Nonlinear refractive-index cross section for InSu at 10.6-μm wavelength.

The authors have directly measured for the first time, using a pulsed CO₂ laser, the refractive-index cross section s = ?n/?N (i.e., the refractive index change contribution per generated electron-hole pair) by monitoring the transmission of an InSb etalon to determine the index change ?n, simultaneously with observing a photo-Hall signal, giving the photogenerated carrier density ?N. The transmittance and photo-Hall signal are shown for an intrinsic sample of InSb of 262-µm thickness. Induced tuning of over p rad is observed in both the rising and falling edges of the transmittance curve, corresponding to tuning between a peak and a trough of the Fabry-Perot transmission function. A factor of approx. 2 discrepancy between the experimental and theoretical values of s remains to be explained.