Measurement of the Lowest-Order Nonlinear Susceptibility in III—V Semiconductors by Second-Harmonic Generation with a CO2Laser

Both the magnitude and sign of the nonlinear susceptibility $d_{14}^{}{}_{}{}^{\mathrm{NL}}(-2\mathrm{}\omega ,\omega ,\omega )$ describing second-harmonic generation at 10.6 μ have been measured in wedge-shaped semiconducting samples using a $Q$-switched C${\mathrm{O}}_2$ laser. The results are (in units of ${10}^{-6\mathrm{}}$ esu): $d_{14}=+1.0\mathrm{}$ for InAs, +0.45 for GaAs, +0.26 for GaP, and +1.5 for GaSb. The limits of error are discussed, and the results are compared with previous experimental data and with several recent theoretical calculations. The effect of uniaxial compression on the coherence length for second-harmonic generation is also measured.