机械抖动棱镜式激光陀螺出射光强度特性

针对棱镜式激光陀螺在抖动状态下出射光强度被调制的现象, 系统地研究了机械抖动对棱镜式激光陀螺中光传输轨迹和光电探测器的影响机理. 在对现有棱镜式激光陀螺性能进行分析的基础上, 应用数值模拟和有限元分析方法, 将对称型全反射棱镜纳入四棱镜陀螺的结构设计方案, 并给出了由机械抖动引起的应力双折射和光电探测器位置偏移与出射光强度的一般关系. 结果表明, 机械抖动会使棱镜产生应力双折射, 使激光光路发生改变, 同时造成光电探测器与出射光束产生相对位移, 导致出射光强度幅值产生调制. 使用全对称型的陀螺结构, 选取具有合适折射率的对称型棱镜, 减小探测器与出射光斑中心的相对位移, 可以将出射光强度调制幅值相比原先减小52.63%以上, 显著地改善出射光强度被调制的现象. 此分析结果为提高激光陀螺的可靠性提供了重要参考.     

激光陀螺中的光学抖动及其对锁区的影响分析

为了提高激光陀螺的性能,提出利用光学抖动改善陀螺锁区的方法.研究了环形光路中背向散射对锁区的影响,理想状态下可以消除陀螺的零阶锁区.在微扰条件下对光学抖动下陀螺腔内的光路变化进行了分析计算,得到了使陀螺锁区达到最佳改善的理论光学抖动量并进行了实验研究.实验结果表明:光学抖动可以起到类似机械抖动加噪的效果,改善陀螺的零偏稳定性.     

激光陀螺抖动控制电路高精度数字化设计

随着激光陀螺电路系统数字化,小型化的不断发展。传统的机抖激光陀螺模拟偏频系统由于存在体积大,难以进行精确控制的缺点而在使用中受到极大限制。本文设计了一种基于DSP的数字机抖偏频控制系统,提出了数字机抖偏频控制系统原理,实现了一种周期性锯齿波噪声的注入。实验结果表明,数字机抖控制系统工作稳定,激光陀螺测量精度高。     

四频差动激光陀螺中的粒子数脉动效应

为研究激光陀螺精细模耦合作用,考虑了增益介质中的粒子数脉动效应.从激光器物理原理出发,分析了粒子数脉动效应的产生机制,结合四频差动激光陀螺特点,得出粒子数脉动效应是一种精细模耦合效应,不同激光模式间的拍频使增益介质中粒子数布居差产生调制,进而对模耦合产生影响.数值计算了粒子数脉动在耦合效应中的大小.计算结果表明:粒子数脉动效应和其他耦合效应随腔频变化基本一致,在大多数腔频范围内数值较小,为其他耦合效应的4%以下;在某些腔频范围(如0.37＜ξ＜0.46,0.02＜ξ＜0.06,0.86＜ξ＜0.88)有较大数值,为其他耦合效应的80%以上,在激光陀螺的模耦合分析中不可忽略.     

Design and optimization of frequency tunable semiconductor laser used in resonator integrated optic gyro

Frequency tunable semiconductor laser has potential applications in resonator integrated optic gyro (RIOG) for its small size and easy to be integrated. An alternative construction of frequency tunable semiconductor laser with planar waveguide external cavity is proposed in this paper. The frequency tuning section, which is placed between the active section and Bragg grating section, is designed to be one part of the waveguide external cavity. The slab etched grating, based on the silicon-on-isolator ridge waveguide, is adopted to narrow the width of reflectivity spectrum. After the theoretical analysis and simulations, the frequency modulation coefficient of 2.1 MHz/mA is obtained, and the power change is less than 3.6 × 10⁻⁴ dB/1.6 GHz. The proposed configuration combines the advantages of wavelength tunable laser and external cavity laser, and it can realize precision frequency tuning, ignored power fluctuation and narrow linewidth, which contribute much to RIOG.     

External-cavity birefringence feedback effects of microchip Nd:YAG laser and its application in angle measurement

External-cavity birefringence feedback effects of the microchip Nd:YAG laser are presented. When a birefringence element is placed in the external feedback cavity of the laser, two orthogonally polarized laser beams with a phase difference are output. The phase difference is twice as large as the phase retardation in the external cavity along the two orthogonal directions. The variable extra-cavity birefringence, caused by rotation of the external-cavity birefringence element, results in tunable phase difference between the two orthogonally polarized beams. This means that the roll angle information has been translated to phase difference of two output laser beams. A theoretical analysis based on the Fabry--Perot cavity equivalent model and refractive index ellipsoid is presented, which is in good agreement with the experimental results. This phenomenon has potential applications for roll angle measurement.     

力学边界对透射型光学元件激光破坏阈值的影响

 建立了激光与透射型光学元件相互作用的热弹性力学模型,解析求解了自由、固定以及一种人为边界条件下光学元件热-力学响应的定解问题。研究发现,不同的边界条件对破坏阈值有很大的影响。针对光学元件中热应力的演变情形,设计了一种“最佳”边界,消除了激光作用过程中产生的拉应力,从而使破坏阈值在理论上达到最大值。     

Polarization switching in a quasi-isotropic microchip Nd:YAG laser induced by optical feedback

This paper demonstrates the influence of external optical feedback on the polarization state of longitudinal modes in quasi-isotropic microchip Nd:YAG lasers. Under optical feedback, the polarization state of longitudinal modes in quasi-isotropic lasers relies strongly on the intracavity anisotropy loss and mode competition. When the intracavity anisotropy loss is small, external optical feedback can cause polarization switching and strong mode competition between two orthogonal linearly polarized eigenstates of one laser longitudinal mode, which leads to the distortion of laser intensity modulation waveform. The polarization switching is independent of the initial external cavity length. By increasing the intracavity anisotropy loss, one polarization eigenstate can be suppressed and the laser works in single-polarization state. A theoretical analysis based on the compound cavity model is presented, which is in good agreement with the experimental results. The results offer guidance to the development of laser feedback interferometers.     

Polarization properties of a single-mode gas laser in transverse magnetic fields

The effect of transversally applied magnetic fields on the polarization behavior of a single-mode gas laser is theoretically investigated, stressing the importance of the additivity of respective contributions influencing the time evolution of polarization parameters. By adding a new element to the existing theory, namely the contribution of magnetic-field-free regions in the active medium, and by considering the relatively large effects that small cavity anisotropies can cause, several apparent discrepancies between experiments and existing theory are resolved.     

Effects of cooling rates on the mechanical properties of a Ti-based bulk metallic glass

Mechanical properties of the glassy specimens fabricated at different cooling rates with a composition of Ti40Zr25Cu12Ni3Be20 were systematically investigated. It was confirmed that faster cooling rates caused not only a larger amount of frozen-in free volume but also a higher glass transition temperature in the bulk glassy alloy. Increase in the free volume was found to favor plastic deformation and then to give rise to larger compressive plasticity, whilst the rise in the glass transition temperature seem...     

Stationary properties of a single-mode laser system with non-Gaussian and Gaussian noise

A single-mode laser system with non-Gaussian and Gaussian noise is investigated. The stationary mean value and the normalized variance of the laser intensity are numerically calculated under the condition that the stationary probability distribution function (SPDF) is derived. The SPDF as a function of the laser intensity exhibits a maximum. The maximum becomes smaller with the increase of the correlation intensity or the non-Gaussian parameter, where the later is a measure of the deviation from the Gaussian characteristic. The maximum becomes larger as the correlation time increases. The laser intensity stationary mean value decreases with the increase of the correlation intensity or the non-Gaussian parameter while increases with the correlation time increasing. The laser intensity normalized variance increases with the increase of the correlation intensity or the non-Gaussian parameter while decreases as the correlation time increases.     

Some characteristics of laser refractometric detection in a cylindrical cuvette

Results of sensitivity measurements in laser refractometric detection in a cylindrical cuvette are reported. A model of laser-beam transmission in a capillary with a liquid is developed. The influence of the laser-beam position, capillary and liquid characteristics, and laser power fluctuations on detection sensitivity is discussed. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 894–899, November–December, 1998.     

Influence of laser intensity in second-harmonic detection with tunable diode laser multi-pass absorption spectroscopy

Tunable diode laser absorption spectroscopy （TDLAS） has been widely employed in atmospheric trace gases detection. The ratio of the second-harmonic signal to the intensity of laser beam incident to the multi-pass cell is proved to be proportional to the product of the path length and the gas concentration under any condition. A new calibration method based on this relation in TDLAS system for the measurement of trace gas concentration is proposed for the first time. The detection limit and the sensitivity of the system are below 110 and 31ppbv （parts-per-billion in volume）, respectively.     

Thermal stability of microstructures and mechanical properties in a Fe-based Fe-Cr-Mn-Cu-Mo multi-component alloy

A Fe-based multi-component alloy, 60Fe-12Cr-10Mn-15Cu-3Mo, was designed and fabricated for nuclear applications in the present study. The crystal structure of the alloy is a ～85% body – and 15% face–centered cubic. A detailed microstructure analysis indicated that Cu segregated in the alloy to form Cu-rich precipitates, and the Cu precipitates grew during high temperature annealing at up to 773?K. The high temperature tensile test of the alloys showed that both the yield stress and tensile strength of the 60Fe-12Cr-10Mn-15Cu-3Mo were greater than those of typical austenitic and ferritic stainless steels at 773?K. The Vickers microhardness of the designed alloy did not change after high temperature annealing for 1?h at up to 1073?K. The results indicated that the designed alloy has the potential to be used for high temperature applications.     

Influences of CO2 laser annealing on mechanical and laser-induced damage properties of ZrO2 thin films

Zirconium dioxide (ZrO₂) thin films were deposited on BK7 glass substrates by the electron beam evaporation method. A continuous wave CO₂ laser was used to anneal the ZrO₂ thin films to investigate whether beneficial changes could be produced. After annealing at different laser scanning speeds by CO₂ laser, weak absorption of the coatings was measured by the surface thermal lensing (STL) technique, and then laser-induced damage threshold (LIDT) was also determined. It was found that the weak absorption decreased first, while the laser scanning speed is below some value, then increased. The LIDT of the ZrO₂ coatings decreased greatly when the laser scanning speeds were below some value. A Nomarski microscope was employed to map the damage morphology, and it was found that the damage behavior was defect-initiated both for annealed and as-deposited samples. The influences of post-deposition CO₂ laser annealing on the structural and mechanical properties of the films have also been investigated by X-ray diffraction and ZYGO interferometer. It was found that the microstructure of the ZrO₂ films did not change. The residual stress in ZrO₂ films showed a tendency from tensile to compressive after CO₂ laser annealing, and the variation quantity of the residual stress increased with decreasing laser scanning speed. The residual stress may be mitigated to some extent at proper treatment parameters.     

Compensation of the thermally induced depolarization in a double-pass Nd:YAG rod amplifier with a stimulated Brillouin scattering phase conjugate mirror

Stimulated Brillouin scattering phase conjugate mirrors (SBS-PCMs) are extensively used to compensate the phase distortion of active media in a high-energy laser system with double-pass amplification. However, the depolarization loss from the thermally induced birefringence of the active medium by a photoelastic effect cannot be avoided despite the uses of phase conjugate mirrors. In this work, the depolarization loss in a double-pass Nd:YAG rod amplifier with a SBS-PCM has been studied with Jones matrix calculations. In addition, the depolarization ratios and the leak beam patterns are obtained experimentally and theoretically for four possible optical schemes. Both experiment and theoretical results show that depolarization is effectively compensated when a Faraday rotator is located after the amplifier.     

不同材料参数薄板振动中的热力耦合效应

 利用有限Hankel变换法,导出了周界等温-弹性支撑圆薄板在激光束辐照下的轴对称耦合热弹性弯曲振动近似解;针对具有不同弹性模量和热膨胀系数的薄板进行了热力耦合和非耦合弯曲振动的解析和有限元计算与分析。结果表明：热力耦合效应使薄板振动的振幅和周期都有所减小,其程度与材料的性能参数（如弹性模量和热膨胀系数等）密切相关,材料弹性模量和热膨胀系数越大,板振动中的热力耦合效应就越明显。     

通过外加应变于高双折射环镜实现掺铒光纤激光器的输出功率控制

本文提出一种基于外加应力于高双折射环镜的输出功率可调控的掺铒光纤激光器新颖结构。通过将高双折射光纤环镜中的部分双折射光纤粘贴于一个等强度梁的中性面上，在梁尾端作用不同的应力，由于双折射光纤的长度和双折射的改变可使环镜的反射率从0.8%变化到100%。以该环镜作为线形腔光纤激光器的输出腔镜，实现了动态范围达33dB的输出功率可调控的掺铒光纤激光器。该激光器不仅具有结构简单、成本低廉的优点，而且利用该机理可以很容易的找出最优腔镜反射率，从而使线形腔光纤激光器的输出性能实现最优化。     

双折射双频激光器输出光偏振特性的实验研究

报道了双折射双频激光器输出光偏振特性的实验研究，实验发现双折射双频激光器两端输出的线偏振光的偏振方向并不一致，而相互有一定的旋转角度，实验也再次证明了激光器输出的是正交线偏振光，而不是晶体本征模的椭圆化了的偏振光。     

Study of the electric field and wall voltage in a high pressure ac-PDP cell by laser induced fluorescence spectroscopy

The electric field in a surface discharge type ac-PDP cell with He or He/Xe(0.1%) mixture has been measured over a wide range of pressure (5－50 kPa) using laser induced fluorescence detection. The wall voltage was estimated from the measured electric field. The Stark manifolds of triplet atomic helium Rydberg state (2s^3S) with principal quantum numbers (n=8 and 9) have been used to measure the electric field, as the lifetime of 2s^3S is longer than the single atomic helium Rydberg state (2s^1S) in high pressure discharge. Comparison of the Stark manifolds between the n=9 and n=8 shows that the measurement accuracy of electric field can be increased by 10%. The maximum electric field strength during discharge and the wall voltage at the end of pulse decreases with the increase of pressure. The comparison of He and He/Xe(0.1%) discharge at 13 kPa showed that He/Xe gas mixture discharge can accumulate more wall charge on MgO surface and the electric field was somewhat higher than those of pure helium discharge during pulse off period under the same discharge conditions.