In a high accuracy strapdown inertial navigation system (SINS), the ring laser gyroscope’s (RLG) bias changes and the performance decreases due to factors in the RLG’s self-heating and changes in ambient temperature. Therefore, it is important to study the bias temperature drift characteristics of RLGs in high, low, and variable temperature environments. In this paper, a composite temperature calibration scheme is proposed. The composite temperature model introduces the derivative term and the temperature derivative cross-multiplier on the basis of the static model and sets the overlap regions for the piecewise least squares fitting. The results show that the composite temperature model can compensate the bias trend term well at ambient temperature, improve the fitting accuracy, and smooth the output curve. The compensation method has a small amount of calculations and flexible parameter design. The precision of the laser gyros in one SINS is improved by about 64.9%, 15.7%, and 3.6%, respectively, which has certain engineering application value.

The coherent noise always exists in digital holographic microscopy due to the laser source, degrading the image quality. A method of speckle suppression using the dynamic speckle illumination, produced by double-moving diffusers, is presented in digital holographic microscopy. The space–time correlation functions are theoretically analyzed from the statistics distribution in the doubly and singly scattered system, respectively. The configuration of double-moving diffusers is demonstrated to have better performance in speckle suppression compared with the single diffuser and moving-static double diffusers cases. The experiment results verify the feasibility of the approach. The presented approach only requires a single shot interferogram to realize the speckle reduction, accordingly it has the potential application in real-time measurement.

In addition to the traditional physical quantities (such as displacement, distance, velocity and vibration) detection that has been widely researched and reported, laser self-mixing interferometry (SMI) has shown great potential in nano-particle sizing during the last two decades, primarily depending on the incoherent stochastic superposition of the laser beam’s interaction with each particle in the illuminating volume. Particle diameter can be determined from the power spectra of self-mixed signals through Lorentz fitting. SMI particle sensing using laser diodes (LDs) always adopts direct current (DC) driving, so the spectrum peak occurs around zero-frequency and merely exhibits the right-hand half. Some other particle sensors using solid-state lasers (SSLs), however, prefer to employ a pair of acousto-optic modulators (AOMs) as frequency shifters, which pronouncedly increase the complexity and the cost of the whole measurement system. In this letter, linearly injected current is applied to a LD to achieve laser frequency tuning and conveniently shift the concerned Lorentz peak to any specified spectrum position, which simplifies the measurement setup and greatly avoids the influence of DC or low-frequency disturbance. The technique proposed is beneficial to developing low-cost, compact and precise SMI particle sensors or instruments.

Laser self-mixing interferometry (SMI) has been widely applied in the fields of precision measurement in scientific research, industry and biomedicine, and most researchers preferentially utilize laser diodes (LD) as light sources due to their compact structure and low cost. In most SMI cases, detection sensitivity rather than structure and cost is always the first concern. So in this article, we concentrate on an influencing factor on detection sensitivity named fluorescence to photon lifetime ratio (FPLR) which is an inherent parameter of the active material in a laser cavity. Derivation and simulation based on the time delayed rate equations are followed to validate the significant role played by the FPLR, then experiments according to different laser types including solid state lasers (SSL) and LDs are implemented to further prove the factor mentioned. Results demonstrate that SSLs always have higher detection sensitivity to feedback light than LDs, and is always more suitable to be applied in precision measurement. Additionally, the Yb:YAG laser is more sensitive than the Nd:YAG one. Increasing the pumping level from the threshold will decrease the SMI signal’s sensitivity, and reducing laser feedback strength will also decrease the SMI signal’s sensitivity. The findings from this article are beneficial to studying laser feedback sensitivity and selecting appropriate laser types in designing SMI sensors or instruments. Though with the disadvantages of large size and high cost, SSLs may be more suitable light sources in the field of high performance SMI sensing if miniaturization and cost are not the significant consideration.

给出了离轴抽运固体激光器多模速率方程组在阈值附近的小信号求解方法, 用这种方法研究了模式随离轴量的变化以及厄米-高斯模的竞争行为. 抽运光斑较小时, 离轴量增加高阶模式依次出现; 抽运光斑较大时, 模式变化呈现复杂性. 用小信号近似得到的模式光子数比例与较高抽运功率下数值求解速率方程组的结果接近, 表明可以用该方法估算实际较高功率激光器的模式分布, 这可以方便这类激光器的研究. 对离轴抽运下的多厄米-高斯模激光器, 阈值附近的模竞争体现为, 随着抽运功率的增加, 第一个净增益由负变正的模式, 光子数随即开始增加, 增加趋势接近线性. 而第二个净增益由负变正的模式, 光子数并不立即开始增加, 而要等到抽运功率进一步增加后才开始增加, 其开始增加后第一个模式的增长趋势变缓. 从动态过程看, 各个模式经过交叉尖峰和交叉弛豫振荡竞争后, 逐渐达到稳态. 实验获得了HG₀₀-HG₅₀模光束, 实验所得到的模式分布与理论计算结果符合很好.