神光-Ⅱ装置三倍频实验中靶场单元技术的改进

 主要介绍为了满足神光-Ⅱ高功率激光装置三倍频光（351nm，3ω）的物理实验要求，靶场三倍频模拟光源和瞄准监视系统两个主要单元技术的改进，即三倍频模拟光源由基频光（1 053nm，3ω）通过腔外的KTP+BBO晶体倍频获得，再经八路分光系统和主激光耦合；瞄准监视系统由透射式光学系统改进为反射式光学系统，避免原系统存在较大的色差，提高瞄准精度。     

大口径高通量三倍频研究

为考核神光Ⅱ升级项目三倍频输出能力,以及研究高功率激光驱动器高通量三次谐波转换过程中相关技术问题,在神光Ⅱ第九路上开展了一轮'Ⅰ+Ⅱ’三倍频实验,实验中三倍频最大输出达到2740 J,最大输出能通量达到3.6 J/cm²以上,最大转换效率为~63%;根据实验结果结合理论分析,初步研究了影响效率转换主要参量;在实验中观察到时间相位调制所引起的振幅调制,以及横向受激拉曼散射所引起的破坏. 实验结果有效验证了神光Ⅱ升级的倍频器的相关设计程序和参数,以及神光Ⅱ升级项目的三倍频输出能力. 关键词： 非线性光学 三次谐波转换 高通量 时间相位调制     

高强度大动态范围高效率三倍频转换的数值模拟

 对高强度大动态范围基频光入射以及偏振态发生部分变化的条件下,Ⅰ/Ⅱ角度失谐和Ⅱ/Ⅱ偏振失配（双倍频和双混频）两种高效三倍频方案的转换特性进行了数值模拟,结果表明在上述条件下Ⅰ/Ⅱ角度失谐方案优于Ⅱ/Ⅱ偏振失配方案。     

相位失配法实现倍频稳定输出的模拟分析

 对BBO晶体Ⅰ类相位匹配倍频过程和KTP晶体XY平面内的Ⅱ类相位匹配倍频过程进行数值模拟，结果表明：Ⅰ类和Ⅱ类相位匹配倍频过程，都可通过引入适量的相位失配量实现稳定倍频输出；随着相位失配量的增大，实现稳定倍频输出所需的晶体长度都变小，倍频稳定输出起伏变小，倍频转换效率有不同程度的下降；相对于XY平面内的Ⅱ类相位匹配倍频过程，BBO晶体的Ⅰ类相位匹配倍频过程对相位匹配偏离角更敏感，且稳定输出时倍频转换效率更低。     

LD侧面抽运Nd∶YAP腔内三倍频蓝光激光器

研制了一台LD侧面抽运Nd∶YAP腔内三倍频447.1nm脉冲蓝光激光器.采用列阵高频激光二极管侧面抽运Nd∶YAP晶体,使用V型折叠腔,LN晶体电光调Q,输出高峰值功率的1341.4nm偏振基频光.选取KTP晶体Ⅱ类临界相位匹配倍频,获得670.7nm红光.使用LBO晶体Ⅰ类临界相位匹配把670.7nm的倍频光与1341.4nm的基频光进行和频,获得三倍频447.1nm的蓝光输出.实验结果表明:优化后的V型折叠腔,可提高非线性转换效率,在平均抽运功率92.4W时,获得了平均功率887mW、峰值功率17.7kW、脉宽50ns的偏振蓝光输出,光-光转换效率为0.96%.     

利用群速度匹配的级联二阶非线性实现超短激光脉冲压缩

提出了一种采用倾斜脉冲的级联二阶非线性来实现超短激光脉冲压缩的方法. 对基于单块BBO晶体中基频光与倍频光群速度匹配的级联二阶非线性的脉冲压缩方案进行了理论分析. 对比研究了群速度匹配与失配情况下利用级联二阶非线性进行脉冲压缩的效果, 并模拟分析了基频光与倍频光的位相失配量、非线性晶体长度、 基频光初始峰值光强和初始脉宽等因素对脉冲压缩效果的影响. 结果表明, 基频光与倍频光的群速度匹配将会大幅度改善压缩脉冲的时间波形和频谱分布. 通过对位相失配量、晶体长度、初始光强等参数的优化和选取可获得较理想的压缩效果. 采用倾斜脉冲的级联二阶非线性的脉宽压缩方法, 针对中心波长800 nm、脉宽100 fs, 峰值光强为50 GW/cm²的基频光脉冲, 采用25 mm厚BBO晶体, 当基频光与倍频光位相失配量Δk=60 mm^-1(对应失谐角1.98°), 晶体外部脉冲前沿倾斜角γ₀=74°时, 计算获得了质量较好的20 fs剩余基频光, 并同时产生了14 fs的倍频光. 关键词： 倾斜波 级联二阶非线性 群速度失配 脉冲压缩     

LD侧面抽运Nd:YAP腔内三倍频蓝光激光器

研制了一台LD侧面抽运Nd:YAP腔内三倍频447.1 nm脉冲蓝光激光器.采用列阵高频激光二极管侧面抽运Nd:YAP晶体,使用V型折叠腔,LN晶体电光调Q,输出高峰值功率的1 341.4 nm偏振基频光.选取KTP晶体Ⅱ类临界相位匹配倍频,获得670.7 nm红光.使用LBO晶体Ⅰ类临界相位匹配把670.7 nm的倍频光与1 341.4 nm的基频光进行和频,获得三倍频447.1 nm的蓝光输出.实验结果表明：优化后的V型折叠腔,可提高非线性转换效率,在平均抽运功率92.4 W时,获得了平均功率887 mW、峰值功率17.7 kW、脉宽50 ns的偏振蓝光输出,光-光转换效率为0.96%.     

稳定高质量光参量啁啾脉冲放大系统优化设计

要实现光参量啁啾脉冲放大(OPCPA)系统稳定、高质量输出,需要同时对光参量放大和泵浦光倍频这两个非线性过程进行优化设计。在光参量放大系统优化设计中,建立了描述光参量放大过程的多种简化物理模型;通过模拟泵浦光和信号光口径匹配关系,分析了放大信号光空间两维对称性并提出了优化方法;建立了非线性晶体最佳长度确定及调谐方法,以实现信号光输出高稳定性。在泵浦光倍频系统优化设计过程中,提出应用位相失配法实现稳定倍频输出,研究表明这种方法不仅能实现倍频光能量起伏抖动远远小于基频光能量的起伏抖动,而且能减小泵浦光近场调制度和时间波形调制,极大地改善输出倍频光光束质量,进而提高OPCPA系统输出信号光质量。     

兼容多波长及多脉宽输出的频率转换系统设计

通过对多种频率转换方案的深入对比分析,设计了一套兼容多波长及多脉宽高效输出的频率转换系统。采用"Ⅱ+Ⅱ"类双晶体级联的方式,可以实现"偏振失配"三倍频和Ⅱ类双晶体正交级联二倍频两种模式间的快速切换。通过数值模拟程序优化了晶体构型,结果表明,当两块晶体厚度均为10mm时,可以兼顾低功率长脉冲和高功率短脉冲对效率和稳定性的需求。     

“神光Ⅱ”装置激光输出波形的数值模拟

推广应用“激光放大一维问题的解”的计算方法,模拟计算了“神光Ⅱ”装置激光束放大链的传输波形,并与实验结果进行比较,符合较好. 为功率平衡的研究提供了有力工具. 关键词： 模拟计算 激光束 波形 功率平衡     

Effect of frequency detuning on the output characteristics of CO<Subscript>2</Subscript> lasers

The effect of frequency detuning away from the line center on the radiative parameters of pulsed CO₂ lasers is studied by numerical modelling. It is shown that the temporal, energy, and spectral characteristics of the output can be controlled by varying the detuning and other parameters. Output pulses with a high peak power have an essentially unremovable, relatively long "tail" owing to the rotational bottleneck effect. The energy of the laser pulse is greatest at the line center. For certain values of the parameters, a maximum peak power is attained in the wings of the line, rather than at its center. The amount of sweeping depends on the sign of the detuning and is typically no more than 10 MHz.     

高通量条件下KDP晶体三倍频参数的优化

 采用四阶龙格-库塔（R-K）数值计算方法,以Ⅰ／Ⅱ角度失谐和Ⅱ／Ⅱ偏振失配两种三倍频方案为例,给出了入射基频光为平面方波,功率密度5GW/cm²的情况下 ,KDP晶体三倍频参数的优化结果。     

高功率高效率三次谐波二维数值模拟研究

 对大口径、高功率情况下的三次谐波转换,选择KDP晶体TypeⅠ/TypeⅡ匹配角度失谐的三倍频方案,并从非线性三波耦合方程组出发,采用离散傅立叶变换和四阶龙格库塔(R-K)积分方法,编制了二维模拟三次谐波转换的计算程序。计算了各种晶体厚度和不同失谐角条件下,二、三次谐波的转换特性和效率。并对入射基频光为六阶超高斯分布时的三倍频器进行了优化,三倍频转换效率达80%,此时具有较大的动态范围和较高的三倍频转换效率。     

A Compact Diode-Pumped Injection Seeded Nd：YAG Laser with Resonance-Detection Technique

A diode pumped injection seeded single-longit udinal-mode （SLM） Nd： YA G laser is achieved by using the resonancedetection technique in Q-switching operation. The pulsed oscillator laser uses a folded cavity to achieve compact construction. This system operates at 100 Hz and provides over 20 m J/pulse of single-frequency 1064 nm output. The M2 values of horizontal and vertical axes are 1.58 and 1.41, respectively. The probability of putting out single-longitudinal-mode pulses is 100%. The 355 nm laser output produced by frequency tripling has a linewidth less than 200 MHz. The laser can run over eight hours continually without, mode hopping     

Compact passively Q-switched green laser with periodically poled MgO:LiNbO<Subscript>3</Subscript>

Passively Q-switched green output with Cr⁴⁺:YAG as saturable absorber and PPMgLN as the frequency doubling crystal was realized in a compact diode end-pumped Nd:YVO₄ laser. The green light output power, pulse width, pulse repetition rate, pulse energy and peak power with three Cr⁴⁺:YAG of different initial transmissions were investigated. The maximum average output power was 1.2 W at the pump power of 4.0 W and the maximum conversion efficiency was 30% with the Cr⁴⁺:YAG of 90% initial transmission. The maximum pulse energy and minimum pulse width were 10.9 μJ and 12 ns with the Cr⁴⁺:YAG of 75% initial transmission.     

六束高功率钕玻璃激光器

本文描述了用于辐照[(CD₂)_n]微球靶的六束高功率钕玻璃激光系统的概貌、有关技术细节以及输出光束特性。激光脉宽在1—4毫微秒内可调。在脉宽为2毫微秒时,每束输出能量约为50焦耳,光束发射角为0.4毫弧度,六束总输出功率约为1.5×10¹¹瓦。 关键词：     

An efficient and compact laser-diode end-pumped intracavity frequency-tripled Nd: YVO4 355 nm laser

By exploiting the intracavity frequency conversion configuration, a diode end-pumped acousto-optic (AO) Q-switched Nd:YVO₄ 355 nm laser was demonstrated in this paper. Two LBO crystals were inserted in the cavity to realize the frequency tripling operation, a cascade of the second harmonic generation (SHG) and sum frequency mixing (SFM). Under the absorbed pump power of 13 W, the maximum average output power at 355 nm was obtained to be 1.32 W at the repetition frequency of 17 kHz, with the optical-to-optical conversion efficiency of 10.2%. The corresponding pulse width was 10.2 ns, with the energy of a single pulse and corresponding peak power estimated to be 77.6 μJ and 7.61 kW, respectively.     

Stationary generation of diode-pumped self-Raman Nd:YVO<Subscript>4</Subscript>/YVO<Subscript>4</Subscript> composite crystal laser

Output power dependences of composite Nd³⁺:YVO₄ Raman laser stationary generation on the longitudinal diode pump power are measured at different transmissions of the output mirror at the Stokes radiation frequency. The deviation of the measured dependences from linear is explained by the influence of thermal effects on both the overlap of the beams and diffraction losses. A method to estimate the laser and Stokes losses in the cavity and the parameters characterizing the overlap of the laser radiation with the pump and Stokes beams is proposed. A Stokes-component of power 2.1 W is obtained and corresponds to 12% diode-to-Stokes efficiency.     

Self-diffraction of frequency-modulated light in the Bi12TiO20 crystal

The self-diffraction of frequency-modulated light in the photorefractive B₁₂TiO₂₀ crystal was studied experimentally. To observe the effect, the crystal was illuminated by two light beams with the relative frequency shift Δf(t). In the experiments, linear frequency modulation was used: Δf(t) = At. As a result of the light self-diffraction on a hologram moving with a constant acceleration, the power of the light beams at the crystal output changed in the form of a chirp pulse. It was found that the pulse appears at the instant of stopping the interference pattern, and its duration is determined by the rate of frequency change A and the hologram recording time τ _sc .