Development of picosecond IR-UV pump probe spectroscopy for molecular clusters

建立了皮秒红外-紫外双共振光谱实验装置。该装置是为了研究超声束中形成的分子团簇的振动弛豫而开发的。该装置由锁模皮秒Nd：YAG激光器和光参量系统组成。利用非线性晶体OPG将Nd：YAG激光器的基频光转换到3 μm，并将团簇抽运到CH或OH伸缩振动上。OPG系统还产生了皮秒可调谐的紫外光，用于共振增强电离监测振动激发的团簇。在超声束中，用两束激光脉冲照射团簇。通过改变红外和紫外光脉冲之间的延迟时间，监测了振动激发态的时间分布。结果表明，苯酚的OH伸缩振动为15皮秒，其团簇的振动速度更快。

An experimental setup for the picosecond IR-UV double resonance spectroscopy has been constructed. The setup was developed to study the vibrational relaxation of molecular clusters formed in a supersonic beam. The setup consists of a mode-locked picosecond Nd:YAG laser and an opto-parametric system. A fundamental of the Nd:YAG laser is converted to 3 μm by OPG with the use of nonlinear crystal, which is used to pump the clusters to the CH or OH stretching vibration. A picosecond tunable UV light was also generated by the OPG system, which is used to monitor the vibratinally excited clusters by resonant enhance ionization. The two laser pulses were irradiated to the clusters in the supersonic beam. By changing the delay time between the IR and the UV pulses, the time profiles of the vibratinally excited states were monitored. It was found that the OH stretching vibration of phenol is 15 picoseconds and those its clusters are much faster.