Generation of High Power Infrared Short Pulse by Cr:Forsterite and Development of Two-Dimensional Vibrational Spectroscopy

我们利用红外脉冲发展了高功率红外短脉冲和红外三阶非线性光学光谱。红外脉冲是由全固态激光器的差频、光学参量产生/放大等光学非线性过程产生的。通过在光路中插入硅板来补偿脉冲中的群速度色散。用自相关方法测得脉冲宽度为55ps，能量大于微焦耳/脉冲，是目前已知的能量如此高的红外脉冲中最短的脉冲。利用这种脉冲，我们构建了非线性光谱的光学系统，如时间积分和频率分辨的瞬变光栅、时间积分和频率分辨的2脉冲和3脉冲光子回波。这些技术是时间和/或频率上的多维方法，频率分辨的3脉冲光子回波是2D核磁共振的零差检测振动版本。我们已经将这些技术应用于极性溶剂中的三原子离子(OCN^-和SCN^-)、有机大分子的-N=C=N-反伸缩模式、金属卟啉的C=O伸缩模式、氰铁络合物的CN伸展模式和氢键液体的OH伸展模式等几种振动模式。我们讨论了这些模的振动动力学，包括振动布居驰豫、纯振动退相、动力学涨落和谱扩散、跃迁频率的不均匀性等。

We have developed high power, infrared (IR) short pulse and third order optical nonlinear spectroscopy in the infrared region using the IR pulse. The infrared pulses are generated by some optical nonlinear processes such as difference frequency mixing and optical parametric generation/amplification with an all-solid-state laser. Group velocity dispersion in the pulse is compensated by inserting a silicon plate in the optical path. The pulse width is measured to be 55 fs with an energy of more than microJ/pulse by an autocorrelation method, which is the shortest pulse of the infrared pulse with such a high energy to our knowledge. Using this pulse we have constructed optical systems of nonlinear spectroscopy such as time-integrated and frequency-resolved transient grating, time-integrated and frequency-resolved 2- and 3-pulse photon echo. These techniques are multi-dimensional methods in time and/or frequency, and the frequency-resolved 3-pulse photon echo is a homodyne detected vibrational version of 2D NMR. We have applied these techniques to several vibrational modes such as three-atom ions (OCN^- and SCN^-) in polar solvents, the -N=C=N- anti-stretching modes of large organic molecules, the C=O stretching modes of metal porphyrines, the CN stretching modes of cyano-iron complexes, and the OH stretching mode of hydrogen bonding liquids. We discuss vibrational dynamics of these modes including vibrational population relaxation, pure vibrational dephasing, dynamical fluctuation and spectral diffusion, inhomogeneity of the transition frequency, and so on.