Diode-laser frequency stabilization by two-frequency Doppler-broadened absorption spectroscopy

We demonstrate a robust method for frequency stabilization of a diode laser by two Doppler-broadened absorption spectra of the cesium D2 line. This technique employs an acousto-optical modulator to generate another frequency component from a diode laser to perform the spectroscopy. The 852-nm diode laser with frequency stabilization at the zero crossing of the error signal showed a peak-to-peak fluctuation of 800 kHz compared with a frequency-stabilized femtosecond laser over a 2-h period. This frequency-locking method is free of modulation and can be applied to frequency discriminators as well as to atomic resonances.     

激光化学诱导液相腐蚀新方法

提出了一种激光诱导液相腐蚀新方法——抗蚀膜掩蔽法。抗蚀膜掩蔽法是指在激光腐蚀中,用抗蚀膜来实现对激光腐蚀区域的控制。理论分析和实验结果都表明,抗蚀膜掩蔽法可以有效地控制激光化学腐蚀的图像形状;因不需要对激光光束进行聚焦,光传播垂直于基片表面,制作出的腐蚀孔侧壁可以具有很高的垂直度;利用激光光束中心区域能量分布近似均匀的特点,使小面积腐蚀区域的腐蚀速率近似相等,腐蚀面内各点没有明显的高度差。因为以上优点,抗蚀膜掩蔽法能克服现有激光腐蚀方法的诸多弊端,简化激光腐蚀工艺,在特殊结构光电器件和光电集成中具有广泛的应用前景。     

激光打印机打印歪斜度的校正方法研究

目的针对激光打印机常见的打印图像歪斜问题,以激光打印原理为理论基础,研究并设计打印歪斜的校正方法。方法首先,利用激光打印机自身的硒鼓结构制作测试组件,详细介绍其制作方法及工作原理;然后,设计专门的测试样张;最后,将测试组件放入打印机,并打印该测试样张。结果按照文中所述的方法可精确检测并调整激光束位置,从而达到校正打印歪斜度的目的。结论该方法可快速、精确地检测激光束的位置和歪斜状态,可将打印歪斜度精准校正至允许范围内,尤其适用于产品试制阶段的样机调试以及产品售后维保阶段。     

测试激光Raman分光计中超低杂散光的一种新方法

本文提出了一种利用高灵敏度的光子计数技术及中性滤光片分段减光方法去测试激光Raman分光计中超低杂散光的新方法。它不仅省去了大量级范围内光电检测系统线性检测与中性滤光片透过率标定的麻烦,提高了测试精度,而且实现了光强变化任意量级的杂散光测试,其测量限最终仪受激光功率大小的限制,获得了10~(-14)量级的杂散光测量限。     

Sub-micrometre distance measurements with a broadly tunable short-external-cavity InGaAsP/InP diode laser

Measurement of distance using a custom-designed, broadly tunable InGaAsP/lnP short-external-cavity diode laser is described. A tuning range of over 100 nm was achieved with the custom-designed laser in a diffractive optical element short external cavity. This tuning range made it possible to achieve a sub-micrometre resolution in measurement of distance with a single laser source for an interferometer. A non-linear, least squares fitting method was used to extract the displacement from the raw data. This fitting method showed a potential for extraction of accurate displacement in the presence of noise.     

Picosecond semiconductor lasers with a multisection saturable absorber, fabricated by heavy ion implantation

A method of implanting high-energy heavy ions across the emitter layer of a semiconductor laser has been developed to create distributed regions of ultrafast saturable absorber integrated into the cavity of a quantum-well laser. This method was used to fabricate picosecond laser diodes having high average powers and to demonstrate colliding-pulse mode-locking of a diode laser with a multisection saturable absorber. Pis’ma Zh. Tekh. Fiz. 25, 4–9 (July 12, 1999)     

一种基于光拍频的连续激光调制光谱测量方法

针对F-P干涉仪分析连续激光调制光谱的局限性,本文提出了一种基于光拍频的连续激光调制光谱的测量方法,该方法可实现调制频率低达千赫兹的连续激光调制光谱的测量.本方法以光电转换理论为基础,利用频谱分析仪测得参考光与连续调制光谱的拍频信号,然后通过相应的数学计算得到连续调制光谱的各个光频的相对电场强度,从而实现连续调制光谱的分析.本文在理论建模与分析的基础上,利用该方法对半导体激光器出射激光经电光调制器调制产生的调制光谱进行了测量,测量结果与F-P干涉仪测量结果一致,验证了该方法的可行性.     

A Double Resonance Method for Studying Collision Rates in an Intense Laser Field

Abstract

We propose a method for studying the modification of atomic collision rates in the presence of an intense laser field. This method employs a three-level lambda-system driven by two laser pulses: one strong and the other weak. The weak laser is used to populate a particular dressed state produced by the intense laser at some time during the pulse history. We show that this point can be selected by tuning the frequency of the weak laser. The spectrum of the emission produced by the dressed state is then recorded. Measuring this spectrum, both in the presence and in the absence of collisions, enables one to deduce the dependence of the collision rates on laser intensity. The method has other advantages discussed in the text.     

Non-contact strain measurement using metal foil gauges with the application of the laser speckle method

This paper presents a new method to measure cyclic strain with no contact using metal foil gauges assisted by the laser speckle method. When aluminium foil is pasted on a specimen and the specimen is loaded cyclically, slip bands are produced on the foil surface. There is a fixed relation between density of the slip bands and the strain amplitude or loading cycles depending on the foil material. Thus the fatigue strain of the base metal can be estimated by observing the surface change of the metal foil by the slip bands at a constant number of loading cycles. The method presented in this paper is intended to make a non-contacting strain measurement by the application of the laser speckle technique for the detection of the surface change. This method is based on observation of the changes in a laser speckle pattern depending on the surface roughness and surface property changes of the foil caused by fatigue. The laser speckle pattern can be analysed automatically and quantitatively using an image processing system.     

Nanosecond laser-induced photochemical oxidation method for protein surface mapping with mass spectrometry

We have developed an ultrafast pulse method for protein surface footprinting by laser-induced protein surface oxidations. This method makes use of a pulse UV laser that produces, in nanoseconds, a high concentration of hydroxyl (OH) free radicals by photodissociation of a hydrogen peroxide (H2O2) solution. The OH radicals oxidize amino acid residues located on the protein surface to produce stable covalent modifications. The oxidized protein is then analyzed by mass spectrometry to map the oxidized amino acid residues. Ubiquitin and apomyoglobin were used as model proteins in this study. Our results show that a single laser pulse can produce extensive protein surface oxidations. We found that monooxidized ubiquitins were more susceptible to further oxidations by subsequent laser irradiation, as compared to nonoxidized ones. This is due to the conformational changes of proteins by oxidation that increases the solvent-accessible surface area. Therefore, it is crucial to perform this experiment with a single pulse of laser so as to avoid oxidation of proteins after conformation of the protein changes. Subsequently, to obtain a high frequency and coverage of the oxidation sites while keeping the number of laser shots to one, we further optimized the laser power and concentration of hydrogen peroxide as well as the concentration of protein. This ultrafast OH radical generation method allows for rapid and accurate detection of surface residues, enabling mapping of the solvent-accessible regions of a protein in its native state.     

Rotating shutters: a mechanical way of flattening gaussian beam profiles in time average

A mechanical method of flattening the Gaussian intensity distribution of laser beams in time average is presented. Specially shaped rotating shutters are the key feature of this method, which has been applied to achieve homogeneous submicrometer patterning of macroscopically large samples by laser interference exposure. This method represents a simple yet useful alternative to applying beam broadening or degaussing plates (apodizing filters).     

Thermal tuning of laser pulse parameters in passively Q-switched Nd:YAG lasers

Modifying the output pulses of a passively Q-switched Nd:YAG laser, operating at 1064 nm, was realized by heating the laser crystal. With the demonstrated laser setups, a 100 K temperature rise led to a more than 50% increase in the pulse energy and a more than 10% decrease in the pulse length. This method offers an effective way to tune the output of the laser without mechanical adjustment or a change of components.     

基于激光多普勒原理的高温振动测量技术研究

为解决表面对激光反射强度极低的试件在持续高温环境下振动响应测量不准确的问题,本文提出了基于激光多普勒原理的高温振动测量技术。从激光反射信号增强、时域响应数据后处理、激光测振仪热防护三个方面进行研究,并通过试验验证了此方法的科学性和可靠性。     

光斑直径对含能材料激光点火性能的影响

用光电探测法研究了激光光斑直径对含能材料激光点火特性的影响.试验结果表明,在相同的激光能量下,光斑直径大,能量密度小;光斑直径小,能量密度高.过小的激光束会引起样品表面产生烧蚀和气化,带走部分激光能量,对点火过程不利,体现在点火延迟期变长了.同样,过大的激光束能量密度太小,不足以点燃含能材料.因此,选择合适的激光束直径对研究含能材料的激光点火特性很重要.     

一种全新的激光自动跟踪方法在激光移动通信中的应用

介绍了传统激光移动通信的特点及其不足，提出一种基于MOEMS(微光机电系统)技术的全新的激光自动跟踪方法。给出一个基于这种方法的激光移动通信系统实例，这种系统结构简单、体积小、重量轻、功耗低、控制简便，在一定的角度范围内能够自动跟踪目标实现移动通信。实验研究结果表明，这种系统能够很好地满足激光移动通信所要求的功能。     

激光深熔焊等离子光焰图像信息提取的研究

激光深熔焊是当今制造技术发展的前沿领域。在激光深熔焊接中产生的光致等离子体光焰会随焊接过程呈周期性的变化，而焊缝的熔透性与光致等离子体光信号的累积强度有对应关系。本文通过图像处理的方法，对光致等离子光焰图像进行分析和处理，为科学分析激光深熔焊光致等离子体的机理和变化规律提供了可靠的量化数据。     

Measuring optical fiber length by use of a short-pulse optical fiber ring laser in a self-injection seeding scheme

A method for measuring the length of an optical fiber by use of an optical fiber ring laser pulse source is proposed and demonstrated. The key element of the optical fiber ring laser is a gain-switched Fabry-Perot laser diode operated in a self-injection seeding scheme. This method is especially suitable for measuring a medium or long fiber, and a resolution of 0.1 m is experimentally achieved. The measurement is implemented by accurately determining the pulse frequency that can maximize the output power of the fiber ring laser. The measurement results depend only on the refractive index of the fiber corresponding to this single wavelength, instead of the group index of the fiber, which represents a great advantage over both optical time-domain reflectometry and optical low-coherence reflectometry methods.     

A Laser Scanner–Stage Synchronized System Supporting the Large-Area Precision Polishing of Additive-Manufactured Metallic Surfaces

This paper proposes a scanner–stage synchronized approach emphasizing a novel control structure for the laser polishing of Inconel 718 components manufactured by selective laser melting in order to address increasing demands for high surface quality in metal additive manufacturing. The proposed synchronized control system is composed of a motion decomposition module and an error synthesis module. The experimental results show that stitching errors can be avoided thanks to continuous motion during laser processing. Moreover, in comparison with the existing step-scan method, the processing efficiency of the proposed method is improved by 38.22% and the surface quality of the laser-polished area is significantly enhanced due to a more homogeneous distribution of the laser energy during the material phase change. The proposed synchronized system paves the way for high-speed, high-precision, and large-area laser material processing without stitching errors.     

Frequency stabilization of a single-frequency Q-switched Tm:YAG laser by using injection seeding technique

A stable single-frequency Q-switched Tm:YAG laser was demonstrated. The laser was injection seeded by a monolithic nonplanar ring oscillator laser utilizing the ramp-hold-fire technique. The measurements of the output parameters were presented. This paper focused on investigation of the frequency stability of the injection-seeded laser, which was measured by optical heterodyne technique. A method used to restrict the frequency jitter of the laser was discussed. The fluctuation of the laser frequency was reduced from 2.36 MHz (rms) to 1.07 MHz (rms) in 1 h by optimizing the voltage of the piezoelectric translator.     

偏振编码型光纤天线激光告警机的设计

为丁在激光告警中实现全方位角度探测,并且在一定探测精度的前提下尽量使结构简单、稳定,提出了基于偏振编码的光纤天线的测量方法.该方法是通过在不同方向上放置不同起偏角的偏振片编码,再将各个方向的光纤耦合成一束,经准直透镜组射入解偏光路中,通过判断电路分析得到激光入射方向.在计算及仿真了经偏振片后激光能量的衰减,求解电路能检测到最弱激光的幅值与偏振衰减最大时激光引起的响应电流的幅值的关系,得到在激光角分辨率为30°时满足探测要求.实验显示,在初始激光功率在20～150 mW的条件下,每20°划分的偏振角度中设定最小识别电压为20 mV时,满足全方位激光方向探测的要求.