激光测深系统中大动态范围压缩技术的实验研究

分析了分通道、距离选通、光电倍增管变增益、正交偏振等多种技术相结合的方法,用以改善机载激光测深系统中激光回波的动态范围。并研制了相应的变增益部件,开展了水池试验以及海上现场试验。试验结果表明,多种方法相结合的技术可对水底信号的动态范围进行有效压缩,满足机载测深系统对浅海测量的动态范围要求;但正交偏振技术对信号测量压缩的改善效果并不明显。报道了试验过程中出现的光电倍增管后脉冲对水深测量的影响。对动态范围压缩技术进一步研究提供了有价值的参考。     

近海机载激光海洋测深技术

本文详细论述机载激光海洋测深的基本原理;讨论机载蓝绿激光的最大探测深度及测深精度等关键指标;对高频率短冲脉激光器及大动态范围的微弱信号检测等关键技术也进行了论述;并简要介绍该技术的国内外发展动态,最后分析机载激光海洋测深技术在我国的现实需要及可行性。     

机载蓝绿激光海洋测深

本文论述了机载蓝绿激光海洋测深的基本原理,讨论了最大探测深度及测深精度,研究了机载激光器选择及大动态范围微弱光信号检测问题,对各国主要机载激光海洋测深系统进行了比较,并分析了我国应用该项技术的紧迫性和可行性.     

Hf-基非晶合金的力学性能研究

 利用MTS810实验机和分离式霍普金森压杆（SHPB）,对Hf_44.5Cu₂₇Ni_13.5Ti₅Al₁₀块体非晶合金进行了准静态和动态压缩实验,应变速率范围为10^-4~10³ s^-1,给出了不同应变速率下非晶合金的应力-应变曲线,并对其压缩断口形貌进行了扫描电镜观察。结果表明：在准静态压缩条件下,Hf_44.5Cu₂₇Ni_13.5Ti₅Al₁₀非晶合金不具有应变速率敏感性,在由放射区和扇形区组成的断口形貌上观察到纳米级韧窝和60 nm左右的周期性条纹结构;在动态压缩条件下,随着应变速率的增加,动态屈服强度明显减小,合金具有应变速率敏感性,同时断裂表面为夹杂着脉络条纹的絮状结构。进一步观察发现,动态压缩断口上存在3种特征断裂形貌：树枝状条纹、典型脉络花纹和合金熔体。     

激光驱动气库靶对铝的准等熵压缩实验研究

利用激光驱动气库材料形成的等离子体射流对材料进行斜波加载, 可以获得高应变率的准等熵压缩. 在神光III 原型高功率激光装置上开展了激光驱动铝材料的准等熵压缩实验, 成像型速度干涉仪VISAR记录到样品自由面连续、光滑的速度历史, 采用反积分法得到60 GPa以上的峰值压强, 加载上升沿约10 ns,应变率可达10⁸ s ^-1, 并且观察到了压缩波在样品后表面的反射效应.     

强激光辐照下纯铝的力学响应和层裂的实验测量与分析

 采用速度干涉（VISAR）测试技术，对强激光辐照下纯铝的动态力学响应和层裂特性进行了实验测量和分析。样品厚度分别为200 μm 和485 μm，激光脉冲的半高宽约为10 ns，功率密度变化范围为10¹⁰~10¹¹ W·cm^-2。实测了样品自由面速度波形，反映了强激光加载作用下材料损伤演化过程以及损伤对材料动态响应的影响。计算得到了冲击波强度(2.0~13.4 GPa) 和不同拉伸应变率下铝的层裂强度(1.6~2.3 GPa)。在所采用的实验条件和1维近似下，激光辐照产生的冲击波强度与激光功率密度之间成线性关系。最后讨论了层裂强度与拉伸应变率之间的关系，显示层裂强度随着拉伸应变率的增加而增大。     

Cl/HN3/I2全气相化学激光体系的化学动力学模拟计算

 对Cl/HN₃/I₂产生NCl(a)/I激光的过程进行了化学动力学计算，主要考察了Cl,HN₃和I₂的初始粒子数密度及其配比对小信号增益系数的影响。结果发现,当温度为400K, 初始Cl粒子数密度为1×10¹⁵，1×10¹⁶和1×10¹⁷cm^-3时,小信号增益系数分别达到1.6×10^-4,1.1×10^-3和1.1×10^-2cm^-1，获得最佳小信号增益系数的HN₃和I₂的初始粒子数密度分别为初始Cl粒子数密度的1～2倍和2%～4%。同时，对Cl，HN₃和I₂配比对小信号增益系数和增益持续时间的影响进行了讨论。     

飞秒激光激发空气电离的阈值研究

报道在脉宽50fs—22ps，波长800nm脉冲激光作用下的空气电离阈值的研究结果.利用探测等离子体发光信号的方法，实验测量了激发空气电离所需的阈值激光强度.结果表明，当激光脉冲宽度从50fs增加到22ps时，阈值光强I_th从8.7×10¹⁴W/cm²下降到2.7×10¹³W/cm²；I_th经历了由迅速降低逐渐发展为缓慢降低的过程.在50fs—1p     

基于受激布里渊散射能量转移的冲击点火激光技术研究

提出一种新型的激光放大技术, 高效地实现冲击点火所需的10² ps级高功率激光脉冲. 该技术耦合了传统的激光驱动器放大技术和受激布里渊散射(SBS) 脉冲压缩技术, 在不改变现有激光装置主体结构的前提下, 使用长脉冲(数 ns) 充分提取主放大器储能, 然后在系统输出端通过SBS进行脉冲自抽运的能量转移, 将长脉冲能量转移给10² ps级的冲击脉冲, 实现高效放大的目的. 该技术在主动控制下实现能量转移, 将克服传统SBS压缩时间特性不可控的缺点, 输出满足冲击点火时域特性要求的精密控制激光脉冲.     

Laser-induced Alignment and Coulomb Explosion of CO2

实验研究了CO₂分子在飞秒强激光脉冲作用下的动力学过程,包括分子取向,隧穿电离和库仑爆炸,激光强度从1×10¹³W/cm²变化到6×10¹⁴W/cm². 当激光强度小于分子的电离阈值时,CO₂分子的非绝热转动激发形成一个相干转动波包,波包演化导致分子沿激光电场方向取向. 激光脉冲结束后,分子取向可以周期性地再现,利用另一束激光可以对取向结构进一步进行修饰. 当激光强度大于分子     

Gain characteristics of 980 nm-pumped Er<Superscript>3+</Superscript>–Tm<Superscript>3+</Superscript>–Pr<Superscript>3+</Superscript>-co-doped fiber

We present a numerical model of Er³⁺–Tm³⁺–Pr³⁺-co-doped fiber amplifier pumped with 980 nm laser for the first time, to the best of our knowledge. The rate and power propagation equations are solved numerically to analyze the effects of the pump power and active ion concentrations on the gains at 1310, 1470, 1530, 1600, 1650 nm windows. The results show that with pump power of 200 mW and when Pr³⁺, Tm³⁺, Er³⁺ concentrations are around 2.0×10²⁴, 3.0×10²⁴, 1.5×10²⁴ (ions/m³), respectively, the signals at 1470, 1530, 1600 nm may be nearly equally amplified with gain of 11–12.0 dB in the active fiber with length of 11.0 m, and the signals at 1310, 1470 and 1600 nm windows may be nearly equally amplified with gain of 12.0 dB in the active gain medium with length of 15.0 m. With pump power of 300 mW, the signals at 1470, 1530, 1600 nm may be nearly equally amplified with a gain of 16.0 dB in the active medium with a length of 15.0 m.     

Ground-state depleted solid-state lasers: principles,characteristics and scaling

A novel class of rare-earth-doped solid-state lasers is described. The ground-state depleted laser is pumped by an intense (more than tens of kW cm⁻²) narrow-band (less than a few nm) laser source and is characterized by: (1) an unusually low laser ion doping density (5 to 10×10¹⁸ion cm⁻³), (2) an unusually large fractional excited population inversion density (4 to 8×10¹⁸ ion cm⁻³, or >75%), (3) a gain element that is optically thick at the pump wavelength and (4) a gain element that has a substantially uniform gain distribution due to a bleaching of the pump transition at the pump intensity utilized. These features enable efficient room-temperature operation of rare-earth-ion laser transitions terminating on the ground manifold. The relationships between laser parameters (cross-sections, saturation fluences and fluxes, bleaching wave velocities, etc.) are given and laser performance scaling relationships are presented and discussed.

     

Ground-state depleted solid-state lasers: principles, characteristics and scaling

A novel class of rare-earth-doped solid-state lasers is described. The ground-state depleted laser is pumped by an intense (more than tens of kW cm^–2) narrow-band (less than a few nm) laser source and is characterized by: (1) an unusually low laser ion doping density (5 to 10×10¹⁸ion cm^–3), (2) an unusually large fractional excited population inversion density (4 to 8×10¹⁸ ion cm^–3, or >75%), (3) a gain element that is optically thick at the pump wavelength and (4) a gain element that has a substantially uniform gain distribution due to a bleaching of the pump transition at the pump intensity utilized. These features enable efficient room-temperature operation of rare-earth-ion laser transitions terminating on the ground manifold. The relationships between laser parameters (cross-sections, saturation fluences and fluxes, bleaching wave velocities, etc.) are given and laser performance scaling relationships are presented and discussed.     

Mobile adaptive holographic laser hydrophone

A mobile adaptive holographic laser hydrophone based on a dynamic hologram formed in a photorefractive crystal is developed. The hydrophone sensitivity is to –163 dB (rel. 1V/μPa) or 8.6 · 10^?3 rad/Pa in the frequency range of 1–15 kHz. Field tests of the hydrophone were performed in water area of a sea bay. The results confirm the efficiency of the use of measuring systems based on adaptive holographic interferometers to solve problems of recording weak signals (acoustic, hydroacoustic, and others) under non-laboratory conditions.     

All-optical clock recovery of 20 Gbit/s NRZ-DPSK signals using polarization-maintaining fiber loop mirror filter and semiconductor optical amplifier fiber ring laser

All-optical clock recovery (CR) from 20 Gbit/s nonreturn-to-zero differential phase-shift-keying (NRZ-DPSK) signals are demonstrated experimentally by using a polarization-maintaining fiber loop mirror filter (PMF-LMF) and a semiconductor optical amplifier (SOA) fiber ring laser. Only by adjusting polarization controller (PC), NRZ-DPSK signals were conveniently and fast converted to pseudo return-to-zero (PRZ) signal via PMF-LMF. Then the PRZ signals are injected into the SOA fiber laser for CR. The recovered clock signals is with the extinction ratio (ER) of 10 dB and the root-mean-square (RMS) timing jitter of 750 fs in 2³¹ − 1 long pseudorandom binary sequence (PRBS) NRZ-DPSK signals measurement. Moreover, the broad wavelength tunability of recovered clock stemmed from the use of SOAs as modulator and the gain medium are shown too.     

Multiplasmon laser gain in low-dimensional systems

The light absorption and laser gain in quantum wells are calculated using the cumulant expansion method and the fluctuation-dissipation theorem with allowance made for the strong Coulomb interaction of charge carriers. It is shown that the multiplasmon transitions result in a smoothening of the absorption spectrum and a shift in the absorption edge toward the long-wavelength range. The theoretical laser gain spectra are in agreement with the available experimental data. For In_0.05Ga_0.95As quantum wells, the laser gain g = 50 cm^?1 is reached at an electron density nd₀ = 1.64 × 10¹² cm^?2.     

Characteristics of amine-based all-gas-phase iodine laser

The characteristics of an amine-based all-gas-phase iodine laser (AGIL) are studied. At constant flow rates of the chemical species, the small-signal gain and laser output power are measured at three different positions in the flow reactor. It is clarified that the positive gain exceeding the threshold (2.3×10^?3%/cm) is maintained over a region more than 80 mm long along the flow. The highest small-signal gain of 7.8×10^?3%/cm and laser output power of 50 mW are observed at 170 mm downstream from the mixing point of HI and H. Numerical simulations suggest that the long positive-gain region is attributable to the following characteristics of the present apparatus: inefficient mixing and inefficient H₂ dissociation. It is confirmed experimentally and numerically that these limitations are beneficial for extending the positive-gain region to the downstream; however, the optimum HI flow rate is limited a small value and results in a much lower gain than the theoretical limit. In order to achieve a higher gain, fast mixing and efficient H₂ dissociation must be simultaneously achieved so as to increase the optimum HI flow rate. Numerical simulation results suggest that a positive gain of 5.4×10^?2%/cm, a 7-times higher gain than that indicated by the present experimental results, should be obtained with the same NCl₃ flow rate.     

Optical gain on the 476.5 nm Argon-ion laser line in a gas-target excited by a heavy ion beam

Optical gain on the 476.5 nm Ar II 4p–4s ion laser transition has been observed in argon-gas excited by 2.5 ns pulses of 90 MeV³²S ions with a repetition rate of 4883 Hz. The energy per pulse was 23 J. The projectiles were stopped in the target at pressures between 5 and 20 kPa. Gain was determined from a measured transient increase of the intensity of a 476.5 nm probe laser beam sent along the ion beam axis and back reflected by an aluminum foil. The maximum gain observed was (0.4±0.1)×10^–3 at a target-gas pressure of 5 kPa. Control experiments using krypton as target-gas were performed and yielded a null result. The optical gain observed in argon is consistent with the result from an analysis of spectroscopic studies of rare-gas targets excited by heavy ion beams.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday. This work has been funded by the German Federal Ministry for Research and Technology (BMFT) under contract No. 06 TM 310 I, Gesellschaft für Schwerionenforschung (GSI), Darmstadt, and the Tandem accelerator laboratory, Munich     

Gain measurements of the anthracene-perylene energy transfer dye laser

Results are presented for the gain of the anthracene-perylene energy transfer dye laser. The results are in agreement with calculations that predict a linear dependence of the gain on the anthracene concentration. The stimulated emission cross section of perylene is estimated to be 1.6 × 10^-18 cm²/molec.     

飞秒超强激光多通预放大过程中的脉冲信噪比研究

从啁啾脉冲放大的基本理论出发,详细计算了啁啾脉冲在多通预放大中各个时间点的增益情况,并设计了一个十通预放大器进行了实验研究. 结果显示,在抽运通量为1.6 J/cm²的非饱和放大情况下,种子脉冲经过十通预放大之后信噪比由10^-5提高到10^-7. 这表明在非饱和抽运通量下,多通预放大器可以有效提高激光脉冲的信噪比. 关键词： 多通预放大 信噪比 飞秒钛宝石激光器