Definition and measurements of high-power laser beam parameters

Three definitions of the beam quality, characterized by waist radius and far-field divergence, of high average power laser beams are investigated. The beam parameters can be defined by their second moments, the power content profile and the power content area. The methods of measurement are described in detail and compared with respect to their suitability for two high-power laser systems: a cw Nd:YAG-rod laser and an annular system. The validity of theABCD law was checked experimentally. Additionally, third and fourth-order intensity moments were used to characterize the laser field in more detail.     

Optimization of laser beam welding process parameters to attain maximum tensile strength in AZ31B magnesium alloy

An empirical relationship is developed to predict tensile strength of the laser beam welded AZ31B magnesium alloy by incorporating process parameters such as laser power, welding speed and focal position. The experiments were conducted based on a three factor, three level, central composite face centered design matrix with full replications technique. The empirical relationship can be used to predict the tensile strength of laser beam welded AZ31B magnesium alloy joints at 95% confidence level. The results indicate that the welding speed has the greatest influence on tensile strength, followed by laser power and focal position.     

Laser cooling with a single laser beam and a planar diffractor

A planar triplet of diffraction gratings is used to transform a single laser beam into a four-beam tetrahedral magneto-optical trap. This "flat" pyramid diffractor geometry is ideal for future microfabrication. We demonstrate the technique by trapping and subsequently sub-Doppler cooling (87)Rb atoms to 30 μK.     

Automatic compensation of laser beam focusing parameters for flying optics

Flying optics technologies are used for a range of applications such as a large workpiece processing and laser texturing. It is essential to compensate the variations of laser beam focus parameters while the focus head is moving. A flying optics automatic compensation approach is proposed to achieve invariable laser focal size, focus depth and focus position through computer controlled objective lens and focus lens position. A simple mechanical control method is also presented for the realization of constant beam parameters for flying optics. Numerical simulation is illustrated for a CO₂ laser texturing application. The flying optics parameters compensation is simple and easy to control.     

Asymmetrical optical fibre coupler for laser side pumping: optimization of its parameters and application in laser

The paper presents an optical fibre coupler with side coupling. The coupler is based on an active double clad fibre and a pumping fibre with an extended core. The optimization of the coupler’s parameters and the initial simulations results are presented. The coupler was used in a ring laser setup and multiwavelength operation with up to 25 wavelengths was achieved.     

Study of the structure and parameters of a KrF excimer laser beam

For a KrF excimer laser with a confocal unstable resonator, energy distribution over the beam cross-section was measured with the aid of luminescence in the glass induced by the UV laser radiation. A complex fine structure of the beam has been found. In an area close to the focus, measurements were carried out by means of two different methods??via thermal paper blackening and via ablation craters on a glass surface. The complex beam structure above has been shown to persist also in the immediate vicinity of the beam waist. Measured cross-sectional waist dimensions varied significantly within a range from 0.3 to 0.6?C1.3 mrad depending on the measuring procedure applied. Using a short-focus nonaberrational lens one could obtain a focal spot with linear dimensions of several tens of micrometers.     

可调谐二极管激光吸收光谱技术参数选择及优化

可调谐二极管激光吸收光谱技术(TDLAS)系统性能受调制参数,如调制度、调制频率、扫描幅度及扫描频率影响,实际测量中各参数不存在明确的选择依据。针对此问题,文章在一定的理论基础上通过实验分别观察各调制参数对二次谐波信号的影响,通过分析检测信号的特征,如幅值、信噪比、对称性及峰宽得出其变化规律,总结出在不同系统功能和需求下系统各调制参数的优化依据及方法。系统在计算浓度和温度时应优先考虑幅值和信噪比,从而使调制度达到最佳值,调制频率和扫描频率取较小值;在线形推导压强时优先考虑信号的对称性和峰宽,根据计算的具体要求确定调制参数;扫描幅度的确定以得到完整谐波信号为准;再根据系统的速度和精度需求调整扫描频率。该研究为此类系统工作状态的确定提供了实验依据。     

Theoretical studies on beam parameters of a self－start ring cavity Ti：sapphire laser

Ｔｈｅｏｒｅｔｉｃａｌ ｓｔｕｄｉｅｓ ｏｎ ｂｅａｍ ｐａｒａｍｅｔｅｒｓ ｏｆ ａ ｓｅｌｆ－ｓｔａｒｔ ｒｉｎｇ ｃａｖｉｔｙ Ｔｉ：ｓａｐｐｈｉｒｅ ｌａｓｅｒ￥ＺＨＡＮＧＧｕｉｚｈｏｎｇ；ＺＨＥＮＧＸｕｅｍｅｉ；ＷＡＮＧＱｉｎｇｙｕｅ（Ｄｅ...     

非相干光纤激光组束中光栅参数的确定

光栅衍射效率是非相干光纤激光组束系统的关键,理论分析和数值仿真表明光栅衍射效率随着光栅频率和光栅厚度的减小而增大。全面综合考虑光栅频率应该选取在200mm-1和400mm-1之间,光栅厚度在1mm到2mm之间。同时提出了一种不等间隔方法提高系统总体衍射效率,该方法较等间隔条件下衍射效率提高了0.1651。     

Laser nitriding of iron: Influence of the laser parameters on the nitriding efficiency

Laser nitriding of Armco iron in nitrogen was studied for KrF-excimer-laser irradiation. The influence of the energy density and number of pulses on the nitrogen take-up and the nitride phases formed was investigated using Resonant Nuclear Reaction Analysis (RNRA) and Mössbauer spectroscopy. Besides the original a-iron, austenite-Fe(N), martensite-Fe(N),-Fe₂₊N, and-Fe₁₆N₂ were identified. The fraction of the e-phase was found to increase with the number of pulses and the energy density. A threshold energy density of 1.8(2) J/cm² for the laser nitriding process was found.     

非相干光纤激光组束系统耦合效率的优化分析

单光束耦合效率是决定非相干组束系统输出功率的关键,它受到透镜焦距、光栅周期和光斑半径等参数的影响。为了寻求较为优化的系统参数,通过理论分析和仿真研究,结果表明对于中心波长1060nm的光纤激光,应当选择透镜焦距20cm,光栅周期5μm,并且需要将光斑半径控制在50μm左右。通过反解光栅频率及组束波长带宽的第一个零点来选择组束阵列宽度一定条件下较优的光栅参数。通过理论分析和数值计算,结果表明较小的光栅频率和光栅厚度对提高衍射效率是有利的。     

Simultaneous optimization of multiple quality characteristics in laser cutting of titanium alloy sheet

Titanium and its alloys have high demand in different industries due to their superior properties. The conventional cutting methods face difficulties for cutting these alloys due to their poor thermal conductivity, low elastic modulus and high chemical affinity at elevated temperatures. Laser cutting may be used for quality cuts by proper control of different process parameters. The aim of present research is to simultaneously optimize kerf taper and surface roughness in the laser cutting of Titanium alloy sheet (grade 5). The developed regression models for kerf taper and surface roughness have been taken as objective functions for the genetic algorithm based multi-objective optimization. The paper presents optimal solutions and improvements in different quality characteristics thereof. The significant control factors have been found with further discussion of their effect on two important quality characteristics kerf taper and surface roughness.     

Temperature variations of susceptibility and magnetization for nickel

Temperature variations of paramagnetic susceptibility and the magnetization for nickel are calculated in the band model. The value of high-field susceptibility at 0 K is also estimated.     

Laser diode beam shaping with GRIN lenses using the twisted beam approach and its application in pumping of a solid-state laser

We report a novel beam shaping method for laser diodes based on the concept of twisted Gaussian Schell-model beams using GRIN lenses. This method enables a more symmetric pump as well as a compact setup for pumping of solid-state lasers. In the experiment with a standard 2 W diode, the beam quality factors in the two orthogonal directions were equalized to and , respectively, which pumped an intra-cavity frequency-doubled Nd:YAG laser at 946 nm with an output of 28 mW at 473 nm.     

Configuration optimization of off-axis parabolic mirror for enhancing the focusability of a laser beam

We demonstrate a configuration optimization process of an off-axis parabolic mirror to maximize the focused peak intensity based on a precise knowledge of the tight focusing properties by using a full vector-diffraction theory and obtain an optimum configuration scaling rule, which makes it possible to achieve the maximum peak intensity. In addition, we also carry out an assessment analysis of the offset and off-axis angle tolerances corresponding to a 5% drop of the maximum focused peak intensity and present scaling laws for the tolerances of the offset and off-axis angle. Understanding these scaling laws is important to enhance the focusability of a laser beam by an off-axis parabolic mirror in the optimum configuration, in particular, which is valuable for structural design and selection of an off-axis parabolic mirror in ultrashort and ultraintense laser–matter interaction experiments.     

Generalized Stokes parameters and polarization behavior of flat-topped array laser beam propagating through oceanic turbulence

In present paper, the analytical expression for the cross-spectral density of the phase-locked Partially Coherent Flat-Topped (PCFT) array beams propagating through oceanic turbulence based on the extended Huygens–Fresnel integral is derived. Then, the polarization behavior and generalized Stokes parameters of the phase-locked PCFT array beam propagating through oceanic turbulence using the cross-spectral density matrix elements have been achieved. In this paper, the case of the clearwater oceanic turbulence has been considered, i.e. it has been assumed that the light wave is not affected by suspended organic and inorganic impurities. Due to the above-mentioned reason and the turbulence importance, the impacts of oceanic turbulence have been scrutinized, while the effects of absorption and scattering have been ignored. The changes in the Stokes parameters, the fluctuation of Stokes parameters, and consequently the state of polarization (including the spectral degree of polarization, the orientation angle and the degree of ellipticity) of the phase-locked PCFT array beams for different turbulence conditions upon propagation have been investigated. The results may find possible applications in underwater communication.     

Experimental determination of electric cross-spectral density matrix and generalized Stokes parameters for a laser beam

We report an experimental method to determine the elements of the electric cross-spectral density matrix for laser light. For this purpose an additional setup consisting of mirrors and reflecting prisms is utilized with the conventional Young's interferometer to overcome existing experimental limitations. The generalized Stokes parameters, which are the characteristics of two spatial points of the electromagnetic field, are also obtained for a pair of points. The knowledge of these two quantities might be useful in determining the change in polarization properties of light in propagation and their effects in optical measurements.     

Laser glazing study of Co-based alloy and Ni-Nb-Cr alloy coating

ＬａｓｅｒｇｌａｚｉｎｇｓｔｕｄｙｏｆＣｏ－ｂａｓｅｄａｌｌｏｙａｎｄＮｉ－Ｎｂ－Ｃｒａｌｌｏｙｃｏａｔｉｎｇ￥ＴＩＡＮＮａｉｌｉａｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＡｐｐｌｉｅｄＰｈｙｓｉｃｓ，ＴｉａｎｊｉｎＩｎｓｔｉｔｕｔｅｏｆＳｃｉｅｎｃｅａｎｄＴ...