Versatile, compact, TEM(00)-mode resonator for side-pumped single-rod solid-state lasers

We propose the use of an auxiliary lens or mirror to design a compact dynamically stable resonator for single-rod lasers. It was found that an intracavity divergent element (divergent lens or convex mirror) is suitable for obtaining a large TEM(00)-mode volume, whereas a convergent one renders the resonator insensitive to mechanical misalignment. A reliable and compact dynamically stable resonator can be designed conveniently by use of such characteristics. Both three- and four-element resonators were designed and tested with a laser-diode side-pumped Nd:YAG laser.     

High power single mode output CO2 laser

Abstract

While attempting to reach TEMoo single mode high output power, the transverse discharge method was adopted. The optic axis, the direction of glow discharge and gas flow velocity are all mutually orthogonal. The discharge region has a 2.3 liter medium volume, and 100 m/sec gas flow. This small signal gain exceeds 0.8/m in the local region. We also adopted a stable multi‐path cavity for coordinating the larger volume laser medium. Under auxiliary discharge, the maximum output power can reach 1500W, at an efficiency of 9%.     

Revising the formula of thermal focal length in a side-pumped laser rod by experiments

The correct formula of the thermal focal length in a side-pumped Nd:YAG laser rod is discussed and confirmed by experimental results. It is shown that thermally induced stresses that cause a distortion of flatness occur within the region of the whole rod. The presented calculations are in agreement with the experimental observations. The results reveal that the temperature-dependent variation of the refractive index and the distortion caused by the thermally induced stresses constitute the major contributions to thermal lensing.     

Influence of thermal deformations of the output windows of high-power laser systems on beam characteristics

By using the well-known Green's function methods, we study the three-dimensional temperature distributions and thermal deformations of the output windows of unstable optical resonators induced by an incident annular laser beam. Some expressions and theoretical profiles of the temperature distributions and thermal deformations as functions of the radius and of the thickness of optical windows are obtained. Moreover, the influence of the thermal deformations of sapphire, silica, and silicon windows within unstable optical resonators on the Strehl ratio and on the far-field laser intensity distribution is also discussed. Under conditions of 50-kW intense laser irradiation during 5 s, the maximum thermal deformation in sapphire, silica, and silicon substrates is 1.993, 0.393, and 6.251 microm, respectively. Under the same conditions the Strehl ratio of sapphire is higher than that of silica.     

Control of the gas laser output power

The paper considers the influence of a transverse magnetic field on the positive column of a glow discharge on the example of the gas discharge laser. The magnetic field was created using a developed system consisting of several electromagnets and an equalizing device for a greater uniformity of the field. It is shown that as a result of application of the magnetic system charged particles in the discharge gap are shifted to the walls of the discharge tube, which reduces the efficiency of the laser and decreases its output power. Thus, changing the current through the electromagnets the output power of the laser can be varied. The inertia of the impact of the magnetic field on the plasma in the discharge gap was of the order of one millisecond.     

Improved pump-beam distribution in a diode side-pumped solid-state laser with a highly diffuse, cross-axis beam delivery system

A new cavity for diode side-pumped solid-state lasers was designed, built, and tested. The results were efficient absorption of pumped light in the media and homogeneous pumped-beam distribution under various pump-power levels, which generated Nd:YAG active media of different radii and concentrations and shifts of the diode wavelength. Full-multimode quasi-continuous pump operation with a slope efficiency of 40.5% was obtained from a plane-plane resonator equipped with two Nd:YAG rods. At a maximum average pump power of 1.33 kW, the optical-to-optical efficiency was 31.4%. Single-transverse-mode operation (M(2) factor of less than 1.1) of 163 W was demonstrated.     

The transfer of TEM00 and TEM01 beams through a hard-aperture

Abstract

We determine the far-field divergence angle θ ₀₀ (θ ₀₁) resulting from the diffraction of a TEM₀₀ (TEM₀₁) beam incident on a circular aperture. It is demonstrated that, with a suitable choice of the aperture radius, the ratio θ ₀₁/θ ₀₀ is enhanced to about 2, while its value is 1.64 without the aperturing effect. It is shown that this effect allows high discrimination between TEM₀₀ and TEM₀₁ modes either in the case of a spatial filter or in the case of an apertured resonator.     

Stability analysis of a diode-pumped,thermal birefringence-compensated two-rod Nd:YAG laser with 770-W output power

Using a ray matrix method, we analyze theoretically how the r and theta polarizations affect the resonator stability condition of two laser heads with or without thermal birefringence compensation. The resonator stability condition is analyzed graphically for a plane-parallel and a concave-concave resonator. The maximum range of stable region is found for both the short and the long cavity. The characteristics of the laser output power are confirmed experimentally in association with the resonator stability condition. The laser output power of 776 W is obtained with the optical-to-optical efficiency of 45% for a plane-parallel resonator with a short crystal separation.     

Analytical method of calculating thermal processes and their effect on emission in solid-state laser with natural cooling

Analytical expressions are derived for calculating the change in energy characteristics of a solid-state laser with natural cooling due to heating and thermal deformation of the active medium.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 2, pp. 307–313, February, 1982.     

Shape-invariance properties of a quartic-aberrated TEM00 Gaussian beam.

The concepts of shape-invariance error (SIE) and shape-invariance range (SIR) have recently been introduced to specify in a quantitative way the shape changes suffered by a beam on propagation. Here such parameters are evaluated for the case of a fundamental Gaussian beam in the presence of a quartic aberration of its wave front. Numerical results are presented for the case of a collimated aberrated beam. Generalization to the case of noncollimated beams is also given.     

连续Nd:YAG激光器输出功率稳定性研究

本文介绍一种用两套LiNbO3晶体作电光调制器,高稳定硅光电二极管作光反馈控制信号的激光稳功率仪串联使用来稳定Nd:YAG激光器输出功率的方法。对于输出功率为5瓦左右,本身输出功率稳定度为10%/小时的Nd:YAG激光器,其输出光束经稳功率系统后,其稳定度为0.2/小时。     

Design of a device for pumping a double-clad fiber laser with a laser-diode bar

Pumping rare-earth-doped double-clad fiber lasers with GaAlAs laser-diode bars typically requires one to transform a 1-cm-long one-dimensional linear array of tens of multimode laser-diode sources into atwo-dimensional oblong cross section that approximately matches the fiber's first cladding shape. I describe the design of a device, henceforth called a high-brightness geometric transformer, that uses a cylindrical microlens to image the laser-diode bar near field onto a linear array of soft-glass, thin-clad, rectangular fibers. In turn, the fibers output ends are arranged to form a stack that matches the required first cladding shape. For a typical laser-diode bar with a brightness of 25 mW·μm(-2)·sr(-1), the geometric transformer output brightness is 0.6 mW·μm(-2)·sr(-1), i.e., there is a 40× intermediate loss of brightness. If the output of the geometric transformer is used to pump a Nd-doped double-clad fiber laser, anoverall brightness gain of 340× can be achieved.     

Modulation of the polarization of semiconductor laser radiation at constant output power

The degree of polarization of “doubly”-modulated (by the pump current and the optical confinement factor) laser radiation is analyzed by applying a method of analyzing the stability of the solutions of systems of Lyapunov differential equations to a system of rate equations. An analysis of the system of rate equations yielded its eigenvalues, also called stability coefficients, which are the characteristic time for a transition of the system from one state to another. The behavior of a doubly modulated laser was modeled mathematically and it was demonstrated that the polarization of the laser output radiation can be controlled with almost constant output power. Pis’ma Zh. Tekh. Fiz. 24, 84–90 (August 26, 1998)     

Thermoacoustic power effect on the refrigeration performance of thermal separators

An experimental investigation on the refrigeration processes occurring in a receiving tube of a thermal separator was conducted in order to determine the primary factors affecting the refrigeration performance of this new type of refrigerator. In the current investigation, the gas in the system is divided into the oscillating gas and driving gas. While the compression/expansion of the oscillating gas caused by the driving gas determines the refrigeration process occurring in the receiving tube of the thermal separator, the temperature gradient on the receiving tube significantly affects the acoustic power generation and refrigeration performance. Experimental results demonstrate that when the tube-wall temperature difference near the open end of the receiving tube increases, the refrigeration coefficient increases. Using the information presented in the paper, a new cryogenic refrigeration system was developed, and the experimental data shows that the temperature of the cryogenic air flow in the system could reach −130 °C within 50 min. It suggests that the thermal separator investigated in the paper can be employed in the field of cryogenic engineering.     

Laser with a nonlinear mirror: application for improving the output power stability of a cw laser

We put forward a new method for improving the output power stability of a cw laser. The basic idea is to replace the output mirror of a laser with a nonlinear mirror that is formed by a dispersive nonlinear Fabry-Perot étalon. Based on the semiclassical dynamic model for this system, first we derive the static conditions for this laser operating with stabilized output power, then we study the dynamic responses of output power to gain fluctuations. Both static and dynamic results show that, compared with normal lasers, the output power stability of our laser can be improved significantly when the output power fluctuations are caused by the fluctuations of the gain. The improvement of the output power can be explained by the fact that there exists an optical servoloop in this laser that is produced by the nonlinear mirror.     

Tunable output power varying with the splitting ratio of a coupler from a fiber ring semiconductor laser

The tunable output power characteristics of a fiber ring semiconductor laser have been studied by use of rate equations. An expression for the tunable output power is deduced. The analysis confirms that there is an optimum coupler splitting ratio to trade off between wavelength tuning width and output power.     

Compression of pulse duration in a laser-diode, end-pumped, double Q-switched laser

By considering the Guassian transversal distribution of intracavity photon density and the longitudinal distribution of photon density along the cavity axis as well as the influence of the turn-off time of the acousto-optic Q switch, we introduce the coupled rate equations of a laser-diode, end-pumped, double Q-switched laser with an acousto-optic modulator and GaAs saturable absorber. In addition the thermal effect of the gain medium is taken into account. These coupled rate equations are solved numerically, and the dependence of pulse width on incident pump power at different pulse repetition rates is obtained for the generated output pulses. It is shown that the pulse duration is obviously shorter in contrast to the actively Q-switched Nd:YVO4 laser with an acoustic-optic modulator, and the maximum compression ratio of the pulse width is more than 60%. In the experiment a laser-diode, end-pumped, double Q-switched Nd:YVO4 laser with both an acousto-optic modulator and GaAs is realized, and the experimental results agree with the numerical solutions.     

基于双纵模热稳频激光源的6D激光测量系统

针对目前数控设备无法实现高速及多参数同时测量的问题,以双纵模热稳频激光源为基础,自主研发了高速6D激光测量系统,不仅允许测速高(可达1.3m/s以上),而且解决了现有5D/6D激光干涉仪未能有效解决的高精度测量滚转角的问题,具有很好的推广应用价值.     

Influence of laser power on photoluminescence of hexagonal ZnO nanodisks

Raman scattering and photoluminescence spectra of hexagonal ZnO nanodisks were investigated. Normal Raman spectrum shows the intense E2 modes, which confirms a typical wurtzite structure. The broadened E2 vibration peak is due to surface/interface defect in ZnO crystal. The influence of laser irradiation heating effect on emission intensity and position has been investigated by power dependent PL and resonant Raman scattering. The threshold value of the power density for laser heating effect is 2 kW/cm2. The shift of LO phonon vibrational peaks from RRS with excitation laser power also confirms laser irradiation heating effect. Beyond the threshold value of power density, the PL intensity and position will be affected by laser heating effect.     

Efficient operation of a solid-state adaptive laser oscillator

We present the results of a cw diode-pumped Nd:YVO4 laser oscillator based on a self-starting adaptive gain-grating resonator. Adaptive laser operation has been demonstrated with 12-W output for 37 W of diode pumping, producing a TEM00 mode that compensates for thermal aberrations. The issue of the finite aperture of the amplifier is discussed, and a design that incorporates an intracavity lens is used to improve the collection efficiency with severe thermal lensing at high pump powers. The powers of the beams involved in the resonator are compared with theory and are found to be in good agreement. Spectral and temporal behavior of the adaptive laser is investigated, and very interesting behavior is shown, including self-induced temporal modulation dynamics and a switching between a narrowband and a broad bandwidth of operation.