Absolute Measurement of the Transient Optical Nonlinearity in N2, O2, N2O, and AR

The absolute time-dependent nonlinear response of O₂, N₂, N₂O, and Ar to intense nonionizing, ultrashort optical pump pulses is measured with single-shot spectral interferometry. The instantaneous and delayed rotational responses are distinguished as a function of pump-pulse duration and probe central wavelength. Our measurements are central to the modeling and understanding of nonlinear propagation of intense ultrashort laser pulses in gases.