Study of nonlinear propagation of femtosecond light pulses by using a Michelson interferometer

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At first linear propagation of light was investigated with a white-light Michelson interferometer. This method gives the full information on the deformation of ultra-short fight pulses by the passage through samples in the linear regime. We observed the delay of pulse propagation for cobalt chloride in pyridine, free-induction decay signal for oxazine-1 in methanol, and the increase of peak velocity for nigrosine in water. By Fourier analysis of the interferograms, complex optical constants of the samples were also obtained.Next the excitation light source was changed from incoherent white light to a coherent ultra-short mode-locked laser. Then the interferometric method by using a Michelson type interferometer was applied to observe the waveform of the accumulared photon echoes in a dye-doped polymer film. By the Fourier analysis of the measured interferograms we obtained detailed shapes of the burned population grating and phase grating in the sample. From the frequency distribution of the dye molecules which are efficient for persistent spectral hole burning, we obtained the inhomogeneous frequency distribution of 0-0 transition from S_0 to S_1 levels of the dye molecules in the polymer film.Finally we applied the interferometric method to pump-probe spectroscopy. Here the waveform of the probe pulse was measured including the information of the phase of light. The sample was a dye jet. We observed a large peak shift and a phase shift induced by the pump pulse. The deformation of the probe pulse was precisely reproduced by a calculation which combines Bloch equation for dye molecules and Maxwell equation for light wave.