optical properties increase. From the performed measurements one can conclude that the incorporation of Mg as constituent into ZnSe and CdSe crystals leads to a change of the third order nonlinear optical susceptibilities.