Mode selection in an unstable-resonator TEA CO2 laser by injection from a waveguide laser

The effect of injecting radiation from a cw waveguide CO₂ laser into a TEA laser through a hole in one mirror of its unstable resonator has been studied experimentally. High-power single longitudinal mode operation of the TEA laser is achieved over a wide but finite range of injection frequencies, the frequency of the single-mode pulse being that of the TEA laser cavity mode lying closest to the injected frequency. Although a simple theoretical model shows good qualitative agreement with observations it underestimates the range of injection frequencies which result in single-mode pulses unless a fast chirping of the cavity mode frequency is postulated.     

Pulse evolution and mode selection characteristics in a TEA-CO2 laser perturbed by injection of external radiation

A grating-tunable TEA-CO₂ laser with an unstable resonator cavity, modified to allow injection of cw CO₂ laser radiation at the resonant transition line by means of an intracavity NaCl window, has been used to study the coupling requirements for generation of single frequency pulses. The width and shape of the mode selection region, and the dependence of the gain-switched spike buildup time and the pulse shapes on the intensity and detuning frequency of the injected radiation are reported. Comparisons of the experimental results with previously reported mode selection behavior are discussed.     

Single mode CO2-laser pulses of high power

Single longitudinal mode CO₂-laser pulses of 200 MW power have been produced by seeding an unstable resonator cavity with single mode radiation from a hybrid low pressure — high pressure CO₂ laser system. The results indicate that a ratio of dominant over residual mode intensities of better than 10⁵ were achieved.     

High energy and high stability Cr:YAG passively Q-switched laser with convex-ARR unstable resonator

A convex-ARR (Anti-resonant Ring) unstable resonator was introduced in a Cr⁴⁺:YAG passively Q-switched Nd:YAG pulsed laser. There are two novel features in this cavity, one is the unstable resonator increasing output energy and improving laser mode; the other is the ARR structure efficiently enhancing the laser stability. A high energy and high stability Q-switched pulse with a single pulse energy of 85.6 mJ, a pulse width of 38 ns and an energy stability of 99.6% was obtained. The experimental results were analyzed well by using the mechanism of transient grating and the properties of the unstable resonator.     

激光非稳腔模式的快速计算方法

对Du Fort-Frankel差分格式用于谐振腔模式计算进行简要分析,以该差分格式为基础,提出基于移动矩阵法的非稳腔模式数值计算快速算法.对空腔共焦非稳腔模式进行数值模拟,将计算结果与参考文献进行对比,两者吻合较好.对有源共焦非稳谐振腔内增益区位置对谐振腔输出功率的影响进行数值计算,结果表明:对于采用共焦非稳腔的大功率激光器,当增益体积一定、小信号增益曲线相同时,随着谐振腔内增益区与凹面镜之间的距离的减小,激光器输出功率会有较为明显的提高.数值算例证明了本文方法的正确性和有效性.     

Single longitudinal and transverse mode operation of a hybrid unstable resonator TE CO2 laser

Single-mode operation of an atmospheric-pressure TE CO₂ laser is reported. Single longitudinal mode emission has been achieved by incorporating a low-pressure, transversely excited gain section in the same laser cavity as the atmospheric-pressure section. The effects of different resonator configurations on the system modal behaviour have been investigated and it is shown that unstable resonators are particularly suitable for controlling the transverse mode structure with a complete coverage of the excited medium. With an unstable resonator configuration, formed by a metallic convex mirror and a plane diffraction grating, single longitudinal and single transverse mode output pulses with energy up to 2 J have been produced on more than 40 lines of both the 9.4 m and 10.4 m bands. This technique can easily be scaled to larger aperture devices at higher extracted energies.     

Laser mode selection in reflective multipass optical cavity

The performance of a simple resonator that couples a reflective multipass interferometer cavity and a Fabry-Pérot etalon to obtain high efficiency tunable single-longitudinal mode (SLM) oscillation in a TEA CO₂ laser is reported. A numerical model of the resonator was explained to predict the mode behavior of the laser as well as to optimize the resonator to achieve SLM operation, and the predicted mode characters are experimentally verified.     

基于同轴TM812模谐振腔的毫米波多注速调管

 研究了群聚电子注穿越同轴TM₈₁₂模谐振腔的换能效率和同轴TM₈₁₂模谐振腔中微波能量的提取方法,论证了其作为毫米波多注速调管的输出腔的可行性。研究结果表明:理想群聚电子注穿越同轴TM₈₁₂模谐振腔的换能效率可达3.29%,一般群聚电子注穿越同轴TM₈₁₂模谐振腔的换能效率可达1.86%;采用同轴TM₈₁₂模谐振腔与沿轴向的同轴线耦合可以实现微波能量的提取;在输出腔工作频率为100.945 GHz,外观品质因数为2 243情形下,根据估算,最大输出功率可达15 kW。     

角锥棱镜激光谐振腔的基本特性

 分析了角锥棱镜对光束的相位变换作用，带二面角误差的角锥棱镜可等效于6块光楔的组合，其楔角的大小和方向由二面角误差决定。对在腔内往返传输的光线在镜面上的位置进行了分析，结果表明：3个二面角误差相同且不为零的角锥棱镜构成的谐振腔为约束非稳腔。用Fox-Li迭代法数值模拟得到了不同棱镜二面角误差情况下的谐振模式。模拟结果表明：圆形镜腔情况下基本振荡模式接近于TEM₀₃模的拉盖尔高斯光束；当3个二面角误差不相同时，模式中各个区域的强度分布不对称。采用3个二面角误差基本接近且绝对值较小的棱镜可以提高光束质量。     

高斯反射率输出镜改善光束质量的实验研究

非稳腔能产生大体积基模,具有好的空间选模特性,但在固体调Q激光器中,由于孔径光阑和热畸变的影响,非稳腔输出的横模并不光滑.使用高斯反射率耦合输出镜可较好地改善其输出光束质量,设计了平-凸非稳腔,使用Nd:YAG,电光调Q固体激光器进行实验,获得了较为平滑的远场光强分布,实验结果表明高斯反射率输出镜可较好地改善固体激光器中非稳腔输出光束质量.     

Squeezing by second-harmonic generation in a monolithic resonator

We have measured the intensity fluctuations of the second-harmonic mode generated in a MgO:LiNbO₃ external monolithic cavity pumped by a Nd:YAG laser. The cavity has mirror coatings for both the fundamental and the second-harmonic mode. We scan the cavity using the electro-optic effect of the crystal and observe that the second-harmonic beam of 2 mW exhibits a quantum noise reduction of 40(±5)%. In addition, we report on the active frequency stabilization of the monolithic device used in our squeezing experiments. Several fast tuning parameters such as the electro-optic effect, the photo-elastic effect, and the laser frequency have been investigated. With these tuning parameters the monolithic resonator can be locked on double-resonance at the phase-matching temperature, which is a prerequisit for observing squeezing in a cw-regime.     

放电型高增益KrF激光器非稳腔的研究

给出了放电型高增益非稳腔KrF激光器具有衍射极限的激光模式建立的时间与非稳腔放大率和腔长之间的关系。实验对放大率M=8,腔长L=1.75m和放大率M=13.3,腔长L=1.85m的正支共焦非稳腔在不同增益下输出光的发散角进行了测量。充电电压为30kV,发散角分别是39倍衍射极限和33倍衍射极限。当充电电压降至26kV,即降低腔内介质的增益时,它们的发散角分别是20倍和5倍衍射极限。表明了具有衍射极限的模式建立时间受放大率、腔长以及饱和效应的影响。要得到衍射极限光,其衍射极限光的建立时间必须小于饱和时间。     

Well-designed rectangular cavity resonator for FMR experiment

The unloaded quality factor of the cavity resonator is the ratio between the stored energy of the cavity resonator to the power loses in the cavity resonator. The homemade rectangular cavity resonator in X-band shows higher unloaded quality factor compare with standard cavity resonator in the TE₁₀₂ mode. Because the inner walls of rectangular cavity resonator are treated through high quality polishing and high purity Au plating. Also the inner walls are made by printed circuit board which has thin Cu foil, two problems such as mechanical vibration and thermal expansion can be solved by minimizing unwanted eddy current. Through the ferromagnetic resonance measurement by using our rectangular cavity resonator, we can be obtained reasonable values of resonance frequency and linewidth by using NiFe thin film. As a result, the Gilbert damping constant from the experimental result is in good agreement with the typical value of damping parameter of the NiFe thin film.     

Spatio-temporal coupling of laser fluctuations — Observations on a laser with internal frequency conversion

The amplitude of standing wave solid state lasers with frequency conversion inside the resonator can become unstable. We investigated the amplitude fluctuations of an end-pumped Nd:YAG-laser at low pump rates (below 160% threshold pump power) and also above. Detecting the individual mode instabilities separately and comparing them with a theoretical laser model, we can trace the origin of the mechanism leading to the observed fluctuations. At certain well defined discrete pump levels above 160% threshold the instabilities disappear. These stable emission states are associated with particular nonconventional mode patterns, some of them exhibiting a helical phase structure. Based on experimental observations and computer simulations of pump induced resonator aberrations we describe a mechanism for the emergence of the peculiar transversal modes and laser fluctuations.     

Design of optical coupling systems between two-dimensional quasi-stadium laser diodes and single-mode optical fibers

Optical coupling systems between a two-dimensional quasi-stadium laser diode and single-mode optical fibers using gradient-index rod lenses are designed for both stable and unstable laser resonators for the first time. A novel numerical approach using a combination of the extended Fox-Li calculation method and Gaussian beam transformations is proposed. In the case of a stable laser resonator, two kinds of beam propagation modes appear, namely the axis mode, in which an optical beam propagates along the cavity axis, and the ring mode, in which optical beams propagate along the diamond-shaped trajectory. The coupling efficiencies are found to be 54% for the axis mode and 52% for the ring mode. In contrast, an unstable laser resonator exhibits complicated modes, in which several highly directional beams are emitted from the end mirrors. The total coupling efficiency for these output beams is calculated to be 9.6%. The 3-dB tolerances for the lens pitch and alignment angles of the gradient-index rod lenses are also discussed.     

Evidence for Stark induced frequency shift in a CH3F fir laser

We report the first direct measurement of the frequency shift induced by the application of an electric field to an optically pumped CH₃F far infrared laser. These shifts are obtained only if the laser resonator is slightly detuned, so that the electric field enhances the cavity pulling effects. The maximum Stark coefficient we observed is about 2 kHz/(Volt/cm), fairly sufficient to allow FM modulation or fast laser frequency stabilization.     

A new grating tuning compound unstable resonator

A proposal of new grating tuning compound unstable resonator is presented. This new type of unstable resonator is profitable for generating single transverse mode, high energy, high-average power tunable laser radiation from TEA CO₂ laser and other gas lasers.     

多纵模激光F-P标准具双边缘测风可行性分析

讨论采用多纵模激光器作探测光源用于双边缘多普勒激光雷达测风的可行性。给出了多纵模激光器谐振腔腔长与边缘滤波器F-P标准具腔长之间的关系。分析了多纵模双边缘测风的主要特性,计算灵敏度、信噪比和径向测速误差,并与单纵模测风性能进行对比。可用类似单纵模测风中动态频率跟踪技术解决多纵模激光器频率漂移问题。     

Thermal-lens measurement of a quasi steady-state repetitively flashlamp-pumped Cr, Tm, Ho:YAG laser

A simple technique using cavity stability conditions is demonstrated to measure the effective dynamic thermal lensing of a flashlamp-pumped Cr, Tm, Ho:YAG laser operated in a low repetition-rate regime of 4–7 Hz. By measuring the flashlamp energy where a stable resonator becomes unstable, the effective focal length of the laser rod can be calculated. When no mode restricting aperture is used in the cavity, the thermal lens behaviour displays a significant deviation from the commonly assumed thin lens approximation.     

Analysis of resonator modes in two-dimensional laser cavities containing a left-handed material

Resonator modes in two-dimensional laser cavities with curved end mirrors filled with a left-handed material were investigated numerically using the extended Fox-Li mode calculation method. The results reveal that the phase profile on the curved end mirrors of a left-handed cavity is inverted relative to that of a cavity filled with a right-handed material. Furthermore, we show that the phase on the end mirrors takes discrete values of zero and ±π under stable resonator conditions, while it varies continuously under unstable resonator conditions. The differences between stable and unstable resonators significantly alter the far-field patterns of the lowest-loss modes.