用质谱和光电子能谱研究飞秒强场中的电离动力学

Photoionization Dynamics in the Intense Femtosecond Laser Field by Analyzing Mass and Photoelectron Spectrum

报导了用自制飞秒激光器通过飞秒多光子电离质谱和光电子能谱对飞秒强激光场与分子（氯、苯）相互作用的研究。飞秒激光脉宽约 １００ ｆｓ，二倍频中心波长 ４０７．５ ｎｍ，聚焦后脉冲功率密度达到 １０１２Ｗ／ｃｍ２。氨的光电子能谱显示了（２＋２）ＲＥＭＰＩ和（２＋２）＋１ ＡＴＩ、（２＋２）＋２ ＡＴＩ三组电子峰，每组峰又包括伸缩振动ｖ１的带系，ＡＴＩ峰的振动布居出现反转。随着光强增加，谱峰加宽而且振动能级出现平移。这些强场效应可用Ｐｏｎｄｅｒｏｍｏｔｉｖｅ Ｐｏｔｅｎｔｉａｌ解释。苯的飞秒质谱图与纳秒情况不同，分子离子为主，碎片峰很少。

The photoionization dynamics of ammonia and benzene was studied by home-built femtosercond laser and TOF mass/Photoelectron spectrometer. Beam intensities of 1012 W/cm2 were used with laser pulse width of 100fs and wavelength of 407.5 nm. In the PE spectra of NH3, three (2+2) REMPI and (2+2)+1 ATI, (2+2)+2 ATI were shown, within each peak a progression of stretching vibrations v1 were found. The vibrational distribution of ATI peaks are inverted compared to normal (2+2)REMPI. High laser power has also caused band broadening and shifting effect, which are given rise to by the pondromotive potential of intense laser. Different from that of nanosecond, benzene phtoionization using femtosecond laser has predominent molecular ion peak with very small percentage of fragments.