飞秒脉冲激光沉积类金刚石膜实验研究

期望用类金刚石膜作为硅的红外保护/增透膜,采用波长为800nm,脉宽50fs,重复频率1KH z的T i:Sapph ire飞秒激光器及石墨靶材在单晶S i片上沉积了约0.7μm~1μm厚的类金刚石膜(d iam ond-like carbon film s,DLC),获得了光滑致密,硬度显著提高,红外透过率有一定增加的样品。通过对薄膜拉曼光谱和X射线光电子能谱等的测试,发现单脉冲能量在0.4m J~1.6m J范围内变动时,单脉冲能量0.8m J获得的类金刚石膜综合性能最佳,其对应的焦斑功率密度计算值为1.4×1014W/cm2。     

9.3μm脉冲CO_2激光倍频实验

介绍了利用9.3 μm脉冲TEACO_2激光通过AgGaSe_2晶体二次谐波产生(SHG)技术实现4.65 μm中红外波段激光输出的实验研究.根据非线性光学原理和倍频技术的基本要求,通过有针对性的技术手段选择TEACO_2激光器的输出谱线并控制脉冲波形的时间分布,使之满足激光倍频实验对泵浦脉冲光源在波长和输出时间分布上的基本要求,并以此为基波光源进行了产生二次谐波的实验研究.实验结果显示,即使是相同的AgGaSe_2倍频晶体材料,也会由于生产厂商的不同而具有完全不同的表面破坏阈值行为,而相同点是体损伤阈值均大于表面损伤阈值.实验获得倍频输出最大能量为12.9 mJ;倍频输出最高平均功率为940 mW. 4.65 μm中红外波段激光输出的实验研究.根据非线性光学原理和倍频技术的基本要求,通过有针对性的技术手段选择TEACO_2激光器的输出谱线并控制脉冲波形的时间分布,使之满足激光倍频实验对泵浦脉冲光源在波长和输出时间分布上的基本要求,并以此为基波光源进行了产生二次谐波的实验研究.实验结果显示,即使是相同的AgGaSe_2倍频晶体材料,也会由于生产厂商的不同而具有完全不同的表面破坏阈值行为,而相同点是体损伤阈值均大 表面损伤阈值.实验获得倍频输出最大能量为12.9     

9.3微米脉冲激光激光倍频实验

本文介绍了利用9.3m脉冲TEACO2激光通过AgGaSe2晶体二次谐波产生（SHG）技术实现4.65m中红外波段激光输出的实验研究。根据非线性光学技术原理和倍频技术的基本要求,通过有针对性的技术手段对于TEACO2激光器实现输出谱线选择和脉冲波形时间分布整形控制,使之尽量满足激光倍频试验对于泵浦的脉冲光源在波长和输出时间分布上的基本要求,并以此作为基波光源进行了产生二次谐波的试验研究工作。实验结果显示,即使是相同的AgGaSe2倍频晶体材料,由于生产厂商的不同具有完全不同的表面破坏阈值行为,而相同点是体损伤阈值均大于表面损伤阈值。实验上获得倍频输出最大能量12.9mJ;倍频输出最高平均功率940mW。     

准基模纯风冷激光二极管泵浦Nd∶YAG激光器

介绍一种纯风冷激光二极管泵浦的脉冲Nd∶YAG激光器,单脉冲能量250mJ,重复频率25Hz,脉冲宽度7ns,光光转换效率13.6%。激光器输出为准基模,垂直和水平方向的M2值测量结果分别为2.81和4.09。同样结构下将风冷系统换成风冷水冷结合方式,激光器脉冲能量345mJ,重复频率提高到50Hz,光光转换效率上升为15.2%。两种形式的激光器连续工作时间5min,并进行了高温+55℃和低温-25℃的环境试验。     

A high-power spatial filter for Thomson scattering stray light reduction

The Thomson scattering diagnostic on the High Beta Tokamak-Extended Pulse (HBT-EP) is routinely used to measure electron temperature and density during plasma discharges. Avalanche photodiodes in a five-channel interference filter polychromator measure scattered light from a 6 ns, 800 mJ, 1064 nm Nd:YAG laser pulse. A low cost, high-power spatial filter was designed, tested, and added to the laser beamline in order to reduce stray laser light to levels which are acceptable for accurate Rayleigh calibration. A detailed analysis of the spatial filter design and performance is given. The spatial filter can be easily implemented in an existing Thomson scattering system without the need to disturb the vacuum chamber or significantly change the beamline. Although apertures in the spatial filter suffer substantial damage from the focused beam, with proper design they can last long enough to permit absolute calibration.     

High-energy optically pumped molecular lasers in the 13- and 16-microm regions

This paper describes the construction of an optically pumped laser device. The device utilizes a line-tunable CO2 TEA laser as a source to optically pump a cell which is capable of cooling candidate laser gases down to approximately 150 degrees K. Laser outputs of 750 mJ in the 13-microm region and 100 mJ in the 16-microm region are obtained by pumping NH3 and CF4 respectively with 10 J of CO2 laser radiation. The measured conversion efficiencies are 15% for NH3 and 3% for CF4. These lasers can be used to photodissociate polyatomic molecules and are attractive sources for practical laser isotope separation.     

小型化单横模单纵模激光二极管泵浦Nd∶YAG激光器

在需要利用光的相干性的场合,如倍频、光参量振荡、全息以及光束的相干合成等对激光器输出的线宽有严格的要求,这时就需要对纵模进行选择。介绍一种小型化单横模单纵模激光二极管泵浦Nd∶YAG激光器,单脉冲能量3.6mJ,重复频率200Hz,脉冲宽度16ns,单横模、单纵模运转。该激光器采用谐振反射器和腔内倾斜标准具对纵模进行选择,试验结果与理论计算比较吻合。该激光器可用作窄脉宽高能激光器的种子源。     

Multiple-circuit pulse generator for high repetition rate rare gas halide lasers

A multiple-circuit high pulse repetition frequency (PRF) pulse generator for the pumping of rare gas halide lasers is reported. With this multiple-circuit design, high PRF can be achieved by the use of existing low PRF thyratron switches and capacitors. A two-circuit pulse generator was constructed, and its performance is described. By means of this pulse generator and a blowdown-type fast transverse-flow system, high PRF laser action in XeF was obtained, typically, 6 mJ/pulse at 1 kHz or 6 W average power. High PRF laser action in N(2) was also observed.     

Effect of process parameters in nanosecond pulsed laser micromachining of PMMA-based microchannels at near-infrared and ultraviolet wavelengths

This paper presents investigations on the effects of nanosecond laser processing parameters on depth and width of microchannels fabricated from polymethylmethacrylate (PMMA) polymer. A neodymium-doped yttrium aluminium garnet pulsed laser with a fundamental wavelength of 1,064 nm and a third harmonic wavelength of 355 nm with pulse duration of 5 ns is utilized. Hence, experiments are conducted at near-infrared (NIR) and ultraviolet (UV) wavelengths. The laser processing parameters of pulse energy (402–415 mJ at NIR and 35–73 mJ at UV wavelengths), pulse frequency (8–11 Hz), focal spot size (140–190 μm at NIR and 75 μm at UV wavelengths) and scanning rate (400–800 pulse/mm at NIR and 101–263 pulse/mm at UV wavelengths) are varied to obtain a wide range of fluence and processing rate. Microchannel width and depth profile are measured, and main effects plots are obtained to identify the effects of process parameters on channel geometry (width and depth) and material removal rate. The relationship between process variables (width and depth of laser-ablated microchannels) and process parameters is investigated. It is observed that channel width (140–430 μm at NIR and 100–150 μm at UV wavelengths) and depth (30–120 μm at NIR and 35–75 μm at UV wavelengths) decreased linearly with increasing fluence and increased non-linearly with increasing scanning rate. It is also observed that laser processing at UV wavelength provided more consistent channel profiles at lower fluences due to higher laser absorption of PMMA at this wavelength. Mathematical modeling for predicting microchannel profile was developed and validated with experimental results obtained with pulsed laser micromachining at NIR and UV wavelengths.     

基于透射式非稳腔的单纵模TEA CO_2激光器

为了获得TEA CO_2激光器高质量的单纵模输出,对种子注入锁定的TEA CO_2激光器进行了研究。首先,本文提出了一种透射耦合输出的虚共焦非稳谐振腔方案,利用Glad软件的Prony法对腔模的演化进行了仿真分析,并实验记录了近场与远场的光斑光强分布。仿真结果与实验结果吻合,验证了此腔型方案的合理性。其次,在此腔型的基础上进行了腔外种子注入锁定实验,实验结果显示:自由振荡时存在频率为195 MHz的拍信号,当种子注入锁定成功后,输出激光拍频消失,波形变光滑,峰值功率降低48.6%,脉冲产生时间缩短20ns。实验结果与已有成果吻合,验证了此种透射式非稳腔的TEA CO_2激光器具有输出高质量单纵模的能力。     

A dye laser with small beam divergence and a stable emission spectrum

The design of a dye-laser head with a hollow cylindrical cell is described. The cell is excited from the inside by a coaxial lamp. The design of the laser head provides the possibility of transverse circulation of the dye solution, which allows generation of sharply directed radiation with a spectrum and a directional pattern that remain constant during the laser pulse. A lasing energy of 290 mJ was obtained in the laser with an ethanol solution of Rhodamin 6G in a 150-mm-long cell with inner and outer diameters of 30 and 35 mm, respectively. The use of a resonator with an interference-polarization filter resulted in the spectrum narrowing to ～0.7 nm and allowed the radiation wavelength to be tuned in a band of ～31.5 nm. The beam divergence was within 5 mrad in all cases.     

CO2 laser pulse shortening by laser ablation of a metal target

A repeatable and flexible technique for pulse shortening of laser pulses has been applied to transversely excited atmospheric (TEA) CO(2) laser pulses. The technique involves focusing the laser output onto a highly reflective metal target so that plasma is formed, which then operates as a shutter due to strong laser absorption and scattering. Precise control of the focused laser intensity allows for timing of the shutter so that different temporal portions of the pulse can be reflected from the target surface before plasma formation occurs. This type of shutter enables one to reduce the pulse duration down to ~2 ns and to remove the low power, long duration tails that are present in TEA CO(2) pulses. The transmitted energy is reduced as the pulse duration is decreased but the reflected power is ~10 MW for all pulse durations. A simple laser heating model verifies that the pulse shortening depends directly on the plasma formation time, which in turn is dependent on the applied laser intensity. It is envisaged that this plasma shutter will be used as a tool for pulse shaping in the search for laser pulse conditions to optimize conversion efficiency from laser energy to useable extreme ultraviolet (EUV) radiation for EUV source development.     

Laser‐induced reversion of precipitates in an Al‐Li alloy: Study on temperature rise in pulsed laser atom probe

The influence of tuning the laser pulse energy during the analyses on the resulting microstructure in a specimen utilizing an ultra‐fast laser assisted atom probe was demonstrated by a case study of a binary Al‐Li alloy. The decomposition parameters, such as the size, number density, volume fraction, and composition of precipitates, were carefully monitored after each analysis. A simple model was employed to estimate the corresponding specimen temperature for each value of the laser energy. The results indicated that the corresponding temperatures for the laser pulse energy in the range of 10 to 80 pJ are located inside the miscibility gap of the binary Al‐Li phase diagram and fall into the metastable equilibrium field. In addition, the corresponding temperature for a laser pulse energy of 100 pJ was in fairly good agreement with reported range of solvus temperature, suggesting a result of reversion upon heating due to laser pulsing. Microsc. Res. Tech. 79:727–737, 2016. © 2016 Wiley Periodicals, Inc.     

Cranz-Schardin camera with a large working distance for the observation of small scale high-speed flows

The Cranz-Schardin camera utilizes a Q-switched Nd:YAG laser and four single CCD cameras. Light pulse energy in the range of 25 mJ and pulse duration of about 5 ns is provided by the laser. The laser light is converted to incoherent light by Rhodamine-B fluorescence dye in a cuvette. The laser beam coherence is intentionally broken in order to avoid speckle. Four light fibers collect the fluorescence light and are used for illumination. Different light fiber lengths enable a delay of illumination between consecutive images. The chosen interframe time is 25 ns, corresponding to 40 × 10(6) frames per second. Exemplarily, the camera is applied to observe the bow shock in front of a water jet, propagating in air at supersonic speed. The initial phase of the formation of a jet structure is recorded.     

High repetition rate laser produced soft x-ray source for ultrafast x-ray absorption near edge structure measurements

Recent progress in high intensity ultrafast laser systems provides the opportunity to produce laser plasma x-ray sources exhibiting broad spectrum and high average x-ray flux that are well adapted to x-ray absorption measurements. In this paper, the development of a laser based x-ray absorption near edge structure (XANES) beamline exhibiting high repetition rate by using the Advanced Laser Light Source (ALLS) facility 100 Hz laser system (100 mJ, 35 fs at 800 nm) is presented. This system is based on a broadband tantalum solid target soft x-ray source and a grazing incidence grating spectrometer in the 1-5 nm wavelength range. To demonstrate the high potential of this laser based XANES technique in condensed matter physics, material science, or biology, measurements realized with several samples are presented: VO2 vanadium L edge, Si3N4 nitrogen K edge, and BPDA/PPD polyimide carbon K edge. The characteristics of this laser based beamline are discussed in terms of brightness, signal to noise ratio, and compared to conventional synchrotron broadband x-ray sources which allow achieving similar measurements. Apart from the very compact size and the relative low cost, the main advantages of such a laser based soft x-ray source are the picosecond pulse duration and the perfect synchronization between this x-ray probe and a laser pulse excitation which open the way to the realization of time resolved x-ray absorption measurements with picosecond range time resolution to study the dynamics of ultrafast processes and phase transition.     

Application of a transmission crystal x-ray spectrometer to moderate-intensity laser driven sources

In the pursuit of novel, laser-produced x-ray sources for medical imaging applications, appropriate instrumental diagnostics need to be developed concurrently. A type of transmission crystal spectroscopy has previously been demonstrated as a survey tool for sources produced by high-power and high-energy lasers. The present work demonstrates the extension of this method into the study of medium-intensity laser driven hard x-ray sources with a design that preserves resolving power while maintaining high sensitivity. Specifically, spectroscopic measurements of characteristic Kα and Kβ emissions were studied from Mo targets irradiated by a 100 fs, 200 mJ, Ti: sapphire laser with intensity of 10(17) W/cm(2) to 10(18) W∕cm(2) per shot. Using a transmission curved crystal spectrometer and off-Rowland circle imaging, resolving powers (E/ΔE) of around 300 for Mo Kα(2) at 17.37 keV were obtained with an end-to-end spectrometer efficiency of (1.13 ± 0.10) × 10(-5). This sensitivity is sufficient for registering x-ray lines with high signal to background from targets following irradiation by a single laser pulse, demonstrating the utility of this method in the study of the development of medium-intensity laser driven x-ray sources.     

Single-shot microscopic electron imaging of intense femtosecond laser-produced plasmas

A simple technique for single-shot microscopic electron imaging was demonstrated for the study of intense femtosecond laser-produced plasmas. Passed through a permanent magnet lens designed for 110-keV electrons, hot electrons emitted from the plasma produced by a single laser pulse of 0.8 mJ with intensity of 3 × 10(16) W/cm(2) were successfully imaged. Analyzing this image, we found that electrons were emitted from an area of 3 μm in diameter. At higher laser intensity of 10(18) W/cm(2), distinct structures were observed in and near the focal spot of the laser; that is, the electrons were emitted from several separate spots. These results show that laser-plasma electron imaging is promising for studying the interactions of femtosecond lasers with high-density plasmas.     

A high-energy YAG: Nd<Superscript>3+</Superscript> laser with a phase conjugation in an optical fiber

An optical scheme and design of a YAG:Nd³⁺ frequency laser with a two-pass amplifier and a mirror with the phase conjugation by the stimulated Brillouin scattering in an optical fiber is described. The maximal radiation energy is 1000 mJ at a 1.064-μm fundamental wavelength and 500, 200, and 20 mJ at the second, fourth, and fifth harmonics, respectively, when the divergence is ∼5 × 10⁻⁴ rad and the pulse duration is 4.5 ns.     

激光诱导空泡微孔抛光机理及实验研究

针对微孔抛光的问题,提出了一种新的抛光方法,该方法利用激光聚焦水中产生空泡,并利用激光等离子体冲击波、空泡溃灭冲击波和射流推送磨粒进行微孔抛光。通过高速摄影仪和高频动态压力传感器对激光诱导空泡机理进行了研究。利用不同激光脉冲能量、脉冲次数和脉冲频率对304不锈钢管进行抛光实验,发现随着激光脉冲能量（7~21.6mJ）和脉冲次数（0~7000）的增加,微孔表面粗糙度也随之改善;同时激光在低脉冲频率（1~10Hz）情况下,改变脉冲频率的大小对微孔的抛光效果影响不大。对微孔在不同位置的抛光效果进行了对比分析,发现孔入口1~1.5mm处的抛光效果较好,孔中和孔尾的抛光效果不佳。通过激光诱导空泡微孔抛光机理和实验研究,表明微孔抛光过程是激光等离子体冲击波、空泡溃灭冲击波和射流共同作用的过程,并得到了激光微孔抛光的一般规律。     

Laser-BasedAmbientIonizationMassSpectrometry

Electrospray-assisted laser desorption ionization (ELDI) and laser-induced acoustic desorption (LIAD) mass spectrometry (MS) are useful techniques for directly characterizing small chemical or large biological components in solid or liquid under ambient conditions. Sample pretreatment is usually unnecessary for both techniques. The analytes molecules in the samples are desorbed by the action of a pulsed laser without the assistance of organic matrix. The desorbed molecules are subsequently ionized in an electrospray plume generated by electrospraying an acidic methanol solution. Recently, we have modified the existing ELDI and LIAD sources so unique applications are performed: 1) High throughput TLC/MS analysis - the TLC plate was linearly scanned by the laser from either side of the plate. Typically the systems allow to continuously screening up to 400 TLC plates per day. 2) Molecular imaging analysis - with the assistance of a stepper motor for precisely moving the sample plate and a high spatial resolution laser, the distribution of the predominant chemical compounds on a particular sample surface were obtained. The molecular images based on volatile and non-volatile chemical compounds on dry fungus and plant slices were obtained. 3) Monitoring chemical reaction - the states of ongoing chemical reactions－nanoparticle catalyzed photodecomposition of dye molecules in different organic solvents, were continuously monitored. 4) Protein structure study - the change of protein structure was studied via H/D and D/H exchange. The amino acids, peptides, and proteins with different exchangeable H atoms were chosen to ascertain the number of H/D or D/H exchanges in a reactive-ELDI/MS system. In addition, a new configuration of the electrospray system was built for both ELDI and LIAD sources. A multiple electrosprayer system was used to generate an atmosphere containing homogenously charged species. The efficiency of post ionization of the desorbed analyte molecules in the new ion sources is greatly increased. Different solvent systems can be simultaneously used to produce electrospray plumes to ionize the analyte molecules with different polarities.