Nonlinear refraction and absorption measurements with chirped femtosecond laser pulses: experiments and simulations

We report an extension of the spectrally resolved two-beam coupling technique to measure the nonlinear intensity index of refraction $(n_2{}^I)$ and the two-photon absorption coefficient (β) by use of chirped laser pulses. The linear chirp parameter b is incorporated into the derivation of a more general model than the previous one [Opt. Lett. 22, 1077 (1997)]. We have also analyzed the validity of this linear chirp model through a comparison of the experimental results for fused silica with the numerically accurate calculation that considers higher-order chirps obtained by second-harmonic generation frequency-resolved optical gating. The results show that this method potentially can be used to extract the chirp. Finally, we applied this transient spectrally resolved nonlinear transmittance spectroscopy to semiconductor-doped glasses to extract their $n_2{}^I$ and β.