Abstract

To clarify the eventual role of confinement in the below-band-gap nonlinear response of semiconductor nanocrystals, we performed two-photon absorption (TPA) measurements in semiconductor doped glasses (SDG). In previous experiments employing 30 ps pulses it was not possible to obtain accurate values of 1mχ⁽³⁾ since the nonlinear transmission was affected by the absorption of free carriers generated by TPA¹. This is a common problem in TPA measurements, and becomes more severe whenever a short thickness of material, or a small semiconductor volume fraction as in our case, forces to use high intensities to have a detectable absorption. A straight way out is to reduce the number of generated free carriers by using shorter pulses¹, and to this end a femtosecond travelling wave parametric generator (TOPG)² appeared the best solution to provide also the desired tunability.

© 1996 IEEE