The multicolour three-photon resonant ionization spectrum studies in uranium atom

The multicolour three-photon resonant ionization spectra of U-238 were measured by using the pulsed dye lasers system synchronously pumped by a frequency doubled Nd:YAG-laser 532 nm output(operated at 10 Hz),a device for atomic beam of U, time-of-flight mass spectrometer and boxcar integrator. The dye laser pulses have a 6 ns duration. Beams from the dye lasers, which have the same polarization direction and are focused by lenses, entered an interaction chamber through opposite windows on a common axis and spatialy overlapped the U atomic beam. The optical pulse from dye laser DL2 was delayed to arrive at the interaction region 8 ns after the pulse from dye laser DL1; in the same way,the pulse from DL3 was delayed 8 ns after from DL2. The atomic beam device was made from stainless steel. We generated the U vapor by heating solid U in a graphite crucible by e-type electron -field on first excited states were studied in uranium atom. The question how to determine single-colour, two-colour and three-colour three-photon resonant ionization peak in the three-colour three-photon resonant ionization spectra diagram were solved.

New high-lying odd-parity excited levels of atomic uranium

We report the measurement of 112 new high-lying odd-parity excited levels of U I in the energy region 35 678-36 696 cm(-1). These levels were obtained with a setup composed of a Nd:YAG-laser-pumped pulsed dye laser system, an atomic beam device, a time-of-flight mass spectrometer, and a boxcar integrator. (C) 2000 Optical Society of America [S0740-3224(99)02309-7] OCIS code: 300.0300.

Stimulated emission in blue wavelength region from a copolymer

A dye laser based on the soluble conjugated polymer, Poly[1,8-octanedioxy-2,6-dimethoxy-1,4-phenylene-1,2-ethenylene-1, 4-phenylene-1,2-ethenylene-3,5-dimethoxy-1,4-phenylene], has been fabricated. The laser was pumped by light pulses from the third harmonic radiation of an Nd:YAG laser. The lasing was observed in the blue wavelength region with the peak at 450 nm. The threshold energy is about 19 mu J. The energy conversion yield of the laser is about 3.4%. The maximum peak power of the laser output pulse arrives at about 20 kW.

激光双光子电离方法对水溶液表面的蒽及其衍生物的测定

激光双光子电离方法用于水溶液表面的蒽及其衍生物分子的检测。Nd-YAG激光的第三谐波355nm用作激发和电离。光电离电荷数在2～3个数量级内随浓度呈线性关系。胺基蒽和甲基蒽的检出限达到0．2μg／L。这个结果与氮分子激光337um的情况一致，略差于在正乙烷液相中测定的结果。

激光诱导等离子体光谱法检测合金钢组分的实验研究

激光诱导击穿光谱技术(LIBS)具有无需样品制备,原位快速分析,可进行实时控制的特点使其在钢铁冶炼控制中具有巨大的实际应用价值。本文以波长为1 064 nm的Nd∶YAG调Q固体激光器为激发光源,CCD为探测器,高合金钢GBW01605—01609系列为样品,在建立的LIBS实验装置上研究激光与合金钢之间的相互作用。系统地研究了观测距离、激光能量对高合金钢样品中激光诱导击穿谱特性的影响,并分析了LIBS信号的时间分辨特性,确定了将LIBS用于合金钢微量元素定量分析时的最佳实验条件。

利用激光诱导击穿光谱对铝合金成分进行多元素同时定量分析

利用激光诱导击穿光谱定量分析了铝合金中多种元素的成分。采用Nd∶YAG脉冲激光器,在空气环境下烧蚀铝合金固体样品获得等离子体。利用多通道光栅光谱仪和CCD检测器对200～980nm波长范围的光谱进行同时检测。研究了检测时延、激光脉冲能量、元素深度分布对光谱强度的影响,考虑这些因素之后对实验参数进行了优化。在优化的实验参数下对国家标准铝合金样品中的八种元素Si,Fe,Cu,Mn,Mg,Zn,Sn及Ni进行了定标,并利用定标曲线对一种铝合金样品进行了定量分析。实验结果表明,测量结果的相对标准偏差(RSD)最大为5.89%,相对误差在-20.99%～15%范围内,说明对铝合金样品成分进行定量分析,激光诱导击穿光谱是一种有效的光谱分析工具,但是分析结果的准确度仍需要提高。

Cluster-assistant generation of multiply charged atomic ions in nanosecond laser ionization of seeded methyl iodide beam

The photoionization of methyl iodide beam seeded in argon and helium is studied by time-of-flight mass spectrometry using a 25 ns, 532 nm Nd-YAG laser with intensities in the range of 2 x 10(10)-2 x 10(11) W/cm(2). Multiply charged ions Of Iq+ (q = 2-3) and C2+ with tens of eV kinetic energies have been observed when laser interacts with the middle part of the pulsed molecular beam, whose peak profiles are independent on the laser polarization directions. Strong evidences show that these ions are coming from the Coulomb explosion of multiply charged CH3I clusters, and laser induced inverse bremsstrahlung absorption of caged electrons plays a key role in the formation of multiply charged ions. (C) 2004 Elsevier B.V. All rights reserved.

Cluster-assisted multiple ionization of xenon and krypton by a nanosecond laser

Multicharged xenon and krypton ions with charge states up to Xe11+ and Kr11+ have been observed in laser ionization of a pulsed xenon or krypton beam by a 25 ns Nd-YAG laser with laser intensity of 10(10)-10(11) W cm(-2) at 532 nm. There is strong evidence to support that those multicharged ions come from cluster-assisted electron recolliding ionizations inside the cluster after multiphoton ionization of atoms in the cluster, the electron can gain its kinetic energy by inverse bremsstrahlung absorption from a laser field quickly.

Supercontinuum generation in air-silica microstructured fibers with nanosecond and femtosecond pulse pumping

We study the generation of supercontinua in air-silica microstructured fibers by both nanosecond and femtosecond pulse excitation. In the nanosecond experiments, a 300-nm broadband visible continuum was generated in a 1.8-m length of fiber pumped at 532 nm by 0.8-ns pulses from a frequency-doubled passively Q-switched Nd:YAG microchip laser. At this wavelength, the dominant mode excited under the conditions of continuum generation is the LP 11 mode, and, with nanosecond pumping, self-phase modulation is negligible and the continuum generation is dominated by the interplay of Raman and parametric effects. The spectral extent of the continuum is well explained by calculations of the parametric gain curves for four-wave mixing about the zero-dispersion wavelength of the LP11 mode. In the femtosecond experiments, an 800-nm broad-band visible and near-infrared continuum has been generated in a 1-m length of fiber pumped at 780 nm by 100-fs pulses from a Kerr-lens model-locked Ti:sapphire laser. At this wavelength, excitation and continuum generation occur in the LP01 mode, and the spectral width of the observed continuum is shown to be consistent with the phase-matching bandwidth for parametric processes calculated for this fiber mode. In addition, numerical simulations based on an extended nonlinear Schrödinger equation were used to model supercontinuum generation in the femtosecond regime, with the simulation results reproducing the major features of the experimentally observed spectrum. © 2002 Optical Society of America.

Optical Thomson scatter from laser-ablated plumes

We have obtained density and temperature informations on an expanding KrF laser-ablated magnesium plume via optical Thomson scatter with a frequency doubled Nd:YAG laser. The electron temperature was found to decay with the expected Te t-1 dependence. However, we have found the electron density to have a time dependence ne t-4.95 which can be explained by strong recombination processes. We also observed atomic Raman satellites originating from transitions between the different angular momentum levels of the metastable 3P0 term in Mg I.

Raman satellites in optical scattering from a laser-ablated Mg plume

Raman satellites have been observed in the scattering of a Nd:YAG laser (532 nm) from a laser-ablated Mg plasma plume. We identify them as originating from transitions between the fine-structure components of the metastable 3s3p P-3(0,1,2) level of Mg. We have calculated the cross sections for Raman and Rayleigh scattering from the metastable state. Comparison of the expected ratio of the satellites to the Rayleigh peak indicates the changing population fraction of the metastable states in the plume.

Comparison of the electron density measurements using Thomson scattering and emission spectroscopy for laser induced breakdown in one atmosphere of helium

Thomson scattering from laser-induced plasma in atmospheric helium was used to obtain temporally and spatially resolved electron temperature and density profiles. Electron density measurements at 5 s after breakdown are compared with those derived from the separation of the allowed and forbidden components of the 447.1 nm He I line. Plasma is created using 9 ns, 140 mJ pulses from Nd:YAG laser at 1064 nm. Electron densities of ~5 × 10 cm are in good agreement with Thomson scattering measurements, benchmarking this emission line as a useful diagnostic for high density plasmas. © 2011 American Institute of Physics.

Configuration-interaction effects in and intensity dependence of F- multiphoton detachment

Two- and three-photon detachment rates have been obtained for F- using several expansions in the R-matrix Floquet approach. These rates are compared with other theoretical and experimental results. The use of Hartree-Fock wavefunctions for the ground state of F with addition of continuum electrons does not lead to agreement with experiment for two- and three-photon detachment. By adding correlation terms, agreement with experiment and other theoretical results is improved considerably, demonstrating the importance of electron correlation effects. However, convergence with respect to the wavefunction expansion cannot be established, we also study the intensity dependence of multiphoton detachment rates for F- at the Nd-YAG frequency. Due to the ponderomotive shift the three-photon detachment channel closes at an intensity of 8.5 x 10(11) W cm(-2) and the influence of this channel closure on the multiphoton detachment peaks is illustrated by determining the heights of the excess-photon peaks obtained using a Gaussian laser pulse.

Pseudophakic retinal detachment

Pseudophakic retinal detachment is a rare, but potentially serious, complication of cataract surgery. The incidence of pseudophakic retinal detachment following current surgical techniques of cataract extraction, including extracapsular cataract extraction by nuclear expression and phacoemulsification, is lower than that found after intracapsular cataract extraction. The risk of pseudophakic retinal detachment appears to be increased in myopic patients, in those patients in whom vitreous loss had occurred at the time of cataract surgery, and in patients undergoing Nd:YAG posterior capsulotomy. Most cases present to the clinician when the macula is already detached and the central vision is affected. When evaluating patients with pseudophakic retinal detachment, the fundal view is often impaired by anterior or posterior capsular opacification, reflections related to the intraocular lens, or poor mydriasis. Scleral buckling, pneumatic retinopexy, and primary pars plana vitrectomy, with or without combined scleral buckling, are the surgical techniques used to treat pseudophakic retinal detachment. Anatomical success rates are high after vitreo-retinal surgery for pseudophakic retinal detachment, although a smaller proportion of patients recover good vision following surgery. © 2003 Elsevier Inc. All rights reserved.

Investigation of magnesium laser ablated plumes with Thomson scattering

Optical Thomson scattering has been implemented as a diagnostic of laser ablated plumes generated with second harmonic Nd:YAG laser radiation at 532 nm. Thomson scattering data with both spatial and temporal resolution has been collected, giving both electron density, and temperature distributions within the plume as a function of time. Although the spatial profiles do not match very well for simple models assuming either isothermal or isentropic expansion, consideration of the measured ablated mass indicates an isothermal expansion fits better than an isentropic expansion and indeed, at late time, the spatial profile of temperature is almost consistent with an isothermal approximation.