Inexpensive, pulsed, tunable ir dye laser pumped by a flashlamp-driven dye laser

A flashlamp-driven dye laser with a 250-ns, 10-mrad divergence, 2-mm-diam beam at 620 nm is used to pump an ir dye laser. The ir laser pulses are tunable from 700 to 900 nm with spectral widths of less than 1 A. Peak ir powers of 100 W have been obtained with a 5-k W pump power.     

Epifluorescence microscopy with a pulsed nitrogen tunable dye laser source

This paper describes an epifluorescence system that uses a pulsed laser source as an excitation source for quantitative fluorescence measurements. A 1 μm diameter portion of the sample can be illuminated with high intensity, short light pulses and the fluorescence can be measured with a fast detection system. Selective excitation is possible at 337 nm and from 357 to 710 nm by using different dyes in the laser system. The spectral bandwidth is 0·1–3 nm. Several advantages over the commonly used systems with continuum spectral sources are indicated, especially when measured intensities are low, as in the case of intrinsic fluorescence of the sample, and where reflection of unwanted excitation light may cause appreciable errors when using conventional light sources.     

Prototypes using metal, carbon fiber and composite field emission sources modulated by a laser beam.

Field emission of electrons from a variety of metallic, carbon fiber and composite metal-insulator micropoint cathodes was employed in this study. Tungsten, carbon fiber and ZrC tips, were studied using a field emission microscope. These cathodes were characterized and the current-voltage (I-V) characteristics were determined. A variety of surface treatment procedures were carried out to increase the stability of emission. These electron sources were mounted in sealed prototype field emission tubes, while others were tested under medium, high and UHV conditions. The emission current switch-on phenomenon was found with all non-metallic cathodes. The emitters were then subjected to a square wave-modulated, maximally focused laser diode beam (lambda = 658 nm, 30mW). The beam impedance (approximately 1 Gohms) and the anode capacitance (approximately 10 pF) act as a low-pass filter.     

Wide-field turbulence imaging with beam emission spectroscopy

Imaging of the size, shape, time-averaged, and time-resolved dynamics of long-wavelength density turbulence structures is accomplished with an expanded, high-sensitivity, wide-field beam emission spectroscopy (BES) diagnostic on DIII-D. A 64-channel BES system is configured with an 8×8 grid of discrete channels that image an approximately 7×9?cm region at the outboard midplane. The grid covers multiple correlation lengths and each channel shape matches the measured radial-poloidal correlation length asymmetry of turbulent eddies. The wide field 8×8 imaging capability allows for sampling of essentially the full two-dimensional spatial correlation function for typical plasma conditions. The sampled area can be radially scanned over 0.4相似文献   

A new confocal scanning beam laser MACROscope using a telecentric,f-theta laser scan lens

A new confocal scanning beam system (MACROscope) that images very large-area specimens is described. The MACROscope uses a telecentric, f-theta laser scan lens as an objective lens to image specimens as large as 7·5 cm × 7·5 cm in 5 s. The lateral resolution of the MACROscope is 5 μm and the axial resolution is 200 μm. When combined with a confocal microscope, a new hybrid imaging system is produced that uses the advantages of small-area, high-speed, high-resolution microscopy (0·2 μm lateral and 0·4 μm axial resolution) with the large-area, high-speed, good-resolution imaging of the MACROscope. The advantages of the microscope/MACROscope are illustrated in applications which include reflected-light confocal images of biological specimens, DNA sequencing gels, latent fingerprints and photoluminescence imaging of porous silicon.     

Proton emission from a laser ion source

At intensities of the order of 10(10) W∕cm(2), ns pulsed lasers can be employed to ablate solid bulk targets in order to produce high emission of ions at different charge state and kinetic energy. A special interest is devoted to the production of protons with controllable energy and current from a roto-translating target irradiated in repetition rate at 1-10 Hz by a Nd:Yag pulsed laser beam. Different hydrogenated targets based on polymers and hydrates were irradiated in high vacuum. Special nanostrucutres can be embedded in the polymers in order to modify the laser absorption properties and the amount of protons to be accelerated in the plasma. For example, carbon nanotubes may increase the laser absorption and the hydrogen absorption to generate high proton yields from the plasma. Metallic nanostrucutres may increase the electron density of the plasma and the kinetic energy of the accelerated protons. Ion collectors, ion energy analyzer, and mass spectrometers, used in time-of-flight configuration, were employed to characterize the ion beam properties. A comparison with traditional proton ion source is presented and discussed.     

Q-switched fiber laser with controllable output spectrum

This paper reviews studies of the possibility of controlling the output spectrum of Qswitched fiber lasers. Various laser configurations for producing output radiation with characteristics optimized for specific applications, such as high-power pulses for micromachining of materials, probe pulses in fiber-optic sensor systems, etc., are considered. The mechanism of broadening of the lasing line is elucidated, and methods for controlling the output spectrum in Q-switched all-fiber lasers are described. Frequency tuning in the amplification line and generation of higher harmonics in nonlinear crystals are considered.     

一种激光束形参数简便测试方法

在以激光作为测试光源的高精度测试装置中,激光器实际输出的束形参数值与其标称值的偏离会直接传递并影响到后续测试结果的准确度。提出一种基于CCD的多点测试方法,此方法在不降低测量精度的条件下可实现激光束形参数的简便测试。在搭建的测试装置上实现了633nm He-Ne激光器束腰半径、远场发散角和M2质量因子的测量,可以方便地评价激光光束质量。将束形参数简便测试方法的结果与法国Phasics公司的SID4波前探测器的测量结果进行了比对,结果表明,激光束形参数简便测试方法不仅能用于激光束形参数的简便检测,而且具有较高的精度。     

Separation of emission lines of multiply charged ions against background of a very noisy spectrum of femtosecond laser plasma

At high intensities of interaction of femtosecond laser pulses with various targets, numerous high-energy particles emitted from plasma in all directions lead to the appearance of parasitic peaks in the X-ray spectra of femtosecond laser plasma (FLP) during detection of these peaks with a detector based on a charge-coupled device (CCD). The algorithm proposed in this study allows identification of parasitic peaks in a series of experimental spectra, which are recorded for each pixel of the CCD detector independently of other pixels, and removal of these peaks. The algorithm is able to detect peaks in the presence of both variations in the intensities of spectral lines and very intense noise. The efficiency of the algorithm has been confirmed via testing with the use of a series of model spectra and spectra of Fe and Al ions recorded in experiments devoted to studies of the interaction of ultrahigh-intensity and ultrashort laser pulses with solid targets.     

Study of a hollow laser beam for cladding

Laser cladding, as a promising manufacturing technology, has been widely used in industry for component recovery and surface modification. In this paper, a hollow laser beam was proposed to optimize the laser intensity distribution. A three-dimensional (3-D) finite element (FE) model was developed using ANSYS to investigate the thermal field in the clad deposited by a hollow laser beam. The thermal results, such as the temperature distribution and the cooling rate, were investigated. The effect of the hollow ratio between the inner and outer radius of the hollow beam on the molten pool shape was also studied. The temperature at the boundary of the molten pool was higher than at the center. A clad with a flat metallurgical bonding was formed. The microstructure in the clad was mainly consisted of fine dendrites except the large columnar structures along the bonding. The hardness distribution of the clad was associated with the grain size distribution and the dilution by the substrate. The molten pool was not able to be generated with a high hollow ratio, while overheated at the center with a low hollow ratio. Based on the comparison with the Gaussian laser beam, the hollow laser beam could effectively alleviate the overheating at the center of the clad.     

Hybrid treatment by a laser beam and surface plastic deformation

The formation of multilayer oriented microstructure and surface roughness under the action of continuous laser radiation and surface plastic deformation is considered.     

Highly precise and stable displacement-measuring laser interferometer with differential optical paths

To achieve sub-nm precision of a displacement-measuring laser interferometer, its optical systematic error should be made as small as possible. In this paper, methods to reduce the optical path length changes and stray light reflections, as well as materials appropriate for main optical elements in the optical layout and the holders, are discussed. As a solution, a complete differential interferometer using a quartz plate inclined 45° to the optic axis is presented. This interferometer has null dead path length, fewer and smaller optical elements, and fewer boundary surfaces with air than conventional differential interferometers. Adopting the athermal glass (Ultran30) for interferometric prisms and aluminum alloy (A5056) for the interferometric prism holder was effective in reducing the drift of measurement caused by thermal changes. The interferometer made of Ultran30 glass with a A5056 holder achieved 0.31 nm/K thermal drift in the displacement measurement.     

Collimation testing of laser beam with holographic optical elements

The shear elements in the shear interferometers of collimation test are commonly plane parallel plates or wedge plates of a small wedge angle. A new holographic shear element that acts as the wedge plate is proposed. The interferometer composed of holographic shear lenses has the advantages of high contrast fringes and adjustable shear amount. It posses the flexibility of altering the measurement sensitivity in a broad range, has more suitability and can meet different measuring requirements. Detailed analysis for the experimental configuration of this system is presented.     

Vacuum electron acceleration and bunch compression by a flat-top laser beam

The field intensity distribution and phase velocity characteristics of a flat-top laser beam are analyzed and discussed. The dynamics of electron acceleration in this kind of beam are investigated using three-dimensional test particle simulations. Compared with the standard (i.e., TEM(00) mode) Gaussian beam, a flat-top laser beam has a stronger longitudinal electric field and a larger diffraction angle. These characteristics make it easier for electrons to be trapped and accelerated by the beam. With a flat-top shape, the laser beam is also applicable to the acceleration of low energy electron and bunch compression.     

Stark spectroscopy of a probe lithium beam excited with two dye lasers as a technique to study a high-power ion-beam diode

A non-disturbing measurement of electric field distributions is a subject of special interest in plasma physics and high-voltage devices. In this paper we describe a diagnostic technique for remote sensing of electric fields via injection of a probe beam of lithium atoms and cascade excitation of resonance fluorescence with two broadband dye lasers. The fluorescence spectrum was recorded using a monochromator equipped with an optical multi-channel analyser. The magnitude of the local electric field was retrieved from the Stark-shifted components of the 3d-2p lithium spectral line. The technique was applied to measurements of the electric field in the applied-B-field high-voltage diode of the 1 TW KALIF ion-beam accelerator.     

A modification of the laser detonation-type hyperthermal oxygen atom beam source for a long-term operation

It has been an impedimental problem, for the laser detonation-type atom beam generator, that a poppet in the pulsed supersonic valve is rapidly eroded by the irradiation of powerful laser light and high temperature plasma. In order to operate the atom beam source for a long duration, a modification was made to hide the poppet from direct irradiation of laser and plasma. The alteration of device configuration resulted in great improvement in endurance of poppet more than 300,000 repetitions. Morphology of a polyimide film exposed to approximately 200,000 pulses of hyperthermal oxygen atom beam showed a shaglike carpet structure, which is a characteristic to that exposed to energetic oxygen atoms. A flux of the oxygen atom beam was estimated to be 5x10(14) atoms/cm2/pulse at a location of 30 cm away from the nozzle throat.     

大变倍比近红外无焦激光扩束系统

为研究闪电特性,设计了用于闪电实验室场景模拟的大变倍比近红外无焦激光扩束光学系统,用于模拟不同光斑尺寸的闪电单元.根据高斯光学几何法计算系统外形尺寸,合理确定了各组份的口径及光焦度;由ZEMAX软件包优化设计得到系统的光学结构参数,并对系统整体性能进行了分析评价.该系统变倍比为13,出射光束光斑均匀、无衍射环,满足研究闪电信号特性的需求.激光扩束系统的中心工作波长为777.4 nm,入射光束直径为1.0 mm,入射激光光束在步进电机驱动下连续可调,使得出射光束可从φ0.8 mm变化到φ10.6 mm.系统具有镜片少,结构简单,变焦轨迹平滑无卡滞等优点,可用于模拟不同尺寸的闪电单元.     

液体表面张力激光快速测量法

基于插板法测液体表面张力系数的基本原理,介绍了一种利用半导体激光器及准直光学系统输出的矩形平行光束,结合线阵CCD传感器,实现液体表面张力系数快速测量的方法。通过测量激光束两边沿在液体表面的入射角来求得表面张力系数,解决了插板法测液体表面张力系数的液面上升高度和接触角检测难题,避免了人为因素的影响。推导了矩形激光束两边沿在液体弯月面的入射角与表面张力系数的关系,以及用CCD测量激光入射角的计算公式,并进行了参数设计和误差分析。结果表明:为了提高液体表面张力系数的测量精度,在满足测量条件下,应采用尽可能大的矩形激光束宽度、激光入射角和CCD相对距离。理论分析表明,当光束宽度的测量误差为5 μm时,水的表面张力系数测量精度为1%。若将光束宽度的测量误差减小到2 μm,则水的表面张力系数理论精度可达0.5%。实验结果证明了水的表面张力系数测量精度达到1%。