高斯反射率镜单谐振光参量振荡器模式分析

采用高斯光束传输矩阵描述光参量谐振腔的行为,通过迭代计算模拟高斯光抽运高斯反射镜单谐振光参量振荡器的振荡过程,分析了谐振腔参数和抽运光口径对腔内输出模式的影响。报道了1 064μm脉冲抽运平 GRM腔单谐振非临界相位匹配KTP光参量振荡器的实验,其结果与理论分析相符。     

Beam quality improvement of the high-energy KTA-OPO based on a confocal unstable cavity with Gaussian reflectivity mirror

A high-energy 100-Hz optical parametric oscillator (OPO) based on a confocal unstable resonator with a Gaussian reflectivity mirror was demonstrated.A KTA-based OPO with a good beam quality was obtained when the magnification factor was 1.5,corresponding to the maximum signal (1.53μm) energy of 56 m J and idler (3.47μm) energy of 20 m J,respectively.The beam quality factors (M²) were measured to be M²_x=5.7,M²_y=5.9 for signal and M²     

Demonstration of improved beam quality in an image-rotating optical parametric oscillator

We performed laboratory and numerical modeling studies of an optical parametric oscillator with 90 degrees intracavity image rotation. We found that the signal beam was more symmetric than that from comparable cavities without image rotation, and it had low values of the beam quality factor, M(2) . Oscillator performance agreed well with our numerical model.     

Effect of resonator length on a doubly resonant optical parametric oscillator pumped by a multilongitudinal-mode beam

The resonator length of an optical parametric oscillator (OPO) is normally made a short as possible to minimize the signal-buildup time and maximize the output energy. We have found that, when a doubly resonant OPO is pumped by a multilongitudinal-mode beam, its output energy has a significant maximum when its optical length matches that of the pump source, even if this length is much greater than the shortest possible for the OPO. We have observed this effect in a ZnGeP>(2)-based OPO and reproduced it in numerical simulations.     

Pulse-series 1.57 μm optical parametric oscillator pumped by a Q-switched Nd:YAG laser with a variable reflectivity mirror

A method of generating 1.57 μm pulse-series eye-safe laser based on optical parametric oscillator (OPO) was developed. The 1.57 μm pulse-series OPO was pumped by a Q-switched Nd:YAG laser with a variable reflectivity unstable resonator. Every pulse-series includes three micro-pulses, and the pulse repetition rates, pulse numbers and pulse intervals were adjustable. The maximum output energy of the 3-micro-pulse-series was 274 mJ. The optical-optical efficiency of the OPO was about 40%.     

圆形高斯镜平凹腔腔内外激光场研究

运用边界元素法把圆形高斯镜平凹腔的自再现模的衍射积分方程转化为有限阶矩阵方程。计算了圆形高斯镜取不同反射率膜斑半径和中心振幅反射率情况下基模的场强分布、相位分布和本征值。研究表明:腔内光场分布半径随反射率膜斑半径的减小而增大,中心振幅反射率不影响光场分布半径;反射率膜斑半径影响远场分布,当其数值较小时,在光束的远场分布主峰周围产生弱衍射环;当高斯镜中心全反射时,远场分布随反射率膜斑半径的变化无明显变化;模式本征值随反射率膜斑半径的增大而增大。     

Low-threshold mid-IR MgO:PPLN optical parametric generation with high reflectivity mirror for signal wavelength

A low-threshold middle-infrared(mid-IR) MgO:PPLN optical parametric generation(OPG)pumped by a laser diode(LDl end-pumped Z-type Nd:YLF laser at 1047 nm is realized with high reflectivity(HR) mirror for signal.At repetition rate of 10 kHz,the OPG threshold of 50μJ has been achieved with HR mirror for signal.Compared with the threshold without mirror,the threshold decreases by 17%.Using HR mirror for pump at output side of crystal,the threshold of 40μJ is achieved.The 2.7-4.1μm continuous tunable output is produced with seven grating periods from 28.5 to 31.5μm and temperatures from 30 to 200℃.When the incident average pump power is 3 W.the OPG idler output power is 0.46 W at 3.26 μm,which corresponds to optical-to-optical conversion efficiency up to 15.3%.     

圆形高斯镜平凹腔腔镜倾斜时光场模式分析

运用边界元素法把圆形高斯镜平凹腔的自再现模的衍射积分方程转化为有限阶矩阵方程。计算了谐振腔在理想情况和高斯反射率平面输出镜倾斜情况下基模的场强分布、相位分布和本征值。研究表明,腔镜倾斜使激光场模式分布沿发生倾斜的方向向镜边缘偏移,而且在腔镜倾斜较严重时模式分布发生畸变,不再是对称的拉盖尔-高斯基模分布。基模本征值随倾斜角增大而变小,光束远场分布变差。减小高斯分布反射率的膜斑半径,则能减弱因倾斜引起的模式畸变。     

非稳腔中调腔孔对光束质量的影响

在中、远红外波段的激光器中，组成谐振腔的反射镜基底材料多数是对可见光不透明的，采用在腔镜上开一小孔输入调腔光方法是最简便的。本文用Ｆｏｘ－Ｌｉ迭代法计算了无开孔及有开孔时正支非稳共焦腔空腔的模式，结果表明当调腔光开孔直径小于３ｍｍ时，对光束质量基本没有影响。     

High beam quality in a HyBrID copper laser operating with an unstable resonator made of a concave mirror and a plano-convex BK7 lens

This paper presents a very simple unstable resonator, made of a concave mirror (total reflector) and a bare plane–convex BK7 lens working as a convex coupling mirror, which is quite efficient for HyBrID copper laser. In addition to a good quality factor (M²=4.9), experimental results showed that it is possible to control the laser output power by introducing a variable aperture iris inside the cavity, close to the coupling lens, without spoiling beam quality. A rough theoretical model helped to explain these results as a combined effect of unstable resonator plus radial gain distribution.     

Analysis of time domain characteristics of high energy nano-second optical parametric oscillator

The time domain characteristics of high energy nano-second optical parametric oscillator are analysed with discrete-approximation method, and the procedure of signal wave is modeled. Different pulse widths result in varied build-up times and optimum crystal lengths, which dominate the efficiency of pulse pump. When the pump energy remains fixed, there is an optimum pulse width for the pump wave, with which the highest efficiency could be expected. In addition, for the first time, the analytic solutions for both small and large signal gain conditions are supplied with the discrete-approximation method. We also give the equations for the build-up time, the optimum crystal length and the efficiency, both in accurate form and simple form for estimation, and finally apply the results to the experiments.     

90% pump depletion and good beam quality in a pulse-injection-seeded nanosecond optical parametric oscillator

We measured 90% pump depletion in a singly resonant image-rotating nanosecond optical parametric oscillator that was pulse-injection seeded by a self-generated signal pulse. The oscillator was pumped by an 8 ns duration single-frequency 532 nm pulse from an injection-seeded Q-switched Nd:YAG laser and resonated an 803 nm signal. The pump and pulsed-seed beams had flat-topped spatial fluence profiles with diameters of approximately 6 mm, giving a cavity Fresnel number at 803 nm approaching 400. The beam cleanup effects of the image-rotating cavity produce a far-field signal spatial fluence profile with approximately 60% of its energy falling within the diffraction-limited spot size.     

Narrowband tuning of an injection-seeded pulsed optical parametric oscillator based on a self-adaptive, phase-conjugate cavity mirror

Narrowband tuning of a pulsed optical parametric oscillator (OPO) is achieved with a self-adaptive injection-seeded optical cavity employing a phase-conjugate reflector. This approach is used in a novel OPO system based on periodically poled KTiOPO4 and pumped at 532 nm by a pulsed Nd:YAG laser. The OPO is injection seeded at 835-855 nm by a continuous-wave tunable diode laser, which also enables a Rh:BaTiO3 photorefractive crystal to act as a wavelength-selective phase-conjugate reflector, with no need for active control of cavity length. The single-longitudinal-mode tunability and operational simplicity of this OPO system are demonstrated experimentally.     

Prediction of the tuning characteristics of an optical parametric oscillator using parametric fluorescence

Knowledge of the tuning characteristics and generation efficiency of optical parametric fluorescence for a nonlinear crystal is of considerable help in defining the operational requirements of a tunable CW parametric oscillator. Detailed observations of the wave-length and temperature dependence of parametric fluorescence from crystals of barium sodium and lithium niobate are reported that extend for the first time to the infra-red. The merit of this approach is illustrated by comparing the temperature tuning curves of two operating argon pumped barium sodium niobate oscillators to the parametric fluorescence tuning curves of the same crystals.This research was jointly sponsored by the Office of Naval Research and the National Aeronautics and Space Administration.     

Propagation properties of the beam generated by Gaussian mirror resonator passing through a paraxial ABCD optical system

By expanding a hard aperture function into a finite sum of complex Gaussian functions, approximate propagation formula is derived in the situation that the beam generated by Gaussian mirror resonator passes through a paraxial ABCD optical system with an annular aperture. The corresponding forms for a circular aperture and a circular black screen are also given. Some numerical simulations are shown to illustrate propagation properties and focusing properties of the beam passing through a paraxial ABCD optical system with the three different kinds of aperture.     

高斯反射镜及其倾斜对平凹腔激光场分布的影响

 从菲涅尔-基尔霍夫衍射积分公式出发，运用边界元法数值计算了平凹腔平面镜均匀反射率时倾斜和未倾斜情况下基模的场强分布、相位分布和本征值，同时与高斯反射率平面镜在腔镜倾斜时的情况做了比较。研究表明，腔镜倾斜使激光场模式分布沿发生倾斜的方向向镜边缘偏移，而且在腔镜倾斜较严重时模式分布发生畸变，不再是对称的高斯分布，基模本征值随倾斜角增大而变小，光束远场分布变差。同等条件下，高斯反射率平凹腔腔镜倾斜对谐振腔引起的模畸变小于均匀反射率平凹腔，且基模光场及本征值随镜倾斜的变化关系稍不同于均匀反射率平凹腔。     

Generation of high energy and good beam quality pulses with a master oscillator power amplifier

A high efficiency and high peak power laser system with short-pulse and good beam quality has been demonstrated by using a master oscillator power amplifier with two-pass amplification configuration. The master oscillator, end-pumped with a fiber-coupled laser diode array, provides low power but excellent beam quality pulses, and the amplifier boosts the pulse energy by orders without significant beam quality degradation. Short pulses of 8.5 ns with energy up to 130 mJ and approximately diffraction limited beam quality have been demonstrated.     

腔镜热变形对非稳腔光场特性的影响

 研究了高功率气体激光器中谐振腔腔镜热变形效应。采用时间离散化方法,利用虚共焦折叠非稳腔3维物理光学负载模型和ANSYS热效应计算程序,将光腔稳态模式的快变过程与镜面变形的慢变过程耦合起来,研究了真实器件的腔镜变形和光场模式的相互作用;计算给出了16 s热变形下硅镜和石英镜面输出功率的下降程度和远场光束质量的退变程度：在16 s热效应下,硅镜实际光斑半径与理想光斑半径的比值变化小于1.5,而石英镜值变化达到4,可知长时运行下选用硅镜明显优越于选用石英镜。     

Growth of high quality non-linear optical crystal zinc germanium phosphide for Mid-infrared optical parametric oscillator

ZnGeP₂ single crystals were grown from Vertical Bridgman method. High-quality near-stoichiometric ZnGeP₂ single crystals were obtained in the diameter of 30 mm and length of 120 mm. The results showed that after thermal annealing of the crystals the optical absorption coefficient was below 0.03 cm^?1 at 2.05 μm, and ～0.02 cm^?1 at 3–8 μm. The low absorption loss ZnGeP₂ samples with dimension of 6 × 6 × 18 mm³ were cut from the annealed ingots for 3–5 μm optical parametric oscillation (OPO) experiments. For OPO experiment, we obtained up to 8.7 W output in the 3–5 μm wavelength range (with signal of 3.80 μm and idler of 4.45 μm, respectively) pumped by a 16.3 W 2.05 μm Tm,Ho:GdVO₄ laser at pulse repetition rate of 10 kHz, which corresponded to a conversion efficiency of 53.4% and slope efficiency of 64.8%, respectively.