以波长可调谐高功率脉冲激光器为激发源，采用共振增强多光子离化（REMPI）光谱技术，对SO2的里德堡态进行实验研究。在420~540 nm波长范围内，得到了与碱金属原子吸收光谱类似的共振增强多光子离化光谱。429.3 nm和452.3 nm处离化峰对应（4+1）共振增强五光子离化，529.4 nm处的离化峰对应（4+2）共振增强六光子离化过程。该离化谱峰序列对应于高激发态F1A2态的np（n=4，5，6）里德堡态序列。对529.4 nm处离化峰的精细扫描表明，该处离化峰呈现为近等间隔的谱峰结构，对应于SO2分子里德堡态4p（0, v2, 0）的共振增强多光子离化光谱序列。实验得到4p里德堡态弯曲振动的基振动角频率Δν2=(387.3±12.4) cm-1。

以纳秒Nd:YAG脉冲激光器三倍频(355 nm)激光抽运的染料激光器为激发光源，在484~520 nm波长范围内，采用共振增强多光子离化光谱（REMPI）方法，对H2S分子里德堡序列的能级特性进行了实验研究，得到了谱峰间隔随激光波长增长而呈近二倍变化的两套谱峰序列嵌套而成的规则序列。该谱峰序列对应于H2S分子的里德堡序列激发。依据H2S分子低位激发电子态及里德堡序列的势能高度，可将离化过程确定为五光子4+1离化过程。并将所得到强谱峰序列归属为集结于态的np（n=5,6,7,8）里德堡序列，将弱谱峰序列归属为集结于态的ns（n=6,7,8）里德堡序列。两套序列的量子亏损分别为δ1=0.92和δ2=1.52。所得结果对H2S分子的光学检测及光谱特性研究具有重要意义。

基于电子密度演化模型，借助数值方法，研究了飞秒激光作用下光学薄膜内的电子密度演化过程，讨论了初始电子密度Ni和激光脉冲宽度τ对光学薄膜激光损伤阈值Fth的影响，分析了激光诱导薄膜损伤过程中MPI和AI的性质和作用.研究结果表明，对应于一定的脉宽，存在一个临界初始电子密度，当Ni低于这一临界密度时，Fth不受Ni影响；当Ni高于临界密度时，Fth随Ni增加而降低.临界初始电子密度随着脉宽的减小而增加。对于FS和BBS介质薄膜，Fth随脉宽的增加而升高。初始电子密度Ni对BBS中的MPI和AI基本没有影响；同样Ni对FS中的AI基本不产生影响，但当Ni>1011 cm－3时，FS中MPI电子密度随Ni增加而降低.在所研究的脉宽范围τ∈［0.01,5］ps，AI是FS介质激光诱导损伤的主要机制.而对于BBS，当脉宽τ∈［0.03,5］ps，AI是激光诱导损伤的主要机制；当脉宽τ∈［0.01,0.03］ps，MPI在激光诱导损伤中占主导地位.

Analytic formula of the efficiency of optical-optical double-color double-resonance multi-photon ionization (OODR-MPI) is derived from the dynamic rate equation about the interaction of photon and material. Based on this formula, the influence of characteristic of the pump and probe laser on the ionization efficiency of (1+2+1) OODR-MPI process is simulated theoretically. It is shown that the pump laser will affect the ionization efficiency by the number control of the molecules excited to the first resonance state. The ionization efficiency is decided by the probe laser directly. Both of the excited molecules and ionization efficiency increase with the intensity and pulse duration of the laser until saturation. It is also found that the longer the delay time of the probe laser to the pump one is, the lower the ionization efficiency would be. The delay time ought to be smaller than the lifetime of the excited molecule in the practical use of the OODR-MPI technique.

Both the nature of avalanche ionization (AI) and the role of multi-photon ionization (MPI) in the studies of laser-induced damage have remained controversial up to now. According to the model proposed by Stuart et al., we study the role of MPI and AI in laser-induced damage in two dielectric films, fused silica (FS) and barium aluminum borosilicate (BBS), irradiated by 780-nm laser pulse with the pulse width range of 0.01-5 ps. The effects of MPI and initial electron density on seed electron generation are numerically analyzed. For FS, laser-induced damage is dominated by AI for the entire pulse width regime due to the wider band-gap. While for BBS, MPI becomes the leading power in damage for the pulse width \tau less than about 0.03 ps. MPI may result in a sharp rise of threshold fluence Fth on \tau, and AI may lead to a mild increase or even a constant value of Fth on \tau. MPI serves the production of seed electrons for AI when the electron density for AI is approached or exceeded before the end of MPI. This also means that the effect of initial electron can be neglected when MPI dominates the seed electron generation. The threshold fluence Fth decreases with the increasing initial electron density when the latter exceeds a certain critical value.

The analytic formula of the ionization efficiency in the process of double resonance enhanced multi-photon ionization (DREMPI) is derived from the dynamic rate equation about the interaction of photon and material. Based on this formula, the ionization efficiency and the laser power index versus laser intensity in the DREMPI process of NO molecule, via A2\sum and S2\sum intermediate resonant states, is numerically simulated. It is shown that the ionization efficiency of NO molecule increases with the laser intensity until getting saturation, while the laser power index decreases with the enhancement of the laser intensity and changes to zero at last. The variation of the laser power index with the laser intensity indicates that the ionization efficiency reaches saturation in the one, two, and three excitation steps respectively. It is also found that the narrower the laser pulse duration is, the higher becomes the laser intensity for saturation.

The optical-optical double-resonant multiphoton ionization (OODR-MPI) spectrum of NO2 molecule in the 460-605 nm wavelength region of the probe photon is presented. The mechanism of the OODR-MPI of NO2 molecule is analyzed. The results show that the resonant features can be assigned to the transitions from the first 3s'sigma'g Rydberg intermediate resonant state to the final np'sigma'u Rydberg series. The ionization pathway is NO2(X2A1)-[3h'nu'1]->3s'sigma'g-[h'nu'2]->np'sigma'u-[h'nu'2 or autoionization]->NO2(+)+e. It is found that the converging potential of the np'sigma'u Rydberg series and the quantum defect of np orbit about NO2 are (78803+-14) cm^(-1) and 0.652+-0.014, respectively. The bending vibration frequency of 5p'sigma'u state is determined also.

利用掺钛的蓝宝石飞秒激光系统输出的单脉冲和多脉冲飞秒激光(中心波长800 nm,脉宽50 fs,靶面聚焦直径ф40 μm),分别对BK7玻璃基底上厚约500 nm的单层HfO2和单层ZrO2薄膜进行辐照,得到了这两种薄膜在1-on-1和1 000-on-1测试方法下的激光损伤阈值.实验发现,两种方法下HfO2单层膜的阈值均比ZrO2单层膜的阈值高.从简化的Keldysh多光子离化理论出发,认为HfO2薄膜材料的带比ZrO2的宽是导致上述结果的主要原因.同时,同一种薄膜的多脉冲下的阈值比单脉冲下的低,原因是多脉冲下,飞秒激光对光学薄膜的损伤存在累积效应.