Two-photon absorption, nonlinear refraction and optical limiting in semiconductors

Two-photon absorption coefficients β/sub 2/ of eight different semiconductors with bandgap energy E/sub g/ varying between 1.4 and 3.7 eV are measured using 1.06 μm and 0.53 μm picosecond pulses. β/sub 2/ is found to scale as E/sub g//sup -3/ as predicted by theory for the samples measured. Extension of the empirical relationship between β/sub 2/ and E/sub g/ to InSb with E/sub g/=0.2 eV also provides agreement between previously measured values and the predicted β/sub 2/. In addition the absolute values of β/sub 2/ are in excellent agreement (the average difference being <26%) with recent theory which includes the effects of nonparabolic bands. The nonlinear refraction induced in these materials is monitored and found to agree well with the assumption that the self-refraction originates from the two-photon generated free carriers