1053-nm-wavelength selection in a diode-laser-pumped Nd:YLF laser

We report on a Nd:YLF laser that operates at 1053 nm without optical intracavity elements for the suppression of the stronger 1047-nm transition. The Nd:YLF crystal is end pumped by a fiber optically coupled 10-W diode-laser bar. The different thermal-lensing focal lengths of the two main lasing wavelengths in a plane-parallel resonator were used to achieve the selection by tilting the end mirror slightly from its optimum position for maximum output power. With 9.8-W cw diode-laser-pumping power the 1053-nm Nd:YLF laser produces a maximum output power of 1.9 W in cw operation and nearly 1 W of average power at a Q-switch repetition rate of 15 kHz. The highest slope efficiency of 47% achieved in cw operation.     

High-power cw 671 nm output by intracavity frequency doubling of a double-end-pumped Nd:YVO4 laser

We report on a high-power (cw) red laser at 671 nm by intracavity frequency doubling of a double-end-pumped 1342 nm Nd:YVO4 laser based on the nonlinear crystal LiB3O5. A red output power of 3.38 W is obtained for a pump power of 27 W, with corresponding optical-to-optical efficiency of 12.5%. The 671 nm beam is nearly diffraction limited.     

1.86 W cw single-frequency 1319 nm ring laser pumped at 885 nm

A 1.86 W cw single-frequency 1319 nm laser was produced by using an 885 nm-pumped Nd:YAG crystal with a compact four-mirror ring cavity, for the first time to our knowledge. The Nd:YAG produced a slope efficiency of 21% and an optical-to-optical efficiency of 18% with respect to the absorbed diode pump power. A near-diffraction-limited beam with M(2)=1.2 was achieved under the maximum output power.     

Efficient continuous-wave radiatively cooled cr(4+):forsterite lasers at room temperature

Results of a detailed experimental investigation aimed at reducing the thermal loading problem in a cw Cr(4+):forsterite laser at elevated temperatures are presented. From a Cr(4+):forsterite crystal with a differential absorption coefficient of 0.57 cm(-1), as much as 900 mW of cw output power has been obtained at 1.26 mum and at a crystal boundary temperature of 15 degrees C with an absorbed pump power of only 4.5 W at 1.06 mum. No chopping of the pump beam was necessary. An efficient radiative cooling technique was further employed to cool the laser and no subsequent power fading was observed. To the author's knowledge, the measured absorbed power slope efficiency of 29.5% represents the highest cw power performance reported to date from a Cr(4+):forsterite laser pumped by a Nd:YAG laser around room temperature. The role of the low differential absorption coefficient in the reduction of thermal loading is further elucidated by presenting comparative cw power performance data with a second Cr(4+):forsterite crystal having a differential absorption coefficient of 1.78 cm(-1) in the temperature range between 12 and 35 degrees C. Finally, some interesting multipulse effects of the laser observed in the millisecond regime during quasi-cw operation at 50% duty cycle are described.     

High-power efficient continuous-wave TEM00 intracavity frequency-doubled diode-pumped Nd:YLF laser

We describe experimental results with a diode-pumped, intracavity-doubled cw Nd:YLF laser in multilongitudinal mode and TEM00 spatial transverse mode with a critical phase-matched lithium triborate crystal. Taking into account the thermal effects of Nd:YLF, energy-transfer upconversion, and the thermal fracture limit, we set up a power-scaling model to optimize and design a fundamental diode-pumped Nd:YLF laser. A highly efficient second-harmonic laser was achieved, based on the optimized cavity design. A second-harmonic-generation output power of 20.5 W at a wavelength of 527 nm was obtained at an incident pump power of 60 W, corresponding to an optical-to-optical efficiency of 34.2%. The TEM00 mode green laser operates at a measured M2 parameter of 1.2. The instability of the green laser power is less than +/- 1% RMS.     

Continuous-wave laser characteristics of a Nd3+:LaB3O6 cleavage microchip and the influence of thermal effects

With pumping by a Ti:sapphire laser, the cw laser characteristic of a 5.6 at. %, 0.5 mm thick Nd3+:LaB3O6 cleavage microchip in an end-pumped plano-plano resonator is researched. A slope efficiency of up to 49% and a maximum output power of 530 mW are obtained at an absorbed pump power of 1.16 W and an optimal output coupler transmission of 3.2%. Choppers with different duty cycles are used to change the thermal effects in the microchip, and the influences of thermal effects on the laser characteristics of the Nd3+:LaB3O6 cleavage microchip are investigated.     

Diode-side-pumped 131 W, 1319 nm single-wavelength cw Nd:YAG laser

A diode-side-pumped high-power 1319 nm single-wavelength Nd:YAG continuous wave (cw) laser is described. Through reasonable coating design of the cavity mirrors, the 1064 nm strongest line as well as the 1338 nm one have been successfully suppressed. The laser output powers corresponding to four groups of different output couplers operating at 1319 nm single wavelength have been compared. The output coupler with the transmission T=5.3% has the highest output power, and a 131 W cw output power was achieved at the pumping power of 555 W. The optical-optical conversion efficiency is 23.6%, and the slope efficiency is 46%. The output power is higher than the total output power of the dual-wavelength laser operating at 1319 nm and 1338 nm in the experiment.     

Laser-diode-pumped Nd:YAG active-mirror laser

We describe a simple design, laser-diode-pumped cw Nd:YAG active-mirror laser and present a thermal analysis of the crystal. A cw output power of 2.4 W and an M(2) beam quality value of less than 1.9 at an incident pumping power of 8.9 W were obtained. From the thermal analysis we predict that the output power can be increased by increasing the pump beam diameter and the pump power at a constant excitation density.     

Chromium-doped forsterite laser with 1.1 W of continuous-wave output power at room temperature

We demonstrate stable continuous-wave operation of a Cr:forsterite laser pumped by a cw Nd:YAG laser at 288 K. We use no choppers to limit the duty cycle of the cw system. The proper adjustment of the pump- and cavity-mode overlap based on the ABCD concept simulation eliminates the output power decrease at the high-level pump power. An output power of 1.1 W and slope efficiency of 26% are derived.     

Passive Q Switching of a Diode-Pumped 946-nm Nd:YAG Laser with 1.6-W Average Output Power

As much as 1.6-W average output power was emitted in a simple setup from a diffusion-bonded Nd:YAG rod with 70-100-ns Q-switched pulses at 946 nm and repetition frequencies between 15 and 45 kHz at 22-W incident diode-pump power. A Cr(4+):YAG crystal with a bleachable loss of approximately 2.5% and a length of 0.5 mm was used as a saturable absorber. The extraction efficiency was 47% in comparison with the continuous-wave laser output power of 3.37 W in the free-running regime.     

Multipass pumped Nd-based thin-disk lasers: continuous-wave laser operation at 1.06 and 0.9 microm with intracavity frequency doubling

The laser performances of the 1.06 microm (4)F(3/2) --> (4)I(11/2) four-level transition and of the 0.9 microm (4)F(3/2) --> I(9/2)4 quasi-three-level transition were investigated using multipass pumped Nd-based media in thin-disk geometry. When pumping at 0.81 microm into the (4)F(5/2) level, continuous-wave laser operation was obtained with powers in excess of 10 W at 1.06 microm, in the multiwatt region at 0.91 microm in Nd:YVO(4) and Nd:GdVO(4), and at 0.95 microm in Nd:YAG. Intracavity frequency-doubled Nd:YVO(4) thin-disk lasers with output powers of 6.4 W at 532 nm and of 1.6 W at 457 nm were realized at this pumping wavelength. The pumping at 0.88 microm, which is directed into the (4)F(3/2) emitting level, was also employed, and Nd:YVO(4) and Nd:GdVO(4) thin-disk lasers with ~9 W output power at 1.06 microm and visible laser radiation at 0.53 microm with output power in excess of 4 W were realized. Frequency-doubled Nd:vanadate thin-disk lasers with deep blue emission at 0.46 microm were obtained under pumping directly into the (4)F(3/2) emitting level.     

Improvement in continuous-wave laser performance of disordered Yb:CNGG crystal

We report on a significant improvement in cw laser performance of the disordered Yb:CNGG crystal. Very efficient cw laser operation is demonstrated at room temperature with a 3.5 mm thick crystal end pumped by a diode laser, generating an output power of 5.15 W with an optical-to-optical efficiency of 46%, whereas the slope efficiency amounts to 80%.     

Theoretical and experimental study on passive mode-locking composite Nd:GdVO4/Nd:GdVO4/Nd:GdVO4 lasers

Stable passive mode-locking multi-segment composite Nd:GdVO₄ lasers with a semiconductor saturable absorber mirror were demonstrated for the first time. For the composite crystals, the output power increased linearly with the increase of the incident pump power, showing excellent thermo-mechanical performances. While for the conventional crystal, power saturation was observed when the incident pump power exceeded 8.79 W. The maximum average output power of 1.465 W was achieved by Nd(0.1%):GdVO₄/Nd(0.5%):GdVO₄/Nd(1%):GdVO₄ composite crystal at an incident pump power of 9.28 W. The largest pulse energy of 14.90 nJ and the highest peak power of 0.53 kW with a pulse duration of 28.0 ps were also obtained by using the same composite crystal, revealing that the multi-segment composite crystal with a proper combination of Nd³⁺-doped concentrations could obtain the optimal laser performance.     

Intracavity frequency doubling and Q switching in diode-laser-pumped Nd:YVO(4) lasers

A highly efficient and compact Nd:YVO(4) laser is proposed. In cw operation, a single-longitudinal-mode output of 95 mW and a multilongitudinal-mode output of 435 mW have been observed at 1.06 μm with a 1-W diode laser. Using a KTP crystal in the short laser cavity, a green output of 105 mW was generated. A Q-switched pulse with a peak power of 230 W and a pulse width of 8 ns was obtained with the intracavity KTP crystal, which was used as both an electro-optic Q switch and a frequency doubler.     

Efficient cw end-pumped, end-cooled Nd:YVO(4) diode-pumped laser

Using a novel end-pumped, end-cooled geometry, we demonstrated a Nd:YVO(4) cw laser that produces close to 2 W of single-mode output when pumped by a high-brightness 100-mum-core diode fiber source. An optical-optical conversion efficiency of 49% was obtained. Beam quality was found to be nearly diffraction-limited (M(2) = 1.08) and independent of pumping power.     

Passively Q-Switched Diode-Pumped Continuous-Wave Nd:YAG-Cr(4+):YAG Laser with High Peak Power and High Pulse Energy

A high peak power and high pulse energy passively Q-switched diode-pumped cw Nd:YAG laser at 1.064-mum wavelength has been demonstrated with Cr(4+):YAG crystal as the saturable absorber. The average output power of 7-12 W and pulse duration of 100-250 ns was obtained with kilohertz repetition rates. The highest peak power and pulse energy obtained were 30 kW and 3.4 mJ, respectively. All the output resulted from the TEM(00) mode with M(2) < 1.1. The thermal lensing effect of the saturable absorber was investigated, demonstrating that it played an important role in optimization of the output.     

Tunable diode-pumped and frequency-doubled Cr:LiSAF lasers

The performance of a diode-pumped Cr:LiSAF laser and its intracavity frequency-doubled operation is reported. Close to 1 W of quasi-cw power at 870 nm was obtained in multimode operation. Power in excess of 20-mW cw of TEM(00) second-harmonic power at 435 nm has also been obtained by using a lithium triborate crystal with an infrared-to-visible conversion efficiency of 33%. This result is believed to be the highest yet reported for a true cw blue output from a diode-pumped Cr:LiSAF system. However, the maximum attainable output power was limited by thermal fluorescence quenching. The effect of the pump size on the temperature rise and on the small-signal gain is investigated.     

Anisotropy in laser performance of Yb:GdCa4O(BO3)3 crystal

We report distinct laser performance of Yb:GdCa(4)O(BO(3))(3) crystals cut along different principal optical axes using an unpolarized diode pump. The continuous-wave (cw) laser oscillation generated with y-cut crystal is polarized either with E parallel x or with E parallel z depending on the output coupling (T) utilized; a specific T=3% leads to a special situation in which the two orthogonal polarization states coexist oscillating at different wavelengths. The laser oscillation achieved with x- and z-cut crystals is also polarized, but with a fixed polarization of E parallel z and E parallel x, respectively. The most efficient laser operation is obtained with the y-cut crystal, generating a cw output power of 7.35 W at 1083-1085 nm with an optical-to-optical efficiency of 63%, the slope efficiency being as high as 84%.     

Efficient Nd:YAG Laser Frequency Doubling with Periodically Poled KTP

Periodically poled flux-grown KTiOPO(4) was used for efficient extracavity 1064-nm Nd:YAG laser frequency doubling. A conversion efficiency exceeding 65% was obtained in Q-switched operation, and 1.34 W of average frequency-doubled power was generated with 2.2 W of mode-locked laser output. The conversion efficiency is approximately two times higher for periodically poled KTP than for conventional type II phase-matched KTP. The measurements indicate that periodically poled KTP is less susceptible to optical damage than type II KTP.     

Efficient Nd:YAG laser end pumped by a high-power multistripe laser-diode bar with multiprism array coupling

A 10-W laser-diode bar, a multistripe monolithic laser-diode array, has been used to end pump Nd:YAG. Twelve beams emitted from 12 stripes, spaced 800 μm apart, of a 1-cm linear diode array were collimated with a multiprism array consisting of 14 prismlets with 800-μm width to pump the Nd:YAG facet. The maximum Nd:YAG cw output power at 1064 nm of 3 W was obtained at 10-W laser-diode-bar power with a slope efficiency of 35%, and a TEM(00) spatial mode with values of beam-quality factor M(2) of 1.29 and 1.76 in the planes perpendicular and parallel to the junction, respectively. A pulse width of 25.2 ns (1-kHz repetition) was obtained in acousto-optic Q-switched operation.