高温合金不同脉宽超快激光作用下多脉冲去除阈值

实验研究了激光脉冲宽度和脉冲个数对镍基高温合金材料去除阈值的影响,分别在290 fs,1 ps和7 ps脉宽的激光下,使用1,10,50,100,300,500和1000个不同能量的激光脉冲辐照高温合金样品表面。实验结果表明,烧蚀坑尺寸会随脉冲数的增加而增加,而脉冲宽度的增加会加大脉冲个数对烧蚀坑直径的影响。通过烧蚀坑直径的平方值与激光脉冲能量之间存在的对数关系,得到了不同脉冲宽度下镍基高温合金的多脉冲材料阈值。3种不同脉宽下的高温合金多脉冲去除阈值都存在显著的累积效应。根据去除阈值计算得到290 fs,1 ps和7 ps脉宽下的累积效应系数分别为0.88,0.86和0.78。     

激光波长及脉宽对光学材料抗损伤性能的影响

 基于能带理论,利用激光与光学材料相互作用的理论模型,研究了激光辐照下材料导带自由电子数密度的变化,讨论了材料损伤阈值与激光波长、脉冲宽度、材料禁带宽度之间的关系,数值分析了激光波长和脉冲宽度对损伤阈值的影响。结果表明:当脉宽小于1 ps时,材料损伤阈值随脉宽增大而减小;当脉宽大于1 ps时,材料损伤阈值随脉宽增大而增大;激光波长为10 fs~10 ns,损伤阈值随着波长的减小而减小。     

Long-cavity Nd:YAG laser used in single-shot spontaneous Raman scattering measurements

The use of a 100 ns pulse Nd:YAG laser is proposed to perform single-shot measurements by spontaneous Raman scattering. The long pulse duration is obtained thanks to a White cell placed inside the laser oscillator. This lengthens the pulse duration within the laser cavity, keeping almost the same beam quality as standard Nd:YAG lasers. The laser system is described, the advantages are compared with extra-cavity stretched lasers, and single-shot measurement of concentration in gas is demonstrated.     

在不同激光脉宽下的高次谐波

用数值计算方法计算了不同强激光脉冲宽度下高次谐波的产生.我们发现对于激光场强度不高,不能有效电离初态的激光场,长脉冲宽度可以更有效产生高次谐波;而对于高场强的激光场,由于它能够在几个光学周期之内把原子的初态全部电离,所以短脉冲的激光场能够更有效产生高次谐波.     

Theoretical and experimental research on the pulse duration of excimer laser output

The effects of discharge stability and cavity buid-up time of pulse laser on thepulse duration of excimer laser are investigated theoretically.The characteristics of the ex-cimer laser pulse duration can be explained by these theoretical analysis.     

Time-resolved STM light emission from an evaporated Au film

STM (scanning tunneling microscope) light emission from an evaporated Au film irradiated by pico second laser pulses has been investigated for various bias voltages of the STM. The observed emission consists of two components. The first component that has the same duration as the incident laser pulse is excited by laser induced tunneling electrons. The second component that has a longer duration than that of the laser pulse is emitted from surface polariton plasmons excited non-linearly by the laser pulse.     

Study on the effect of laser parameters on wakefield excitation in femtosecond pulsed laser–plasma interaction using PIC method

Propagation of an intense short laser pulse through under-dense plasma can produce huge amplitude plasma wake field. A 3D particle in cell (PIC) method was used to simulate the wakefield generation for different laser parameters such as intensity, pulse duration, spot size and temporal pulse shape. Our study shows that the amplitude of wakefield is increased with laser intensity, but it is decreased with spot size. The results for pulse shape and pulse duration depend on their optimum values.     

增益调制高重频脉冲光纤激光器实验研究

采用脉冲泵浦方案,研制出了基于增益调制技术的全光纤结构高重频脉冲激光器。采用电路直接调制的激光二极管作为泵浦源,双包层光纤作为增益介质,构造了光纤光栅选模的线形腔结构。实验中通过调整泵浦光脉冲宽度和光纤激光器谐振腔长度,得到了稳定的高重频脉冲。在100kHz重复频率下,采用21W的峰值泵浦功率和2.5μs的泵浦脉冲宽度,获得了1.06μm波长,脉冲宽度247ns的稳定脉冲激光输出。脉冲峰值功率一致性好,平均功率长期功率稳定性为2%。观察并分析了由于纵模拍频在脉冲包络上产生的次脉冲特性。通过一级放大实现89.6 W输出。     

高频激光脉宽对原子光电子发射谱的影响

采用广义含时伪谱方法数值求解原子在激光脉冲作用下的动量空间含时薛定谔方程,研究了高频激光脉宽对原子光电子发射谱的影响.数值模拟表明,随着激光脉冲宽度的增加,光电子谱干涉结构的振荡幅值逐渐减小,其最大峰值的强度和位置取决于产生有效电离的最大即时强度.通过分析光电子谱的变化规律能进一步加深对高频强场电离产生的动力学干涉效应的理解.     

Optimum pump-pulse duration for optical parametric oscillators

It is shown that for pulsed optical parametric oscillators there is an optimum pumppulse duration at which the threshold fluence is a minimum. The dependence of the threshold fluence on pump laser pulse duration is found to be substantial for lossy narrowband optical parametric oscillators. The pulse energy requirement for the pump laser may be substantially lowered by operating it at a pulse duration close to the optimum.     

激光带宽抑制光束小尺度自聚焦效应的条件

激光带宽有利于抑制光束的小尺度自聚焦效应,从而突破非线性效应的限制提高高能固体激光器的输出功率。研究表明,带宽抑制小尺度自聚焦效应的程度与带宽和脉宽之比密切相关,相同脉宽条件下带宽越大对空间小尺度自聚焦的抑制作用越明显,而带宽一定时随着脉冲宽度的增大,带宽的抑制作用则逐渐变弱。在实际的钕玻璃激光放大系统中,由有限的增益带宽以及增益窄化等因素所限制的带宽量,决定了在这类固体激光系统中需要脉冲宽度短至皮秒量级才能有效利用激光带宽抑制小尺度自聚焦效应,而对于长至数十皮秒,甚至纳秒量级的长脉冲而言,如此有限的带宽量对小尺度自聚焦的抑制几乎不起作用。     

具有几个光振荡周期的飞秒激光脉冲

从麦克斯韦方程组出发 ,推导出了具有几个光振荡周期的飞秒激光脉冲在非线性光纤中传输的方程和非线性光纤的折射率。给出了描述具有几个光振荡周期的飞秒激光脉冲在非线性光纤中传输方程的解。研究了在非线性光纤中自相位调制导致具有几个光振荡周期的飞秒激光脉冲频谱展宽 (脉宽压缩 )的详细物理过程。研究了非线性光纤中飞秒光孤子产生的条件     

飞秒激光在空气和水中对硅片烧蚀加工的实验研究

采用1 kHz,800 nm,50 fs—24 ps的钛宝石激光脉冲对单晶硅样品在空气和水溶液环境中的烧蚀加工特性进行了研究.实验观察到了超短脉冲激光在空气氛围中烧蚀形成的双层环状结构,分析揭示了加工区域中心和边缘的烧蚀物理机制分别为热熔化和库仑爆炸,并测量了双层环状结构半径随入射激光能量、脉冲数及持续时间等的变化关系,结果表明获取较大深-宽比的加工效果需选择小能量脉冲激光的多次作用.在水溶液环境中,实验发现飞秒激光在样品表面诱导产生了亚微米量级的多孔状结构,而皮秒激光则更容易实现对硅表面的非热性去除.这是由于激光诱导的光机械应力和空泡效应随脉冲宽度变大而增强所致,在实验上确立了区分这两种不同加工状态的临界脉冲宽度. 关键词： 飞秒激光 硅片 激光加工     

Pump pulse characteristics of quasi-continuous-wave diode-side-pumped Nd:YAG laser

The influence of pumping laser pulse on the property of quasi-continuous-wave (QCW) diode-side-pumped Nd:YAG laser is investigated theoretically and experimentally. Under remaining a fixed duty cycle, the average output power increases, and the corresponding thermal focal length shorten with the increase of the pump pulse duration, which attributes to the decrease of the ratio of pulse buildup time to the pulse duration. At a pump power of 146 W, the laser output power changes from 65.1 W to 81.2 W when the pulse duration is adjusted from 150 μ s to 1000 μ s, confirming a significant enhancement of 24.7%. A laser rate equation model incorporating the amplified spontaneous emission is also utilized and numerically solved, and the simulated results agree well with the experimental data.     

高气压预电离短脉冲XeCl准分子激光产生研究

研究了在高气压、大体积、泵浦功率1.395 9 MW·cm-3抽运下,产生的XeCl*准分子激光光谱,波段307.7～308.5 nm,结果显示有两个谱线峰值307.98和308.19 nm,谱线最强的跃迁是B—X跃迁,脉冲宽度11.13 ns。在气体配比HCl∶Xe∶He=0.1%∶1%∶98.9%下,采用预电离初始电子,产生稳定辉光放电过程,获得了0.5～5 Hz,单脉冲能量450 mJ,束散角3 mrad, 短脉冲的准分子激光。     

对撞锁模染料激光器中锁模脉冲列的耦合效应

论述了在对撞锁模染料激光器中必然存在锁模脉冲列耦合效应,此效应使输出脉冲较宽,且脉宽不稳定。用适当加厚锁模染料层等办法减弱该效应会使脉冲变窄且脉宽稳定。     

Pulse compression in AO Q-switched diode-pumped Nd:GdVO4 laser with V3+:YAG saturable absorber

By simultaneously using both an acoustic-optic (AO) modulator and a V³⁺:YAG saturable absorber in the cavity, for the first time to our knowledge, a diode-pumped doubly Q-switched Nd:GdVO ₄ laser has been realized. The dependence of pulse width, pulse energy and peak power on the incident pump power at determinate pulse repetition rate are measured. Under the absorbed pump power of 8.59 W, the pulse temporal profile of the AO-switching with the pulse duration of 14.5 ns, the double Q-switching with pulse duration of 7.6 ns at 10 kHz, and the passive Q-switching with pulse duration of 22.3 ns are obtained. The pulse duration is obviously compressed in contrast to the purely actively AO Q-switched laser or the purely passively Q-switched laser with V³⁺:YAG.     

不同脉冲宽度355 nm波长激光诱导DKDP晶体损伤特性

研究了用于三倍混频的Ⅱ类DKDP晶体在35 ps,850 ps和7.6 ns三种不同脉宽355 nm波长激光作用下的损伤特性。实验对比分析了损伤阈值、概率和损伤针点形貌、尺寸和密度,并根据损伤阈值及概率得到前驱体阈值及密度。结果表明,前驱体的激光能量吸收量与脉宽线性相关。35 ps激光作用下DKDP有一种前驱体吸收激光能量形成熔融状损伤针点。850 ps激光作用下有两种前驱体吸收激光能量并产生力学破坏形成中心熔融四周断裂的损伤针点。7.6 ns激光作用下只有一种前驱体吸收激光能量,并且形成的损伤针点与850 ps对应的损伤针点有相同特征。     

Effect of pulse duration on generation of attosecond pulse with coherent wake emission

High-order harmonics and attosecond pulse generation with coherent wake emission are theoretically investigated for the effect of pulse duration and carrier envelope phase (CEP) of few-cycle laser pulse. We find that short pulse duration will cause the negative chirp for the high harmonics. When the laser pulse is shortened to a few cycles, the influence of the laser CEP on the chirp of the harmonics will also become more prominent.     

Design Method for Ultrabroadband Optical Parametric Chirped Pulse Amplification

Multiple amplification stages with different phase-matching angles were designed to yield stable and ultrabroadband amplification in optical parametric chirped pulse amplification by optimally controlling the idler laser pulses. Numerical results showed that the overall temporal duration of the amplified seed laser pulse and subsequently the spectral bandwidth can be amplified by using multiple amplification stages in comparison with those of the initial seed pulse laser, which is suitable to generate a high-energy pulse with ultrashort pulse duration in a simple manner.