<title>Optical Phase Conjugation In (Hg,Cd)Te</title>

Abstract

Abstract Optical phase conjugation by degenerate and spin-resonant four-wave mixing in Hg1_xCdxTe has been studied. Three mechanisms have been identified: conduction band nonparabolicity, electron spin resonance, and photoexcited plasma. Values of the third order nonlinear susceptibility x for x-values of 0.216 - 0.232 range from 10~8 - 10~7 esu (conduction band nonparabolicity) through ^10~4 esu (electron spin resonance) to ^3 x 10~^ esu (photo- excited plasma). These measurements are of use in evaluating the potential of Hg^_xCdxTe for correction of wavefront distortions by optical phase conjugation.*IntroductionHgi_xCdxTe is an alloy semiconductor which has found widespread use in infrared detec- tors(D. By adjusting the ratio of Hg to Cd during crystal growth, the composition can be adjusted between that of CdTe (x = 1) and HgTe (x = 0). The composition of greatest inter­ est for infrared detectors is x = 0.20, for which the energy gap is 0.1 eV at 77K. For 0.15 <. x <. 0.27 the conduction band is nonparabolic, and the electron effective mass me at the bottom of the band is small, e.g., me = 0.001 meo at x = 0.20, where meo is the free electron mass.The same properties give rise to large third order nonlinear susceptibilities for small gap (i.e. 0.15 <. x 0.27) Hg^_xCdxTe. Following earlier investigations of the spin-flip Raman laser^2) and resonant four-wave mixing^3), we have recently been studying optical phase conjugation in Hg^_ xCd Te by both degenerate four-wave mixing and spin-resonant four- wave mixing, in the forward and reflective modes. Phase conjugation by three mechanisms has been studied, namely, conduction band nonparabolicy'4)9 photoexcited plasma^ ', and electron spin resonance^). These experiments are discussed below.Optical phase conjugation is potentially useful for correcting wavefront distortion in optics for high power lasers. The measurements described here are useful in evaluating the potential of Hg^_xCdxTe in this application.