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

首先用白光迈克尔逊干涉仪研究了光的线性传播。该方法给出了超短脉冲通过线性区域中的样品的变形的全部信息。我们观察到氯化钴在吡啶中的脉冲传播延迟，恶嗪-1在甲醇中的自由感应衰减信号，以及苯胺黑在水中的峰值速度增加。通过对干涉图的傅里叶分析，得到了样品的复光学常数。接着，将激发光源由非相干白色光改为相干超短锁模激光。利用迈克尔逊干涉仪的干涉测量方法，观察了染料掺杂聚合物薄膜中光子回波的波形。通过对所测干涉图的傅里叶分析，得到了样品中燃烧布居数光栅和相位光栅的详细形状。从对持续光谱烧孔有效的染料分子的频率分布出发，我们得到了聚合物薄膜中染料分子从S_0到S_1能级的0-0跃迁的非均匀频率分布，最后将干涉方法应用于泵浦探测光谱学。这里，测量了包括光的相位信息的探测脉冲的波形。样本是一个染料喷射器。我们观察到一个大的峰值位移和相移引起的泵浦脉冲。结合染料分子的布洛赫方程和光波的麦克斯韦方程，精确地再现了探测脉冲的形变。

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.