ac-Stark autocorrelator for ultrafast laser pulses

The ac-Stark shift of the A ²∑^÷ n′ = 2 ← X ²π_rn″ = 0 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. Interferometrio autocorrelation traces are obtained by detection of A ²∑⁺ n′ = 2 → X ²π_r, n″ 2 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 Schrb'dinger equation for one-dimensional motion of an electron in an electric field, which procedure yields a measure of the incident pulse width.