Diode-pumped short pulse passively Q-switched 912 nm Nd:GdVO<Subscript>4</Subscript>/Cr:YAG laser at high repetition rate operation

A diode-end-pumped passively Q-switched 912 nm Nd:GdVO₄/Cr:YAG laser is demonstrated for the first time. In a concave-piano cavity, pulsed 912 nm laser performance is investigated using two kinds of Cr:YAG crystal with different unsaturated transmission (T _U) of 95% and 90% at 912 nm as the saturable absorbers. When the T _U = 90% Cr:YAG is used, as much as 2.6 W average output power for short pulsed 912 nm laser is achieved at an absorbed pump power of 34.0 W, corresponding to an optical efficiency of 7.6% and a slope efficiency of 20.3%. Moreover, 10.5 ns duration pulses and up to 2.3 kW peak power is obtained at the repetition rate around 81.6 kHz.     

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.     

Efficient CW Nd:GdVO<Subscript>4</Subscript>-BiBO deep-blue laser at 456 nm under direct 888 nm diode laser pumping

We report an efficient laser emission on the 912 nm ⁴ F _3/2 to ⁴ I _9/2 transition in Nd:GdVO₄ under the pump with diode lasers at 888 nm. Continuous wave (CW) 4.91 W output power at 912 nm is obtained under 18.3 W of incident pump power; the slope efficiency with respect to the incident pump power was 57.5%. Moreover, intracavity frequency doubling with BiB₃O₆ (BiBO) nonlinear crystal yielded 1.33 W of deep-blue light at 456 nm.     

All-solid-state CW Nd:GdVO<Subscript>4</Subscript>-LBO red laser under direct 912 nm pumping

We report a red laser at 670.5 nm generation by intracavity frequency doubling of a continuous wave (CW) laser operation of a 1341 nm Nd:GdVO₄ laser under in-band diode pumping at 912 nm. An LBO crystal, cut for critical type I phase matching is used for second harmonic generation of the laser. At an incident pump power of 8.9 W, as high as 347 mW of CW output power at 670.5 nm is achieved. The fluctuation of the red output power was better than 3.7% in the given 30 min, and the beam quality factor M ² is 1.65.     

Efficient blue emission of ytterbium-doped Sr<Subscript>5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>F under quasi-three-level intracavity pumping

We report an Yb:Sr₅(PO₄)₃F (Yb:S-FAP) laser emitting at 985 nm intracavity pumped by a 912 nm diode-pumped Nd:GdVO₄ laser. A 808 nm diode laser is used to pump the Nd:GdVO₄ crystal emitting at 912 nm, and the Yb:S-FAP laser emitting at 985 nm intracavity pumped at 912 nm. With incident pump power of 17.5 W, intracavity second harmonic generation has been demonstrated with a power of 131 mW at 492.5 nm by using a LBO nonlinear crystal.     

912 nm laser operation in diode-pumped grown-together composite Nd:GdVO4/GdVO4 crystal

Novel grown-together Nd:GdVO₄/GdVO₄ composite crystals were presented for the first time, which would be longitudinally pumped by 808 nm diode-laser to efficiently operate on continuous-wave (CW) 912 nm laser at room temperature. The maximum output power of 8.15 W at 912 nm laser was obtained successfully at the absorbed pump power of 28.0 W, giving the corresponding optical-to-optical conversion efficiency of 29.1% and the average slope-efficiency of 44.2%. Comparative experimental results show that the laser performance was influenced significantly by the Nd³⁺-doped concentration of the crystals, which would be optimized according to its energy-transfer upconversion (ETU) spectrum.     

Continuous-wave simultaneous dual-wavelength operation at 912 nm and 1063 nm in Nd:GdVO<Subscript>4</Subscript>

A continuous-wave, diode-pumped Nd:GdVO₄ thin disk laser with simultaneous dual-wavelength emission at the 912 nm ⁴ F _3/2→⁴ I _9/2 quasi-three-level transition and the 1063 nm ⁴ F _3/2→⁴ I _11/2 four-level transition is demonstrated and analyzed. Output powers of 1.7 W at 912 nm and of 1.6 W at 1063 nm were achieved simultaneously from a 0.3-at.%, 300-μm thick Nd:GdVO₄ crystal that was multi-pass excited with 26.8 W of available diode pump power. Second harmonic generation to 456 nm with LiB₃O₅ yielded 0.96 W in 912 nm single-wavelength operation and 0.73 W in 912 nm/1063 nm dual-wavelength operation. PACS 42.55.Rz; 42.60.By; 42.65.Ky     

Theoretical and experimental investigations of a diode-pumped high-power continuous-wave 912 nm Nd:GdVO4 laser operation at room temperature

Based on the rate equation of Nd³⁺-doped quasi-three-level lasers, a theoretical model of diode-end-pumped continuous-wave 912 nm Nd:GdVO₄ laser is presented. Lasing threshold and slope efficiency considering reabsorption effect are calculated and analyzed. It is found that the output performance of 912 nm laser operating at room temperature is influenced remarkably by the reabsorption loss and spatial distribution of the pump beam and laser beam. In experiments, the output power and average slope efficiency of 912 nm laser were investigated under different conditions. After optimization at the parameters of laser medium, working temperature and spatial distribution of the pump beam, up to 16.2 W continuous-wave 912 nm laser output was obtained at incident pump power of 67.0 W, with an average slope efficiency of 41.7%, to the best of our knowledge, this is the highest output power of diode-pumped 912 nm Nd:GdVO₄ laser by far.     

High repetition rate passive Q-switching of diode-pumped Nd:GdVO<Subscript>4</Subscript> laser at 912 nm with V<Superscript>3+</Superscript>:YAG as the saturable absorber

The character of a diode-pumped passively Q-switched Nd:GdVO₄/V³⁺:YAG 912 nm laser was demonstrated for the first time to our knowledge. With an absorbed pump power of 7.4 W, an average output power of 360 mW with a Q-switched pulse width of 328 ns at a pulse repetition rate of 163 kHz was obtained. The Q-switching efficiency was found to be 32.7%. Our work further indicated V³⁺:YAG could be an effective fast passive Q-switch for 0.9 μm radiation.     

494 nm blue laser based on sum-frequency mixing of diode pumped Nd<Superscript>3+</Superscript> lasers

We report for the first time a continuous-wave (CW) blue radiation at 494 nm by intracavity sumfrequency generation of 912 nm Nd:GdVO₄ laser and 1079 nm Nd:YAlO₃ (Nd:YAP) laser. Using type-I critical phase matching LiB₃O₅ (LBO) crystal, 494 nm blue laser was obtained by 912 and 1079 nm intra-cavity sum-frequency mixing, and output power of 179 mW was demonstrated. At the output power level of 179 mW, the output power stability is better than 3.5% and laser beam quality M ₂ factor is 1.21.     

494.5 nm generation by sum-frequency mixing of diode pumped neodymium lasers

We report a coherent radiation at 494.5 nm by intra-cavity sum-frequency generation of 912 nm Nd:GdVO₄ laser and 1080 nm Nd:CaYAlO₄ laser. Blue laser is obtained by using a doubly folded cavity, type-II critical phase matching KTP (KTiOPO₄) crystal sum-frequency mixing. With total pump power of 33 W (13.8 W pump power for 1080 nm Nd:CaYAlO₄ laser and 19.2 W pump power for 912 nm Nd:GdVO₄ laser), TEM₀₀ mode blue laser at 494.5 nm of 1.6 W is obtained. The power stability in 30 min is better than 3.5%.     

Characteristics of Nd：GdVO4 Laser with Different Nd-Doping Concentrations

We report the properties of a compact diode-pumped continuous-wave Nd：GdV04 laser with a linear cavity and different Nd-doped laser crystals. In a 0.2at.% Nd-doped Nd：GdVO4 laser, 1.54 W output laser power is achieved at 912nm wavelength with a slope efficiency of 24.8% at an absorbed pump power of 9.4W. With 0.3at.% Nd-doping concentration, we can obtain the either single-wavelength emission at 1064nm or 912nm or the dual-wavelength emission at 1064nm and 912nm by controlling the incident pump power. From an incident pump power of 11.6 W, the 1064nm emission between ^4Fa/2 and ^4I11/2 is suppressed completely by the 912nm emission between ^4Fa/2 and ^4I9/2. We obtain 670 mW output of the 912nm single-wavelength laser emission with a slope efficiency of 5.5% by taking an incident pump power of 18.4 W. Using a Nd：GdV04 laser with 0.4at.% Nd-doping concentration, we obtain either the single-wavelength emission at 1064nm or the dual-wavelength emission at both 1064nm and 912nm by increasing the incident pump power. We observe a strong competition process in the dualavelength laser.     

Compact diode-directly-pumped passively mode-locked TEM<Subscript>00</Subscript> Nd:GdVO<Subscript>4</Subscript> laser at 1341 nm using a semiconductor saturable absorber mirror

We report on a compact 880-nm diode-directly-pumped passively mode-locked TEM₀₀ Nd:GdVO₄ laser at 1341 nm with a semiconductor saturable absorber mirror (SESAM) for the first time. Under the absorbed pump power of 14.6 W, the maximum output power of 1.27 W was obtained at the repetition rate of 85.3 MHz with the pulse width of 45.3 ps, corresponding to an optical-optical efficiency of 8.8% and the slope efficiency of 33.3%, respectively. The beam quality factor was measured to be M ² = 1.18, indicating a TEM₀₀ mode.     

A comparative study on diode-pumped continuous wave Tm:Ho:YVO<Subscript>4</Subscript> and Tm:Ho:GdVO<Subscript>4</Subscript> lasers

In this paper, we presented experimental results concerning on the laser characteristics of two microchip lasers emitting in the 2 μm range, Tm:Ho:YVO₄ microchip laser and Tm:Ho:GdVO₄ microchip laser. At a heat sink temperature of 283 K, the maximum output power of Tm:Ho:YVO₄ laser and Tm:Ho:GdVO₄ laser is 47 and 34 mW under absorbed pump power of 912 mW, respectively. High efficiency can be achieved for both lasers at room temperature. Nevertheless, compared with Tm:Ho:GdVO₄ laser, Tm:Ho:YVO₄ laser can operate on single frequency with high power easily. At the heat sink temperature of 288 K, as much as 16.5 mW of 2052.3 nm single-longitudinal-mode (SLM) laser was achieved for Tm:Ho:YVO₄ laser. Under the same condition, only 8 mW of 2048.5 nm SLM laser was achieved for Tm:Ho:GdVO₄ laser.     

Continuous-wave Nd:GdVO<Subscript>4</Subscript>/LBO laser at 541.5 nm under diode pumping into the emitting level

We report a green laser at 541.5 nm generation by intracavity frequency doubling of a continuous wave (cw) laser operation of a 1083 nm Nd:GdVO₄ laser under 880 nm diode pumping into the emitting level ⁴ F _3/2. A LiB₃O₅ (LBO) crystal, cut for critical type I phase matching at room temperature is used for second harmonic generation of the laser. At an incident pump power of 17.8 W, as high as 2.52 W of cw output power at 541.5 nm is achieved. The optical-to-optical conversion efficiency is up to 14.2%, and the fluctuation of the green output power was better than 3.6% in the given 30 min.     

Diode-pumped Yb:Y<Subscript>2</Subscript>SiO<Subscript>5</Subscript>-LiB<Subscript>3</Subscript>O<Subscript>5</Subscript> cyan laser at 501.7 nm

We describe the output performances of the 928 nm ⁴ F _3/2 → ⁴ I _9/2 transition in Nd:CLNGG under diode-laser pumping. An end-pumped Nd:CLNGG crystal yielded 1.3 W of continuous-wave output power for 17.8 W of absorbed pump power. The slope efficiency with respect to the absorbed pump power was 11.2%. Furthermore, with 17.8 W of diode pump power and the frequency-doubling crystal LiB₃O₅ (LBO), a maximum output power of 260 mW in the blue spectral range at 464 nm has been achieved. The blue output power stability over 4 h is better than 3.2%.     

All solid-state CW Nd:GdVO<Subscript>4</Subscript>-GdCOB laser at 670 nm

We report the efficient compact red laser at 670 nm generation by intracavity frequency doubling of a continuous wave laser operation of a diode pumped Nd:GdVO₄ laser on the ⁴ F _3/2 → ⁴ I _13/2 transition at 1340 nm. An GdCa₄O(BO₃)₃ (GdCOB) crystal, cut for critical type I phase matching at room temperature is used for second harmonic generation of the laser. At an incident pump power of 18.2 W, as high as 1.32 W of continuous wave (CW) output power at 670 nm is achieved with 15-mm-long GdCOB. The optical-to-optical conversion efficiency is up to 7.3%, and the fluctuation of the red output power was better than 3.5% in the given 30 min.     

Passively Q-switched GdVO<Subscript>4</Subscript>/Nd:GdVO<Subscript>4</Subscript> laser with Cr<Superscript>4+</Superscript>:YAG saturable absorber under direct 879 nm diode pumping to the emitting level

A passively Q-switched 1.06 μm laser with Cr⁴⁺:YAG saturable absorber by direct 879 nm diode pumping grown-together composite GdVO₄/Nd:GdVO₄ crystal to the emitting level was demonstrated in this paper. The characteristics of pulsed laser were investigated by using two kinds of Cr⁴⁺:YAG crystal with the initial transmissivity of 80 and 90%, respectively. When the T ₀ = 90% Cr⁴⁺:YAG was used, an average output power of 1.59 W was achieved at an incident pump power of 10 W. The pulse width and repetition rate were 64.5 ns and 170 kHz, respectively. The thermal lens effect of laser crystal was analyzed.     

Improvement of diode-end-pumped 912 nm Nd:GdVO<Subscript>4</Subscript> laser performance based on microchannel heat sink

To solve the thermal dissipation problem in diode-end-pumped solid state lasers and improve the performance of 912 nm Nd:GdVO₄ lasers, a novel microchannel heat sink is designed and used in the experiments. Heat-transfer coefficients for the common heat sink and microchannel heat sink are calculated. The results obtained for the heat-transfer coefficient for the heat sink with a channel width of 0.2 mm is almost 5 times higher than that of the common one. The heat resistance for the novel heat sink is analyzed. Simulation results show that the maximum temperature in the laser crystal is reduced by 19°C at an absorbed pump power of 24.0 W, and the heat transfer ability significantly increases if the microchannel heat sink is used. Experimental results also indicate that the performance for a 912 nm laser is improved significantly using the novel heat sink, especially from the aspects of laser-beam quality and power scaling.     

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.