Four-wave mixing efficiency in InSb at 10.6 μm

Abstract

Optimal conditions for achieving maximal four-wave mixing (FWM) efficiency in InSb at 10.6 μm are defined on the ground of experimental and theoretical investigations of InSb characteristics. It is shown that the highest nonlinear FWM phase shift Δϕ (Δϕ m), which defines FWM reflectivity R = tg 2 Δϕ, can be ~3 when a signal and the fair pump wave are coherent. The conditions for the highest Δϕ realisation is: (i) the room temperature of a sample; (ii) the material with total concentrations of dopants, impurities and defects ⩽10 16cm −3; (iii) the minimal passive optical losses in this sample and (iv) equal intensities of counterpropagating pump waves. For such conditions Δϕ M in InSb at 10.6 μm is weakly dependent on individual parameters of the sample material. The only advantage which gives the fall of sample temperature T is the reduction of the optimal pump wave intensity. That is minimal (on the level of 2–3 kW cm 2 ) at T = 130–200 K in the purest material of n-type. The highest Δϕ in this temperature range, however, is lower than that is at the room temperature and can't be higher ~1. It is shown that the dependence of the nonequilibrium free carriers lifetime τ on the laser radiation local intensity should be taken into account at 10.6 μm FWM in InSb. The proper equations for Δϕ and τ are obtained. The correspondent dependences of Δϕ and τ on pump wave intensities, sample thickness and T are calculated and the results are compared with experiments.