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.     

Pulse compression in AO Q-switched diode-pumped Nd:GdVO4 laser with Cr4+:YAG saturable absorber

By simultaneously using both an acoustic-optic (AO) modulator and a Cr⁴⁺:YAG saturable absorber in the cavity, for the first time, a diode-pumped doubly Q-switched Nd:GdVO₄ laser has been realized. The pulse duration is obviously compressed in contrast to the actively acoustic-optic Q-switched laser. By considering the Gaussian transversal distribution of the intracavity photon density and the longitudinal distribution of the photon density along the cavity axis as well as the influence of turnoff time of the acoustic-optic (AO) Q-switch, we provide the coupled rate equations for a diode-pumped doubly Q-switched Nd:GdVO₄ laser with both an acoustic-optic (AO) modulator and a Cr⁴⁺:YAG saturable absorber. These coupled rate equations are solved numerically, and the dependence of pulse width, pulse energy and peak power on the incident pump power at different pulse repetition rates is obtained. The numerical solutions of equations agree well with the experimental results.This revised version was published online in August 2005 with a corrected cover date.     

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.     

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.     

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.     

Theoretical and experimental study of a diode-pumped doubly Q-switched Nd:GdVO4 1.34 μm laser with acousto-optic (AO) modulator and V:YAG saturable absorber

A diode-pumped doubly Q-switched c-cut Nd:GdVO₄ laser at 1.34 μm with acousto-optic (AO) modulator and V³⁺:YAG saturable absorber is demonstrated. This doubly Q-switched laser can generate shorter pulse width and higher peak power than the singly Q-switched laser only with an AO modulator or a V³⁺:YAG saturable absorber. By considering the thermal lens effect of the laser gain medium, the coupled rate equations for the doubly Q-switched laser at 1.34 μm under Gaussian approximation are given. The numerical solutions of the equations are in agreement with the experimental results.     

Theoretical and experimental study of single mode-locking pulse generation with low repetition rate in a dual-loss-modulated QML YVO4/Nd:YVO4 laser with EO and GaAs

Using electro-optic (EO) modulator and GaAs saturable absorber, a diode-pumped doubly Q-switched and mode-locked (QML) YVO₄/Nd:YVO₄ laser at 1.06 μm is realized. The experimental results show that the number of the mode-locking pulses underneath the Q-switched envelope decreased with increasing pump power. With an output coupling of 6.5 %, the single mode-locking pulse underneath the Q-switched envelope with 1 kHz repetition rate was obtained when the pump power exceeded 4.65 W. At a pump power of 8.25 W for an output coupling of 10 %, a stable mode-locking pulse train at a repetition rate of 1 kHz was achieved with pulse energy as high as 582 μJ and pulse duration of about 580 ps, corresponding to a peak power of 1 MW. Using a hyperbolic secant square function and considering the Gaussian distribution of the intracavity photon density, the coupled rate equations for diode-pumped doubly QML YVO₄/Nd:YVO₄ laser are given and the numerical solutions of the equations are basically in accordance with the experimental results.     

Effect of turnoff time on characteristics of the output pulse in an AO Q-switched laser

A laser-end-diode-pumped actively Q-switched Nd:YVO₄ laser with acoustic-optic (AO) modulator is realized. By changing the position of AO in the cavity for changing the transit time of the acoustic-wave, the effect of the AO turnoff time on the characteristics of the output Q-switched pulse is obtained. The experimental results show that the longer transit time leads to the wider pulse duration. By considering the Gaussian spatial distribution of the intra-cavity photon density and the AO turnoff time including the electronic turnoff time and the transit time of the acoustic-wave, the numerical solutions of the coupled Q-switched rate equations are consistent with the experimental results.     

Theoretical and experimental study of a laser-diode-pumped actively Q-switched Nd:YVO4 laser with acoustic–optic modulator

By considering the Gaussian spatial distribution of the intracavity photon density and initial population-inversion density as well as the longitudinal distribution of the photon density along the cavity axis and turnoff time of the acoustic–optic Q-switch, the coupled equations of an LD-pumped actively Q-switched Nd:YVO₄ laser with acoustic–optic modulator are given. These coupled rate equations are solved numerically on a computer, and the dependences of pulse width, single-pulse energy and peak power on incident pump power are obtained. In the experiment, a laser-diode-pumped actively Q-switched Nd:YVO₄ laser with acoustic–optic modulator is realized, and the experimental results are in fair agreement with the numerical solutions.     

Diode-pumped Actively Q-switched Nd:GdVO<Subscript>4</Subscript> Green Laser with Periodically Poled KTP

A diode-pumped actively Q-switched Nd:GdVO₄ green laser with periodically poled KTP (PPKTP) and Acoustic-optic (AO) modulator has been realized. The dependences of pulse energy, pulse width, and peak power on incident pump power are measured. At the pump power of 4.1 W and repetition rate of 10 kHZ, we can obtain a 19.2 ns pulse with pulse energy of 0.11 mJ and peak power of 5.8 kW, which are almost three times of that in the conventional KTP green laser, respectively. A rate equation model is introduced to theoretically analyze the results obtained in the experiment, in which the Gaussian spatial distribution of the intracavity photon density is taken into account. The numerical solutions of the rate equations agree with the experimental results.     

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.     

Numerical solutions of diode-pumped dual-loss-modulated Q-switched and mode-locked green laser with acousto-optic modulator and Cr: YAG saturable absorber

By considering the influence of the acousto-optic (AO) modulator and the nonlinear loss due to harmonic conversion in the intra-cavity frequency-doubling laser, a developed rate equation model for diode-pumped dual-loss-modulated Q-switched and mode-locked (QML) Nd:LuVO₄/KTP green laser with acousto-optic (AO) modulator and Cr⁴⁺:YAG saturable absorber is presented. With this developed model, the pulse width, single-pulse energy and the other dual-loss-modulated QML green laser characteristics are numerically simulated. The simulation results show that the turnoff time is of great importance for the pulse energy and pulse width of the Q-switched pulse. A diode-pumped dual-loss-modulated QML Nd:LuVO₄/KTP laser is constructed to successfully demonstrate the numerical simulation application.     

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.     

Analysis of a laser-diode end-pumped passively Q-switched Nd:GdVO4 laser with V3+:YAG saturable absorber

By considering both the transversal and longitudinal Gaussian spatial distribution of the intracavity photon density, a couple of rate equations describing a laser-diode end-pumped passively Q-switched Nd:GdVO₄ laser with V³⁺:YAG saturable absorber have been proposed. Solving these space-dependent rate equations numerically, we obtain the dependences of pulse width, pulse repetition rate, single-pulse energy and peak power on pump power. In the experiment, a laser-diode end-pumped Nd:GdVO₄ laser passively Q-switched by a V³⁺:YAG saturable absorber has been realized, and the experimental results are consistent with the theoretical calculations.     

Pulse width compression and enhancement of peak power in a diode-pumped doubly Q-switched Nd:GdVO<Subscript>4</Subscript> 1.34 μm laser with AO and V<Superscript>3+</Superscript>:YAG saturable absorber

By using both acousto-optic (AO) modulator and V³⁺:YAG saturable absorber, a diode-pumped doubly Q-switched a-cut Nd:GdVO₄ laser at 1.34 μm is realized. The average output power and the pulse width for different AO repetition rate f have been measured. The experimental results show that the doubly Q-switched laser can compress the pulse width and improve the pulsed peak power in comparison to the singly Q-switched laser with AO or V³⁺:YAG saturable absorber. At the pump power 10.34 W and f = 10 kHz, the greatest pulse width compression ratio 72% and the highest peak power improvement 8.8 times have been obtained, respectively.     

Passive Q-switching performance with Co:LMA crystal in a diode-pumped Nd:LuVO<Subscript>4</Subscript> laser

A diode-pumped passively Q-switched Nd:LuVO₄ 1.34 μm laser using Co:LMA saturable absorber was successfully demonstrated. The average output power, pulse width, repetition rate of a-cut and c-cut Nd:LuVO₄ lasers were studied with different output couplers. The maximum average output power of 164 mW was obtained at the pump power of 10.3 W and the narrowest pulse width of 168 ns was achieved at repetition rate of 457 kHz under pump power of 8.59 W in a-cut Nd:LuVO₄ laser with T = 8%.     

Passively Q-switched and mode-locked laser performance of the mixed crystals with GaAs saturable absorber

By using the mixed crystals Nd:Lu_0.33Y_0.37Gd_0.3VO₄, Nd:Lu_0.5Y_0.5VO₄ and Nd:Lu_0.15Y_0.85VO₄ as laser media, the LD pumped passively Q-switched and mode-locked (QML) lasers with GaAs saturable absorber are realized. The average output power, the pulse width and the repetition rates have been measured and compared. The experimental results show that the passively Q-switched and mode-locked Nd:Lu_0.33Y_0.37Gd_0.3VO₄ laser can generate shorter pulse width with higher peak power due to broader fluorescence line-width. By considering the Gaussian distribution of the intracavity photon density and the influence of the continuous pump rate, the coupled rate equations for QML lasers with GaAs saturable absorber are given. The theoretical solutions of the equations are in agreement with the experimental results.     

Passively Q-switched laser performance of a diode-pump mixed Nd:Lu<Subscript>0.15</Subscript>Y<Subscript>0.85</Subscript>VO<Subscript>4</Subscript> crystal

A diode-pumped passively Q-switched Nd:Lu_0.15Y_0.85VO₄ laser with a GaAs output coupler is demonstrated. By using a mixed crystal Nd:Lu_0.15Y_0.85VO₄ as laser medium, the passively Q-switched laser can generate shorter pulse width with higher peak power in comparison with the passively Q-switched Nd:LuVO₄ or Nd:YVO₄ lasers under the same laser cavity. At the incident pump power 11.9 W, the minimum pulse width of 3.23 ns and the maximum peak power 1.67 kW can be obtained. The average output power and the pulse repetition rate of the laser are also measured. The experimental results show that the mixed crystal is a promising laser medium for shorter Q-switched pulse with higher peak power.     

Passively Q-switched mode-locking in a diode-pumped Nd:LuVO<Subscript>4</Subscript> laser with V:YAG

A passively Q-switched and mode-locked Nd:LuVO₄ laser with V:YAG at 1.34 μm was successfully demonstrated. Comparisons between c-cut and a-cut Nd:LuVO₄ lasers were experimentally made. The maximum average output power of 170 mW, the highest Q-switched pulse energy of 4.5 μJ were obtained in c-cut Nd:LuVO₄ laser. The duration of mode-locked pulse was estimated to be less than 540 ps with repetition rate of 110 MHz.     

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.