A simple method for automatic cavity alignment of a solid-state laser

Misalignment of a laser cavity would result in the displacement of beam location on the cavity mirrors. We present a simple method for automatic cavity alignment of a solid-state laser through detecting the location of the laser beam on the rear mirror, with which neither external alignment beams nor modifications to the cavity are required. The rear mirror of the laser cavity is replaced by a tip/tilt mirror to compensate for the misalignment. Experiments show that this method could effectively correct the misalignment of the laser cavity and restore the output power to almost the original value when the resonator is well aligned.     

Unstable resonator alignment based on the fringe analysis

The existing cavity mirrors alignment method aligns cavities according to the symmetry of the near-field interference fringes of the guided lights by the unstable resonator. Its precision is restricted due to the lack of objective criterion for the fringe symmetry. This article proposes a high-precision cavity mirrors alignment method using the grey projection of fringe patterns as a solution to the problem. First, vertical and horizontal grey projection on the concerned fringe patterns; then an evaluation function for the cavity mirrors alignment is established using the distances between peak/valley values of all the levels in the projection curve as variables; finally, the function value is employed to characterize the fringe symmetry and thus to provide an objective criterion for the alignment effect of the stable resonator cavity mirrors. Experiments show that the proposed method is able to give effective evaluation for the symmetry of the near-field interference fringes of the guided lights and improve the alignment precision greatly.     

基于图像边沿特征的强激光腔镜准直处理方法

 激光束光路自动准直系统用于高功率激光装置光束精密准直。基于某激光原型装置总体对腔镜准直调整流程,针对高功率激光系统腔镜准直过程光斑图像,仿真处理并定量分析了光斑边缘特征;结合腔镜准直监测单元光传输分析,使用激光光斑边缘不同部分曲率的相似性和光斑圆形度实现了对腔镜调节的量化评估。在腔镜准直结束时圆形度指标为12.222;边缘相似度达到99.62%。     

多程放大腔镜准直研究

 针对高功率激光装置对多程放大器腔镜准直的要求,利用小孔的像传递和光路自动准直的原理,设计出一套创新的腔镜准直调整方法,并且在SG-Ⅲ原型装置4程放大模拟实验平台上进行了实验验证。实验结果表明：自动准直系统能够在15min之内顺利完成主放大级系统的光路调整,光束近场调整精度值小于近场光斑直径的0.5%,光束远场调整精度小于0.3"。     

Alignment locking to suspended Fabry-Perot cavity

In this paper we report on the alignment locking of an in vacuum 77 m long suspended mirror Fabry-Perot cavity. Lock was achieved by mode-matching a 500 mW Nd:YAG NPRO onto a pre-mode cleaner, the output of which was then mode-matched to the suspended cavity. The longitudinal locking was achieved by feeding back to the laser frequency actuator to follow the cavity resonance. Subsequent implementation of a hybrid auto-alignment system enhanced the stability of the circulating power inside the cavity. Preliminary results are presented.     

国产首台交变相位聚焦漂移管加速器的冷测与试运行

质子直线注入器是质子治癌系统的重要组成部分。出于项目进度的考虑,上海先进质子治癌示范装置APTRON采用了进口自美国的直线注入器。为了加快质子治癌产业进程,掌握质子放疗关键技术,保证产业链安全可控,注入器团队研发了国产医用质子直线注入器。该直线注入器采用了电子回旋共振（ECR）离子源和四翼型射频四极加速器（RFQ）的技术方案,并在漂移管加速器（DTL）段创新性地采用了交变相位聚焦（APF）结构。在这个过程中,通过研究APF DTL的束流运动规律和设计思想,自主开发了APF DTL的底层物理设计软件,相继完成了物理设计、电磁设计、机械设计、加工建造、腔体冷测、高频老练和载束实验等多个阶段的工作,最终成功引出了7 MeV、7 mA的质子束流。经过束诊系统的测量分析,认定束流中心能量为6.975 MeV,动量分散在±0.35%以内的束流流强为6.07 mA。成为国产首台医用质子直线注入器和首个实现成功载束的APF加速腔。     

外腔式He-Ne激光器的调整方法

本文提出了一套外腔式He-Ne激光器的调整方法,研究了腔长变化对纵模的影响,进而发展出一种可以有效提高谱线单色性的技术.     

高斯光束与谐振腔基模模式光路谐振匹配的分析与校准

为了降低高斯光束与谐振腔耦合过程中失调量和失配量对基于无源谐振腔测量技术精度的影响, 采用高斯光束变换规律、模式耦合有关理论以及光束传播坐标变换等相关理论, 就失调量和失配量对基模耦合效率的影响分别进行分析和模拟, 并据此给出了一般情况下两个参考量同时存在时基模耦合效率的表达式. 分析表明: 失配量的存在主要影响激光器与谐振腔的耦合效率, 而对高阶模式的激发影响较小, 因此对谐振腔的衰减线型影响较小; 失调量的存在对谐振腔高阶模式的激发起主要作用, 给测量带来严重误差. 该结论为利用腔出射光信号来确定误调参量值的实验方案提供了依据. 因此, 在考虑光源光谱线宽的情况下, 就光源光谱线宽的特性提出两种装调校准方案: 基于法布里-珀罗干涉仪法和基于多维象限探测器探测谐振腔出射光的调节回路, 这将为分析基于无源谐振腔的相关技术测量误差来源以及实现测量系统的高精度装调提供理论指导.     

高功率高重频U型腔激光器的仿真与实验研究

 为了得到结构紧凑的高功率、高重复频率固体激光器,设计了“U”型光学谐振腔,并利用LAS-CAD软件分析了激光晶体的热效应和激光输出特性。根据仿真结果进行了具体实验,最终得到了腔长400 mm的紧凑型固体激光器。在重复频率为100 kHz,泵浦功率为60 W时,输出功率达到21.6 W,光-光转换效率为36%,斜率效率为39.9%。     

Positioning photonic crystal cavities to single InAs quantum dots

We have investigated the optical properties of planar photonic crystal cavities formed by removing a single hole from a two-dimensional square lattice of air holes etched through a thin GaAs slab. We have demonstrated cavity resonances with quality factors (Q’s) as high as 8500, using an internal light source provided by an ensemble of InAs quantum dots (QDs) grown by molecular beam epitaxy (MBE). The high-Q modes are confined to a very small mode volume, V = 0.7(λ/n)³, making them attractive to study in the context of cavity quantum electrodynamics with single QDs, where a high is needed to observe the strong coupling between an electronic state of the dot and the optical cavity mode. To this end, we have developed an accurate and robust alignment technique that positions a photonic crystal cavity to a single QD with 25 nm resolution. We present the details of this new technology and demonstrate its effectiveness by strategically positioning a number of QDs within photonic crystal cavities at points where the electric field intensity is high.     

A technique for the alignment of a ring laser cavity

An alignment technique for a ring laser cavity is presented which is suitable for a resonator into which auxillary laser beams cannot pass.     

Dissipative preparation of entanglement in optical cavities

We propose a novel scheme for the preparation of a maximally entangled state of two atoms in an optical cavity. Starting from an arbitrary initial state, a singlet state is prepared as the unique fixed point of a dissipative quantum dynamical process. In our scheme, cavity decay is no longer undesirable, but plays an integral part in the dynamics. As a result, we get a qualitative improvement in the scaling of the fidelity with the cavity parameters. Our analysis indicates that dissipative state preparation is more than just a new conceptual approach, but can allow for significant improvement as compared to preparation protocols based on coherent unitary dynamics.     

Cavity-enhanced absorption spectroscopy for shocktubes: Design and optimization

Cavity-enhanced absorption spectroscopy (CEAS) has generated much interest in shocktube kinetics studies because of its recent success in achieving improved sensitivity and high time resolution with robust optical alignment. While recent progress demonstrated experimental schemes including off-axis scanned-wavelength approach and on-axis ps-pulsed laser approach, that both successfully suppressed the laser-cavity coupling noise, this paper develops a theoretical model to predict the CEAS sensor performance that can be used as a design tool applicable to more generalized cases. The method models the optical field in the cavity based on the decentered Gaussian beam model, from which the cavity transmission spectrum and the laser-cavity coupling noise can be numerically calculated. The simulation results predict sensor performance for different cavity configurations and laser characteristics, including various degrees of laser-cavity mode-matching, laser linewidths, scanning rates, and cavity filling conditions. Simulation with example wavelengths in the ultraviolet, near-infrared, and mid-infrared showed increasing mode-matched beam waist size for increasing wavelengths. An off-axis alignment scheme was found to be capable of suppressing the coupling noise by two orders-of-magnitude at a moderate laser linewidth of 1?GHz. Coupling noise level on the order of 1e-5 for scanned-wavelength off-axis alignment case with a narrowband mid-infrared laser was obtained by model calculation and agreed with experimental results within acceptable uncertainty range. The developed method can serve to guide future design and optimization of CEAS system in shocktube studies.     

Stable mode-locking operation in a Cr:forsterite laser with a five-mirror cavity

The experimental finding of more-stable mode-locking operation in a five-mirror cavity than in a conventional four-mirror cavity for a Cr:forsterite laser [IEEE J. Quantum Electron. 33, 1975 (1997)] was interpreted by ABCD-matrix formalism. Since the optimum cavity configuration operation for mode-locking operation was attainable in the middle of the stable cavity condition, we conclude that one can easily achieve KLM alignment and stable mode locking with a five-mirror cavity.     

应用在高性能贴片机上的一种快速视觉定位算法

针对高性能贴片机须具有快速、准确的视觉定位的要求,通过改进一种混合空间增强的预处理方法,采用Hough变换与最小二乘法相结合的方法提取出了较为精确的边缘直线,实现了一种利用十字叉标记几何信息,并能进行快速对准的算法。实验结果表明,该算法具有较快的速度,对比例变化和局部残缺不敏感。     

An alignment technique for a ring laser cavity

We present a practical method for fast alignment of a ring laser cavity. With the aid of an auxiliary HeNe laser a closed path is formed in the cavity so that laser action can be quickly attained.     

Transmitting intensity distribution after a Gaussian beam incidenting nonnormally on a wedged Fabry-Perot cavity

After deriving the expression of the intensity of the transmitted beam for a Gaussian beam nonnormally passing through a wedged Fabry-Perot cavity, the influence of the wedged angle in Fabry-Perot cavity mirrors alignment at a different tilted angle on the transmission of a Gaussian beam has been investigated theoretically. Numerical simulations show that the incidental angle and the wedged angle in Fabry-Perot cavity mirrors alignment have an important effect on the intensity distribution, the peak intensity, and the position of the peak intensity of the transmitted beam.     

波长扫描法布里-泊罗光纤加速度计的研究

利用光纤传感器的独特优点 ,用波长扫描法将 Fabry- Perot干涉仪 (以下简称 FPI)和传统加速度计相结合 ,得到了较好的分辨率。分析了在 FPI中多光束干涉对双光束干涉的影响。实验研究表明 ,它对由振动引起的位移 (加速度 )变化相当灵敏     

Optical gain by simultaneous photon and phonon confinement in indirect bandgap semiconductor acousto-optical cavities

Optical gain that could ultimately lead to light emission from silicon is a goal that has been pursued for a long time by the scientific community. The reason is that a silicon laser would allow for the development of low-cost, high-volume monolithic photonic integrated circuits created using conventional CMOS technologies. However, the silicon indirect bandgap—requiring the participation of a proper phonon in the process of light emission—is a roadblock that has not been overcome so far. A high-Q optical cavity allowing a very high density of states at the desired frequencies has been proposed as a possible way to get optical gain. However, recent theoretical studies have shown that the free-carrier absorption is much higher than the optical gain at ambient temperature in an indirect bandgap semiconductor, even if a high-Q optical cavity is formed. In this work, we consider a particular case in which the semiconductor material is engineered to form an acousto-optical cavity where the photon and phonon modes involved in the emission process are simultaneously confined. The acousto-optical cavity confinement effect on the light emission properties is characterized by a compound Purcell factor which includes both the optical as well as the acoustic Purcell factor (APF). A theoretical expression for the APF is also introduced. Our theoretical results suggest that creating an acousto-optical cavity the optical gain can overcome the photon loss due to free carriers as a consequence of the localization of phonons even at room temperature, paving the way towards the pursued silicon laser.     

Generation of four-atom Greenberger-Horn-Zeilinger state via adiabatic passage

We propose a scheme to generate a Greenberger-Horn-Zeilinger (GHZ) state of four atoms trapped in a two-mode optical cavity via an adiabatic passage. The scheme is robust against moderate fluctuations of the experimental parameters. Numerical calculations show that the excited probabilities of both the cavity modes and the atoms are tiny and depend on the pulse peaks of the classical laser fields. For certain decoherence due to the atomic spontaneous emission and the cavity decay, there exits a range of pulse peaks to get a high fidelity.