激光测距仪信噪比与激光发散角最佳值的选取

研讨激光测距仪的信噪比和激光发散角如何选取最佳值的问题。如果信噪比为SNR，激光发散角为θt，则取SNR θt^2最小时的信噪比和激光发散角为最佳值。     

Lasers for ICF with a Controllable Function of Mutual Coherence of Radiation

The current status of laser thermonuclear fusion research in the leading world scientific centers is characterized by the development of superhigh-power multi-channel laser facilities of megajoule pulse-energy level. The development of such laser installations operating in the pulse-repetition mode with a large number of laser beams, which are necessary for high-symmetry irradiation of a spherical thermonuclear target, is an extremely difficult physical and engineering problem. The concept of a special laser with a controllable function of mutual coherence of radiation is proposed. The studies performed demonstrate that a laser based on such a principle has a number of advantages as compared to the conventional schemes of lasers. In particular, the optical scheme of the laser is significantly simplified, and the cost of the output-energy unit is reduced by several times. The influence of radiation coherence on the homogeneity of the thermonuclear target irradiation is analyzed. The feasibility of suppressing the small-scale self-focusing without application of spatial filtration is shown. A module of the laser facility has been triggered to check the validity of the principles proposed for constructing a laser driver for power stations, and the first experimental results are reported. The possibility of controlling the coherence of laser beams used in ICF experiments without violation of the laser--target system matching is demonstrated, as well as controlling the distribution of the laser radiation intensity in the lens focus.     

倍频纳秒激光驱动类氖锗X射线激光的研究

利用JB19等程序分别对基频和倍频激光驱动条件下类氖锗X射线激光进行了模拟计算,结果表明利用倍频激光驱动同样也能够获得高强度的类氖锗X射线激光输出,只是对驱动激光的输出要求要高3.3倍.尽管如此,这也为将来在大型激光装置上开展类氖系列X射线激光研究指明了方向.初步的实验研究也证实了利用倍频纳秒激光驱动能够获得类氖锗X射线激光输出的结果. 关键词： X射线激光 类氖锗 数值模拟     

A comparative study on diode-pumped single-frequency Tm:YAG and Tm:GdVO<Subscript>4</Subscript> lasers

In this paper, we present experimental results concerning on the laser characteristics of Tm:YAG laser and Tm: GdVO₄ laser. At room temperature, the maximum output power of Tm:YAG laser and Tm:GdVO₄ laser is 210 and 145 mW, respectively. High efficiency can be achieved for both lasers at room temperature. Nevertheless, compared with Tm:GdVO₄ laser, Tm:YAG laser can operate on single frequency with high power easily. As much as 60 mW of 2013.9 nm single-longitudinal-mode (SLM) laser was achieved for Tm:YAG laser. For Tm:GdVO₄ laser 51 mW of 1919.7 nm SLM laser was achieved. The SLM Tm:YAG laser is better for using as a seed laser for coherent wind measurements and differential absorption LIDAR systems.     

激光器与轨道的相对位置对动态加热的影响

 通过分析光束入射的角度因子将激光器在地平面上的安放位置进行分类,采用了几何分析和数值模拟的方法,探讨了聚焦激光束在加热运动圆柱体过程中,为了达到一定的加热功率水平和能量水平以取得最好的加热效果而应采取的措施,即应当以激光垂直入射的轨道点为中心,以激光的有效工作时间为取值范围,并参考大气对激光能量的衰减,相对于轨道选取适当的距离进行加热。该研究从理论上说明了激光器与圆柱体运动轨道的相对位置对激光动态加热的影响可以看作一个优化问题,存在最优解,进而对于合理使用激光器进行动态加热具有参考价值。     

光束指向稳定性高精度检测方法研究北大核心CSCD

光束指向稳定性是高能激光应用研究中的一项关键指标,光束指向稳定性的检测是高能激光系统性能实现的重要环节。以长焦距聚焦反射镜与高分辨率CCD(charge coupled device)为主要元件,构建高精度的光束指向检测装置。采用灰度重心法定位光斑中心,并以理想光斑与实测光斑为例进行验证,误差小于1个像元。利用CCD高频采样,统计单位时间内光斑中心位移,获得光束指向稳定性指标,检测实例精度可达1.25μrad。该方法简便易行,测量精度高,适用于各种波长的激光光束指向检测以及其他相关参数的测量。     

Wakefield generation by elliptically polarized femtosecond laserpulse in ionizing gases

Wakefield generation by a femtosecond laser pulse is described in the frame of the slowly varying amplitudes approximation. The amplitude of the wakefield A, is studied as a function of laser pulse and background gas parameters, and is compared with well-known results for preformed, completely ionized plasma A_p,i. It is found that the ionization processes can increase A_p as compared to A_p,i at comparatively high laser peak intensities. It is shown that the increase of the wakefield amplitude due to gas ionization is more pronounced for circularly polarized laser pulses than for linearly polarized laser pulses. The strongest enhancement of A_p in comparison with A_p,i takes place for longer laser pulses with a duration in excess of the plasma wave period when the resonant conditions for ponderomotive excitation of the wakefield are not matched. Thus, ionization processes can expand the region of parameters for efficient generation of the laser wakefields     

Single-longitudinal-mode fiber laser with a passive multiple-ring cavity and its application for video transmission

A single-longitudinal-mode erbium-doped fiber laser with a passive multiple-ring cavity (MRC) is proposed for the first time to the authors' knowledge. The laser is fundamentally structured by insertion of three different short ring cavities, which serve as mode filters, into the main cavity. When it is combined with a mode-restricting intracavity fiber Bragg grating, the MRC resonator ensures single-longitundinal-mode laser oscillation. The laser can successfully suppress side-mode frequencies of as much as 1 GHz and provide an output power of 23 mW with a side-mode suppression ratio of 51 dB at 1533 nm. The short-term linewidth of the laser output measured is ~2 kHz . The ability of this fiber laser to act as an AM transmitter source is also demonstrated.     

The Intra-cavity Mode Competition and Laser Absorption Spectroscopy with CO2 Laser

A mathematical model is developed for analysis the dynamics of an intra-cavity laser spectroscopy and mode competition using the CO₂ laser as the coherent source. The governing equations of system are derived and effect of the absorbing material on the laser modes, as a time-dependent term is considered. Thus, the application of the CO₂ laser for intra-cavity laser spectroscopy with considering an inhomogeneous medium and effect of the absorbing material is investigated.     

基于等离子体紫外辐射的强激光自动寻焦系统

精准定位激光束焦点位置是提高激光雕刻、切割、焊接等加工精度的重要基础，而传统测量方法不适用于自动寻找强激光焦点。基于激光烧蚀金属后等离子发光含大量紫外谱线的原理，以日盲的氮化镓肖特基光电二极管为传感器，设计了以304不锈钢靶材为耗材的红外强激光束自动寻焦方法及其装置。该方法与共聚焦显微镜检测平均烧蚀坑深的方法相比，当以脉冲宽度100 ns、重复工作频率20 kHz、平均功率10 W的1064 nm光纤激光雕刻机为实验对象时，二者定焦位置相差24 μm。     

Mass spring lattice modeling of the scanning laser source technique

The scanning laser source (SLS) technique is a promising new laser ultrasonic tool for the detection of small surface-breaking defects. The SLS approach is based on monitoring the changes in laser generated ultrasound as a laser source is scanned over a defect. Changes in amplitude and frequency content have been observed for ultrasound generated by the laser over uniform and defective areas. In this paper, the SLS technique is simulated numerically using the mass spring lattice model. Thermoelastic laser generation of ultrasound in an elastic material is modeled using a shear dipole distribution. The spatial and temporal energy distribution profiles of typical pulsed laser sources are used to model the laser source. The amplitude and spectral variations in the laser generated ultrasound as the SLS scans over a large aluminum block containing a small surface-breaking crack are observed. The experimentally observed SLS amplitude and spectral signatures are shown to be captured very well by the model. In addition, the possibility of utilizing the SLS technique to size surface-breaking cracks that are sub-wavelength in depth is explored.     

低功率激光热透镜效应的模拟及研究

与高功率激光相比,低功率激光更安全,其热透镜效应对激光功率变化更敏感,更适合用于实验教学.本文利用有限元法模拟低功率激光的热透镜效应,模拟介质温度场和等效热透镜焦距,定量探究低功率激光热透镜焦距与激光功率以及介质热吸收率、厚度的关系.模拟结果与实验数据符合良好,为探究低功率激光热透镜效应实验提供理论依据.     

Comparison of Laser Chemical Processing and LaserMicroJet for structuring and cutting silicon substrates

This paper deals with the development of a new cutting method for thin silicon solar wafers with liquid-jet-guided lasers (LaserMicroJet®, LMJ, and Laser Chemical Processing, LCP). Several laser systems with different wavelengths were tested to find the optimum laser system and processing parameters in terms of efficient material removal and deep laser cutting. Water and potassium hydroxide were used as carrier liquids to enhance laser ablation. The ablation efficiency was defined as a target parameter and experimentally determined by performing single laser grooves. It is demonstrated that the ablation process of LMJ is mainly affected by silicon melting and then removing by the liquid-jet momentum for single laser grooves. Best result for deep laser grooves is achieved if evaporation dominates the ablation process. Better surface quality referred to laser-induced crystalline damage is presented for a cut wafer with LMJ in comparison to a standard multiwire slurry saw. This shows a great potential of wafering with liquid-jet-guided lasers although no optimal liquid media was used.     

高能光纤激光经准直系统后的光束质量研究

应用光线光学的理论,对透镜的几何像差、热非线性等因素对光纤激光光束质量的影响进行了分析和计算,给出了激光通过多透镜光学系统后,光束质量参数M²与系统参数的一般关系. 研究了高能光纤激光通过准直系统后的光束质量. 研究结果表明,随着激光功率的增大,经准直系统后光束的光束质量存在最佳值,其对应的激光功率与准直系统参数有关,为高能光纤激光准直系统的设计提供了参考. 关键词： 高能光纤激光 光束质量 准直系统 光线光学     

Multiwavelength investigation of laser-damage performance in potassium dihydrogen phosphate after laser annealing

The laser-induced damage performance of potassium dihydrogen phosphate and deuterated potassium dihydrogen phosphate nonlinear optical crystals after pre-exposure to lower-energy laser pulses (laser annealing, also known as laser conditioning) is investigated as a function of wavelength for both the damaging and conditioning pulses. We obtain a quantitative evaluation of the bulk damage performance of these materials by measuring the density of damage events as a function of laser parameters. This new method allows for a detailed assessment of the improvement of material performance from laser conditioning and reveals the key parameters for optimizing performance depending on the operational wavelength.     

An investigation of pulsed laser cutting of titanium alloy sheet

Subsequent welding requirement calls for high-quality laser cut surfaces in the laser cutting of bladed ring parts for aeroengines. This paper presents pulsed laser cutting of titanium alloy sheet and investigates the influences of laser cutting parameters on laser cut quality factors including heat-affected zone (HAZ), surface morphology and corrosion resistance. The thickness of HAZ lasers is studied in detail as a function of laser cutting parameters. For different assist gases the surface morphology and corrosion resistance show great differences. In comparison with air- and nitrogen-assisted laser cutting, argon-assisted laser cutting comes with unaffected surface quality and is suitable for laser cutting with subsequent welding requirement.     

Cutting and welding using a CO2 laser

Of all the types of lasers now available, the CO₂ laser is particularly suitable for materials working. It has a very high efficiency (15–20%) and a high out-put power (up to several kW). When the laser light is focused by means of a lens or a mirror, a c.w. power density of more than 10⁹ W cm^-2 can be attained. The laser need not be used in vacuum.

The CO₂ laser is a suitable cutting tool for numerous materials. These include metals such as titanium or steel; combustible materials such as paper, textiles and wood; and plastics. The CO₂ laser can also cut hard and brittle materials such as aluminum oxide and silicon carbide. If metals are cut in an oxidizing atmosphere, the cutting speed may be increased. The cutting width, however, is determined by the size of the laser spot. Another important field of application is the growth of single crystals.

Experiments are reported in which the CO₂ laser was used for welding steel, titanium, plastics, quartz, and glass. The advantages of the laser for this application are discussed. A comparative study of laser and electron beam techniques is included.     

Diagnostic system for two dimension intensity distribution of laser beam

The diagnostic system for two dimension(2-D)intensity distribution of laserbeam is a measuring instrument for many parameters of laser beam.2-D intensity distributionplot of laser beam is obtained by the two dimension scanning mirror which is controlled by amicrocomputer to scan the laser beam on a detector.Many parameters of laser beam such asthe isointensity distribution plot,the beam diameter,the beam waist diameter,the laser pow-er,the diverge angle and the beam brightness,are given by means of the microcomputer pro-cessing the data measured.Theoretical analysis of beam parameter transform is given.     

大芯径空气包层微结构光纤实现kW级激光传输

kW级高功率激光柔性传输是激光清洗、激光焊接、激光刻蚀等高功率激光加工领域中必备的环节,而实现高功率激光低损耗传输的光纤是其关键器件。目前高功率激光传输光纤采用大芯径传能光纤,仍然存在着弯曲损耗大、柔性差等问题,并且使用过程中要经常维护。华南师范大学特种光纤研究中心提出一种大芯径空气包层微结构光纤,利用包层的空气孔可以极大降低激光泄露的风险,降低光纤制备过程中对耐高温涂敷层的严苛要求,实验结果证实该光纤在室温无制冷条件下可实现kW级激光传输,从而为10 kW级高功率激光柔性传输奠定基础。     

Diode-pumped regenerative amplifier delivering 100-mJ single-mode laser pulses

We report on a side-pumped Nd:phosphate laser regenerative amplifier that delivers laser pulses of as much as 100 mJ in a single TEM mode. The laser beam is mode matched to the amplification medium by an intracavity fused-silica phase plate for mode shaping and a telescope for adjustment of the beam mode to the amplification rod section such that most of the energy stored in the rod is transferred to the laser pulses. As a result of the good overlap and the low loss, an optical-to-optical conversion efficiency of as much as 10% was measured for a pumping current of 80 A and greater than 100-mJ output pulses.