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.     

Diode-pumped passively Q-switched Nd:GdVO4 laser at 1342 nm with V:YAG saturable absorber

We have demonstrated an efficient diode-pumped passively Q-switched Nd:GdVO₄ laser working at 1342 nm by using an uncoated V³⁺:YAG crystal as the saturable absorber, in which both a-cut and c-cut Nd:GdVO₄ crystals are employed. At the maximum absorbed pump power of 9.45 W, the maximum average output power can reach 519 mW and 441 mW corresponding to the output coupler with different transmission of 3% and 10% by using an a-cut Nd:GdVO₄ crystal at 1342 nm, while the shortest pulse duration could be as low as 21.7 ns and 22.3 ns with the repetition rate of 48.41 kHz and 53.25 kHz by using a c-cut Nd:GdVO₄ crystal, corresponding to the output coupler with different transmission of 3% and 10% at 1342 nm, and the single Q-switched pulse energy are 6.67 uJ and 7.06 uJ, the pulse peak power are 307 W and 316 W, respectively. The experimental results show that c-cut Nd:GdVO₄ laser can generate shorter pulse with higher peak power in comparison with a-cut one.     

Quasi-continuously pumped passively mode-locked operation of a Nd:GdVO4 and Nd:YVO4 laser in a bounce geometry

The comparative study of pulsed diode pumped Nd:GdVO₄ and Nd:YVO₄ slab lasers in a bounce geometry in a free running and a passively mode-locked regime was performed. The better efficiency of Nd:GdVO₄ in both regimes was obtained. In the free running regime the efficiency of 39% was achieved from Nd:GdVO₄ comparing with 28% from Nd:YVO₄. Passive mode-locking of both lasers using a semiconductor saturable absorber in the transmission mode was demonstrated. Trains containing 6 pulses were generated in both cases but the pump energy for Nd:GdVO₄ was 50% lower. The single pulse extraction using cavity dumping was demonstrated with contrast better than 10^?3.     

Passive mode-locking in diode-pumped c-cut Nd:LuVO<Subscript>4</Subscript> laser with a semiconductor saturable-absorber mirror

We demonstrated a diode-pumped passively mode-locked c-cut Nd:LuVO₄ picosecond laser with a semiconductor saturable-absorber mirror (SESAM) at a wavelength of 1067.8 nm. Due to the wide bandwidth of 0.48 nm, stable mode-locking has been generated with a duration as short as 3.7 ps, which is shorter than for the a-cut Nd:LuVO₄ laser. A maximum output power of 1.67 W was achieved to give a highest peak power of 3.47 KW at 18 W absorbed pump power.     

Efficient pulse operation of Nd:GdVO4 laser with AO Q-switch

We realized an efficient laser diode-pumped Nd:GdVO₄ laser with crystals grown by the floating zone method. In the lasing experiment, a slope efficiency of 78% was achieved with a 1 at.% Nd-doped crystal by pumping at 879 nm. Furthermore, excellent pulsed laser operation was demonstrated with the Nd:GdVO₄ crystal by using an acousto-optical (AO) Q-switch. A pulse width of 7 ns was observed when the pulse-repetition frequency was 40 kHz. It is the shortest pulse width recorded in the case of the AO Q-switched Nd:GdVO₄ laser.     

High power diode-pumped passively Q-switched and mode-locking Nd:GdVO4 laser at 912 nm

A high power diode-end-pumped passively Q-switched and mode-locking (QML) Nd:GdVO₄ laser at 912 nm was demonstrated for the first time, to the best of our knowledge. A Z-type laser cavity with Cr⁴⁺:YAG crystals as the intracavity saturable absorber were employed in the experiments. Influence of the initial transmission (T_U) of the saturable absorber on the QML laser performance was investigated. Using the T_U = 95% Cr⁴⁺:YAG, as much as an average output power of 2.0 W pulsed 912 nm laser was produced at an absorbed pump power of 25.0 W, then the repetition rates of the Q-switched envelope and the mode-locking pulse were ~ 224 kHz and ~ 160 MHz, respectively. Whereas the maximum output power was reduced to 1.3 W using the T_U = 90% Cr⁴⁺:YAG, we obtained a 100% modulation depth for the mode-locking pulses inside the Q-switched envelope.     

Systematic study on thermal lens effect and passive Q-switching of diode-pumped 1.34-μm Nd:GdxY1 ? xVO4 laser with different output couplers

The thermal lens effect and passively Q-switched laser performance of mixed Nd:Gd _x Y_{1 − x} VO₄ crystals at 1.34 μm with 5 and 10% as the output transmissions have been systematically studied. Compared with the single vanadate crystal Nd:GdVO₄, the mixed Nd:Gd _x Y_{1 − x} VO₄ crystals can enhance passively Q-switched laser characteristics due to their smaller emission cross sections, although they have stronger thermal lens effects which result in decreasing the average output power. The largest peak power and pulse energy, obtained for Nd:Gd_0.63Y_0.37VO₄, were 2.9 and 1.7 times as those of Nd:GdVO₄ under the uniform conditions.     

Actively Q-switched laser performance of Nd:Gd x Y1−x VO4: a class of mixed vanadate crystals

We report for the first time the actively Q-switched laser performance of a class of mixed Nd:Gd _x Y_1−x VO₄ crystals. In comparison with the ordered Nd:GdVO₄ and Nd:YVO₄, an enhancement in both pulse energy and peak power is demonstrated in the low pulse-repetition frequency (PRF) range of 5–20 kHz, confirming Nd:Gd_0.64 Y_0.36VO₄ as the most advantageous in this respect. Laser pulses of 8.3-ns duration are generated at PRF=10 kHz with pulse energy and peak power being respectively 171 μJ and 20.6 kW. While for high-PRF operation (>∼40 kHz), the ordered Nd:GdVO₄ and Nd:YVO₄ prove to be superior to the mixed crystals.     

Diode-pumped continuous-wave and passively Q-switched 1.06 μm YVO4/Nd:GdVO4 laser

In this letter, a diode-pumped continuous-wave and passively Q-switched 1.06 μm laser with a novel composite YVO₄/Nd:GdVO₄ crystal was demonstrated for the first time. Theoretical calculations showed that the temperature distribution in YVO₄/Nd:GdVO₄ crystal was lower than that in GdVO₄/Nd:GdVO₄ and Nd:GdVO₄ crystals under the same conditions. After optimizing the mode matching degree, a CW output power of 5.6 W of YVO₄/Nd:GdVO₄ laser was obtained at the incident pump power of 12 W when the output coupler with transmission of 30% was employed. Using Cr^4 +:YAG crystals with initial transmission (T₀) of 80% and 90% as saturable absorbers, the pulsed YVO₄/Nd:GdVO₄ laser characteristics were investigated. At the incident pump power of 12 W, the maximum average output power of 2.76 W and the maximum repetition rate of 189 kHz was achieved when T₀ = 90% Cr^4 +:YAG was used. The shortest pulse width was 28.1 ns when the initial transmission of the used Cr^4 +:YAG was 80%.     

Diode-pumped passively Q-switched Nd:GdVO4 lasers operating at 1.06 μm wavelength

With a 10-W diode laser to pump Nd:GdVO₄ crystal in a folded cavity, we demonstrated Cr⁴⁺:YAG passively Q-switched Nd:GdVO₄ lasers at 1.06 μm. The maximum average output power of 2.1 W and the highest peak power of 625 W were, respectively, obtained when the initial transmissions of the Cr⁴⁺:YAG crystals were 90% and 80%. Received: 8 September 1999 / Revised version: 30 December 1999 / Published online: 8 March 2000     

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.     

Mode-locked diode-pumped vanadate lasers operated with PbS quantum dots

The use of glasses doped with PbS nanocrystals as intracavity saturable absorbers for passive Q-switching and mode locking of c-cut Nd:Gd_0.7Y_0.3VO₄, Nd:YVO₄, and Nd:GdVO₄ lasers is investigated. Q-switching yields pulses as short as 35 ns with an average output power of 435 mW at a repetition rate of 6–12 kHz at a pump power of 5–6 W. Mode locking through a combination of PbS nanocrystals and a Kerr lens results in 1.4 ps long pulses with an average output power of 255 mW at a repetition rate of 100 MHz.     

High power diode-side-pumped rod Nd:GdVO4 laser

A compact high power diode-side-pumped Nd:GdVO₄ laser has been presented, which can generate an output power of 52 W at 1.063-μm for continuous-wave (CW) operation. The absorption characteristics of the Nd:GdVO₄ in different pump directions is measured, which were used to optimize the diode-side-pumped Nd:GdVO₄ laser head. The laser characteristics of both CW and Q-switched Nd:GdVO₄ and Nd:YAG in are compared and it was found that Nd:GdVO₄ may surpass Nd:YAG for high power laser application.     

Passive stabilization of a passively mode-locked Nd:GdVO4 laser by inverse saturable absorption

A diode-pumped Nd:GdVO₄ laser mode-locked by a semiconductor saturable absorber and output coupler (SESAOC) is passively stabilized to suppress Q-switched mode-locking. A phase mismatched BIBO second-harmonic generation (SHG) crystal is used for passive stabilization. The continuous wave mode-locking (CWML) threshold is reduced and the pulse width is compressed. The pulse width is 6.5 ps as measured at the repetition rate of 128 MHz.     

A comparative study of continuous laser operation on the F3/2-I9/2 transitions of Nd:GdVO4 and Nd:YVO4 crystals

A comparative study of Nd:GdVO₄ and Nd:YVO₄ crystal lasers pumped by a fiber-coupled diode array has been conducted at the ⁴F_3/2-⁴I_9/2 transitions wavelengths of 912 nm and 914 nm, as well as when intracavity frequency-doubled to 456 nm and 457 nm, respectively. At the fundamental wavelength of 912 nm and second harmonic wavelength of 456 nm, maximum output powers from the Nd:GdVO₄ crystal laser were 7.85 W and 4.6 W at a pump power of 29 W. All the results obtained from Nd:GdVO₄ were superior to those of Nd:YVO₄, indicating that Nd:GdVO₄ is a more efficient laser crystal than Nd:YVO₄ for laser operation on the ⁴F_3/2-⁴I_9/2 transitions.     

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.     

High efficiency 1341 nm Nd:GdVO<Subscript>4</Subscript> laser in-band pumped at 912 nm

A high-efficiency 1341 nm Nd:GdVO₄ laser in-band pumped at 912 nm is demonstrated for the first time. Using an all-solid-state Nd:GdVO₄ laser operating at 912 nm as pump source, 542 mW output was obtained with 1.14 W absorbed pump power. The slope efficiency with respect to the absorbed pump power was 56.6%, and the fluctuation of the output power was better than 2.6% in the given 30 min. The beam quality factor M ₂ is 1.15.     

Diode-pumped passively mode-locked Nd:GdVO4 laser at 912 nm

We have demonstrated the stable mode-locked Nd:GdVO₄ laser operating on the ⁴F_3/2-⁴I_9/2 transition at 912 nm. With a four-mirror-folded cavity and a semiconductor saturable absorber mirror for passive mode-locking, we have gained 6.5 ps laser pulses at a repetition rate of 178 MHz. The laser is diode-end-pumped, and the total output power from the out coupler is 128 mw at an incident pump power of 19.7 W.     

High efficiency 1341 nm Nd:GdVO<Subscript>4</Subscript> bounce laser in-band pumped at 879 nm

A high-efficiency Nd:GdVO₄ bounce laser in-band pumped at 879 nm is demonstrated for the first time. From a side-pumped Nd:GdVO₄ crystal, 8.2 W output was obtained with 18.5 W absorbed pump power. Corresponding slope efficiency with respect to the absorbed pump power was 51.4%, and the beam quality factor M2 is 1.13 and 1.15 for tangential direction and sagittal direction, respectively. Effects of crystal’s doping concentration and temperature on laser power and conversion efficiency were also investigated.     

Diode-laser-array end-pumped 14.3-W CW Nd:GdVO4 solid-state laser at 1.06 μm

A diode-laser-array end-pumped efficient CW Nd:GdVO₄ laser at 1.06 μm has been developed. A low-order-mode output power of 14.3 W was obtained at the maximum available pump power of 26 W, giving an optical conversion efficiency of 55% and an average slope efficiency of 62%. The laser output beam quality factor at full pump power was determined to be M²<1.8. It is also shown that only lightly doped Nd:GdVO₄ crystals are suitable for high-power end-pumped lasers. Received: 4 May 1999 / Published online: 29 July 1999