The ac-Stark shift of the two-photon Bohr resonance of nitric oxide at 409.8 nm is utilized to autocorrelate intense, ultrashort optical pulses at 400 nm. When they are temporally and spatially overlapped, two identical pulses shift the absorption into transient resonance with the applied two-photon energy. Interferometric autocorrelation traces are obtained by detection of fluorescence as a function of the time delay between the two pulses: The method is background free and highly nonlinear. Experimental measurements are simulated through solutions to the time-dependent Schrödinger equation for one-dimensional motion of an electron in an electric field, which procedure yields a measure of the incident pulse width.
© 2002 Optical Society of America