Magnetic field dependence of second harmonic generation, coherence lengths, and second order susceptibilities near the band edge in InSb

Resonant effects in second harmonic generation (shg) in InSb near the energy gap have been studied by radiating with a high power Q-switched CO ₂ laser at 10.6 mu m and tuning the energy gap by applying magnetic fields up to 55 kG in samples of carrier concentrations from 8*10 ¹⁴ to 5*10¹⁶ cm^-3 at a temperature of 12 K. Absolute, independent measurements of the coherence lengths l_c+- were made as a function of magnetic field, using circularly polarized radiation and wedge shaped samples, by a modification of the original 'Maker' experiment. These results, together with measurements of SHG _+- and absorption coefficients alpha _+- have yielded the magnetic field dependence of the second order nonlinear susceptibilities chi _+- at 5.3 mu m. Virtual transition processes have been used to formulate the theory for the resonant behaviour of chi and l_c and the effect of blocking by conduction band population is demonstrated experimentally.