纳秒激光电离分子团簇产生高离化离子的激光波长效应

 利用脉冲分子束-激光电离-飞行时间质谱仪，在10⁹～10¹² W·cm^-2激光功率密度条件下，考察了Nd：YAG激光器输出的1 064，532，266 nm波长的激光与苯、氨、硫化氢等团簇的相互作用。发现1 064 nm的激光可以电离分子束产生高离化态的C⁴⁺，N⁵⁺，S⁶⁺等离子；波长为532 nm的激光则电离产生价态较低的C³⁺，C²⁺，N³⁺，N²⁺， S⁴⁺，S³⁺以及S²⁺ 等离子；在266 nm波长条件下进行实验，没有产生任何高价离子。提出了一个“多光子电离引发-逆轫致吸收加热-电子碰撞电离”模型来解释高价离子的产生。激光场下电子在团簇内部的逆轫致加热是整个过程的关键步骤，电子被加热的速度正比于激光波长的平方。这可以解释为何长波长的激光有利于更高价态离子的产生。

Wavelength dependences of generation of highly charged ions by intense nanosecond laser-cluster interaction

The highly stripped ions of C4+, N5+, and S6+ were produced when 1 064 nm laser with an intensity of 1011 W·cm-2 was used to irradiate the molecular beam of benzene, ammonia and sulfide hydrogen. The ratio of the produced multiply charged ions to the total ion signals decreased scarcely as the laser intensity decreased by almost two magnitudes. When 532 nm laser was used, the main ion products turned to be C2+, C3+, N2+, N3+, S4+, S3+ and S2+ with lower charge states. While when 266 nm laser was used, no multiply charged ions were detected. The highly charged ions are speculated to arise from the electron impact ionization process in the cluster. The initial electrons are produced by multiphoton ionization and then heated by inverse bremsstrahlung, where the heating rates scale with the