Stable Q-switch mode-locking of Nd:YVO<Subscript>4</Subscript> lasers with a semiconductor saturable absorber

This paper reports on a passively mode-locked and Q-switched Nd:YVO₄ laser generating picosecond pulses with an average output power exceeding 7 W. In a first step Q-switch mode-locking was obtained by self Q-switching of a mode-locked oscillator with appropriate cavity design, pump power and output coupling. In a second system the Q-switching was actively controlled and stabilized by modulating the resonator internal losses with an acousto-optic modulator. In the Q-switch mode-locking operation the laser provided 12.8 ps long mode-locked pulses with a repetition rate of 80 MHz. The repetition rate of the Q-switch envelope was 185 kHz. The maximum pulse energy of a single ps pulse was 0.55 μJ which is 5.5 times the pulse energy measured for cw mode locking. The total energy of the pulses within the Q-switch envelope was 42 μJ. PACS  42.55.Xi; 42.60.Fc; 42.60.Gd     

全固态kHz啁啾脉冲飞秒激光放大器

要建造大功率超强激光系统,必须将nJ量级的种子进行放大,以得到mJ量级以及更高能量的激光输出.为达到这个目的,必须使种子能量指数增加,再生腔放大器是实现这一目的的良好途径;同时,为了得到更稳定的激光输出,须采用高重复频率的泵浦源.为此,设计了一种kHz重复频率激光泵浦的再生放大器,使用15 mJ的527 nm的绿光泵浦,得到了约2.3 mJ的800 nm放大激光输出,同时,对其输出激光的光谱特性进行了测量,将带宽为40 nm的种子注入后,得到了光谱带宽约为30 nm激光输出.     

Efficient, kHz repetition rate, gain-switched Cr:forsterite laser

We have developed a gain-switched room-temperature Cr:forsterite laser operating at repetition rates of between 1 and 34 kHz, and pumped by a continuous wave, Q-switched Nd:YAG laser. With optimised output coupling, an output pulse energy of 52 μJ was measured at 1.5 kHz repetition rate, corresponding to 11% efficiency and 13% slope efficiency. Threshold pulse energy was 53 μJ. Output power of 370 mW was obtained at 10 kHz repetition rate and 4.4 W pump power. Water cooling was not required for repetition rates up to 10 kHz. In a tunable, folded resonator, the Cr:forsterite wavelength tuned between 1173 and 1338 nm. This laser operated with maximum pulse energy of 34 μJ, efficiency of 13%, and power of 307 mW. The laser output was close to diffraction-limited with M² of 1.2. Received: 6 January 1999 / Published online: 29 July 1999     

Numerical simulation of a CW-pumped Cr:YAG passively Q-switched Yb:YAG pulsed laser

A general model of a CW-pumped passively Q-switched laser is presented which considers the pump power and excitation state of the absorber. The recovery time of the absorber is affected by the Q-switched laser pulse length and repetition rate, which results in changes of the output power, peak power and pulse duration of a CW-pumped passively Q-switched solid-state laser. At low pump power, the final inversion population density alters slowly by a small amount and the effect of the absorber's finite recovery time on laser output energy can be ignored. At high pump power, the final inversion population density increases quickly with pump power increase and the output energy decreases greatly. Simulation results of a CW-pumped, Cr:YAG Q-switched, Yb:YAG laser are reported. The numerical simulation results agree with the theoretical analytical analysis.     

声光调Q CO2激光器的输出特性

采用谐振腔内插入声光调制器（AOM）的方法获得了小型CO2激光器的高重频、窄脉宽、高峰值功率输出。通过分析CO2激光器声光调Q的工作原理,利用基于小信号增益和饱和光强的耦合输出数学模型给出了激光器最佳输出镜透过率的数值解,并运用相关实验装置对该数学模型进行了实验验证。理论分析和实验结果均表明：该声光调Q CO2激光器的最佳输出镜透过率为39%。研究了激光器输出性能随脉冲重复频率的变化规律,当脉冲重复频率〉1 kHz时,激光器输出峰值功率下降,这与CO2分子上能级寿命有关,并受声光调Q开关热效应的影响。实验中获得的激光器脉冲频率在1 Hz～100 kHz可调。在脉冲频率为1 kHz时,获得的激光脉冲宽度为156 ns,脉冲峰值功率为10 kW,且稳定性较好,非常适合于作激光与物质相互作用的光源。     

预脉冲灯泵钛宝石可调谐激光器

利用预脉冲技术,可减小氙灯放电初始阻抗,使主放电电流脉冲前沿变陡,脉冲包络变窄,峰值变高,泵浦能量集中,有利于灯泵钛宝石激光输出。试验证明,在低能量（４７Ｊ）注入时,电光转换效率提高１８％,输出９５０ｍＪ;在高能量（１１６Ｊ）注入时,效率提高５％,输出能量１８１０ｍＪ。该激光器可调谐范围为６９５～９４０ｎｍ。     

The influence of stimulated temperature-dependent emission cross section on intracavity optical parametric oscillator

In this paper, the influence of temperature on the intracavity optical parametric oscillator(IOPO) is investigated by using the stimulated temperature-dependent emission cross section of laser crystal. The rate equations under plane wave approximation have been used for simulation of signal output pulse. Results show that the signal output pulse width is decreased by increasing the laser crystal temperature. Also, the signal output energy is increased by the increasing of the laser crystal temperature. The simulation results for IOPO based on Nd:YAG and Nd:YVO_4, show that the signal pulse energies are increased by 3.2 and 5.6 times respectively when the laser crystal temperature increased from 15℃ to 300℃. The presented model indicates that the temperature sensitivity of Nd:YVO_4-based IOPOs is more than that of Nd:YAG-based IOPOs which is expected from a physical point of view.     

A Diode-Pumped Actively Q-Switched and Injection-Seeded Tm:LuAG Laser at Room Temperature

We elaborate a diode-end-pumped actively Q-switched injection-seeded Tm:LuAG laser. To achieve power scaling with good beam quality, we construct a more flexible laser with longer cavity accommodated strongly aberrated thermal lens in a Tm:LuAG laser and took special care in designing the laser resonator. Under Q-switched operation, we achieve a maximum output energy of 2.6 mJ with a pulse width of 318.2 ns at a pulse repetition frequency of 50 Hz. To control the spectral, temporal, and phase characteristics of the Tm:LuAG laser, the ring laser is injected by a seed laser, which provides a 50 mW single longitudinal-mode laser output at a wavelength of 2,022.6 nm. We achieve an output energy of 1.8 mJ with a pulse width of 293.0 ns after employing the injection seed.     

1064nm纳秒激光脉冲激发的外腔式PbWO4拉曼激光器

研究了外腔式PbWO4拉曼激光器在纳秒脉冲抽运下的输出特性。利用主动调Q的Nd:YAG激光器产生的脉冲宽度为31.4ns,最大输出能量为200mJ的1064nm激光作为抽运源。拉曼激光谐振腔采用的是平凹腔设计。测量了输出的拉曼光脉宽与抽运能量的关系,分析了输出的拉曼光脉冲波形图和光谱图,测量了输出的拉曼光脉冲能量与抽运能量的关系,计算了转换效率与抽运能量的关系。当注入抽运光能量达到42mJ时,得到了一阶斯托克斯光脉冲的最大能量和转换效率分别为10mJ和24%,获得外腔式PbWO4拉曼激光器的一阶斯托克斯光脉冲波长为1177.6nm,典型的一阶斯托克斯光脉冲脉宽为20ns。     

Continuous-wave and Q-switched laser operation of Nd:Gd0.18Y0.82VO4 mixed crystal

Efficient continuous-wave (cw), passively Q-switched, and actively Q-switched laser operations are demonstrated with a mixed vanadate crystal of Nd:Gd_0.18Y_0.82VO₄ under diode pumping. In a cw operation, an output power of 8.25 W is obtained at a maximum available incident pump power (P_in) of 15 W, with a slope efficiency of 56%. Using a Cr⁴⁺:YAG crystal of initial transmission of 62% as the saturable absorber for Q-switching, an average output power of 3.05 W is generated at pulse repetition frequency (PRF) of 16.7 kHz when the laser is pumped with the same maximum P_in. The pulse energy, pulse duration, and peak power are 183.3 μJ, 6.0 ns, and 30.6 kW, respectively. When actively Q-switched by an acousto-optic modulator, the laser produces an average output power of 5.5 W at PRF of 30 kHz with 16.2 W of pump power incident upon the laser crystal. The pulse energy, duration, and peak power are measured to be 183 μJ, 10.5 ns, and 17.5 kW, respectively.     

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.     

LD连续泵浦Nd:YVO4声光调Q激光器

 利用半导体激光器（LD）连续单端泵浦Nd:YVO₄晶体，实现了声光调Q输出1 064nm的短脉冲。分析并用实验验证了不同透过率输出耦合镜及不同重复频率条件下，输出调Q脉冲能量、脉冲宽度及平均输出功率的规律。在泵浦功率为20.7W，重复频率为50kHz时，获得了最大平均输出功率为5.72W的脉冲，光 光转换效率为28%，斜效率为32.4%；在重复频率为10kHz时，最大单脉冲能量为0.286mJ，脉宽为22ns，峰值功率为13kW。     

Experimental study of electro-optical Q-switched pulsed Nd:YAG laser

We report the specification of a compact and stable side diode-pumped Q-switched pulsed Nd:YAG laser. We experimentally study and compare the performance of the pulsed Nd:YAG laser in the free-running and Q-switched modes at different pulse repetition rates from 1 Hz to 100 Hz. The laser output energy is stabilized by using a special configuration of the optical resonator. In this laser, an unsymmetrical concave-concave resonator is used and this structure helps the mode volume to be nearly fixed when the pulse repetition rate is increased. According to the experimental results in the Q-switched operation, the laser output energy is nearly constant around 70 mJ with an FWHM pulse width of 7 ns at 100 Hz. The optical-to-optical conversion efficiency in the Q-switched regime is 17.5%.     

Dynamical analysis of acousto-optically Q-switched CO2 laser

A compacted size high power CO₂ laser has been developed using an acousto-optically (AO) Q-switch. Performance characteristics have been investigated as a function of output mirror transmittance. The theory of six-temperature model for CO₂ lasers has firstly been utilized to analyze the dynamical process in the AO Q-switched CO₂ laser. This theory perfectly explains the behavior of energy transfer between different molecules in laser gain medium, and describes the shape of pulse laser. The calculated pulse waveforms are in good agreement with the experimental result. Both the experimental and theoretical results present that the optimal value of output mirror transmittance is 39%. Under this condition, the measured peak power is 4750 W and pulsed width is 160 ns, which is consistent with the calculations. Six-temperature model is a perfect theory for CO₂ laser kinetics, which will lay a theoretical foundation for the laser optimum design.     

基于大基模体积的10mJ飞秒钛宝石激光再生放大器

文章报导了基于大基模体积的高能量飞秒钛宝石激光再生放大器的设计与实验研究,在重复频率10 Hz、抽运能量60 mJ的激励下,得到了单脉冲能量17.4 mJ的种子脉冲放大结果,压缩后的脉冲宽度为40.6 fs,能量为13.9 mJ.借助于此大基模体积再生腔,仅增加一级多通放大,实现了峰值功率达1.9 TW飞秒激光脉冲输出.结果表明,大模体积再生放大不仅降低了后续放大对抽运能量的要求,也可以单独压缩实现再生腔直接输出10 mJ量级的飞秒激光脉冲,是大能量高峰值功率飞秒激光系统的优质前端.     

LD-pumped passively Q-switched Nd:GdVO<Subscript>4</Subscript> laser at 1342 nm with high initial transmission V:YAG saturable absorber

We have realized, for the first time to our knowledge, the passive Q-switching operation of an LD-pumped Nd:GdVO₄ laser at 1342 nm with V:YAG saturable absorber of initial transmission as high as 96%. This laser is investigated under different transmissions of the output coupler. The dependences of average output power, pulse width, pulse repetition rate, single-pulse energy and peak power on incident pump power are also measured. The shortest pulse width of 80 ns, the maximum single-pulse energy of 19.5 μJ and the highest peak power of 244 W are obtained with the output coupler of T = 15% and the pump power of 7.93 W. We find a special experimental phenomenon that the pulse repetition rate begins to drop after reaching the peak with the increase of the pump power. This phenomenon is analyzed and the theoretical calculations are consistent with the experimental results.     

千赫重复率固体激光器可行性实验结果

本文介绍用Nd:YAG激光器进行输出千赫重复率激光脉冲可行性判断实验结果。间歇输出激光脉冲的指标为:重复率f=1700pps。激光能量E_L>100mJ/pulse。     

LaMgAl11O19:Co2+被动调Q铒玻璃激光器研究

综述了被动调Q铒玻璃激光器的发展概况,推导了被动调Q铒玻璃激光器输出脉冲能量、脉宽的解析表达式,数值模拟了腔内损耗与输出脉冲能量、脉宽及峰值功率的关系以及输出脉冲能量与输入抽运能量的关系.设计了一台LaMgAl11O19:Co2 被动调Q铒玻璃激光器,实验验证了数值模拟分析结果.结果表明,腔内损耗增加将导致输出脉冲能量下降,脉宽变大,从而峰值功率降低.输入能量低于12 J时,输出只有单脉冲,当输入能量大于12 J时,输出会出现双脉冲.在8 J的电输入下,获得了峰值功率50 kW,2.7 mJ的1.535 tm激光输出.最后讨论了提高单脉冲能量的方法.     

Short pulse eye-safe laser with a stimulated Raman scattering self-conversion based on a Nd:KGW crystal

We present the results of a solid self-Raman laser based on a Nd:KGW crystal that is transversely pumped by laser diode bars. A beam of an eye-safe laser with a 31.8 mJ output energy and a 2.0 ns pulse width was obtained by applying a special s-polarized reflective resonator configuration in which the length of the Raman resonator was shorter than that of the fundamental radiation resonator. The eye-safe laser has the highest output energy and the shortest pulse width among the Nd:KGW lasers ever reported.     

6.1 MW, 10 kHz Side-Pumped Burst-Mode Nd:YAG Laser

We present a compact high-peak-power, high-repetition-rate burst-mode laser from a master-oscillator power amplifier (MOPA) at 1064 nm for laser-based measurement applications. The oscillator is an 808 nm pulsed laser diode side-pumped acousto-optical (A-O) Q-switched Nd:YAG laser at repetition rates ranging from 10–100 kHz, producing a pulse train with a pulse number of 2–25. The maximum output energy of the oscillator is 15.6 mJ at 10 kHz, whereas it is 1.7 mJ at 100 kHz. After twostage amplifiers, a single-pulse energy of 85.2 mJ with a pulse-width of 14.5 ns is achieved at 10 kHz, which produces a peak power of 6.1 MW. At 100 kHz, the total burst energy reaches 220 mJ with a single-pulse energy of 8.8 mJ in the pulse burst laser system.