Time-Resolved Investigation of Ionization of Clusters Irradiated by a Strong Laser

Ionization dynamics of clusters irradiated by chirped femtosecond lasers is investigated by using a linearly chirped pulse spectral interferometry with a time resolution of less than lOOfs. The production of an average charged-Xe^18 and -Kr^9 ions indicates a strong energy coupling between laser and cluster. Ultrafast depletion of the probing laser is observed to be strictly coincident with the ionization front as seen in other experiments. Moreover,a two-step ionization process for Xe and Kr clusters irradiated by high-intensity lasers has been observed, which implies the role of resonance enhancement during the cluster explosion.     

Interaction of intense laser pulses with atomic clusters at different gas densities

The interaction of intense femtosecond laser pulses with rare gas clusters was studied experimentally, the time-of-flight spectra of ions from exploding clusters at different gas densities have been measured. It is found that while the relative components of ions in low and high energy of the ion energy spectrum decrease with the increase of the gas density, the average ion energies are the same for different gas densities, which indicates that the effect of gas density on laser-cluster interaction is not important under our experimental conditions.     

传播效应对宽带极紫外连续谱的影响

宽带极紫外连续谱是获得阿秒脉冲的重要途径,在此过程中传播效应是影响宽带极紫外连续谱产生的重要因素,本文针对传播效应对宽带极紫外连续谱的影响,采用慢变波近似的一阶传播方程,研究了传播过程对双色场周期量级激光脉冲产生宽带连续谱及其对应的单个阿秒脉冲的影响.通过分析不同聚焦位置和介质长度的传播过程,发现介质位于焦点之后有利于...     

传播效应对宽带极紫外连续谱的影响

宽带极紫外连续谱是获得阿秒脉冲的重要途径,在此过程中传播效应是影响宽带极紫外连续谱产生的重要因素,本文针对传播效应对宽带极紫外连续谱的影响,采用慢变波近似的一阶传播方程,研究了传播过程对双色场周期量级激光脉冲产生宽带连续谱及其对应的单个阿秒脉冲的影响.通过分析不同聚焦位置和介质长度的传播过程,发现介质位于焦点之后有利于产生连续谱,同时随着介质长度的变长,虽然单个阿秒脉冲峰值强度有所提高,但是产生的阿秒脉冲宽度也会增加.进一步的分析表明,在特定的双色场延迟优化下,传播效应不仅使得阿秒脉冲强度增强,还可以获得与单原子模型下具有同样脉宽的单个阿秒脉冲,而不会因为传播效应导致阿秒脉冲宽度变宽.     

Interaction of intense laser pulses with atomic clusters at different gas densities

The interaction of intense femtosecond laser pulses with rare gas clusters was studied experimentally,the time-of-flight spectra of ions from exploding clusters at different gas densities have been measured. It is found that while the relative components of ions inlow and high energy of the ion energy spectrum decrease with the increase of the gas density,the average ion energies are the same for different gas densities,which indicates that the effect of gas density on laser-cluster interaction is not important under our experimental conditions.     

飞秒强激光场中大尺寸氩团簇爆炸机理的实验研究

利用飞行时间谱，研究了在飞秒强激光场（60 fs，2×1016 W/cm2）作用下，大尺寸氩原子团簇Arn（n—=3×103—3×106原子/每团簇）的电离爆炸过程，测量了 团簇爆炸所产生的氩离子的平均能量与团簇尺寸（气体背压）的关系.实验发现，随着气体 背压的升高（团簇尺寸增大），氩离子的平均能量也相应升高.通过分析两个不同几何尺寸 锥形超声喷嘴所产生团簇爆炸后的离子能量，结合Hagena团簇尺寸规律，发现在激光参数保 持不变的情况下，离子的平均能量由团簇尺寸唯一确定.分析表明，团簇尺寸在3×105原 子/每团簇以下时，团簇膨胀的主要机理是库仑爆炸.随着团簇尺寸的进一步增大，团簇膨胀 机理将由库仑爆炸向流体动力学膨胀过渡，在3×105关键词： 原子团簇 飞秒强激光 库仑爆炸 流体动力学膨胀     

脉冲啁啾对于阿秒脉冲的影响

采用单电子近似和软核势模型, 通过数值求解一维含时薛定谔方程, 理论研究了当脉冲分别带有正、负啁啾的情况下所产生的阿秒脉冲.分析了不同脉冲啁啾特性对阿秒脉冲的强度和宽度的影响. 研究结果表明, 无论是正啁啾还是负啁啾, 随着啁啾量的增加, 都将使激光脉冲由产生单个阿秒脉冲趋向于产生阿秒脉冲链. 正啁啾和负啁啾对于阿秒脉冲宽度的影响是不同的, 负啁啾对于阿秒脉冲宽度影响很小, 适当的负啁啾有利于缩小阿秒脉冲的宽度; 而正啁啾脉冲产生的阿秒脉冲较无啁啾时展宽, 且随着啁啾量的增加, 其阿秒脉冲宽度迅速增大.     

飞秒强激光经氩气和氩团簇的传播

通过数值求解三维电场传播方程,理论模拟了飞秒强激光脉冲（50 fs,1016 w/cm2）在氩气和中等尺寸氩团簇中的传播效应.结果表明,飞秒强激光脉冲经氩气传播将发生频谱蓝移展宽和光束发散;而经中等尺寸氩团簇传播,则存在一定程度的自聚焦效应.     

Anisotropic Energetic Ion Emission from Explosionof Intense Laser Irradiated Argon Clusters in a Jet

The interaction of an intense femtosecond laser field (～ 10^16 W/cm^2) with argon clusters in a dense jet has been studied by measuring the energy and angle distributions of emitted ions. A directional anisotropy in the ion explosion energies is observed. The experimental results indicate that the average ion energies are up to 40% in the detection direction parallel to the laser polarization higher than that perpendicular to it. The measured ion yield increases about 80%, correspondingly. The findings are interpreted by charge-dependent ion acceleration and explosion of elliptic microplasma spheres.     

Generation of Very Energetic Ions from Intense Femtosecond Laser Interactions with Rare Gas Clusters in a Dense Jet

Very energetic ions, which are detected by time-of-flight spectrometry with maximum energy up to 1.3 MeV and an average energy of 68keV, are generated in the explosion of large Xe clusters in a dense jet irradiated with a high-intensity (～10^16 W/cm2) 50fs laser pulse from a Ti:sapphire TW laser at 79Ohm wavelength. The interaction of intense laser pulses with a jet of argon clusters is also performed and high average ion energies are observed. The dependence of energy of the ions on the gas backing pressure is examined, suggesting that the results are consistent with the absorption efficiency of the laser energy by the cluster plasmas.