光载微波信号抗大气干扰的研究

为了研究射频强度调制激光信号光源的参量,特别是调制深度对调制波的抗干扰能力产生的影响,采用干涉法对射频强度调制激光信号在通过大气湍流干扰后其相位的变化进行了理论分析和实验验证。搭建了Mach-Zehnder干涉仪,参加干涉的两束光分别为未经调制的单频光和调制后的双频光。以干涉条纹对比度作为信号相位起伏的衡量标准,比较不同大气湍流干扰条件下,干涉条纹的对比度随调制深度的变化。大气湍流由空间光调制器模拟产生,分别在26.32%,42.04%,67.59%和85.04% 4种调制深度下,比较有无大气湍流时干涉条纹的对比度的变化。结果表明,调制信号的调制度越深,其抗大气湍流干扰的能力越强。该结论对双频激光雷达光源的选择具有一定的参考意义。     

利用相位闪耀光栅的光学相控阵扫描性能分析

针对透射型和反射型光学相控阵器件,分别进行扫描衍射效率和扫描角精度的理论及仿真研究。首先,以阶梯相位闪耀光栅为理论模型,推导了光学相控阵器件的扫描衍射效率及扫描角精度的表达式;其次,以器件的实际特性对表达式进行修正,给出了近似实际情况的扫描性能表达式;最后,在假设的器件参数条件下,对0°入射透射型器件和45°入射反射型器件的扫描性能进行了仿真分析。仿真结果表明:两种器件的扫描衍射效率与扫描角精度都随扫描角的增大而加速下降;透射型器件的扫描衍射效率和扫描角精度关于阵面法线对称分布,而反射型器件关于45°出射角不对称。最后还讨论了激光线宽对扫描角精度的影响,说明了此影响在10-9°量级。     

激光二极管抽运的高光束质量的Yb∶YAG薄片激光器

演示了激光二极管(LD)端面抽运Yb∶YAG薄片固体激光器,抽运源是美国相干公司(COHERENT)光纤耦合输出半导体激光器,光纤输出芯径为800μm,在940nm处最大输出功率为1356W,由于光纤输出芯径较大,不利于抽运光和振荡光的模式匹配,为了得到较小的抽运光斑,采用了焦距比为30∶12的耦合透镜组压缩入射到晶体端面的抽运光光腰半径,晶体为原子掺杂浓度8at.%,几何尺寸为7mm×16mm国产Yb∶YAG晶体,整个实验装置采用温差电致冷(TEC)和循环水冷却方式,实验中得到了306W的连续激光输出,激光器的斜率效率为331%,测得M2因子在x和y方向分别为154和173,具有良好的光束质量。     

太阳光直接抽运的Nd:YAG激光器

太阳光直接轴运固体激光器由于能量转换环节最少,有可能获得较高效率,在空间激光器和太阳能利用方面存在重要的应用前景.     

单向非平面环形腔单频激光器输出耦合面偏振膜系的研究

研究了单块非平面环形腔输出耦合面偏振膜反射系数对器件实现单频振荡及输出功率的影响.在给定晶体尺寸,磁场及抽运功率的情况下,通过计算,合理选择S偏振光和P偏振光的反射率,在保证激光单频输出的前提下,使器件的耦合输出膜的透过率接近最佳值.     

Fizeau Interferometery for THz-Waves＇ Frequency and Intensity Measurement

A terahertz-wave generator based on optical parametric oscillator principle, detection based on combination of Fizeau wedged interferometer and an electro-optical crystal ZnTe has been studied. The analytical solution based on the basic principle of operation of solid wedge Fizeau interferometer has been realized. The mathematical calculations for THz frequency and intensity measurement dependent on wedge angle and fringe spacing have been considered. The efficiency of THz wave detection depends upon optimized wedge angle has been also realized. The feasibility of detection of THz waves＇ frequency and intensity by solid Fizeau interferometer （THz-waves＇ range of 1 - 3 THz） has been studied. By optimization of other parameters like thickness of Fizeau film, refractive index, material of Fizeau film, we can proceed towards the design of Fizeau interferometer for required research plans as it is a simple and inexpensive interferometer.     

Design of Efficient Tunable Terahertz-Wave Parametric Oscillator

The terahertz(THz)region of the electromag-netic spectrum covers the frequency range from0·1THz to10·0THz(the wavelengthisinthe range30-3000μm),which is between the microwavesandinfrared regi mes.Recently,this range has beenextended to40-50THz.Sources in this region havefound many applications,such as THz spectroscopyfor studies of carrier dynamics andinter molecular dy-namicsin liquids[1].THz sources in this region havefound many applications,suchasin material sciences,solid state phys…     

激光二极管泵浦可调频差双频固体激光器

研究了可调频差范围0～1.5 GHz的LD泵浦可调频差的双频固体激光器.激光增益介质是2 mm厚的1 at%掺杂Nd:YAG波片,利用端面泵浦和F-P标准具的选模得到单频连续输出,在单频的基础上将λ/4波片加入谐振腔中,造成本征光频率分裂,实现频差连续可调的双频激光输出.采用琼斯矩阵分析光腔内的本征值及本征向量,证明了双频激光两个电矢量偏振态之间总是正交的.两个偏振激光频率间隔由改变λ/4波片快轴之间的交角实现调谐.实验中得到80 MHz-1.3 GHz范围可调频差的双频激光输出,最大输出功率85 mW.     

人工光源条件下夜间雾天图像建模及去雾

夜间有雾图像光照不均匀,整体亮度较低,色偏严重,且人工光源周围存在光晕。现有的去雾模型和算法大多针对白天图像,其并不适用于夜间场景,夜间图像去雾颇具挑战性。该文深入分析夜间有雾图像的成像规律,建立含有人工光源的夜间雾天图像成像新模型,并在此基础上提出夜间图像去雾新算法。针对夜间图像光照不均问题,提出基于低通滤波的环境光估计方法,利用估计出的环境光可准确预测夜间场景传输率;针对目前夜间图像去雾后存在光源光晕问题,提出根据图像色度估计场景点属于近光源区域的程度,使算法能自适应地处理光源区域和非光源区域;针对非一致色偏问题,利用直方图匹配方法进行颜色校正。对大量图像进行实验,并与现有白天、夜晚图像去雾算法进行比较,验证了该文提出的夜间雾天图像成像模型及去雾算法的有效性。     

Fizeau Interferometery for THz-Waves' Frequency and Intensity Measurement

A terahertz-wave generator based on optical parametric oscillator principle,detection based on combination of Fizeau wedged interferometer and an electro-optical crystal ZnTe has been studied.The analytical solution based on the basic principle of operation of solid wedge Fizeau interferometer has been realized.The mathematical calculations for THz frequency and intensity measurement dependent on wedge angle and fringe spacing have been considered.The efficiency of THz wave detection depends upon optimized wedge angle has been also realized.The feasibility of detection of THz waves' frequency and intensity by solid Fizeau interferometer(THz-waves' range of 1-3 THz)has been studied.By optimization of other parameters like thickness of Fizeau film,refractive index,material of Fizeau film,we can proceed towards the design of Fizeau interferometer for required research plans as it is a simple and inexpensive interferometer.