Interactions of a Femtosecond Intense Laser with Rare Gas Clusters in a Dense Jet

A study on the interactions of high intensity (- 10^16 W/cm^2) femtosecond laser pulses with rare gas clusters in a dense jet is performed. Energy absorption by Ar and Xe clusters is measured and it can be as high as 90%. Very energetic ions produced in the laser interaction with a dense cluster jet are detected by time-of-flight spectrometry and the maximum ion energy of Xe is up to 1.3 MeV. The average ion energies are found to increase with increasing cluster size and get saturated gradually. The average ion energies also show a strong directionality and the average ion energy in the direction parallel to the laser polarization vector is 40% higher than that perpendicular to it. The findings are discussed in terms of a model of charge-dependent ion acceleration.     

飞秒强激光脉冲与氢团簇相互作用产生的最大质子能量与团簇尺寸的相关性

报道了飞秒强激光脉冲(60 fs,790 nm,2×1016W/cm2)与纳米尺寸的氢团簇(半径rc约为1~3 nm)相互作用,产生的最大质子能量Emax对于团簇半径rc相关性的实验研究结果。从激光-氢团簇相互作用产生的质子的飞行时间谱测量以及团簇尺寸的瑞利散射诊断结果,得到Emax与r2c成线性正比关系,比例系数为0.75,与报道的理论模拟结果一致,表明氢团簇发生纯库仑爆炸。实验结果同时提示,进一步的理论模拟应考虑气体喷流中团簇的尺寸分布。     

Ionization Induced Scattering of Femtosecond Intense Laser Pulses in Cluster Plasmas

The 45°scattering of a femtosecond (60 fs) intense laser pulse with a 20 nm FWHM (the full width at half maximum) spectrum centered at 790 nm has been studied experimentally while focused in argon clusters at intensity - 1016 W/cm2. Scattering spectra under different backing pressures and laser-plasma interaction lengths were obtained, which showed spectral blueshifting, beam refraction and complex modulation. These ionization-induced effects reveal the modulation of laser pulses propagating in plasmas and the existing obstacle in laser cluster interaction at high laser intensity and high electron density.