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     

Diode-pumped Q-switched and mode-locked Nd:LuVO4/KTP green laser with AO and Cr4+:YAG saturable absorber

A diode-pumped Q-switched and mode-locked (QML) Nd:LuVO₄/KTP green laser with acousto-optic modulator (AOM) and Cr⁴⁺:YAG saturable absorber is presented. By inserting an AOM into the laser cavity, the stability of the QML green laser pulse with AO and Cr⁴⁺:YAG is improved, the modulation depth is increased and the pulse width of Q-switched pulse envelope is significantly compressed in comparison with that of the singly passively QML green laser with Cr⁴⁺:YAG. The experimental results show that the peak power of the doubly QML green laser pulse is much higher than that of the singly passively QML green laser pulse.     

Doubly passively Q-switched and mode-locked laser with V<Superscript>3+</Superscript>:YAG and Co:LMA saturable absorbers

By using both V³⁺:YAG and Co:LMA saturable absorbers, an xenon-lamp-pumped doubly passively Q-switched and mode-locked (QML) Nd:YAG laser at 1.3 μm in a straight cavity is realized for the first time. The modulation depth of QML pulse has nearly reached 100%. The experimental results shows that the doubly passively Q-switched and mode-locked (QML) laser can generate shorter Q-switch envelope pulse with higher average peak power in comparison to the singly passively QML laser with V³⁺:YAG or Co:LMA saturable absorber.     

Passively Q-switched Nd:YAG ceramic laser towards large pulse energy and short pulse width

A large pulse energy and high peak power passively Q-switched ceramic neodymium-doped yttrium aluminum garnet (Nd:YAG) laser has been demonstrated with Cr⁴⁺:YAG crystals as the saturable absorbers. By employing a continuous wave (CW) laser-diode (LD) as the pump source, as high as 11.3 W CW output power of 1064 nm was obtained under the pump power of 21.6 W, with an optical conversion efficiency of 52.3%. Inserting different initial transmissions Cr⁴⁺:YAG as saturable absorbers, under the incident pump power of 15.6 W, the largest pulse energy, shortest pulse width, and highest peak power are measured to be 188 μJ, 3.16 ns, and 59.5 kW, respectively. As we has known, this is the best passively Q-switched results ever reported by Nd:YAG ceramic material.     

Optimization of Yb:YAG/Cr<Superscript>4+</Superscript>:YAG composite ceramics passively Q-switched microchip lasers

The laser characteristics of laser-diode end-pumped Yb:YAG/Cr⁴⁺:YAG composite ceramics microchip passively Q-switched lasers were studied by solving the coupled rate equations numerically taking into account the reabsorption of Yb:YAG ceramics at laser wavelength. Effects of the reflectivity of the output coupler, the concentrations and thickness of the saturable absorbers, and pump beam area on the laser performance were investigated analytically. The simulation results of the Yb:YAG/Cr⁴⁺:YAG composite ceramics passively Q-switched microchip lasers were in good agreement with the experimental data. Better laser performance (high peak power, short pulse width and good optical-to-optical efficiency) of the composite Yb:YAG/Cr⁴⁺:YAG ceramics passively Q-switched laser can be obtained by using a thin Cr⁴⁺:YAG ceramic with high concentration, suitable reflectivity of the output coupler and proper pump beam diameter under high pump power intensity according to our simulations.     

Doubly passively Q-switched laser with V<Superscript>3+</Superscript>:YAG and Co:LMA saturable absorbers

By using both V³⁺:YAG and Co:LMA saturable absorbers, a doubly passively Q-switched laser is realized for the first time. The shorter pulse with the higher peak power is generated in comparison to the singly passively Q-switched laser with V³⁺:YAG or Co:LMA saturable absorber. The experimental results shows that it is possible to obtain a shorter pulse with the higher peak power in a doubly passively Q-switched laser.     

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.     

Diode-pumped doubly passively Q-switched c-cut Nd:GdVO4 1.34 μm laser with V:YAG and Co:LMA saturable absorbers

By simultaneously using both V³⁺:YAG and Co:LMA saturable absorbers in the cavity, a diode-pumped doubly passively Q-switched c-cut Nd:GdVO₄ laser at 1.34 μm is demonstrated for the first time. The average output power, the pulse width and the pulse repetition rate have been measured. The experimental results show that the doubly passively Q-switched laser can generate shorter pulse width with higher peak power in comparison to the singly passively Q-switched laser only with V³⁺:YAG or Co:LMA saturable absorber. At the pump power 13 W, the pulse width has been compressed 83% and the peak power has been improved 15 times, respectively.     

Diode-pumped passively Q-switched intracavity frequency doubled Nd:GdVO4/KTP green laser

A compact diode-pumped passively Q-switched intracavity frequency-doubled Nd:GdVO₄/KTP green-pulse laser was demonstrated, using Cr⁴⁺:YAG as a saturable absorber in a simple flat–flat cavity. With a 5.9 W incident pump power, a passively Q-switched green laser was obtained with an average power of 397 mW, repetition rate of 40 kHz, and pulse width of 40 ns, when the initial transmission of Cr⁴⁺:YAG was 85%. The shortest pulse width of 30 ns, the highest green peak power of 696 W and the maximum pulse energy of 21 μJ were obtained when the initial transmission of Cr⁴⁺:YAG was 70%. Under CW green operation, we obtained 440 mW output power.     

Passive Q-switching of a laser-diode-pumped intracavity-frequency-doubling Nd:Nd<Superscript>3+</Superscript>:NaY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>/KTP laser with Cr<Superscript>4+</Superscript>:YAG saturable absorber

Nd³⁺:NaY(WO₄)₂, known as Nd:NYW, is a new type crystal. By using laser-diode as pump source, a passive Q-switching of intracavity-frequency-doubling Nd:NYW/KTP laser has been realized with Cr⁴⁺:YAG saturable absorber. The dependence of pulse repetition rate, pulse energy, pulse width, and peak power on incident pump power for different small-signal transmissions of Cr⁴⁺:YAG 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.     

Sub-nanosecond passively Q-switched Yb:YAG/Cr4+:YAG sandwiched microchip laser

We report on laser-diode pumped low-threshold, and compact passively Q-switched Yb:YAG microchip lasers, with Cr⁴⁺:YAG crystals as the saturable absorbers. The laser threshold at the fundamental wavelength of 1.03 μm is as low as 0.25 W, and the slope efficiency is as high as 36.8%, and the optical-to-optical efficiency is as high as 27% for the 95% initial transmission of the Cr⁴⁺:YAG crystal. A pulse width of 1.35 ns and peak power of over 8.2 kW was obtained. Using a 5 mm thick KTP crystal as the second-harmonic generation medium, 514.7 nm green light of 155 mW power was generated. The pulse duration of 480 ps was generated at 1.03 μm by using 85% of the initial transmission of the Cr⁴⁺:YAG saturable absorber. Stable single-longitudinal-mode oscillation and wide-separated multi-longitudinal-mode oscillation due to the etalon effect of the Cr⁴⁺:YAG thin plate was achieved at different pump power levels. PACS 42.55.Sa; 42.55.Xi; 42.60.Gd     

Optimization of passively Q-switched and mode-locked laser with Cr:YAG saturable absorber

By considering the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density, the coupled rate equations for a diode-pumped passively Q-switched and mode-locked (QML) laser with Cr⁴⁺:YAG saturable absorber are given. These coupled rate equations are solved numerically and the key parameters of an optimally coupled passively QML laser are determined for the first time. 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. The optimal calculations for a diode-pumped passively QML Nd:GdVO₄ laser with Cr⁴⁺:YAG saturable absorber are presented to demonstrate the numerical simulation applicable.     

Diode-pumped doubly Q-switched YVO4/Nd:YVO4 laser with BBO electric-optic Q-switch and Cr4+:YAG saturable absorber

In the experiment, we have demonstrated the performance of a laser-diode, end-pumped, doubly Q-switched YVO₄/Nd:YVO₄ laser with both a BBO electric-optic (EO) Q-switch and Cr⁴⁺:YAG saturable absorber. At a maximum incident pump power of 15 W and an EO Q-switch repetition rate of 8 kHz, the stable laser pulses with the pulse duration 5.28 ns, the single pulse energy 0.14 mJ, and the pulse peak power 26 kW are obtained. The experimental results show that the double Q-switched laser with EO and Cr⁴⁺:YAG can generate the shorter pulse and the higher peak power in comparison to singly Q-switched laser with EO.     

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.     

Diode-pumped Q-switched Nd:Y<Subscript>0.5</Subscript>Lu<Subscript>0.5</Subscript>VO<Subscript>4</Subscript> laser double-modulated with an acousto-optic modulator and Cr<Superscript>4+</Superscript>:YAG saturable absorber

A diode pumped Nd:Y_0.5Lu_0.5VO₄ pulse laser modulated with an acousto-optic (AO) Q-switcher and Cr⁴⁺:YAG saturable absorber is first demonstrated in this paper. The laser is shown to generate shorter pulse width than AO Q-switched laser alone, and have a higher peak power and single pulse energy than passively Q-switched laser with only Cr⁴⁺:YAG. A laser pulse width of 6.16 ns and a peak power of about 43.83 kW are achieved at the incident pumping power of 14.09 W.     

Diode pumped Nd:YAG laser repetitively Q-switched with Cr4+:YAG

Based on the rate equations of passively Q-switched solid state lasers, the performance of laser at a fixed pump power can be optimized through the proper choice of output coupler and the low-intensity transmission of saturable absorber. A simple expression for optimizing these two parameters is derived in this paper. We also demonstrate the performance of an efficient diode-pumpe Cr⁴⁺:YAG passively Q-switched Nd:YAG laser to generate a high-repetition-ate, high-peak power 1064 nm laser pulses, which providing pulses peak power > 10 kW with high repetition rate up to 150 kHz, and the pulse width as short as 6.8 ns.     

Characteristics of a passively Q-switched Nd:NaY(WO4)2 laser with Cr:YAG saturable absorber

By using xenon flash lamp as pump source and Cr⁴⁺:YAG as passive Q-switcher, we have performed the Q-switched laser operation at 1.06 μm with an Nd³⁺:NaY(WO₄)₂ (known as Nd:NYW) crystal. Meanwhile, the pulse width, the single pulse energy and the repetition rate under different small-signal transmissions of Cr⁴⁺:YAG and different reflectivities of output reflector are measured, and the numerical solutions of the coupling wave rate equations agree with the experimental results.     

LD-pumped passively Q-switched Nd:YVO4/YVO4 laser with an Nd3+:Cr4+:YAG saturable absorber

By using a piece of codoped Nd³⁺:Cr⁴⁺:YAG crystal as a saturable absorber, a laser-diode pumped passively Q-switched Nd:YVO₄/YVO₄ laser has been realized. The maximum laser output power of 2.452 W has been obtained at the incident pump power of 8.9 W for an 8.8% transmission of the output coupler at 1064 nm, corresponding to a slope efficiency of 30%. The other output laser characteristics of the laser have also been investigated. The laser with a Nd³⁺:Cr⁴⁺:YAG saturable absorber has a lower threshold pump power and a higher slope efficiency compared to that with a similar small-signal transmission of a Cr⁴⁺:YAG saturable absorber.     

Passively Q-switched Nd:LuVO4 laser using Cr:YAG as saturable absorber

A passively Q-switched all solid-state Nd:LuVO₄ 1.06 μm laser was demonstrated by using Cr⁴⁺:YAG as saturable absorber. The characteristics of average output power, pulse width, repetition rate, pulse energy, and peak power were studied with different output couplings and initial transmission of saturable absorbers. When output coupling with the transmission of 20% was used, the shortest pulse width of 16 ns at the repetition rate of 12.5 kHz was obtained, which results in the pulse energy of 71 μJ and peak power of 4.43 kW with the initial transmission of 70% of Cr⁴⁺:YAG crystal.     

Doubly Q-switched GdVO4/Nd:GdVO4 laser with AO modulator and Cr4+:YAG saturable absorber under direct 879 nm diode pumping to the emitting level

In this letter, a doubly Q-switched 1.06 μm pulse laser with AO modulator and Cr⁴⁺:YAG saturable absorber by direct pumping grown-together composite GdVO₄/Nd:GdVO₄ crystal is demonstrated for the first time. Compared to purely AO Q-switching, the simultaneous use of AO Q-switch and Cr⁴⁺:YAG saturable absorber can generate shorter pulses and more symmetric temporal profiles. The thermal lens effect of laser crystal was analyzed.