Time resolved excited state absorption of Mn

Excited state absorption (ESA) of Mn²⁺ in spinel MgAl₂O₄ is investigated in detail. For excitation ps-pulses of 351 nm wavelength from a tripled Nd phosphate glass laser are used. During relaxation down to the lowest excited state ESA is measured for various delay times between exciting pulse and probe pulse. The resulting absorption spectra are interpreted in terms of the Mn²⁺ configurational model.     

Electron spectrometry study of associative and penning ionization in laser excited sodium vapor

The first observation, by electron spectrometry, is reported in laser-excited sodium vapor of the primary low energy electrons produced by associative ionization and by Penning ionization of sodium atoms in highly excited n1 states. The sequential heating of these primary electrons has been observed in 1, 2 or 3 superelastic collisions with Na(3p) atoms. The variation of associative ionization was measured as a function of the excited state density by using inner-shell photoionization produced by synchrotron radiation. Finally, an associative ionization cross section of 3.8 X 10^-17 cm² and a Penning ionization cross section for the 5s state of 1.1 X 10^-12 cm² were found (within 50% uncertainty) for an oven temperature of 520 K.     

脉冲放电激励的钡蒸气激光的研究

设计和制作了新型结构的金属蒸气激光放电管.用钡为激光介质,通过纵向高频快脉冲放电激励,在国内首次实现波长为113μm和150μm的红外钡蒸气激光振荡,激光成分主要集中在150μm这条谱线上,激光输出功率和功率密度分别达12W和333mWcm3.测量并讨论了各工作参量和激光输出特性之间的关系     

Spatiotemporal spectroscopic diagnostics of a pulse-periodic strontium vapor laser

Results of spectroscopic investigations into plasma of a pulse-periodic strontium vapor laser operating in the superradiance mode on the infrared transition at λ = 6.45 μm are presented. The method of determining the electron temperature and concentration as well as the gas temperature – T _e , n _e , and T _g – based on measuring the absolute intensities of some SrI and SrII and buffer gas (helium or neon) spectral lines is used. Time dependences of the line intensities during a current pulse (τ = 150 ns) and near afterglow (up to 3 μs) are obtained under conditions of non-equilibrium plasma ionization and recombination. The optical system collects radiation from the entire length of the plasma column by means of separating radial volume zones, includingthe central zone and the zone closer to the walls, with the monochromator slit. The results obtained allow us not only to calculate T _e , n _e , and T _g values, but also to trace the spatiotemporal plasma evolution.     

Time resolved spectroscopy in laser grade organic dyes

Time resolved spectroscopy is discussed along with the theoretical and experimental methods used to measure the fluorescence lifetimes in various laser grade organic dyes. The role of solvents and their viscosities in the fluorescence life time is also discussed. Different photophysical parameters have been obtained in rigid and non-rigid dye molecules.     

脉冲放电激励的钡蒸气激光的研究

设计和制作了新型结构的金属蒸气激光放电管.用钡为激光介质,通过纵向高频快脉冲放电激励,在国内首次实现波长为1.13μm和1.50μm的红外钡蒸气激光振荡,激光成分主要集中在1.50μm这条谱线上,激光输出功率和功率密度分别达1.2W和33.3mW/cm3.测量并讨论了各工作参量和激光输出特性之间的关系.     

Time resolved pattern evolution in a large aperture laser

We have measured quasiinstantaneous transverse patterns in a broad aperture laser. Nonordered patterns yielding to boundary determined regular structures in progressive time-integrated recording are observed. The linear analysis and numerical integration of the full Maxwell-Bloch equations allow us to interpret the features of the experiment. We show that this system being far from threshold cannot be fully understood with a perturbative model.     

Time resolved Nomarski interferometery of laser produced plasma plumes

We report results from optical interferometric probing of a laser generated Zn plasma plume. The experiment was performed in a vacuum and O₂ rich environments where the background pressure of O₂ was maintained at 1000 Pa and the results from both regimes are compared. The focus of our work is very much on the early stages in the life of the plasma plume which remains, to date, a largely unexplored area of study, at least in the pulsed laser deposition research domain. It was found that the electron density profile normal to the target is different in the background gas at early times (∼30 ns) compared to that of the vacuum case. At later times (∼80 ns) both profiles have a very similar shape. We also observe the formation of a shock wave at the plasma-gas interface shortly after plasma breakdown (<15 ns).     

Infrared laser-emission study in a resonantly excited sodium vapor

We report on a study of time dependence of ir laser emission at 3.41 μm in a dense Na vapor that is resonantly excited to the 3² P levels by a flashlamp, pumped dye laser. Energy-pooling collisions (excitation transfer) between excited atoms create a large population inversion among the 5² S _1/2 and 4² P _3/2 states which is destroyed by electron collisions as a result of subsequent plasma formation. The ir laser emission may serve as a new diagnostic tool to follow the time evolution of such media.     

Formation of an alignment in collisions of laser excited sodium with xenon atoms

By photon absorption from a monomode dye-laser beam a spatially ordered velocity distribution (‘atomic beam’) of sodium atoms excited to the 3p ² P _1/2-state, is created. It is predicted theoretically that in collisions of these atoms with atoms of a heavy foreign gas an alignment of the electronic orbital angular momentum is produced. This alignment leads to the appearance of a linear polarization in the sensitizedD ₂-fluorescent light. This polarization is verified experimentally and interpreted in terms of a simplifiedT-operator. It turns out that the scattering distribution for sensitizing collision is of the wide-angle type.     

Time resolved schlieren study of highly refracting CO2 laser produced plasma

We report temporal evolution of high intensity CO₂ produced plasmas by introducing a Schlieren technique. The method allows the density step produced by radiation pressure to be followed during the pulse duration. We deduce the expansion velocity of the critical layer for different intensities.     

Time resolved calorimetry of te films during pulsed laser annealing

Using a pyroelectric thin-film calorimeter the temperature of 30 nm thick Te films during pulsed laser annealing was studied in real-time. A XeCl excimer laser pumped dye laser with Raman shifter was utilized to study the wavelength and energy dependence. No significant wavelength dependence was noticed. Depending on the pulse energy, however, melting, boiling and crystallization of the Te films was observed. These findings support a strictly thermal model for laser annealing and optical recording with Te based media. In addition boiling was identified as the prevalent mechanism for the loss of material.     

Time resolved spectroscopy of second harmonic emission from laser irradiated microballoons

Time resolved second harmonic spectra from glass microballoons irradiated by neodymium laser pulses (∽ 10¹⁶W cm^-2, ∽ 100 ps) have been recorded with a resolution of ∽ 10 ps in time, ∽ 1 Å in wavelength and ∽ 10μm in the target plane. Intense, time and wavelength resolution-limited spots appear, whose origin has not yet been explained.     

Emission of laser pulses due to transitions from metastable to metastable levels in strontium vapor

Multi-line laser transitions from one metastable triplet state to another at wavelengths of 2.92, 3.01, 2.69 and 2.60 μm have been obtained through high pulse repetition frequency longitudinal discharge in a mixed gas of strontium vapor and helium buffer gas. The intensity ratio of these laser lines was 5:4:4:1. As far as we know, these laser lines have never been reported except for 3.01 μm. Some mechanisms for forming a population inversion are initially discussed on the basis of analyzing features of corresponding energy-level structure and experimental phenomena. It is reasonable to name this kind of laser as an M–M transition laser according to the feature of the lasing process. Received: 15 October 2002 / Published online: 9 April 2003 RID="*" ID="*"Corresponding author. Fax: +86-0571/8795-1328, E-mail: pbl66@zju.edu.cn     

Fluorescence of Na2 and K2 excited by a gold vapor laser

The gold vapor laser has been used to irradiate the alkali dimers Li₂, Na₂, K₂, and Rb₂. Significant fluorescence was found only from Na₂ and K₂. Six fluorescent series in the A¹Σ_u⁺-X¹Σ_g⁺ system of Na₂ and three in the B¹Π_u-X¹Σ_g⁺ system of K₂ were assigned, respectively. New spectroscopic constants for the X¹Σ_g⁺ state of ³⁹K₂ are derived, and new RKR potential energy curves for the X¹Σ_g⁺ and B¹Π_u states of ³⁹K₂ are given.     

Al激光等离子体电子温度的时间分辨诊断

将门控分幅相机与平面晶体谱仪耦合,构成时间分辨光谱测量系统,对Al激光等离子体的K壳层发射谱进行测量,获得了相对入射激光延迟约1ns,积累时间约200ps的光谱信号。利用稳态碰撞-辐射平衡（CRE）近似条件下的等离子体光谱辐射动力学模型,给出了Al激光等离子体Ly-β线与He-β线强度比以及Ly-γ线与He-γ线强度比与电子温度的函数关系。在此基础上,根据实验谱线强度比,得到激光强度为2.319×1014,1.937×1014和3.946×1014 W/cm2时,等离子体冕区电子温度分别为1.190(1±27%),1.165(1±27%)和1.525(1±27%)keV。     

锶离子R—M跃迁激光和复合激光的参量研究

在9mm内径和42cm电极间距的石英放电管中，用氦气为缓冲气体，通过纵向快脉冲放电激励，对锶离子红外R—M跃迁激光和蓝色复合激光进行了系统的参量研究.分析和解释了两种谐振腔时各激光谱线输出功率与工作参量（氦压，频率和充电电源电压）的关系曲线，观察和讨论了对应的光电脉冲波形，获得了一组较好的工作参数. 关键词： 脉冲放电激励 锶离子 R—M跃迁激光 复合激光 光电脉冲波形     

Classical study of and collisions in intense laser fields

In this paper, ion-atom and ion-ion collisions in the presence of intense laser fields are qualitatively studied by Classical Trajectory Monte Carlo (CTMC) simulations. It is found that in contrast to the field-free collisions, the colliding ion and the target nucleus could absorb energy from the applied laser fields when the electrons escape from the collision system. This result is explained in terms of Coulomb explosion induced by the enhanced ionization at the so-called critical internuclear distance. Also, the corresponding energy gain cross-sections are evaluated. Received: 7 October 1998 / Received in final form: 28 January 1999