End-pumped 20.2-W Nd:YVO4 cw slab laser at 1342 nm with a hybrid resonator

A 20.2 W laser-diode-end-pumped Nd:YVO₄ slab laser with a hybrid resonator at 1342 nm was demonstrated. The slope efficiency and optical-to-optical conversation efficiency were 30% and 23%, respectively. At output power of 16 W, the M² factor in stable direction was 2.3, and in the unstable direction was 1.2.     

Diode-pumped passively Q-switched 912 nm Nd:GdVO4 laser and pulsed deep-blue laser by intracavity frequency-doubling

A diode-end-pumped passively Q-switched 912 nm Nd:GdVO₄/Cr⁴⁺:YAG laser and its efficient intracavity frequency-doubling to 456 nm deep-blue laser were demonstrated in this paper. Using a simple V-type laser cavity, pulsed 912 nm laser characteristics were investigated with two kinds of Cr⁴⁺:YAG crystal as the saturable absorbers, which have the different initial transmissivity (T_U) of 95% and 90% at 912 nm. When the T_U = 95% Cr⁴⁺:YAG was used, as much as an average output power of 2.8 W 912 nm laser was achieved at an absorbed pump power of 34.0 W, and the pulse width and the repetition rate were ∼ 40.5 ns and ∼ 76.6 kHz, respectively. To the best of our knowledge, this is the highest average output power of diode-pumped passively Q-switched Nd³⁺-doped quasi-three-level laser. Employing a BiBO as the frequency-doubling crystal, 456 nm pulsed deep-blue laser was obtained with a maximum average output power of 1.2 W at a repetition rate ∼ 42.7 kHz.     

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 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.     

1097 nm Nd:YVO4 self-Raman laser

An acousto-optically Q-switched self-Raman laser emitting at 1097 nm is demonstrated with a c-cut Nd:YVO₄ crystal, using a fiber-coupled 880 nm diode laser as the pumping source. Raman laser performances in concave-plane and plane-plane oscillating cavities are studied and compared. With an absorbed diode power of 12.4 W and a pulse repetition rate of 50 kHz, the highest output power of 1.45 W is obtained from the plane-plane cavity, corresponding to an optical-to-optical conversion efficiency of 11.7%.     

An efficient and compact laser-diode end-pumped intracavity frequency-tripled Nd: YVO4 355 nm laser

By exploiting the intracavity frequency conversion configuration, a diode end-pumped acousto-optic (AO) Q-switched Nd:YVO₄ 355 nm laser was demonstrated in this paper. Two LBO crystals were inserted in the cavity to realize the frequency tripling operation, a cascade of the second harmonic generation (SHG) and sum frequency mixing (SFM). Under the absorbed pump power of 13 W, the maximum average output power at 355 nm was obtained to be 1.32 W at the repetition frequency of 17 kHz, with the optical-to-optical conversion efficiency of 10.2%. The corresponding pulse width was 10.2 ns, with the energy of a single pulse and corresponding peak power estimated to be 77.6 μJ and 7.61 kW, respectively.     

Diode-end-pumped passively Q-switched Nd:Y0.8Lu0.2VO4 laser with Cr:YAG crystal

A diode end-pumped passively Q-switched Nd: Y_0.8Lu_0.2VO₄ laser with a Cr⁴⁺: YAG crystal is first demonstrated in this paper. The maximum continuous wave (CW) output power of 5.59 W is obtained at the incident pump power of 13.07 W with the output transmission T = 20%, resulting in an optical-to-optical efficiency of 42.7%. For Q-switching operation, the measured pulse duration of 8.5 ns, the pulse energy of 45.24 μJ and the peak power of 5.32 kW are respectively obtained for the output transmission of 50% when the Cr⁴⁺: YAG crystal is used with an initial transmission (T₀) of 60%.     

LD end-pumped intracavity frequency doubled Yb:YAG laser

A laser diode end-pumped 10 at.% doped Yb:YAG microchip crystal intracavity frequency doubled all solid-stated green laser is reported in this paper. Using one plano-concave resonator, with the pump power of 1.2 W, 44.2 mW TEM₀₀ continuous wave (CW) laser at 525 nm was obtained, the optical conversion efficiency was about 3.7%. When a Cr:YAG crystal with initial transmission of 95.5% inserted in the resonator, the maximum output power of 6.4 mW, pulse duration width of 49.1 ns, pulse repetition rate of 2.45 kHz, and peak power of 53.1 W at 515 nm were achieved when the pump power was 1.2 W. The wavelength changed from 525 nm to 515 nm and the threshold was only 725 mW.     

Efficient and compact intracavity-frequency-doubled YVO4/Nd:YVO4/KTP laser through analysis of the interaction length

In this paper, a stable end-pumped intracavity-frequency-doubled green laser was demonstrated. The interaction length of different pump systems before setting up the experiment was analyzed in order to find out an effective pump system. The experimental results indicate that the pump system in our configuration is beneficial to the efficient CW Nd lasers. A continue-grown composite crystal YVO₄/Nd:YVO₄, with Nd³⁺ concentration doping of 0.3 at.%, is used as laser medium. With an incident pump power of 27.5 W, as high as 7.2 W of CW output power at 532 nm was achieved. The optical-to-optical conversion efficiency of 26.2% was obtained in CW modes with a flat-flat cavity design.     

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.     

Passively Q-switched laser operation in a composite Nd:YVO4/Nd:YVO4/Nd:YVO4 crystal with a GaAs saturable absorber

By using a piece of GaAs wafer as the saturable absorber, the performance of the passively Q-switched composite Nd:YVO₄ laser with different output couplers has been demonstrated for the first time as far as we know. The largest continuous wave output power of 1.52 W is obtained at the incident pump power of 5.31 W, giving an optical conversion efficiency of 28.7% and a slope efficiency of 30.2%. The shortest pulse width of 11 ns, the largest single-pulse energy of 2.49 μJ and the highest peak power of 190 W are also obtained.     

Laser diode pumped actively Q-switched Nd:GdVO4 self-Raman laser operating at 1173 nm

A laser diode pumped actively Q-switched Nd:GdVO₄ self-Raman laser operating at 1173 nm is presented. The maximum output power was 2.26 W at an incident pump power of 18 W, with the corresponding optical conversion efficiency of 12.6%. Two different resonator configurations were investigated in order to achieve high output power and efficiency.     

Multi-wavelength operation of LD side-pumped Nd:YAG laser

A dual-wavelength laser at 1064 nm and 1319 nm is obtained by a single Nd:YAG crystal rod. On the basis of 1064 nm and 1319 nm dual-wavelength laser installation, the second harmonic waves at 532 nm and 660 nm can be achieved by using non-linear frequency conversion technology. When 1064 nm and 1319 nm lasers oscillate simultaneously, the maximum output power is 30.5 W and 8.78 W, respectively. When the 1319 nm laser is restrained, we obtain a 35.6 W maximum output power at 1064 nm and by contrary 11.2 W at 1319 nm. The maximum output powers of 532 nm and 660 nm lasers are 5.34 W and 1.353 W when oscillating simultaneously. With one of them restrained, the maximum output power is 6.72 W at 532 nm and 1.90 W at 660 nm. The optimum repetition rate of the acousto-optic Q-switch is 10.5 KHz and 20.5 KHz for 532 nm and 660 nm lasers, respectively. The optical-to-optical conversion efficiency from the fundamental waves to the harmonic waves is 17.5% and 15.4%. The instability is less than 2%.     

Continuous-wave high-power multi-pass pumped thin-disc Nd:GdVO4 laser

A thin-disc Nd:GdVO₄ laser in multi-pass pumping scheme was developed. Continuous-wave output power of 13.9 W at 1.06 μm for an absorbed power at 808 nm of 22 W was demonstrated from a 250-μm thick, 0.5-at.% Nd:GdVO₄ in a 4-pass pumping; the slope efficiency in absorbed power was 0.65, or 0.47 in input power. Output performances were also investigated under diode laser pumping at 879 nm, directly into the emitting ⁴F_3/2 level: maximum power of 3.6 W was obtained at 6.2 W of absorbed power with 0.69 slope efficiency. Compared with pumping at 808 nm, into the highly absorbing ⁴F_5/2 level, improvements of laser parameter in absorbed power (increase of slope efficiency, decrease of threshold) were obtained, showing the advantages of the pumping into the emitting level. However, the laser performances expressed vs. the incident power were modest owing to the low absorption efficiency at 879 nm. Thus, increased number of passes of the medium would be necessary in order to match the performances in input power obtained under 808-nm pumping.     

A new Yb-doped oxyorthosilicate laser crystal: Yb:Gd2SiO5

A new Yb-doped oxyorthosilicate laser crystal, Yb:Gd₂SiO₅ (Yb:GSO), has been grown by the Czochralski (Cz) method. The crystal structure was determined by means of X-ray diffraction analysis. Room temperature absorption and fluorescence spectra of Yb³⁺ ions in GSO crystal were measured. Then, spectroscopic parameters of Yb:GSO were calculated and compared with those of another Yb-doped oxyorthosilicate crystal Yb:YSO. Results indicated that Yb:GSO crystal seemed to be a very promising laser gain media in generating ultra-pulses and tunable solid state laser applications. As expected, the output power of 2.72 W at 1089 nm was achieved in Yb:GSO crystal with absorbed power of only 4.22 W at 976 nm, corresponding to the slope efficiency of 71.2% through the preliminary laser experiment.     

Continuous-wave Ho:GdVO4 laser pumped by Tm-doped fiber laser with a fiber Bragg grating at room temperature

We reported the Ho:GdVO₄ laser pumped by Tm-doped laser with a fiber Bragg grating. 2.03 W continuous-wave Ho:GdVO₄ laser output power is obtained under 10.5 W incident pump power, with the optical-to-optical conversion efficiency and slope efficiency of 19.3% and 32.3%, respectively, at 7 °C. We can see that, the lower the temperature is, the better the laser output character is. The beam quality factor is M² ∼ 1.29 measured by the traveling knife-edge method.     

Generation of 7.8 W at 355 nm from an efficient and compact intracavity frequency-tripled Nd:YAG laser

A high power, quasi-continuous wave ultraviolet laser at 355 nm was obtained by intracavity frequency tripling of a diode side-pumped acousto-optic (AO) Q-switched Nd:YAG laser. Type II critical phase-matched KTP and LBO crystals were used for the second harmonic generation and the third harmonic generation, respectively. Under the pump power of 180 W, 7.8 W average output power at 355 nm was obtained at 8 kHz with the pulse width of 50 ns, corresponding to the pump-to-ultraviolet conversion efficiency of 4.3%. The peak power and single pulse energies were estimated to be 18.8 kW and 938 μJ. Its far-field divergence was measured to be about 3.8 mrad. The instability of the 355 nm laser was less than 1% at an output power of 6.3 W for 2 h operation.     

Bulk and surface properties of spinel Co3O4 by density functional calculations

DFT calculations are employed to bulk and surface properties of spinel oxide Co₃O₄. The bulk magnetic structure is calculated to be antiferromagnetic, with a Co²⁺ moment of 2.631 μ_B in the antiferromagnetic state. There are three predicted electron transitions O(2p) → Co²⁺(t_2g) of 2.2 eV, O(2p) → Co³⁺(e_g) of 2.9 eV and Co³⁺(t_2g) → Co²⁺(t_2g) of 3.3 eV, and the former two transitions are close to the corresponding experimental values 2.8 and 2.4 eV. The naturally occurring Co₃O₄ (1 1 0) and (1 1 1) surfaces were considered for surface calculations. For ideal Co₃O₄ (1 1 0) surfaces, the surface relaxations are not significant, while for ideal Co₃O₄ (1 1 1) surfaces the relaxation of Co²⁺ cations in the tetrahedral sites is drastic, which agrees with the experiment observation. The stability over different oxygen environments for possible ideal and defect surface terminations were explored.     

Compact 7.8-W 1-GHz-repetition-rate passively mode-locked TEM00 Nd:YVO4 laser under 880 nm diode direct-in-band pumping

We demonstrate a compact high-power passively mode-locked TEM₀₀ Nd:YVO₄ laser with 1 GHz repetition rate by 880 nm diode direct-in-band pumping. At the absorbed pump power of 19.9 W, a stable mode-locked output power of 7.8 W was obtained with the pulse width of 21.4 ps and a beam quality factor of M² < 1.5, corresponding to an optical-optical conversion efficiency of 39.2%.     

Diode-end-pumped Nd:CaYAlO4 mode locked laser

A diode pumped passively mode locked Nd:CaYAlO₄ (Nd:CYA) laser is demonstrated for the first time to the authors' knowledge. Using a V-shaped cavity and a semiconductor saturable absorbing mirror (SESAM), self-started mode locking of the laser is experimentally achieved. The mode-locked pulses are as short as 3.9 ps at a central wavelength of 1080.2 nm. The mode-locked laser produced a maximum average output power of 2.25 W with a slope efficiency of 23.2%.