Construction heuristics for generating tool paths for laser cutters

This paper deals with generating paths for cutting irregular parts nested on thin or thick metal sheets. The objective is to minimise the total time required to cut all parts from the metal sheet explicitly taking the cost of piercing and pre-cutting into account. The problem is modelled as a generalised travelling salesperson problem with special precedence constraints. A set of construction heuristics is presented that incorporates the constraints originating from inner–outer contours, common cuts, piercing points and pre-cuts. Computational tests on a set of real-life cutting problems show that our solution approach is able to generate tool paths that for thick plates spend on average 33.4% less time than those generated by a commercial package for air movements, pre-cuts and sharp angle macros with cutting and piercing times being equal.     

椭圆柱透镜组准直半导体激光束的优化设计

采用光线矢量法设计了两个相互垂直的椭圆截面柱透镜组来准直半导体激光束。利用多目标优化中的加权和法进行优化计算,并提出自适应加权系数优化法。此方法能根据计算结果自动调整加权系数,从而达到最佳的优化结果。计算结果表明,该准直系统可达到45μrad左右的发散角,远远优于其它截面柱透镜组（毫弧度数量级）的准直效果。同时两柱透镜间距取适当值,还可在远场形成圆形光宽。     

正弦脉冲激光激发声波的热膨胀机制理论

阐述了激光与液体媒质作用通过热膨胀机制激发平面光声源的理论;针对激光脉冲为正弦波形的情况,求解出δ脉冲和长脉冲分别在约束界面和自由界面下产生声脉冲的解析解,通过仿真得到了声脉冲剖面,并对每种情况下产生的声波进行了对比分析;然后对液体中激光致声的光声转换效率进行了理论研究,对正弦波形δ脉冲和长脉冲激光分别在约束界面和自由界面下产生声脉冲的光声转换效率分别进行了理论分析和仿真,并讨论了液体媒质特性参数和激光参数对转换效率的影响,提出了提高转换效率的方案。     

凹凸透镜准直半导体激光器的极限

提出了用凹凸透镜校正半导体激光器(LD)光束的极限,给出了该极限的方程.分析了该极限随LD光束的线度、透镜的折射率和凹凸透镜镜面曲率半径的函数关系,并作出了函数关系图.     

Throughput comparison of microscope objectives and custom lenses for laser diode output beam collimation

The efficiency with which various microscope objectives and custom lenses collimate laser diode emission has been measured. Throughput efficiencies for diode operation above and below threshold are presented.     

Tungsten tri-oxide (WO3) film absorber for generating Q-switched pulses in erbium laser

ABSTRACT

This paper reports a new type of passive saturable absorber (SA) made of transition metal oxide (TMO) embedded in polyvinyl alcohol (PVA). The Tungsten trioxide (WO₃)-PVA SA is placed in an erbium-doped fibre laser cavity to produce Q-switched pulses operating at 1562.82?nm. The pulse laser starts to manifest at the threshold pump power of 40?mW and continues to exist until the maximum pump power of 195?mW. Within that pump power range, its pulse energy, repetition rate and pulse width vary from 98 to 142.85?nJ, 29.86 to 56.7?kHz and 5.032 to 1.85?µs, respectively. The pulse train is stable with a signal to noise ratio of 70?dB. This is the first demonstration of a Q-switched laser using such a SA.     

Generation of flattened Gaussian beam profiles in a Nd:YAG laser with a Gaussian mirror resonator

We report the experimental generation of a family of flattened Gaussian beams with bell-shaped, flattened, and annular intensity profiles in an electro-optically Q-switched Nd:YAG laser with a variable reflectivity mirror of a Gaussian reflectivity profile as an output coupler. The laser beams of different profiles were generated by modifying the resonator magnification. The propagation characteristics of the experimentally generated flat Gaussian beams were found to be in agreement with theory. To the best of our knowledge this is the first time such a family of flattened Gaussian beams is experimentally generated intracavity using a single variable reflectivity mirror.     

Spherical aberration in spatial and temporal transforming lenses of femtosecond laser pulses

We study the influence of third-order spherical aberration on the group velocity dispersion and on the propagation time delay of a plane pulse that is focused by a thin lens. Applications in refractive-diffractive propagation time delay compensation systems and in Gaussian temporal-shaped pulses are analyzed.     

Discontinuous free-form lens design for prescribed irradiance

For the problem of point source forming prescribed irradiance, a new, to the best of our knowledge, method-variable separation mapping method is presented, which establishes separately the correspondence between variables on the light source and the target plane. The role played by the optical surfaces is then to redirect the light rays to their corresponding target points. The surface of the lens is determined by first calculating the surface points and then their normal vectors. Considering that normal deviations are produced in the surface construction process, a normal deviation control method is also presented to restrict the deviation. With this normal deviation control method, discontinuities are introduced onto the lens surface. From these mapping and normal control methods, a fast and efficient algorithm has been developed for several prescribed irradiance problems with simple nonrotational shape of the illuminated region.     

Delay line length selection in generating fast random numbers with a chaotic laser

The chaotic light signals generated by an external cavity semiconductor laser have been experimentally demonstrated to extract fast random numbers. However, the photon round-trip time in the external cavity can cause the occurrence of the periodicity in random sequences. To overcome it, the exclusive-or operation on corresponding random bits in samples of the chaotic signal and its time-delay signal from a chaotic laser is required. In this scheme, the proper selection of delay length is a key issue. By doing a large number of experiments and theoretically analyzing the interplay between the Runs test and the threshold value of the autocorrelation function, we find when the corresponding delay time of autocorrelation trace with the correlation coefficient of less than 0.007 is considered as the delay time between the chaotic signal and its time-delay signal, streams of random numbers can be generated with verified randomness.     

Study of the growth of infrared-transparent non-spheric layer lenses by continuous-wave laser deposition

The fabrication of non-spheric microns-thick layer lenses by continuous-wave laser deposition has been monitored by using an interferometric method. An infrared-transparent amorphous chalcogenide alloy has been used as base material. Results evidence the thermodynamic nature of this laser-assisted deposition process, with two distinct stages occurring in the deposition rates, namely, a first induction stage with thickness increasing at non-constant rate, and a second steady-state stage with thickness increasing at constant rate. The deposition process has been shown to be reproducible and it allows the tailoring of the thickness profile for promising fabrication of non-spheric layer lenses and free-form optics.     

Particular solution for geodesic lenses

On the basis of the analytical method of designing aspherical optical waveguide geodesic lenses [J. Opt. Soc. Am. 69, 1248 (1979)], a particular solution for geodesic lenses without any curvature singularity was obtained.     

Salient features of using a free-electron laser with a crossed fluted cavity for generating coherent tunable gamma radiation

A new way of generating high-power tunable coherent gamma radiation in a free electron laser with a crossed fluted cavity is proposed. The gamma rays are generated in the inverse Compton scattering of intracavity radiation on the electron beam of the free-electron laser. The use of a crossed fluted cavity makes it possible to raise substantially the intracavity power and thereby the power of the gamma radiation and also to solve the problem of extraction of the hard radiation while eliminating the hitherto unavoidable losses in passage through the material of the cavity mirror. Pis’ma Zh. Tekh. Fiz. 25, 89–94 (May 26, 1999)     

Paraxial theory for birefringent lenses

The generalized ray tracing for the extraordinary ray through uniaxial crystals developed by Avenda?o-Alejo and Stavroudis [J. Opt. Soc. Am. A 19, 1674 (2002)] has been applied to derive paraxial refracting equations. Paraxial equations are derived for three cases where the incident, ordinary, and extraordinary rays lie in the incident plane: (a) the crystal axis is parallel to the optical axis, (b) the crystal axis is orthogonal to the optical axis and lies in the plane of incidence, and (c) the crystal axis is orthogonal to both the optical axis and the incident plane. The paraxial ray-tracing equations for the extraordinary ray are represented by matrix operators. The elements of the matrix system give all the information of the focal points and of the principal points. Gaussian formulas are derived, and some examples are presented.     

Designing light-emitting diode arrays for uniform near-field irradiance

We analyze the first-order design of light sources consisting of multiple light-emitting diodes (LEDs) to uniformly illuminate a near target plane by considering each single LED as an imperfect Lambertian emitter. Simple approximate equations and formulas are derived for the optimum LED-to-LED spacing, i.e., the optimum packaging density, of several array configurations to achieve uniform near-field irradiance.     

Optical beam-shaping design based on aspherical lenses for circularization, collimation, and expansion of elliptical laser beams

We present two optical system designs using aspherical lenses for beam circularization, collimation, and expansion of semiconductor lasers for possible application in lidar systems. Two different optical lens systems are investigated; namely, two aspherical lens and single aspherical lens systems. Software package programs of ZEMAX and MATLAB to simulate the optical designs are used. The beam reshaping results are presented for one specific laser beam output.