长脉冲高能激光能量测试技术的研究

用锥形腔量热式激光能量计,测量了在不同脉冲宽度条件下,脉冲激光能量和激光吸收腔温升之间的关系,并用传统的方法得到不同激光能量对应的温升,并按照有关公式计算得到激光能量,结果表明实际激光能量和按传统方法计算得到的激光能量之间存在较大的差距;我们从理论上分析了由于热辐射、热传导影响,得出锥形吸收腔时间温度曲线关系的数学模型;用该数学模型对测量得到温度时间曲线进行最小二乘法拟合,拟合曲线和实际曲线非常吻合;通过该曲线我们对测量结果进行修正,和传统数据处理方法比较,该方法得到的结果更接近真值.     

大气传输对激光后向散射式能见度测试的影响及理论研究

激光在大气传输时,大气中的气体分子、气溶胶粒子、雾、雨等对激光的吸收和散射将导致激光回波能量衰减,这是影响激光后向散射式能见度测量的主要因素。通过对大气散射、大气湍流、大气吸收和气象条件与激光后向散射的关系进行理论分析,对后向散射式能见度测量的可行性进行了理论分析和论证,并提出了利用激光后向散射进行大气能见度测试的数学模型,为进一步研究和提高激光后向散射式能见度测距仪的性能提供了理论依据。     

光线追迹在高能激光能量计系统设计中的应用北大核心CSCD

将光线追迹方法用于高能激光能量计的系统设计中。针对锥形腔激光能量计后向散射问题,使用光线追迹方法进行能量仿真模拟,并将其结果与理论计算结果进行对比,验证了该方法的可行性。同时将其应用于实际的高能激光能量计系统设计中。     

输出能量4mJ的1kHz飞秒掺钛蓝宝石激光再生放大研究

针对高能量千赫兹重复频率飞秒激光的应用需求,设计了一套采用线性再生腔结构的高效率飞秒钛宝石激光啁啾脉冲放大系统.通过优化腔型设计,在重复频率为1 kHz、单脉冲能量为20 mJ的527 nm激光抽运下,将展宽后的800 nm啁啾脉冲激光的能量放大到5.8 mJ,对应斜效率达到30.7%.进一步通过色散补偿压缩脉冲宽度,获得了单脉冲能量为4 mJ、脉冲宽度为45.7 fs的输出,稳定性测量表明激光的能量抖动仅为0.18%(均方根值).     

绝对式高能量激光能量计温度特性研究

对绝对式量热法高能量激光能量计吸收腔的内、外壁温度差特性进行了详细的理论研究和实验验证。用第二非齐次边界条件和第二齐次边界条件的热传导方程分别建立了吸收腔在激光加热过程中和激光加热结束后的温度分布，利用模拟实验对激光照射吸收腔的过程进行模拟，得到内、外壁温度差的实验数据。利用数值模拟法，对理论分析结果作数值分析，理论分析结果与实验数据非常接近，从而证明了在激光加热过程中，虽然吸收腔内外壁存在固定的温度差，但当激光结束后，该温度差将迅速减小，吸收腔达到热平衡。     

空腔靶激光能量沉积的数值模拟

本文采用随机模拟方法和几何光学追踪方法。研究了不同条件下空腔靶中的激光传播光路:采用线性收缩假设,考虑了激光入射时注入孔的堵口问题 激光在等离子体中吸收的物理机制,包括了逆韧致吸收和共振吸收,还考虑了反向布里渊散射对吸收的影响。在此基础上,改变靶的不同尺寸,计算了不同激光入射条件下激光能量在腔内的沉积,并对一些计算结果进行了讨论     

高能激光能量计测温电阻温度标定研究

对绝对量热式高能激光能量计测温电阻丝的温度特性进行了研究.以锥形吸收腔高能激光能量计为实验模型，分别对处于自由状态下以及缠绕于能量计吸收腔表面后的测温电阻丝的温度电阻特性进行了实验分析.结果表明,两种状态下测温电阻丝的电阻随温度变化规律并不相同.用最小二乘法对测温电阻丝的电阻与温度实验数据进行数据处理并建立补偿模型，从而对缠绕于吸收腔表面后的测温电阻丝的电阻温度关系标定，经修正后能量计的测温电阻和Pt100电阻的偏差小于0.01 Ω，温度偏差小于0.02 ℃，从而提高了能量计测温准确度.     

水流吸收型高能激光能量计溯源方法及其溯源体系研究

提出了一种利用电加热丝作为校准源的高能激光能量计校准方法,将水流从吸收腔前端导入至加热容器,在加热后流入吸收腔。通过精确计量水流吸收的热能并与能量计测量结果进行比较,达到对高能激光能量计校准的目的。研究表明校准系统的热交换模型与吸收腔内的热交换模型一致,均经历了储能和功率平衡两个阶段。水流及相变气体的散射效应对测量结果的影响较小,经过修正后可以忽略其影响。通过深入分析各个环节的测量不确定度表明,残留能量和流量变化对测量不确定度的影响最显著,增加水箱的容积可以有效降低残留能量对测量不确定度的影响。在对各个环节的影响修正后估算出系统的测量不确定度约为4.8%(k=2),被校高能激光能量计校准后的测量结果与其他类型的参考高能激光能量计进行比对,两者具有很好的一致性,修正因子仅为1.006,标准偏差为1.4%。     

绝对吸收式激光能量计高准确度校准技术研究

采用量热法的高能激光能量计用于测量能量大于50 kJ的连续波高能激光能量,通常用已知功率的连续激光开展激光能量计的光电校准需要激光照射时间超过20 min,而由于热损失等原因,进行长时间激光能量校准时,校准不确定度高达12%。以量热式平面吸收高能激光能量计为模型,从理论上分析了热辐射、热对流对连续波高能激光能量测量结果的影响,得到了较准确的平面吸收腔激光能量计冷却数学模型,实现了能量计热损失补偿,并通过建立相应的实验装置验证了该模型,用其对装置的测量结果加以修正,可使光电校准的测量不确定度减小到1%以下。     

一种激光雷达测量海洋光学参数的新方法

为了拓展海洋光学参数的激光遥感测量手段,借鉴高光谱分辨率多普勒激光雷达对大气散射信号的测量机制,提出了一种利用激光雷达水下后向散射信号测量海洋固有光学参数的新方法。在原理方面,描述了测量系统的组成和利用碘分子吸收滤波器实现水分子瑞利散射信号和悬浮物米散射信号的光谱分离测量方法, 在结论方面,给出了利用海水激光后向散射信号实现海水悬浮物后向散射系数和海水体消光系数的具体反演算法。     

利用康普顿后向散射产生X光源的研究

 利用高能电子对电磁波的康普顿后向散射可以获得波长短、方向性好的X光辐射,这种具有亮度高、发散角小、光子能量可调等特点的辐射,有很好的应用前景。由于电子对电磁场的散射截面很小,要获得较高强度的辐射,不仅要求很强的电磁场作为散射场,而且要求电子束的亮度高;利用光阴极RF腔注入器及30MeV射频加速器产生的30MeV电子束同Nd:YAG激光光腔中的强光场作用,可以获得较高强度的康普顿后向散射,其波长为0.07~0.14nm,发光本领可以达到2.5×10¹¹光子/s。     

527 nm激光辐照盘靶受激布里渊散射光角分布

 在“星光Ⅱ”激光装置上，开展了527 nm激光与金盘靶和铝盘靶相互作用实验，研究了激光辐照盘靶的受激布里渊散射光散射机制，获得了散射光能量角分布。实验结果表明：激光辐照金盘靶时，在入射激光能量大致相同的情况下，受激布里渊散射光能量在匀滑的条件下比没有匀滑时低一个数量级以上（背反能量除外），束匀滑对散射光的抑制作用十分明显。在匀滑条件下，越靠近背反方向，散射光能量越大。散射光能量分布沿方位角的变化不大。激光辐照铝盘靶时，散射光能量分布的离散性较大。     

Scattering of CO2 laser beam by a plasma of air breakdown at pressures of 1–300 torr

Results from experiments with a TEA CO₂ laser with an unstable cavity and a power of 10⁷ W are presented. Laser radiation was focused by a lens with a focal length of 100 or 150 mm in air free of dust (grains larger than 0.1 μm were filtered out). The power and energy of radiation scattered within a central cone of an annular laser beam was recorded. The dependences of the threshold (for scattering) laser power and the scattered power on pressure were determined. The angular divergence of the collimated scattered beam was found to be 3.9 mrad, which was close to the divergence of the laser beam (2.5 mrad). The amplification of the scattered radiation pulse was performed.     

Energy scaling of a carbon nanotube saturable absorber mode-locked femtosecond bulk laser

We report successful energy scaling of a room-temperature femtosecond Cr⁴⁺: forsterite laser by using a single-walled carbon nanotube saturable absorber (SWCNT-SA). By incorporating a q-preserving multipass cavity, a repetition rate of 4.51?MHz was realized, and the oscillator produced 121?fs, 10?nJ pulses at 1247?nm, with an average output power of 46?mW. To the best of our knowledge, the peak power of 84?kW is the highest generated to date from a SWCNT-SA mode-locked oscillator. Furthermore, energy scaling of a femtosecond multipass-cavity laser, mode-locked using a SWCNT-SA, is demonstrated for the first time.     

High-resolution spectroscopy at steady-state lasing with multiphoton backscattering

A steady-state self-consistent lasing regime in a laser cavity is investigated with allowance for the back action of the output radiation at four-wave low-frequency scattering in the external sample. The scattering is by the photoelastic potential in the field of the additional opposing laser. General expressions for steady-state amplitudes of field oscillation in the cavity are obtained and employed for investigation of lasing features. Experiments were carried out with narrow-band (line width 1 MHz) continuously tunable diode lasers. The four-wave scattering occurred in solid and liquid dielectrics. It is shown that the fourwave scattering of the pumping laser radiation into the cavity of the signal laser substantially changes its lasing spectrum and can be used to measure dispersion of acousto-optic parameters.     

Performance Characteristics of Power Build-Up Cavity for Raman Spectroscopic Measurement

Performance characteristics of power build-up cavity (PBC) as the light source of a Raman spectroscopy based gas sensor were studied. The key parameter to optimize stable and high intra-cavity power operation was beam diameter of the back reflected beam from external cavity to diode laser. The optimum diameter determined by an appropriate distance between the cavity and diode laser was found to be comparable with the waveguide cross section of diode laser for the effective spatial filtering, where inevitable cavity coupling loss caused by slight spatial mode mismatching existed. A PBC with a finesse of ∼10300 achieved a stable TEM₀₀ mode in excess of intra-cavity power of 80 watts pumped by a 10 milliwatts diode laser. Simultaneously, the PBC wavelength is found to be passively locked effectively at 670 +/− 0.15 nm where the center of the gain region exists. A Raman spectrum of nitrogen measurement was demonstrated.     

Effect of Rayleigh-scattering distributed feedback on multiwavelength Raman fiber laser generation

We experimentally demonstrate a Raman fiber laser based on multiple point-action fiber Bragg grating reflectors and distributed feedback via Rayleigh scattering in an ~22-km-long optical fiber. Twenty-two lasing lines with spacing of ~100 GHz (close to International Telecommunication Union grid) in the C band are generated at the watt level. In contrast to the normal cavity with competition between laser lines, the random distributed feedback cavity exhibits highly stable multiwavelength generation with a power-equalized uniform distribution, which is almost independent on power.     

Polarization-tunable Yb:KGW laser based on internal conical refraction

Using internal conical refraction, we demonstrate an Yb:KGW laser where the polarization state can be arbitrarily altered without any additional cavity components. The extinction ratio can also be altered between 1:1 and 40:1. The maximum output power achieved was 8.6 W at a slope efficiency of 60.5% with respect to incident pump power. This equals the power performance of a standard Yb:KGW laser used for reference.     

抽运能量对受激布里渊散射光限幅特性的影响

采用布里渊噪声起源模型,数值模拟了受激布里渊散射介质CCl4对波长1064nm的Nd：YAG纳秒激光脉冲的传输特性及光限幅特性。入射抽运脉冲能量较低时,非线性介质对纳秒激光脉冲呈光学透明。入射抽运脉冲能量高于受激布里渊散射产生阈值后,透射脉冲峰值受限,脉宽压缩,能量趋于饱和,说明该光学系统同时具有光功率限幅和能量限幅的光限幅特性。利用理论模型模拟了如下光限幅参量：透射脉冲峰值功率、透射能量、能量透射率、脉宽压缩率依赖抽运光能量的变化关系。相应的理论模拟计算结果由实验进行验证,实验结果与理论模拟相符合。