金属卟啉化合物激发态折射与激发态吸收增强瞬态热折射竞争研究

应用激发态吸收增强瞬态热折射理论结合激发态折射理论研究了新型锌卟啉化合物Zn-porphyrin 中激发态吸收增强瞬态热折射与激发态折射间的相互竞争. 样品在不同脉宽激光激发下呈现自聚焦-自散焦间的转化. 当入射激光脉宽为4 ns时,激发态折射占主要地位,样品呈现自聚焦性质;当入射激光脉宽为8ns时,激发态吸收增强瞬态热折射占主要地位,激发态折射占次要地位,样品呈现自散焦性质. 关键词： 金属卟啉化合物 激发态折射 瞬态热折射     

Experiment Study on Active-passive Mode-locking Using Cr4+:YAG as Saturable Absorber

Cr4+:YAG crystal was used as a saturable absorber in an active-passive mode-locked Nd:YAG laser. The stable and complete mode-locked pulse train was achieved at 1064 nm. The duration of ～0.8 ns to 2.4 ns for a single pulse was obtained by using Cr4+:YAG crystals with the different initial transmissions, and there was a shortest pulse width. The mode-locking dynamic process of Cr4+:YAG crystal was discussed to explain the experimental result, and the effect of excited-state absorption was considered.     

Experiment Study on Active-passive Mode-locking Using Cr4+∶YAG as Saturable Absorber

Cr4+∶YAG crystal was used as a saturable absorber in an active-passive mode-locked Nd∶YAG laser. The stable and complete mode-locked pulse train was achieved at 1064 nm. The duration of ～0.8 ns to 2.4 ns for a single pulse was obtained by using Cr4+∶YAG crystals with the different initial transmissions, and there was a shortest pulse width. The mode-locking dynamic process of Cr4+∶YAG crystal was discussed to explain the experimental result, and the effect of excited-state absorption was considered.     

萘酞菁铅化合物的光限幅特性研究

应用调Q倍频ns/ps Nd：YAG脉冲激光,在波长为532nm,脉冲宽度为8ns,重复频率为1Hz的条件下,研究了溶于二甲基亚砜(DMSO)中的萘酞菁铅溶液的反饱和吸收和光限幅特性。实验表明,萘酞菁铅具有良好的光限幅特性,它的有效激发态吸收截面与基态吸收截面的比值约为15．21,大于萘酞菁铜。研究结果表明,萘酞菁铅的光限幅特性优于C60,激发态吸收是其主要的光限幅机理。实验结果证实了重原子效应可以通过增强系际跃迁而使三重态的反饱和吸收增强,从而提高光限幅的能力。     

A study of photophysics using the Z-scan technique: lifetime determination for high-lying excited states

We report a novel method of determining the lifetimes of the high-lying excited singlet states of dye molecules in solution. The method is based on simulating the Z-scan technique with ground-state and excited-state absorptions of an incident laser pulse having Gaussian temporal and spatial distributions. This leads to the important finding that the use of laser pulses as long as tens of picoseconds can resolve subpicosecond lifetime.     

强耦合腔-QED系统中原子的纳秒脉冲激发光谱研究

本文在多原子强耦合腔-QED系统中,利用脉冲宽度为5 ns的强脉冲光在垂直于腔轴方向直接激发原子,脉冲的峰值功率为40 mW,通过光学腔观测激发原子辐射到腔中的光子获得相应的激发光谱。我们发现当光场频率和原子跃迁失谐±80 MHz时原子激发率达到最大,而在共振时原子激发被抑制。我们建立了脉冲光与三能级原子相互作用的模型,通过缀饰态能够解释此现象。     

Temporal compression of short-wavelength laser pulses by coherent control in rare gases

We present a theoretical study of temporal compression of a short-wavelength laser pulse predicted in a real, Doppler-broadened, atomic system. The compression is the result of the coherent control peculiarities of electromagnetically induced transparency-propagation dynamics. Numerical results are reported and discussed, showing a temporal compression of 2 orders of magnitude (from 10 ns to 100 ps) of a 106.7-nm laser pulse in argon atoms at room temperature.     

Concentration dependent nonlinear refraction in chloroaluminum phthalocyanine/ethanol solution

Nonlinear refractive properties of chloroaluminum phthalocyanine (CAP) in ethanol solution are studied using the Z-scan technique with picosecond (ps) and nanosecond (ns) laser pulses at a wavelength of 532 nm. A transition from self-focusing to self-defocusing in CAP solution excited by 10 ns pulses is observed during the decrease of its concentration. This transition is due to co-existing excited-state refraction and transient thermal lensing effects. The experimental results are described very well using the rate-equation model and the theory of transient thermal refraction in liquids. The refractive cross sections of the excited-state are also obtained.     

Dual-beam ablation of fused silica by multiwavelength excitation process using KrF excimer and F2 lasers

A new technique of dual-beam laser ablation of fused silica by multiwavelength excitation process using a 248-nm KrF excimer laser (ablation beam) coupled with a 157-nm F₂ laser (excitation beam) in dry nitrogen atmosphere is reported. The dual-beam laser ablation greatly reduced debris deposition and, thus, significantly improved the ablation quality compared with single-beam ablation of the KrF laser. High-quality ablation can be achieved at the delay times of KrF excimer laser irradiation shorter than 10 ns due to a large excited-state absorption. The ablation rate can reach up to 80 nm/pulse at the fluence of 4.0 J/cm² for the 248-nm laser and 60 mJ/cm² for the F₂ laser. The ablation threshold and effective absorption coefficient of KrF excimer laser are estimated to be 1.4 J/cm² and 1.2᎒⁵ cm^-1, respectively.     

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.     

Active–passive mode-locking using Cr:YAG crystal as saturable absorber

Cr⁴⁺ : YAG crystal was used as a saturable absorber in an active–passive mode-locked Nd : YAG laser. The stable and complete mode-locked pulse train was achieved at 1064 nm. The duration of a single pulse was obtained from 0.8 to 2.4 ns by changing the Cr⁴⁺ : YAG crystal with different initial transmission, when there was the shortest pulse width. The mode-locking dynamic process of Cr⁴⁺ : YAG crystal was analyzed by the rate equations to explain the experimental result, and the effect of excited-state absorption was considered.     

超冷里德堡原子的产生以及探测

利用激光冷却与俘获技术获得冷原子,由双光子激发产生超冷里德堡原子,利用场电离法得到了里德堡原子ns和nd态的离子谱图;再将激光波长固定在6p3/2-34d态的共振跃迁线上,得到了离子和里德堡原子的TOF(Time of Flight)图,并对实验结果做了分析.     

基于波长330nm激光激发多色激光导星回波光子数的数值计算与探讨

采用无模激光器发射波长为330 nm的激光激发多色激光导星,需要考虑脉冲激光重频率、激光带宽、激光初始光斑直径以及大气透过率对回波光子数的影响.通过数值模拟,计算了高斯光束的脉冲激光和连续激光激发多色激光导星在实际大气中后向辐射330 nm和2207 nm波长的回波光子数.数值计算结果表明,在垂直发射和接收的情况下,当到达大气中间层的激光能量为1 W时,连续激光能够获得更多的回波光子数,并且回波光子数几乎无起伏.对于脉冲激光,提高脉冲激光重频率达到50 kHz以上时,多色激光导星330 nm的回波光子数随脉冲重频率的增加趋于有限值;当大气能见度小于5 km且大气相干长度为12.8 cm时,大约需要34 W以上的激光发射能量,才能获得满足使用自然星全倾斜探测的330 nm回波光子数.对于连续激光,相同情况下,大约需要20 W以上的激光发射能量.     

Laser-induced incandescence for soot particle size and volume fraction measurements using on-line extinction calibration

A novel technique for two-dimensional measurements of soot volume fraction and particle size has been developed. It is based on a combined measurement of extinction and laser-induced incandescence using Nd:YAG laser wavelengths of 532 nm and 1064 nm. A low-energy laser pulse at 532 nm was used for extinction measurements and was followed by a more intense pulse at 1064 nm, delayed by 15 ns, for LII measurements. The 532-nm beam was split into a signal beam passing the flame and a reference beam, both of which were directed to a dye cell. The resulting fluorescence signals, from which the extinction was deduced, together with the LII signal, were registered on a single CCD detector. Thus the two-dimensional LII image could be converted to a soot volume fraction map through a calibration procedure during the same laser shot. The soot particle sizes were evaluated from the ratio of the temporal LII signals at two gate time positions. The uncertainty in the particle sizing arose mainly from the low signal for small particles at long gate times and the uncertainty in the flame temperature. The technique was applied to a well-characterized premixed flat flame, the soot properties of which had been previously thoroughly investigated. Received: 21 June 2000 / Revised version: 11 September 2000 / Published online: 7 February 2001     

准分子激光等离子体开关控制脉宽研究

 利用准分子激光等离子体技术，在紫外预电离XeCl准分子激光器上获得了最短1.58 ns的短脉冲激光输出。实验中分析了聚焦到薄膜表面的光束能量密度对所产生的等离子体密度的影响，并对不同等离子体密度及维持时间情况下脉冲压缩效果进行了讨论，给出了激光器谐振腔在稳定腔及非稳腔两种工作方式下的实验结果。激光器在稳定腔工作时，脉宽可压缩至2.87 ns；采用非稳腔结构时，在脉冲能量不变情况下减小聚焦光斑面积，提高入射到薄膜表面的能量密度，得到了最短1.58 ns的短脉冲激光输出。该技术适用于任何其它准分子器件。     

High-dynamic-range laser-pulse-contrast measurement with a plasma-shuttered streak camera

The dynamic range of a picosecond visible streak camera has been improved by the combination of a plasma shutter and multishot averaging performed with a photoconductive switch sweep circuit. We use this technique to measure the contrast of a 100-fs laser pulse over 2 ns with a dynamic range of 7 orders of magnitude.     

GaAs被动调Q兼输出耦合Nd∶YVO4激光特性研究

利用可饱和吸收半导体GaAs作为被动调Q元件和FP输出耦合镜,实现了半导体激光器(LD)抽运Nd:YVO4激光调Q运转,获得脉宽度为47ns,重复频率为1183kHz,平均功率为430mW,光束质量为M2=113的TEM00激光基横模输出,调Q抽运阈值为1700mW.并数值求解了含有GaAs被动调Q兼输出耦合的速率方程,分析了GaAs被动调Q机理以及脉宽宽度、重复频率、平均功率随抽运速率、腔长的变化关系,理论与实验结果相一致.为多功能综合型微型调Q固体激光器提供了简单有效的方法. 关键词： 被动调Q 输出耦合 GaAs     

Simple electro-optic technique to generate temporally flat-top laser pulses

A simple technique is presented to generate temporally flat-top shaped laser pulses using electro-optic modulator (Pockels cell). It involves splitting of input laser pulse into two halves of equal intensity and then stacking together with appropriate optical delay to get a temporally flat-top laser pulse. It also allows generation of other pulse shapes by varying the relative intensity, delay, and phase between two halves of the input laser pulse. Temporally flat-top laser pulses of duration ~ 9 ns have been generated using ~ 7 ns duration incident laser pulses from a flash lamp pumped Q-switched Nd:glass laser oscillator. The rise and fall-time of the shaped pulse is limited by speed of electro-optic switch (Pockels cell), which is ~ 2 ns in the present case.     

Single-frequency, Q-switched Ho:YAG laser at room temperature injection-seeded by two F-P etalons-restricted Tm, Ho:YAG laser

We demonstrated a 1.91 μm pumped, injection-seeded Q-switched Ho:YAG laser operating at room temperature. By inserting two Fabry-Perot etalons into the laser cavity, single-frequency Tm, Ho:YAG seed lasing was achieved at a wavelength of 2090.9 nm, with a typical output power of 60 mW. Single-frequency, nearly transform-limited Q-switched operation of the Ho:YAG laser was achieved by injection seeding. The output energy of the single-frequency Q-switched pulse is 7.6 mJ, with a pulse width of 132 ns and a repetition rate of 100 Hz. We measured the pulse spectrum, half-width of which was 3.5 MHz, by a heterodyne technique.     

利用脉冲负反馈压缩准分子激光脉冲

 分析了准分子激光脉冲在放大过程中的展宽现象。将饱和开关技术应用于放电泵浦激光器放大腔的放大压缩,发展了脉冲负反馈饱和压缩技术。利用该技术在天光一号系统前端LPX-150激光器上成功获得能量100 mJ、脉宽10 ns的脉冲输出,其空间分布均匀性保持在3%以内。这证明该技术可与无阶梯诱导非相干技术联合使用,在保证光束均匀性基础上进行脉冲压缩。