Output Laser Beam Research Articles

Single-crystal laser-heated pedestal-growth sapphire fibers for Er:YAG laser power delivery

The Er:YAG laser-induced damage (LID) threshold and modal properties of single-crystal sapphire fibers grown by the laser-heated pedestal-growth method have been measured. The lowest loss (~0.4-dB/m) sapphire fibers produce little mode mixing and therefore deliver a near-single-mode output profile if the Er:YAG laser input beam profile is also nearly Gaussian. Normally, however, Er:YAG laser output beam profiles are multimode with numerous high-energy spikes. This leads not only to a multimode output from the fiber but also increased fiber loss that is due to higher-order mode coupling. The results of LID testing give a damage fluence of ~1.4 kJ/cm(2) for 300-mum core-only sapphire fibers at 2.94 mum.

Bifurcation diagram in case of ring interferometer containing liquid crystal: effect of diffusion

The bifurcation phenomena in optical ring interferometer containing nonlincar (Kerr) medium — liquid crystal — are investigated by means of a computer simulation. It has been found out that bifurcation points on a bifurcation diagram are displaced to area of greater parameter of medium nonlinearity when the diffusion factor increases. The distribution of intensity in cross section of output laser beam of system is constructed for the more evident description of hysteresis and bifurcations phenomena.

Doughnut-like laser beam output formation by intracavity flexible controlled mirror

The formation of the given low loss and large beamwidth doughnut-like fundamental mode of stable resonator by an intracavity flexible mirror is discussed. The mirror is a bimorph one with one round and two ring controlling electrodes. An inverse propagation method is used to determine the appropriate shape of the controlled mirror. The mirror reproduces the shape with minimal RMS error by combining weights of experimentally measured response functions of the mirror sample. The voltages applied to each mirror electrode are calculated. The calculations are carried out for industrial CW CO2 laser.

Investigation into first and second law efficiencies of solid state laser head: A case study

The efficiency of a solid state pulsed laser is very low which is generally ascribed to the poor optical and electrical efficiencies of the components used in the laser head. The temperature of the laser rod rises during the optical pumping process which causes thermally induced distortions in the laser output beam and hence a low quality laser beam is obtained. In the present study, the temperature rise in the laser rod during the pulsed optical pumping process is investigated, and the first and second law efficiencies relevant to the laser head are calculated. The radial temperature profiles are predicted for different optical pumping repetition rates. The energy dissipation chart during the lasing process in the laser head is developed. The first and second law efficiencies of the laser head and the laser rod are computed for different repetition rates of the optical pumping process.

Broad-area semiconductor lasers with diffraction-grating mode control

Broad-area semiconductor lasers with stripe patterns formed on their front mirrors and the properties of such lasers are described. The stripes are of alternately different reflectivity and therefore the pat- tern acts as a low frequency grating. Such a grating significantly affects the shape of the laser output beam. The envelope of its intensity profile becomes almost Gaussian and the beam cross section is much closer to a circle than in the case of standard lasers. © 1997 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(97)01207-5) Subject terms: semiconductor lasers; broad-area lasers; diffraction gratings; spa- tially modulated reflectivity; mode control.

A power distribution model of industrial CO2 lasers for system diagnosis

Industrial lasers are high power pieces of equipment that occasionally function under undesirable operating conditions. For example, the performance of a transverse‐flow d.c.‐excited gas laser can be adversely affected by many factors such as electrode arcing, poor lens and mirror cleanliness, focusing problems, improper gas mixture composition, poor gas quality, poor beam stability, poor beam path cleanliness, operator error, poor maintenance, poor chiller water temperature and flow rate stability, and improper laser beam ramp‐in/ramp‐out rates. Many of these factors which occur in the production environment are unpredictable and therefore difficult to simulate in the laboratory or the laser manufacturer's facilities. In this paper, a power distribution model of a transverse flow d.c.‐excited CO2 laser is developed and validated to link the input discharge power to the output laser beam power, as well as the heat losses. This model establishes a foundation for monitoring the laser performance by measuring signals critical to the laser performance such as temperature, pressure, voltage, current, and gas mixture flow rate and quality. The results show that quantitative thresholds can be defined based on the proposed model to detect some impending system faults for preventative maintenance purposes.

Phase shift of stepwise reflectivity profile mirrors

The effects of phase shifts in laser beams transmitted by output couplers with a stepwise reflectivity profile have been experimentally investigated with a XeCl laser. It is shown that the phase distortions of the cavity output coupler affect significantly the propagation properties of the output laser beam but do not affect the output beam energy and pulse width.

The Nike electron-beam-pumped KrF laser amplifiers

Nike is a recently completed multikilojoule krypton-fluoride (KrF) laser that has been built to study the physics of direct-drive inertial confinement fusion. The two final amplifiers of the Nike laser are both electron-beam-pumped systems. This paper describes these two amplifiers, with an emphasis on the pulsed power. The smaller of the two has a 20/spl times/20 cm aperture, and produces an output laser beam energy in excess of 100 J. This 20 cm Amplifier uses a single 12 kJ Marx generator to inject two 300 kV, 75 kA, 140 ns flat-top electron beams into opposite sides of the laser cell. The larger amplifier in Nike has a 60/spl times/60 cm aperture, and amplifies the laser beam up to 5 W. This 60 cm amplifier has two independent electron beam systems. Each system has a 170 kT Marx generator that produces a 670 kV, 540 kA, 240 ns Bat-top electron beam. Both amplifiers are complete, fully integrated into the laser, meet the Nike system requirements, and are used routinely for laser-target experiments.

Broad-area semiconductor lasers with spatially modulatedreflectivity of the mirrors

Emission properties of broad-area semiconductor lasers with stripes etched on one of the laser mirrors, perpendicular to the p-n junction plane, are described. Spatial modulation of the mirror reflectivity induced lasing of individual, phase coupled filaments and significantly affected the shape of the laser output beam. The cross-section of the beam became almost circular and had an intensity distibution along its horizontal and vertical axes that could be approximated by a Gaussian function.

Design of a 2.5 THz submillimeter wave laser with optical pump beam guiding

A ring resonator design using the same set of mirrors for pump beam and submillimeter wave (SMMW) beam guiding is introduced. Optimal design is discussed on the example of a 2.5 THz methanol laser. It turns out that due to refocussing of the pump beam on the pinhole certain focal lengths of the focussing mirror, which mainly is responsible for the beam guiding, should be avoided. Diffraction losses and pinhole losses determine optimal g-parameters for which the pump beam guiding losses of the resonator are minimum, and optimal pump beam waist radii. The setup of an experimental laser with the optimized resonator and the experimental setup to measure laser performance are described, and results concerning laser output power, beam quality and efficiency are discussed.

Numerical modeling of short-pulse excimer lasers with negative branch unstable cavities

A one-dimensional code for the numerical simulation of negative branch unstable resonators with an intracavity aperture that are applied to high-gain, short-pulse XeCl lasers is described. The model predicts near- and far-field performance of the output laser beams. The intracavity aperture size is shown as an important parameter for control of the output beam energy and divergence. A comparison with experimental measurements is presented.

Graded reflectance mirrors and phase-unifying mirrors for XeCl lasers

Graded reflectance mirrors and phase-unifying mirrors used as output couplers of laser resonators are both intended to improve the output laser beam quality. In the first case one takes advantage of the Gaussian or super-Gaussian profile of the reflected intensity, in the second case the most relevant feature is the ability to cancel out phase variations in the transmitted beam. In this work both types of mirrors are fabricated to be used in an XeCl unstable resonator and the possibility of obtaining graded reflectance mirrors that do not introduce significant phase distortion in the transmitted and reflected beam is demonstrated.

Application of generalized self-filtering unstable resonators to a N 2-laser pumped dye laser

Generalized self-filtering unstable resonators (GSFURs) were successfully applied to a N 2-laser pumped dye laser. The output laser beam in both near- and far-field has nearly gaussian distributions with a smooth pulse duration of ≈4 ns fwhm and ≈5 μJ output energy at the lasing threshold. For a typical cavity configuration of M=-2.5 a diffraction-limited laser beam of 0.76 mrad, corresponding to a brightness of 4.3×10 10 W cm −2 sr −1, was obtained. In order to determine the effect of ASE on the radiation field, a double slit Young's interferometer was used to measure the spatial coherence of the dye laser beam. The effect of the diameter of the field limiting aperture on the beam divergence and the field distribution was also investigated.

On the peak reflectivity of supergaussian mirrors for unstable resonators applied to a XeCl laser

Supergaussian mirrors of different peak reflectivity R 0 have been used in an unstable resonator of magnification factor M = 7, to investigate the effect of R 0 on the output laser beam energy and divergence. It has been found that output laser beams of higher energy and lower divergence are obtained by increasing the supergaussian mirror peak reflectivity from 0.49 up to 0.78. A laser beam of 46 mJ, 10.5 ns long and with a brightness B = 1.6×10 14 W cm −2 sr −1 was obtained with the R 0 = 0.78 supergaussian mirror, whereas the output beam brightness reduces to 0.8×10 14 W cm −2 sr −1 with the R 0 = 0.49 mirror.

Traveling-wave excitation of the Ar ii shake-up laser at 4765 nm

We describe the construction and operation of a single-pass laser in Ar ii at 476.5 nm pumped by soft x rays from a laser-produced plasma. Temporal and spatial coherence properties have been characterized by means of a variety of experimental techniques. We use a 5-J, 100-ps, 1053-nm laser pump pulse in a traveling-wave geometry to measure a maximum output energy of 550 μJ. The aspect ratio of the unsaturated gain region directly affects the divergence of the output laser beam, resulting in a half-angle divergence of 10 mrad for 10 cm of excitation length. A small-signal gain coefficient of 2.1 cm−1 was observed, with the onset of saturation occurring after just 2 cm of excitation.

Measurement of x-ray laser beam divergence with CADIX, a time-resolved diagnostic tool using an insertable multilayer mirror

To study the x-ray laser beam deflection and divergence due to the refraction within the plasma, a specific diagnostic called CADIX has been developed at the Centre d’Etudes de Limeil-Valenton (CEL-V). When the beam refraction analysis is required a multilayer mirror is inserted on the x-ray laser output beam. It selects the lasing wavelengths and reflects them to an off-axis streak camera which records x rays as a function of time and angle. A detailed description of the instrument is presented including multilayer mirror calibration at the LURE (Laboratoire pour L’Utilisation du Rayonnement Synchrotron, Orsay, France). An experimental measurement on neon-like silver amplification is presented and analyzed with the response of the mirror. An important refraction effect is observed.

Performance of a XeCl laser with super-gaussian reflectivity unstable resonators

Super-gaussian reflectivity unstable resonators of different magnification factor M have been applied to a high-gain, short-pulse XeCl laser, to investigate to what extent the output laser beam characteristics depend on M. It has been found that high magnification factors are required to get a fast establishment of a diffraction limited mode. However, as M is increased, the cavity feedback and then the super-gaussian mirror peak reflectivity should be also increased to get a good mode control of the laser oscillating radiation.

The Effect of Low-level Laser Treatment on Maxillary Arch Dimensions after Palatal Surgery on Beagle Dogs

The effect of low-level laser treatment on maxillary arch dimensions after palatal surgery was investigated in Beagle dogs at an age of 12 weeks. A total of 30 dogs was used, and they were assigned to either a control group (Group C, n = 6) or one of two experimental groups (Group L, n = 12; and group LL, n = 12). After Von Langenbeck's palatal repair in the two experimental groups, denuded bony areas in the LL group were irradiated with a continuous Ga-As-Al laser beam (830 nm) and energy output set at 30 mW. A dosage of 1 J/cm2 wound surface area was used. Treatment was carried out three times a week, with a total of ten treatments. The animals of the L group served as non-treated control animals. Dental casts were made of all animals of all groups at regular intervals until they reached 25 weeks of age. Maxillary arch dimensions were studied. Dental arch dimensions in the deciduous dentition of both experimental groups were not disturbed by surgery, but after eruption of permanent teeth, mainly transverse maxillary arch dimensions in the premolar region increased less in both experimental groups than in the control group. It was concluded that low-level laser treatment under the conditions used in this study did not decrease the adverse iatrogenic effects of palatal surgery on maxillary arch dimensions.

Pumping with diodes

The development of semiconductor lasers for pumping solid-state laser crystals is discussed. The basic operating principles of solid-state devices are reviewed to show why this new development is so important. Among the first of the new diode-laser technologies to be applied to pumping was the phase-locked array, which produced much higher power outputs and higher brightness from room-temperature CW diode-laser systems. With diode-laser arrays capable of power outputs between 0.2 and 2 W, and relatively good beam quality, it became possible to pump Nd:YAG and other crystals longitudinally, with the pump and laser output beams either parallel or antiparallel in the laser crystal. Diode pumping allows the flowing cooling liquids and fluctuating arc lamps used in conventional lamp-pumped lasers to be replaced by solid heat sinks and stabilized pump lasers. As a result, designers can build low-power solid-state lasers having high mechanical and thermal stability. Short-term linewidths in the kilohertz range can be obtained from diode-pumped devices, and the long-term drift of monolithic devices can be kept within 50 MHz for over an hour (for a center frequency of 3*10/sup 8/ MHz) by controlling the laser-crystal temperature.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Los Alamos FEL photoinjector drive laser

The drive laser system of the photoelectric injector for the Los Alamos free-electron laser (FEL) is described. This system consists of a 1.053 mu m mode-locked Nd:YLF oscillator, a grating-rhomb pulse compressor, a fast electrooptic shutter to reduce pulse repetition frequency, a pulsed Nd:YLF amplifier chain, and a KTP frequency doubler. The bright electron beams required for high performance FELs demand stringent specifications on drive laser output levels, beam quality, and stability. The design specifications, laser architecture, and operating performance following the most recent round of upgrades are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>