Ultrashort pulse generation and measurement techniques

The first section will discuss the generation of picosecond and femtosecond laser pulses, their propagation and compression in optical fibers, and their amplification for nonlinear spectroscopic applications. Laser systems for different wavelength regimes and pulse measurement techniques will be described. The second section will extend the discussion of picosecond and femtosecond measurement to studies of ultrafast processes in materials. Pump-probe and transient four-wave-mixing methods will be analyzed. Examples of application to both molecular and solid state systems will be presented.     

双色激光脉冲辐照下38 as孤立短脉冲的产生

通过数值求解一维含时薛定谔方程, 本文研究了具有特定波长的双色激光脉冲与氦原子相互作用产生的高次谐波和阿秒脉冲, 这里双色激光脉冲由5 fs较低强度基频钛宝石主脉冲与另一束较高强度的1330 nm 红外附加脉冲构成. 研究发现, 若两束脉冲之间的相对相位选择合适, 可以获得宽带连续辐射的高次谐波谱, 叠加该连续辐射谱可获得脉宽为38 as的孤立短脉冲. 进一步研究发现, 不同于以往孤立阿秒脉冲研究中选出长、短量子路径之一作为辐射源, 这里单阿秒脉冲来源于长、短两个量子路径的贡献, 只是这两个量子路径在很宽的谐波次数变化范围内辐射时刻比较集中. 关键词： 双色激光脉冲 阿秒脉冲 量子路径     

亚飞秒脉冲的产生与控制——饶毓泰基础光学一等奖介绍

亚飞秒脉冲是研究和控制发生在阿秒时间尺度超快物理过程的有效工具.基于分子调制过程,文章作者提出并发展了一系列亚飞秒脉冲产生和操控的技术;围绕频谱合成方案,利用级联二阶非线性效应,实现了多色圆锥辐射注入放大和二维多色阵列及其参量上转换放大;同时,还开展了基于飞秒振荡器及外腔增强技术的高重复频率高次谐波产生与输出耦合的相关研究.     

亚飞秒脉冲的产生与控制——饶毓泰基础光学一等奖介绍

亚飞秒脉冲是研究和控制发生在阿秒时间尺度超快物理过程的有效工具.基于分子调制过程,文章作者提出并发展了一系列哑飞秒脉冲产生和操控的技术;围绕频谱合成方案,利用级联二阶非线性效应,实现了多色圆锥辐射注入放大和二维多色阵列及其参量上转换放大;同时,还开展了基于飞秒振荡器及外腔增强技术的高重复频率高次谐波产生与输出耦合的相关研究.     

Optimization of attosecond pulse generation

The generation of attosecond pulses by superposition of high harmonics relies on their synchronization in the emission. Our experiments in the low-order, plateau, and cutoff regions of the spectrum reveal different regimes in the electron dynamics determining the synchronization quality. The shortest pulses are obtained by combining a spectral filtering of harmonics from the end of the plateau and the cutoff, and a far-field spatial filtering that selects a single electron quantum path contribution to the emission. This method applies to isolated pulses as well as pulse trains.     

基于场效应晶体管的高压电脉冲产生技术

 以高速MOSFET器件为基础,对超快高压电脉冲产生技术进行了实验研究。采用多路并联的高速MOSFET与感应叠加相结合的形式,得到脉冲半宽度为300 ns、上升时间约为60 ns、时间间隔600 ns的超快方波双脉冲;在负载电阻为11.5 Ω时,可以产生365 A的脉冲峰值电流,并且能够提供1.5 MW的峰值输出功率。     

Adaptive pulse compression for transform-limited 15-fs high-energy pulse generation

We demonstrate the use of a deformable-mirror pulse shaper, combined with an evolutionary optimization algorithm, to correct high-order residual phase aberrations in a 1-mJ, 1-kHz, 15-fs laser amplifier. Frequency-resolved optical gating measurements reveal that the output pulse duration of 15.2 fs is within our measurement error of the theoretical transform limit. This technique significantly reduces the pulse duration and the temporal prepulse energy of the pulse while increasing the peak intensity by 26%. It is demonstrated, for what is believed to be the first time, that the problem of pedestals in laser amplifiers can be addressed by spectral-domain correction.     

飞秒激光脉冲整形技术及其应用

通过频域上控制飞秒激光脉冲幅度、相位和偏振在时域上可以获得几乎任意形状的飞秒激光脉冲,这种飞秒激光脉冲整形技术可为研究光与原子分子非线性相互作用提供一种全新实验技术手段.本文介绍飞秒激光脉冲整形发展历史、技术方法、控制方式及其相关应用,并展望飞秒激光脉冲整形技术未来的发展方向.     

High-power third-harmonic flat pulse laser generation

The generation of a high-power laser pulse at 266 nm that is longitudinally shaped according to a prefixed intensity profile is reported. The main features of the pulse shape modifications due to second- and third-harmonic conversions are measured, and the results are in good agreement with the theory. The UV temporal shape depends on the chirp of the fundamental pulse and on the crystal phase-matching angle. Exploiting the large stretching imposed on the third-harmonic signal, we show that the pulse intensity profile can be obtained by spectral single-shot measurements.     

Ultrashort pulse generation in diode lasers

The basic ideas and current state of the art of ultrashort pulse generation by injection lasers are reviewed. All developed techniques, including gain switching,Q-switching, and mode-locking are described and compared. A simple theoretical treatment of a diode laser which emits picosecond light pulses is discussed. Some fundamental limits of the pulse parameters are discussed. Finally, compression of chirped optical pulses by optical fibres and the soliton effect is considered.     

Supercontinuum generation and pulse compression in hollow waveguides

We present a theoretical study of temporal and spectral characteristics and pulse compression in hollow waveguides, using a global approach to dispersion without application of the slowly varying envelope approximation. A novel ultrawide self-phase modulation-induced spectral-broadening regime with spectra covering almost 3 octaves is predicted for a pressure at which the group-velocity dispersion parameter is small and anomalous. Compression to subcycle pulses by an appropriate broadband modulator and pulse shortening without chirp control by a spectral filter are studied.     

Entropy generation rate during laser pulse heating: Effect of laser pulse parameters on entropy generation rate

Laser pulse heating of solid surface and entropy generation during the heating process are considered. Time exponentially decaying pulse is accommodated in the analysis and the laser pulse parameter (β₁/β₂) resulting in minimum entropy generation rate is computed. Analytical solutions for temperature rise are presented and volumetric entropy generation rate is formulated. Two laser pulses resulting in low volumetric entropy generation rate are examined in detail and volumetric entropy generation rate is associated with the laser pulse parameter (β₁/β₂). It is found that volumetric entropy generation rate attains high values in the early heating period due to large (1/T²). Moreover, the laser pulse with high-peak intensity results in lower volumetric entropy generation rate than that corresponding to the low-intensity laser pulse with the same energy content.     

170 fs pulse generation by optical pulse compression at 308 nm

Pulses of 170 fs duration have been obtained by compression of 220–250 fs pulses of a hybrid excimer-dye laser setup.     

采用组合脉冲驱动生成单一的X射线阿秒脉冲

采用组合激光脉冲(800 nm/9.4 fs 24 nm/1 fs)辐照联合两原子体系产生高次谐波,获得了单一的X-射线阿秒脉冲.我们发现,当固定钛宝石激光的峰值强度并改变高频谐波脉冲的峰值强度Ih时,存在一个优选的Ih范围,在该范围内相应的阿秒脉冲最优化,即强度达到最强,对此,本文从受激复合的角度给出了合理解释.     

Subfemtosecond pulse generation and multiplicative increase of pulse spacing in high-order stimulated Raman scattering

We demonstrate a technique for multiplicatively increasing the pulse spacing of subfemtosecond pulse trains generated by high-order stimulated Raman scattering, which uses pairs of off-resonant two-photon excitation of a molecular Raman mode to establish strong molecular modulation in the medium. Every laser pair has two single-mode laser beams tuned slightly off two-photon resonance, and the laser pairs have their corresponding carrier frequencies shifted from each other by one half, one third, or one fourth of the selected molecular Raman mode frequency. Theoretical analyses and calculations based on the fundamental vibrational transition of solid hydrogen show that the pulse spacing of the subfemtosecond pulse trains thus generated can readily be doubled, tripled, or even quadrupled.     

Ultrashort pulse generation using fiber FM laser

Ultrashort optical pulse generation using a fiber FM laser is presented and analyzed in detail. Fiber FM laser operation is realized using a fiber ring with an internal phase modulator and an erbium-doped fiber amplifier. To compress FM laser pulses, an external dispersive single-mode fiber is employed. Furthermore, by external intensity modulation, the pulse background is removed. The background ratio of the generated ultrashort pulse is calculated and compared with the experimental results. The experimental results show an output optical pulse width of 1.77 ps and a spectral bandwidth of 0.5 THz.     

细线径螺旋线长脉冲产生技术

提出了双路输出的螺旋脉冲形成线(PFL)结构,该结构内置用于充电的高耦合变压器,在螺旋PFL的两端各自输出一个脉冲,副路匹配输出时主路输出脉冲波形具有良好的平顶品质,主路输出脉冲能量占储能的大部分,解决了Korovin提出的螺旋PFL充电问题。对比分析双路输出的螺旋 PFL与SINUS-700/130两种技术路线,结果发现双路输出的螺旋 PFL改善了输出脉冲的平顶质量,输出功率提高29%,但是副路输出占用11%的储能,不易充分利用。     

Tunable-chirp pulse compression in quasi-phase-matched second-harmonic generation

We demonstrate continuously tunable compensation of linear chirp on a first-harmonic pump pulse to produce a near-transform-limited second-harmonic output pulse through the use of a chirped, fanned, periodically poled lithium niobate quasi-phase-matching grating. Compensation of positive and negative chirps is possible through reversal of device orientation. The device is simple and monolithic and can be applied to compensation of a higher-order phase with minor modification.     

Short laser pulse generation: part two

The status of short laser pulse generation is reviewed. Achievements, limitations and potential of techniques producing pulses shorter than 50 ns, from the ultra-violet to the infra-red, are examined.In this second half of the paper the physical principles underlying the generation of ultra-short pulses by gating, interferometric techniques, pulse compression and pulse shaping are considered.