Diode-pumped doubly Q-switched mode-locked YVO4/Nd:YVO4 laser with AO and GaAs saturable absorber

By using both acousto-optic (AO) modulator and GaAs saturable absorber, a diode-pumped doubly Q-switched and mode-locked (QML) YVO₄/Nd:YVO₄ laser is presented. The average output power and the pulse width of the Q-switched envelope have been measured. The Q-switch pulse energy of the doubly QML laser are higher than that only with GaAs. The stability of the QML laser with the dual-loss-modulation is significantly improved if compared to that only with GaAs.The experimental results show that the doubly QML YVO₄/Nd:YVO₄ laser has nearly 80% modulation depth and deeper than that of the singly passively QML pulse. The doubly Q-switched mode-locked pulse inside the Q-switched envelope has a repetition rate of 111 MHz and its pulse width is estimated to be about 700 ps. By using a hyperbolic secant square function and considering the Gaussian distribution of the intracavity photon density, the coupled equations for diode-pumped dual-loss-modulated QML laser is given and the numerical solutions of the equations are in good agreement with the experimental results.     

GaAs被动调Q Nd:YAG激光器激光特性的研究

报道了用半导体材料 Ga As实现氙灯抽运 Nd:YAG激光器的被动调 Q运转 ,测量了激光器的阈值、脉冲宽度和输出能量。从 Ga As的能级结构出发 ,理论上研究了 Ga As材料的饱和吸收原理 ,建立了调 Q激光器速率方程并给出了数值解 ,对理论结果与实验结果进行了比较和讨论。     

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     

Diode-pumped doubly Q-switched Nd:LuVO4 laser with AO modulator and GaAs saturable absorber

A diode-pumped doubly Q-switched Nd:LuVO₄ laser with an acousto-optic (AO) modulator and GaAs saturable absorber has been realized. The pulse profile of the doubly Q-switched Nd:LuVO₄ laser has an almost absolutely symmetric shape. The dependences of pulse width, single-pulse energy and peak power on the incident pump power under different AO repetition rates are measured. By considering the transverse Gaussian distribution of the intracavity photon density and the longitudinal distribution of photon density along the cavity axis, the coupled rate equations of the laser are given. These coupled rate equations are solved numerically and the theoretical results are in agreement with the experimental results.     

Optimization of the pulse energy of GaAs saturable absorber Q-switched lasers

By taking into account the single-photon absorption (SPA) and two-photon absorption (TPA) processes of GaAs, the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density, and the pumping and the spontaneous emission during the pulse formation, the new normalized rate equations of a GaAs saturable absorber Q-switched laser are solved. The key parameters of an optimally coupled GaAs saturable absorber Q-switched laser are determined, including the optimal normalized coupling parameter and the optimal normalized GaAs saturable absorber parameters, which can maximize the pulse energy, and a group of general curves are generated for the first time, which clearly show the dependence of the optimal key parameters on the parameters of the gain medium, the GaAs saturable absorber, and the resonator. In addition, the influence including the space variation, the pumping and the spontaneous emission is also shown. Sample calculations for a diode-pumped Nd³⁺:YVO₄ laser with a GaAs saturable absorber are presented to demonstrate the use of the curves and the relevant formulas.     

Optimization of pulse width of double passively Q-switched lasers with GaAs and Cr-doped saturable absorbers

Compared with a single passively Q-switched laser, a double passively Q-switched laser with a GaAs saturable absorber and a Cr⁴⁺-doped saturable absorber can produce more symmetric and shorter pulses with high pulse peak power. New normalized coupled rate equations for a double passively Q-switched laser with both a GaAs saturable absorber and a Cr⁴⁺-doped saturable absorber are solved numerically, where the single-photon absorption (SPA) and two-photon absorption (TPA) processes of GaAs are combined. The Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density are considered. The optimization of a double passively Q-switched laser to obtain the shortest pulse width is performed, and a group of general curves are generated for the first time. The curves clearly show the dependence of the optimal normalized parameters on the parameters of the gain medium, the GaAs saturable absorber, the Cr⁴⁺-doped saturable absorber and the spatial distributions of the intracavity photon density. Sample calculations for a diode-pumped Nd³⁺:YVO₄ laser with both a GaAs saturable absorber and a Cr⁴⁺:YAG saturable absorber are presented to demonstrate the use of the curves and the related formulas.     

Investigation of cutting of engineering ceramics with Q-switched pulse CO2 laser

In this paper, the cutting of Si₃N₄ engineering ceramics with Q-switched pulse CO₂ laser is studied. Considering the influence of the cut front shape on the absorption of the laser beam, a simplified 2D mathematic model is developed based on a pulsed laser vaporization cut process. This model is based on the conservation of energy. The experimental results show that it would realize crack-free cutting by using high-speed and multi-pass feed cutting process.     

Optimization of diode-pumped passively Q-switched mode-locked c-cut Nd:GdVO4 laser with a GaAs saturable absorber

By considering the single-photon absorption (SPA) and two-photon absorption (TPA) processes in the GaAs saturable absorber, the coupled rate equations for a diode-pumped passively Q-switched and mode-locked (QML) laser with GaAs coupler under Gaussian approximation are given. The key parameters of an optimally coupled passively QML laser can be obtained by numerically solving these equations. These key parameters include the parameters of the gain medium, the saturable absorber and the resonator, which can maximize the pulse energy of singly Q-switched envelope. Sample calculations for a diode-pumped passively Q-switched mode-locked c-cut Nd:GdVO₄ laser with a GaAs saturable absorber are presented to demonstrate the optimal method applicable.     

Doubly Q-switched intracavity-frequency-doubled c-cut Nd:GdVO4/KTP green laser with AO and GaAs

By simultaneously using both active and passive Q-switches in the same cavity, a diode-pumped doubly Q-switched intracavity-frequency-doubled c-cut Nd:GdVO₄/KTP green laser with acoustic-optic (AO) modulator and GaAs semiconductor saturable absorber is realized. A comparison between c-cut and a-cut Nd:GdVO₄ crystals shows that the doubly Q-switched c-cut Nd:GdVO₄/KTP green laser can generate narrower pulse and higher peak power when the incident pump power is higher than 4.4 W. In addition, the doubly Q-switched c-cut Nd:GdVO₄/KTP green laser can generate more symmetric and shorter pulse in comparison with singly AO- or GaAs-Q-switched laser. The coupled rate equations are used to simulate the process of these lasers.     

电光调QCO2激光器的六温度模型理论与速率方程理论比较分析

分别利用速率方程理论和六温度模型理论对Q开关CO₂激光器动力学过程进行了理论分析比较,实验上测得电光调Q射频波导CO₂激光器脉冲激光建立时间及峰值功率与速率方程理论和六温度模型理论计算结果一致.但速率方程理论计算的激光脉冲宽度较“窄”,并且几乎没有拖尾,而六温度模型理论计算的脉冲激光波形有明显的拖尾,符合实际测量的波形.另外,六温度模型理论可以全面反映激光器工作气体中不同分子能级的能量转移过程,因此六温度模型理论分析更全面 关键词： 2激光器')" href="#">电光调QCO₂激光器 六温度模型理论 速率方程理论     

Intracavity-frequency-doubled Q-switched and mode-locked Nd:Lu0.15Y0.85VO4/KTP green laser with AO modulator and central SESAM

By using mixed crystal Nd:Lu_0.15Y_0.85VO₄ as laser medium, KTP as frequency-doubling crystal, a diode-pumped intracavity-frequency-doubled Q-switched and mode-locked (QML) Nd:Lu_0.15Y_0.85VO₄/KTP green laser with acousto-optic (AO) modulator and central semiconductor saturable absorption mirror (C-SESAM) is realized by using a V-type cavity. The QML laser characteristics such as the pulse width, single-pulse energy, have been measured for different modulation frequencies of the AO modulator. In comparison with the singly passively QML green laser with central SESAM, the doubly QML green laser can generate more stable and shorter pulses with higher peak power. Based on the coupled rate equations for a diode-pumped doubly QML green laser with AO and C-SESAM, in which the saturated absorption mechanism of C-SESAM is considered, the recurrence relation of the relative amplitude of the mode-locking pulses is given and the related numerical simulations are in good agreement with the experimental results.     

Theoretical and experimental study of a diode-pumped doubly Q-switched intracavity-frequency-doubling Nd:LuVO4/KTP green laser with acoustic-optic (AO) modulator and GaAs saturable absorber

By considering the Gaussian transversal and longitudinal distributions of the intracavity photon density as well as the walk-off effect of KTP crystal, the coupled rate equations of the doubly Q-switched intracavity-frequency-doubling Nd:LuVO₄/KTP green laser with acoustic-optic (AO) modulator and GaAs saturable absorber are given. These equations are solved numerically and the doubly Q-switched green laser characteristics, such as the pulse width and the pulse symmetry, have been obtained. In the experiment, a diode-pumped doubly Q-switched intracavity-frequency-doubling Nd:LuVO₄/KTP green laser with AO and GaAs is presented. This doubly Q-switched green laser can generate the almost absolutely symmetric pulse profile with the shorter pulse width and the higher power than the singly Q-switched green laser. The experimental results are in agreement with the theoretically numerical calculations.     

Improvement of stability and pulse energy in a diode-pumped dual-loss-modulated QML Nd:Lu0.2Y0.8VO4 laser with EO modulator and GaAs

The Q-switched and mode-locked (QML) performance in a diode-pumped Nd:Lu_0.2Y_0.8VO₄ laser with electro-optic (EO) modulator and GaAs saturaber absorber is investigated. In comparison with the solely passively QML laser with GaAs, the dual-loss-modulated QML laser with EO and GaAs can generate pulses with higher stability and shorter pulse width of Q-switched envelope, as well as higher pulse energy. At the repetition rate 1 kHz of EO, the pulse width of Q-switched pulse envelope has a compression of 89% and the pulse energy has an improvement of 24 times. The QML laser characteristics such as the pulse width, pulse peak power etc. have been measured for different small-signal transmittance (T₀) of GaAs, different reflectivity (R) of output coupler and modulation frequencies of the EO modulator (f_e). The highest peak power and the shortest pulse width of mode-locked pulses are obtained at f_e = 1 kHz, R = 90% and T₀ = 92.6%. By considering the influences of EO modulator, a developed rate equation model for the dual-loss-modulated QML laser with EO modulator and GaAs is proposed. The numerical solutions of the equations are in good agreement with the experimental results.     

用1064nm激光脉冲触发半绝缘GaAs光电导开关的研究

报道了用1064nm激光脉冲触发电极间隙为8mm的半绝缘GaAs光电导开关的实验结果.在触发光能为1.9mJ,偏置电压分别为3kV和5kV条件下,光电导开关分别工作于线性和非线性模式,结果表明半绝缘GaAs光电导开关可以吸收1064nm波长的激光脉冲.讨论了半绝缘GaAs材料对1064nm激光脉冲的非本征吸收机制,指出GaAs材料禁带内的EL2深能级和双光子吸收对半绝缘GaAs吸收1064nm光脉冲起主导作用.     

Nd: Laser induced absorption in semiconductors and aqueous PrCl3 and NdCl3

The insertion of a multi-photon absorber within a laser cavity has practical importance in providing stabilised laser amplitude and variable pulse duration. We report the relative non-linear absorption coefficients of semiconductors Si, CdSe, CdTe, and GaAs at 1.064m using a Q-switched Nd:YAG laser. The measurements on Si were carried out from 77 to 450° K, and the results confirm a stepwise process giving rise to induced absorption. The effects of the spatial and temporal distributions of the laser emission on the absolute non-linear coefficient values are briefly discussed. Preliminary observation of stepwise multi-photon absorption in aqueous PrCl₃ and NdCl₃ measured with a pulsed Nd:glass laser is also reported. The possibility of using a combination of inducible and saturable absorbers, placed within the laser cavity, as a means of providing laser intensities confined to a narrow range centred about a pre-set intensity, is raised.Alfred P. Solan Foundation Fellow.     

Pulse symmetry and pulse duration compression in a diode-pumped doubly passively Q-switched Nd:YVO4 lasers with Cr4+:YAG and GaAs saturable absorbers

We present a simple technique to improve the symmetry of pulse emitted by doubly passively Q-switched lasers. Using both Cr⁴⁺:YAG and GaAs saturable absorbers in the same cavity, a diode-pumped doubly passively Q-switched Nd:YVO₄ laser is realized for the fist time. This laser can generate more symmetric pulse with shorter pulse width and higher peak power compared with the solely passively Q-switched laser with Cr⁴⁺:YAG saturable absorber or GaAs coupler. The pulse symmetry factor ε of such a doubly passively Q-switched laser is experimentally shown to reach 1.05. Simulations by a rate-equation model for doubly passively Q-switched laser are in close agreement with the experimental results.PACS 42.55.Xi; 42.55.Rz; 42.60.Gd     

InAs/GaAs quantum-dot saturable absorbers for diode-pumped passively Q-switched Nd-doped 1.3-microm lasers

A low-loss semiconductor saturable absorber based on InAs/GaAs quantum dots was developed for Q switching of a diode-pumped Nd-doped laser operating at 1.3 microm. With an InAs/GaAs quantum-dot saturable absorber, a diode-pumped Nd:YVO4 laser at 1342 nm was achieved. With an incident pump power of 2.2 W, an average output power of 360 mW with a Q-switched pulse width of 90 ns at a pulse repetition rate of 770 kHz was obtained.     

Laser–diode-pumped passively Q-switched Nd:NaY(WO4)2 laser with GaAs saturable absorber

A laser–diode-pumped passively Q-switched new type crystal Nd³⁺:NaY(WO₄)₂ (known as Nd:NYW) laser with GaAs semiconductor saturable absorber has been realized. The dependence of pulse repetition rate, pulse energy, pulse width, and peak power on pump power for different output coupler reflectivities are measured. The coupled rate equations are used to simulate the Q-switched process of laser, and the numerical solutions agree with the experimental results.     

Diode-pumped doubly passively Q-switched Nd:LuVO4/KTP green laser with Cr:YAG and GaAs saturable absorbers

A diode-pumped doubly passively Q-switched intracavity-frequency-doubling Nd:LuVO₄/KTP green laser with Cr⁴⁺:YAG and GaAs saturable absorbers is demonstrated. This laser can generate the shorter pulse width with higher peak power compared with the singly passively Q-switched green laser with Cr⁴⁺:YAG or GaAs saturable absorber. The relations between the pulse symmetry and the ratio of the small-signal transmissions of two saturable absorbers are investigated. By reasonably choosing the small-signal transmissions of both saturable absorbers, the doubly passively Q-switched green laser can generate the much more symmetric pulse profile. The coupled rate equations are used to simulate the passively Q-switched process of the green laser by considering the Gaussian transversal and longitudinal distributions of the intracavity photon density. The numerical results of the equations are consistent with the experimental results.     

LD泵浦Nd∶YVO4晶体GaAs被动调Q激光理论和实验研究

考虑LD泵浦光强和腔内振荡光强的空间高斯分布以及晶体热效应的影响，给出了Nd∶YVO₄晶体GaAs被动调Q1.06 μm激光的耦合速率方程组，数值求解该方程组获得了输出激光的平均输出功率、脉冲宽度、重复率随泵浦功率的变化特性，所得理论值与实验结果相符.