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.     

Double-loss-modulated q-switched and mode-locked Nd:Lu<Subscript>0.15</Subscript>Y<Subscript>0.85</Subscript>VO<Subscript>4</Subscript> laser at 1.34 μm with single-walled carbon nanotube saturable absorber and AO modulator

A diode-pumped dual-loss-modulated Q-switched and mode-locked (QML) Nd:Lu_0.15Y_0.85VO₄ laser at 1.34 μm with single-walled carbon nanotube saturable absorber (SWCNT-SA) and acousto-optic (AO) modulator is demonstrated. The modulation depth of the dual-loss-modulated QML laser reaches 90%, being deeper than 75% that obtained by the single passively QML laser. The stability of the hybrid QML laser is significantly improved if compared to that only with SWCNT-SA. The Q-switched pulse energy and the Q-switched pulse width of the QML laser with the dual-loss-modulation are 487 and 27% of those only with SWCNT-SA, respectively.     

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.     

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 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.     

Experimental study on doubly QML Nd:Lu<Subscript>0.15</Subscript>Y<Subscript>0.85</Subscript>VO<Subscript>4</Subscript> laser with AO modulator and central SESAM

By using double-mixed crystal Nd:Lu_0.15Y_0.85VO₄ as laser medium, a diode-pumped doubly Q-switched and mode-locked (QML) Nd:Lu_0.15Y_0.85VO₄ laser with acousto-optic (AO) modulator and central semiconductor saturable absorption mirror (SESAM) is realized for the first time. The Q-switched envelope modulation depth is nearly 100%.The average output power and the pulse width of the Q-switched envelope etc. for different AO modulator repetition rates have been measured. The experimental result show that Nd:Lu_0.15Y_0.85VO₄ crystal is an excellent laser medium for doubly QML lasers.     

Characteristics of diode-pumped dual-loss-modulated Q-switched and mode-locked Nd:Lu<Subscript>0.15</Subscript>Y<Subscript>0.85</Subscript>VO<Subscript>4</Subscript> laser

A diode-pumped dual-loss-modulated Q-switched and mode-locked (QML) Nd:Lu_0.15Y_0.85VO₄ laser with acousto-optic (AO) modulator and Cr⁴⁺:YAG saturable absorber is presented. The stable QML laser pulse with high peak power and complete modulation depth has been obtained. The QML laser characteristics such as the pulse width, single-pulse energy etc. have been measured for different small-signal transmissions (T ₀) of Cr⁴⁺:YAG, different reflectivity (R) of output coupler and modulation frequencies of the AO modulator (f _p ). The results show that the pulse energy increases with decreasing f _p and increasing T ₀, while the pulse width decreases with decreasing f _p and increasing T ₀. At f _p = 10 kHz, R = 90%, and T ₀ = 91%, the highest pulse energy and peak power of mode-locked pulses is obtained.     

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.     

Characteristics of Q-switched and mode-locked pulses generation in <Emphasis Type="Italic">c</Emphasis>-cut Nd:LuVO<Subscript>4</Subscript> laser by acousto-optic modulator

The characteristics of Q-switched and mode-locked operation in c-cut Nd:LuVO₄ laser has been first time investigated by using an acousto-optic modulator. In our study, higher pulse energy and shorter width of Q-switched envelope can be generated using output coupler with R = 80% as compared to those of R = 60%. However, deeper modulation depth and shorter pulsewidth of mode-locked pulses can be generated by using R = 60% instead of R = 80%. In our laser, the pulsewidth of QML pulses are measured by the FROG method and pulsewidth of about 212 ps was produced in the c-cut Nd:LuVO₄ laser.     

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.     

Diode-pumped Q-switched intracavity frequency-doubled Nd:LuVO<Subscript>4</Subscript>/KTP green laser

A simple and compact diode-pumped acousto-optically Q-switched intracavity frequency-doubled Nd:LuVO₄/KTP green laser were demonstrated successfully for the first time. At an incident pump power of 6.5 W, an average output power of 663 mW, a pulse width of 26 ns were obtained with a PRF of 10 kHz. The pulse energy and peak power of the green light were determined to be 66.3 μJ and 2.55 kW, respectively.     

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.     

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.     

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.     

Symmetric and short green-pulse generation by doubly Q-switched Nd:YVO<Subscript>4</Subscript> laser

A compact diode-pumped doubly Q-switched extracavity frequency-doubled Nd:YVO₄/KTP green-pulse laser was demonstrated, using both an acoustic-optic (AO) modulator and a GaAs saturable absorber in a simple flat-flat cavity. The green laser can generate a more symmetric and shorter pulse when compared with purely AO and passively Q-switched lasers. A peak power of 7.54 kW with the corresponding pulse width of 3.2 ns has been achieved with the incident pump power of 7.76 W and f _p = 15 kHz. A reasonable analysis about the experimental results has been given.     

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.     

Analysis of a laser-diode end-pumped intracavity frequency-doubled passively Q-switched and mode-locked Nd:GdVO<Subscript>4</Subscript>/KTP laser with a semiconductor saturable absorber

A diode-pumped passively Q-switched mode-locked (QML) intracavity frequency-doubled Nd:GdVO₄/KTP green laser with a semiconductor saturable absorber is presented. Nearly 100% modulation depth for the mode-locked green pulses can be achieved at any pump power over 1.92 W. The width of the mode-locked green pulse was estimated to be about 150 ps. The mode-locked pulse interval within the Q-switched envelope of 320 ns and the repetition rate of 97.5 kHz were obtained, at an incident pump power of 4.4 W. The repetition rate of the mode-locked green pulses inside the Q-switched envelope was 140 MHz.     

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.     

Improvement of laser characteristics for diode-pumped passively Q-switched and mode-locked Nd:Lu0.15Y0.85VO4 laser by AO modulator

The hybrid Q-switched and mode-locked (QML) operation of Nd:Lu_0.15Y_0.85VO₄ crystal at 1.34 ??m with V:YAG saturable absorber and acousto-optic (AO) modulator has been realized. The laser characteristics are distinctly improved by the hybrid QML if compared to those with the single V:YAG QML. At the pump power of 5.04 W, the Q-switched pulse energy is enlarged to 5.6 times and the Q-switched pulse width is shortened to 40% by the AO modulator in contrast to those of the single passively QML.