Internal Optical Parametric Oscillator with SBS Phase Conjugate Resonator

It is reported a novel optical parametric oscillator with KTP as medium crystal inside a Nd∶YAG phase conjugate resonator. In the phase conjugate resonator, the laser beam quality is promoted by phase-conjugate mirror, which is realized by stimulated Brillouin scattering effect, and Q-switch is generated simultaneously. With this device, the laser output at 1.57 μm with 15 mJ energy and 8 ns pulse width is obtained.     

利用受激布里渊散射实现在轨运动目标激光跟踪瞄准研究

利用受激布里渊散射相位共轭技术,补偿激光大气传输过程中由于大气湍流等因素所造成的激光波前畸变,并且引入速度补偿镜方法,对模拟运动目标进行激光跟踪瞄准。利用高斯光束的无限腔长相位共轭腔理论分析了这种跟瞄方法的可行性。在室外1．27km距离,进行了在轨运动目标跟踪瞄准的原理性实验研究,实验结果表明,利用受激布里渊散射相位共轭技术和速度补偿镜方法,可以实现对在轨运动目标的跟踪瞄准,并且通过此方法,可以把激光能量能较好地集中于目标上一个很小的区域内。到达目标的最大共轭光能量为24．0mJ。     

用SF6气体作SBS相位共轭镜的激光谐振腔

利用高压SF_6气体中的受激布里渊散射作相位共轭镜,将其用于Nd:YAG激光谐振腔,得到了能量在100mJ左右的脉冲激光输出.与利用液体介质的受激布里渊散射相位共轭腔的激光输出相比,其光斑的空间模式大大改善,基本达到TEM_(00)模,功率密度在150MW/cm~2输出能量的稳定性也有所提高.     

Large-signal results for degenerate four-wave mixing and phase conjugate resonators

A numerical calculation procedure and various large-signal numerical solutions are presented for degenerate four-wave mixing in optical Kerr media, and for phase conjugate resonators using degenerate four-wave mixing. The solutions presented take full account of nonlinear refractive index changes, pump depletion, signal saturation, distributed losses, and possible external mirrors with laser gain. We find that including the nonlinear index change generally causes little change in the reflectivity or power output of degenerate four-wave mixing devices, at least with symmetric pumping. The optimum power output from a phase conjugate resonator with and without a laser gain medium is calculated. The results provide some theoretical guidance for designing phase conjugate resonators.     

Raman phase conjugate resonator for intracavity aero-optic turbulence aberration correction

A cw degenerate phase conjugate resonator (PCR) with intracavity aero-optic turbulent flow is demonstrated using sodium vapor pumped with a low intensity cw laser. A turbulent helium jet at a high flow velocity of 250 m/s and forcing frequency of 18 kHz generated the spatio-temporal aberrations. The intracavity normalized peak-to-peak intensity fluctuations at 18 kHz measured with a pinhole-detector are ten times smaller in the corrected beam than in the aberrated beam. The threshold pump intensity for the resonator is 4.5 W/cm² in the absence of the turbulent flow. The pump frequency is tuned well within the Doppler width of the Na D₁ transition. Evidence of a degenerate (laboratory frame) double-Λ mechanism involving Zeeman sublevels is also shown.     

光纤环形谐振腔的频率锁定及其特性

基于可调分束比的光纤分束器,制作了光纤环形谐振腔并通过调节分束比实现了对光纤环形谐振腔的欠耦合、临界耦合和过耦合的状态控制.实验测量了腔最小反射率与腔损耗之间的关系,获得光纤环形谐振腔的腔内衰减率为κ_0=2π×(1.60±0.03) MHz ,品质因子为Q=(1.10±0.02)×10.8.在此基础上,结合了压电陶瓷拉伸光纤以控制腔长和Pound-Drever-Hall锁频两大技术优势,克服了之前温度反馈控制等方法的反馈带宽窄、噪声大和稳定性差等问题,实现了对光纤环形谐振腔共振频率的快速、灵敏的控制和锁定.结果表明,锁频过程中相位调制功率与相位调制引起腔反射光的强度调制之间的关系为线性关系,进而通过降低相位调制信号的功率以减小相位调制对腔反射光强度调制的影响.当调制功率设定最低为–9 dBm时,光纤环形谐振腔仍能被稳定锁定.该光纤环形谐振腔为其与原子、金刚石色心等发光粒子相互作用的腔量子电动力学实验研究奠定了坚实的基础.     

相位共轭谐振腔改善激光器波前像差特性研究

在高功率激光器中采用相位共轭谐振腔技术可以补偿动态波前像差,在校正畸变的输出光束方面有极其重要的应用。分析了相位共轭腔的模式结构特性及稳定性,在实际高功率激光器中采用相位共轭谐振腔,使得激光系统的光束质量得到了极大改善。通过实验数据分析,提出在激光器系统中描述光束质量只用PV值和RMS值来量度是不足的,并利用结合光束环围能量分布图像和平均离焦系数来评价系统光束质量。实验结果表明,采用相位共轭谐振腔使得焦平面环围能量更为集中,同时平均离焦系数更接近零,结合上述方法评价系统光束质量更具实际意义。     

Phase-locking resonator with annular gain media

A new type of laser resonator that is designed to extract good phase coherence and circular beams from an annular gain region is developed. We also calculated the parameters theoretically by applying the resonator to a CO₂ laser. And the transfer characteristics of the output beam from the phase-locking laser resonator through a lens are also discussed.     

带受激布里渊散射池的位相共轭激光器输出的空间特性

本文应用传输矩阵的方法对受激布里渊散射位相共轭腔输出的空间特性进行了分析及编程计算，给出了各种参数下受激布里渊散射－位相共轭腔的传输光束轮廓图，同时给出了实验结果与之相比较，提出了设计受激布里渊散射共轭腔时应注意的问题及几种实用的受激布里渊散射位相共轭腔的腔型。     

输出环状光束的新型激光谐振腔

提出一种输出环状光束的新型激光谐振腔,即在稳定激光谐振腔中采用外环耦合方式得到环状光束的输出。利用For-Li数值迭代算法求解此类激光谐振腔的积分方程,通过计算机编程计算了平面一凹球面稳定谐振腔的输出端平面镜在不同半径的情况下,谐振腔镜面上和衍射耦合输出场基模的振幅和相位分布。计算结果预示了当输出端平面镜半径小于通常的稳定腔的基模半径时,衍射耦合输出场有稳定的环状光束输出。实验中TEA CO2激光器采用印刷电路板预电离结构,增益长度90cm,腔长5m,球面全反射镜曲率半径20m,输出端平面镜半径4．5mm,得到了内环半径为4．5mm、外环半径为5．5mm的基模环形光斑输出。从而在理论上和实验上证实了该方案产生环状光束的可行性。     

To narrow laser linewidth by utilizing dispersion characteristics of Gires-Tournois etalon

A longer laser resonator length is benefit for laser linewidth, but harmful for single-frequency operation. A novel way is suggested to narrow the bandwidth of a Fabry-Perot （FP） cavity through increasing the derivative of one round-trip phase shift with respect to the frequency. It can be implemented by replacing one of two FP mirrors with a Gires-Tournois etalon （GTE）, called FPCT, as a dispersion element. FPGT resonator has additional axial modes due to the GTE reflection phase shift. Theoretical analyses show that the bandwidth of additional axial modes can be 1% of that of a conventional FP cavity. A distributed feedback （DFB） laser diode can employ FPGT resonator to achieve ultra-narrow linewidth laser. It is shown that the effect of refractivity fluctuation in the gain medium on the linewidth is little, and kilohertz linewidth is achievable for such a device.     

Folded diffractive laser resonators with user-defined fundamental mode

The adjustment effort required for the alignment of laser resonators with arbitrarily shaped end mirrors can be significantly reduced by folding the resonator path half-way between the two end mirrors and by slightly tilting the resonator axis. Thus the resulting resonator consists only of one diffractive mirror and a plane mirror, and the separate alignment of both diffractive end mirrors with respect to each other can be avoided. This principle is demonstrated by a Nd:YAG laser with super-Gaussian output beam. Furthermore, it is shown theoretically that the influence of phase quantization effects on the beam quality can be strongly reduced as a consequence of the tilted resonator axis.     

Verfahren zur hochgenauen Bestimmung des Reflexionsvermögens von Laserspiegeln in einer Resonatoranordnung

Method for Accurate Determination of the Reflectivity of Laser Mirrors in an Optical Cavity If a high frequency intensity chopped laser beam is passing a passive optical resonator a phase lag between its output and input signal results. Due to the limited photon lifetime inside the resonator the measurable phase lag is determined by resonator length and mirror reflectivities. Changing the resonator length in a time-proportional regime a time dependent phase lag results from which the product of mirror reflectivities is calculable unambiquously.     

介质不均匀性对激光模式相位与光强分布的影响

将不均匀介质势函数进行泰勒展开,取其前3项近似,与描述光腔模式的亥姆霍兹方程中的特殊函数结合,根据光腔边界条件推导出光腔模式的本征解、激光输出功率以及不均匀介质与激光模式的相位与强度分布关系表达式。将表达式应用于氧碘化学激光器的功率与输出耦合率的非线性拟合以及近场光强分布的分析,预测趋势与文献结果相符。     

受激布里渊散射相位共轭腔及腔内光学参量振荡器

利用受激布城渊散射相位共轭特性和Ｑ开关特性组成Ｎｄ：ＹＡＧ激光谐振腔,代替传统激光器全反镜和调Ｑ装置,获得能量１００ｍＪ,脉宽１３ｎｓ的线偏振相位共轭激光输出,相应的激光器总体转换效率为０．４７％,同时将单共振ＫＴＰ光学参量振荡器置入腔内,得到波长１．５７μｍ、能量１５ｍＪ的参理振荡激光,实验证实了受激布城渊散射相位共轭腔内光学参量振荡器运行的可行性。     

Passively mode-locked Raman laser

We report on the observation of a mode-locked laser generated with a crystalline whispering gallery mode resonator pumped with a continuous wave laser. Optical pumping of the resonator generates an optical frequency comb with phase locked components at the Raman offset of the resonator host material. Phase locking of the modes is confirmed via measurement of the radio-frequency beat note produced by the comb on a fast photodiode. Neither the conventional Kerr comb nor hyperparametric oscillation is observed when the comb is present. We present a theoretical explanation of the effect.     

激光辐照下非稳腔镜变形对激光模式的影响

 分析了正支虚共焦非稳腔中腔镜变形对激光模式的影响，采用时间离散化、快速傅里叶变换（FFT）和有限元分析(FEA)方法解决腔镜变形和激光模式两者之间的耦合问题。计算结果表明，随着激光器工作时间的增加，腔镜温升和变形相应增大，谐振腔模式变差，输出光场相位均匀性变差，呈现散焦现象，输出光束质量下降。实验验证了激光器输出光束质量随出光时间的延长而逐渐变坏。     

Optical nucleation of bubble clouds in a high pressure spherical resonator

An experimental setup for nucleating clouds of bubbles in a high-pressure spherical resonator is described. Using nanosecond laser pulses and multiple phase gratings, bubble clouds are optically nucleated in an acoustic field. Dynamics of the clouds are captured using a high-speed CCD camera. The images reveal cloud nucleation, growth, and collapse and the resulting emission of radially expanding shockwaves. These shockwaves are reflected at the interior surface of the resonator and then reconverge to the center of the resonator. As the shocks reconverge upon the center of the resonator, they renucleate and grow the bubble cloud. This process is repeated over many acoustic cycles and with each successive shock reconvergence, the bubble cloud becomes more organized and centralized so that subsequent collapses give rise to stronger, better defined shockwaves. After many acoustic cycles individual bubbles cannot be distinguished and the cloud is then referred to as a cluster. Sustainability of the process is ultimately limited by the detuning of the acoustic field inside the resonator. The nucleation parameter space is studied in terms of laser firing phase, laser energy, and acoustic power used.     

Study of second harmonic generation by non-linear crystals with phase conjugation

We present the correction of the phase distortion which occurs during the second harmonic generation by non-linear crystals, such as KDP and KTP at high average power laser. This is due to the optical quality and thicknesses of the crystals which in turn influence the quality of the incident laser beam. This phase distortion is corrected by reflecting back the laser beam into the crystal using a phase conjugate mirror. It is found that the conversion efficiency of second harmonic generation without phase conjugation is more than that with phase conjugation. Far field pattern shows that the distortion of the laser beam can be corrected by using the phase conjugate mirror. Fidelity of the beam profile increases significantly with phase conjugation in the case of KDP crystal.     

Response of a BaTiO3 phase conjugate mirror to broadband and narrowband radiation

The bandwidth of a BaTiO₃ self-pumped phase conjugate mirror is measured in three different ways. 1) The crystal is exposed to infrared light with a phase change that is sinusoidal in time and the degree of phase modulation on the reflected wave is measured. As the modulation frequency is increased from 0.1 to 3 GHz, the modulation transfer function of the phase conjugate mirror decreases by a factor of 2. 2) The crystal is exposed to visible light from a laser operated both in a single longitudinal mode and in multiple longitudinal modes. When the laser bandwidth is increased from 20 MHz to 2 GHz the reflectivity of the phase conjugate mirror increases by up to a factor of 7. 3) A laser cavity is formed with the crystal as one end mirror and the lasing bandwidth is measured. Depending on the exact conditions, lasing bandwidths range from 2 to 240 GHz.