Fast fabrication of silicon based microstructures using 355 nm UV laser

Abstract

In this study, a 355 nm UV Nd:YAG laser is used to process silicon wafers. In order to obtain microstructures with high aspect ratio, a dual prism optical system is set up to control the cutting linewidth of the UV laser beam. During the laser beam propagation through the prisms, the two prisms are rotated with the same angular velocity, which results in the focal spot of the laser beam moving in a circular path on the silicon substrates. When the laser beam moves relative to the holder (workstation), a laser cutting process can be carried out. With this laser system, the cutting linewidth is controllable ranging from 10 μm to 1 mm by adjusting the initial phase difference in the two prisms. The experimental results show that arbitrary shaped silicon based microstructures with high aspect ratio can be fabricated by this 355 nm UV laser system, and the aspect ratio over 10 can be obtained.     

Closed form analytical inverse solutions for Risley-prism-based beam steering systems in different configurations

Nonparaxial ray tracing through Risley prisms of four different configurations is performed to give the exact solution of the inverse problem arisen from applications of Risley prisms to free space communications. Predictions of the exact solution and the third-order theory [Appl. Opt. 50, 679 (2011)] are compared and results are shown by curves for systems using prisms of different materials. The exact solution for the problem of precision pointing is generalized to investigate the synthesis of the scan pattern, i.e., to create a desirable scan pattern on some plane perpendicular to the optical axis of the system by controlling the circular motion of the two prisms.     

长距离同轴度测量方法及实验

本文介绍了一种新型的自适应双频激光同轴度测量系统，该系统利用两个完全对称的渥拉斯顿棱镜，一个作为测量元件，另一个作为补偿元件，采用比相技术处理测量信号，因而测量元件可以暂时移出光路，能够进行同轴度的测量，系统的光学设计使激光光束的平衡和角漂不影响测量结果，对激光的漂移有自适应性，两束干涉光基本符合共光路原则，因而对大气湍流，空气扰动的影响具有更强的适应性，可用于长距离直线度，同轴度的测量。该系统与     

Self-referenced prism deflection measurement schemes with microradian precision

We have demonstrated several inexpensive methods that can be used to measure the deflection angles of prisms with microradian precision. The methods are self-referenced, where various reversals are used to achieve absolute measurements without the need of a reference prism or any expensive precision components other than the prisms under test. These techniques are based on laser interferometry and have been used in our laboratory to characterize parallel-plate beam splitters, penta prisms, right-angle prisms, and corner cube reflectors using only components typically available in an optics laboratory.     

Risley prisms to control wave-front tilt and displacement in a vectorial shearing interferometer

A pair of thin prisms is used to deviate a light beam without changing the image orientation in a vectorial shearing interferometer. The relative angle between prisms determines the displacement of the wave front and its tilt. The direction of the beam displacement is controlled by means of changing the relative angle between prisms. This system is employed to control the displacement of a sheared wave front as a vector quantity and to introduce a controlled amount of tilt in what we believe is a novel interferometric shearing system. The predicted performance of this wave-front director is confirmed experimentally.     

Analytical solutions for image orientation changes in prisms

Optical prisms are most commonly employed because of their ability to output an image of different orientation relative to the input object. Previous papers have presented a systematic but numeric approximation for designing a single prism, which outputs an image with a specific image orientation. Instead of a numerical solution, an exact analytical solution for the same problem is offered. Further, how to design prism systems by using off-the-shelf right-angle prisms and roof prisms as building blocks to obtain an output image with a specific image orientation is addressed. Illustrative examples are given to verify the proposed approach and demonstrate its use.     

Polarization-independent optical circulator for high accuracy Faraday depolarization lidar

A high precision, polarization-independent optical circulator was developed for high accuracy Faraday depolarization lidar. Glan laser prisms and other novel optics were utilized in the circulator optics, resulting in a high extinction ratio of polarization of >30 dB. High accuracy is needed to detect a small rotation angle in the polarization plane of the propagating beam. It is generated by the Faraday effect due to the lightning discharge. The developed circulator delivered high performance of insertion loss and isolation as laser transmitter and echo receiver in the inline lidar optics.     

Compound prism design principles, II: triplet and Janssen prisms

Continuing the work of the first paper in this series [Appl. Opt. 50, 4998-5011 (2011)], we extend our design methods to compound prisms composed of three independent elements. The increased degrees of freedom of these asymmetric prisms allow designers to achieve greatly improved dispersion linearity. They also, however, require a more careful tailoring of the merit function to achieve design targets, and so we present several new operands for manipulating the compound prisms' design algorithm. We show that with asymmetric triplet prisms, one can linearize the angular dispersion such that the spectral sampling rate varies by no more than 4% across the entire visible spectral range. Doing this, however, requires large prisms and causes beam compression. By adding a beam compression penalty to the merit function, we show that one can compromise between dispersion linearity and beam compression in order to produce practical systems. For prisms that do not deviate the beam, we show that Janssen prisms provide a form that maintains the degrees of freedom of the triplet and that are capable of up to 32° of dispersion across the visible spectral range. Finally, in order to showcase some of the design flexibility of three-element prisms, we also show how to design for higher-order spectral dispersion to create a two-dimensional spectrum.     

Research on a scanner for tilting orthogonal double prisms

The original scanner for tilting orthogonal double prisms is studied to test the tracking performance in intersatellite laser communications. With a reduction ratio of more than 100 times from the change rate of the angle of beam deviation to that of the tilting angle of each prism, the theoretical analysis performed, as well as the verification experiment, indicates that the scanner can meet the requirements of the scanning accuracy superior to 0.5 microrad with the scanning range greater than 500 microrad and can facilitate the mechanical structure design.     

Optisches Sensorsystem für die 3D-Nahtverfolgung beim Laserstrahlschweißen

The knowledge of the accurate laser tool position is of extreme importance for quality assurance during the laser beam welding. Already minimum deviations of the desired track can impair the result of the manufacturing process, e.g. due to tolerances of thermal deformation. A contribution of this problem is an optical sensor system, which detects the three-dimensional position of the weldseam in on-line coupling parallel to the welding process and then derives the actual laser beam position relative to the workpiece. Under laboratory conditions the function of the sensor system for the on-line tracking of the laser tool was tested successfully in connection with a handling system.     

Kilohertz scanning optical delay line employing a prism array

A kilohertz scanning optical delay line is demonstrated by means of employing a prism array formed by identical wedge prisms. The wedge prisms are lined up with one another and uniformly disposed on a rotational wheel. The optical path length of a light beam can thus be scanned as the prisms pass through the beam periodically. Scanning rate of 2 kHz, scanning amplitude of 3.5 mm, linearity of 99%, and duty cycle of 95% can be achieved simultaneously. Simplicity and rigidity are embedded in the design. Preliminary test results are presented.     

Heterodyne measurements of laser light scattering by a turbulent phase screen

We report experiments in which a fiber-coupled heterodyne laser system operating at a wavelength of 1.5 microm is used to measure the phase fluctuations induced on a laser beam by passage through a thin layer of turbulent air and subsequent propagation through free space. We investigate the statistical properties and power spectra of the phase and its rate of change, in addition to the intensity statistics. We find that the power spectrum of the rate of change of phase has a simple negative exponential form. We discuss our results in the context of the problem of detection of phase variations over an extended turbulent atmospheric path.     

Experimental investigation of new concentration measurements using nonlinear dynamics through laser-induced thermal lens oscillation

The laser-induced thermal lens oscillation that is generated in an organic solution by Ar-ion laser irradiation was studied as a nonlinear dynamic system. The different dynamic states depend on three control parameters: laser beam power (P), depth (d) from a surface to a laser beam position, and solvent concentration. The transitions of dynamic states including several complicated states, for example, periodic, double periodic, were investigated by varying the parameters (P, d) for 27%, 30%, and 33% of tri-n-butyl phosphate solution diluted with n-dodecane. It was found that these transitions were strongly dependent on the concentration of the TBP solution. Based on this result, we also propose an application to solvent concentration measurement with a difference of 3%.     

Two-photon resonance-enhanced refractive-index change and self-focusing in a dye-solution-filled hollow fiber system

The general behavior of two-photon absorption-enhanced refractive-index change in a third-order nonlinear optical medium is briefly described. The nonlinear medium was the solution of a new dye, trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methyl pyridinium iodide (ASPI) in dimethyl sulfoxide as the solvent, that was poured into a 20-cm-long quartz hollow fiber of 100-mum internal diameter. This dye solution has a strong two-photon absorption and subsequent upconversion fluorescence emission when excited with 1064-nm laser radiation. When the input peak intensity reached 500-1500-MW/cm(2) levels, obvious changes in beam profiles of the output IR laser beam were observed due to a self-focusing or self-trapping process occurring inside the fiber system. As a result of this process, highly directional frequency-upconverted superradiant lasing output was obtained with a beam size ~5 times smaller than that of a linearly transmitted He-Ne probe laser beam. The demonstrated mechanism can be useful for fiber laser-amplifier and fiber-integrated optics devices.     

Stray Light Rejection in Rotational Coherent Anti-Stokes Raman Spectroscopy by use of a Sodium-Seeded Flame

A common experimental problem with rotational coherent anti-Stokes Raman spectroscopy (CARS) is undesired spectral interference that is due to stray light from the primary laser beams. Also, for the most developed approach, dual-broadband rotational CARS, practical measurements often suffer from stray light interference from the narrow-band laser, inasmuch as the CARS signal is produced inherently in the spectral vicinity of the narrow-band laser beam. An optical filter does not provide a sufficiently sharp transmission profile, thus leading to signal loss and spectral distortion of the rotational CARS signal. An atomic filter consisting of a sodium-seeded flame is presented here as a solution to the problem, and its usefulness was demonstrated in dual-broadband rotational CARS experiments.     

Plasmonics for Laser Beam Shaping

This paper reviews our recent work on laser beam shaping using plasmonics. We demonstrated that by integrating properly designed plasmonic structures onto the facet of semiconductor lasers, their divergence angle can be dramatically reduced by more than one orders of magnitude, down to a few degrees. A plasmonic collimator consisting of a slit aperture and an adjacent 1-D grating can collimate laser light in the laser polarization direction; a collimator consisting of a rectangular aperture and a concentric ring grating can reduce the beam divergence both perpendicular and parallel to the laser polarization direction, thus achieving collimation in the plane perpendicular to the laser beam. The devices integrated with plasmonic collimators preserve good room-temperature performance with output power comparable to that of the original unpatterned lasers. A collimator design for one wavelength can be scaled to adapt to other wavelengths ranging from the visible to the far-IR regimes. Plasmonic collimation offers a compact and integrated solution to the problem of laser beam collimation and may have a large impact on applications such as free-space optical communication, pointing, and light detection and ranging. This paper opens up major opportunities in wavefront engineering using plasmonic structures.      

Variable linewidth high-power TEA CO2 laser

A variable linewidth high-power TEA CO2 laser, utilizing a multiple-prism beam expander in conjunction with a Littrow-mounted grating, is described. Linewidths of approximately 250-MHz (FWHM) at a total output energy exceeding 250 mJ have been obtained at the P20 (00 degrees 1-10 degrees 0), lambda = 10.59-microm line. Laser linewidths can be varied continuously in the 250-650-MHz range for a corresponding change in output energy from 250 to 400 mJ. The present frequency selectivity method, which employs ZnSe prisms, can be applied directly to considerably higher-power CO2 lasers.     

基于微透镜阵的外腔谱组束系统光束质量分析

针对基于微透镜阵的光纤激光外腔谱组束系统的光束质量评价问题,利用高斯光束的传输变换理论,建立了评价谱组束激光光束质量的理论模型.通过数值模拟,详细分析了各相关参数对谱组束光束质量的影响,结果表明:在基于微透镜阵的谱组束系统中,离焦量、微透镜焦距及模场半径是影响谱组束激光光束质量的主要因素;阵列宽度对谱组束激光光束质量影...     

Simulation of inverse heat conduction problems in fusion welding with extended analytical heat source models

The paper presents bounded volume heat sources and the corresponding functional-analytical expressions for the temperature field. The power density distributions considered here are normal, exponential and parabolic. The sources model real heat sources like the welding arc, laser beam, electron beam, etc., the convection in the weld pool as well as the latent heat due to fusion and solidification. The parameters of the heat source models are unknown a priori and have to be evaluated by solving an inverse heat conduction problem. The functional-analytical technique for calculating 3D temperature fields in butt welding is developed. The proposed technique makes it possible to reduce considerably the total time for data input and solution. It is demonstrated with an example of laser beam welding of steel plates.