Abstract
Resonant effects in second harmonic generation (shg) in InSb near the energy gap have been studied by radiating with a high power Q-switched CO2 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*1014 to 5*1016 cm-3 at a temperature of 12 K. Absolute, independent measurements of the coherence lengths lc+- 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 lc and the effect of blocking by conduction band population is demonstrated experimentally.