Femtosecond continuum interferometer for transient phase and transmission spectroscopy

We measure difference phase spectral (DPS) over the whole visible spectrum by frequency-domain interferometry (FDI), using chirped femtosecond continuum pulses. The effects of the probe-pulse chirp on time-resolved dispersion relations are studied. Because of the correspondence between time and frequency in the chirp, temporal evolution of the optical Kerr response in CS2 is projected into DPS. In addition, it is found that the chirped continuum shows unexpected frequency shifts owing to induced phase modulation even when the continuum has a flat spectrum. The chirp character can be readily obtained from the projected traces, and the potential application to the single-shot pulse-shape measurement by FDI is discussed. It is shown that the delay-time-corrected spectra satisfy the Kramers-Kronig relations if the continuum has a flat spectrum and does not have higher chirp than the linear chirp but that the distortion caused by the induced modulation of the continuum remains unremoved in the corrected spectra. (C) 1996 Optical Society of America