High-power continuous-wave cr(4+):forsterite laser

The temperature and pump power dependence of infrared luminescence of Cr(4+):forsterite are measured. It is demonstrated that temperature-dependent fluorescence in Cr(4+):forsterite is the major reason for saturation of the output power of a continuous-wave laser. At higher pump intensities the temperature rise inside the crystal becomes significant, and even outside cooling does not help to prevent significant reduction of the laser performance. These measurements serve as a guideline to construct a high-power continuous-wave Cr(4+):forsterite laser.     

Saturable Absorber Cr(4)+:(Sr, Ca)Gd(4)(SiO(4))(3)O Crystals as Q Switches for a Diode-Pumped Nd(3)+:KGd(WO(4))(2) Laser

Passive Q switching of a diode-pumped Nd(3+):KGd(WO(4))(2) laser is demonstrated by use of Cr(4+):SrGd(4)(SiO(4))(3)O and Cr(4+):CaGd(4)(SiO(4))(3)O crystals as saturable absorbers. An average output power of 40 mW was obtained with a pulse repetition rate of ~0.4 MHz.     

Continuous-Wave and Passively Mode-Locked Operation of a Cunyite (Cr(4+):Ca(2)GeO(4)) Laser

Continuous-wave and mode-locked Cr(4+):Ca(2)GeO(4) lasers that use a fiber laser pump source were demonstrated. The continuous-wave Cr(4+):Ca(2)GeO(4) laser yielded a maximum output power of 415 mW at 1420 nm and a tuning range of 1335-1492 nm. With a saturable-absorber mirror, 60-ps pulses and 110-mW maximum output power were generated from a passively mode-locked Cr(4+):Ca(2)GeO(4) laser.     

Passively Q-Switched Yb:YAG Laser with Cr(4+):YAG as the Saturable Absorber

By using a continuous-wave Ti:sapphire laser as a pumping source, we demonstrated a passively Q-switched Yb:YAG laser at room temperature with Cr(4+):YAG as the saturable absorber. We achieved an average output power of as much as 55 mW at 1.03 mum with a pulse width (FWHM) as short as 350 ns. The initial transmission of the Cr(4+):YAG has an effect on the pulse duration (FWHM) and the repetition rate of the Yb:YAG passively Q-switched laser. The Yb:YAG crystal can be a most promising passively Q-switched laser crystal for compact, efficient, solid-state lasers.     

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.     

Semianalytical thermal analysis on a Nd:YVO(4) crystal

Based on analytical theory of anisotropy, distributions of thermal distortion and temperature field within a diode-end-pumped rectangular Nd:YVO(4) laser crystal are investigated. A thermal model that matches the actual working state of the laser crystal is established by analyzing the working characteristics of the Nd:YVO(4) laser crystal. A novel method, to the best of our knowledge, is adopted to solve the heat conduction equation of the anisotropic medium. General solutions of the temperature field, thermal strain field, and thermal distortion field of the Nd:YVO(4) crystal are obtained. The effect of anisotropic thermal parameters on the thermal strain field of the Nd:YVO(4) laser crystal is also analyzed quantitatively. Research results show that a maximum temperature rise of 244.9 degrees C and a maximum thermal distortion of 1.99 mum can be obtained in the center of the pump face when the Nd:YVO(4) laser crystal doped with 0.5 at. % Nd(3+) is diode end pumped in the center of the front end face with 15 W output power. This method can be applied to other thermal analyses of laser crystals and offers a theoretical basis to solve thermal problems effectively in the laser system.     

Efficient quasi-continuous-wave and passively Q-switched laser operation of a Nd3+:BaGd2(MoO4)4 cleavage plate

Pumped by a Ti:sapphire laser at 807 nm, efficient quasi-cw and passively Q-switched laser operations have been realized from a 1.1 mm thick, 1.2 at. % Nd(3+):BaGd(2)(MoO(4))(4) cleavage plate in a plano-plano cavity. When the absorbed pump power was 1060 mW, the achieved maximum quasi-cw output power was 580 mW. The slope efficiency and absorbed pump threshold power were 60% and 50 mW, respectively. Using a Cr(4+):YAG crystal with an initial transmission of 85% as the saturable absorber, a pulse laser with 3.0 microJ energy, 30 ns duration, and 52 kHz repetition rate has been obtained when the absorbed pump power was 1060 mW. The polarization characteristic and laser spectra of both the quasi-cw and passively Q-switched lasers have been measured.     

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.     

Polarization-resolved study of diode-pumped passively Q-switched Nd:GdVO4 lasers

By using the natural birefringence of an a-cut Nd:GdVO(4) crystal, we experimentally investigate laser operation under different light polarizations (pi- and sigma-polarized emissions) and compare their performance. The laser performance is further compared with a diode-pumped c-cut Nd:GdVO(4) laser of the same parameters. We show experimentally that the c-cut Nd:GdVO(4) laser could have good passively Q-switched performance in a low-pump-power region but is influenced by other intrinsic laser effects, such as the thermally induced cavity losses; its performance is severely degraded under high pump power. The best passively Q-switched performance obtained in our experiments is from the a-cut pi-polarized laser, which gives the narrowest pulse of 5.4 ns with the highest peak power of 20 kW. Our experimental results show that, to achieve the best performance of the passively Q-switched laser operation, an overall consideration of laser parameters is important.     

Intracavity frequency-doubled femtosecond cr(4+):forsterite laser

The generation of femtosecond optical pulses centered at ~620 nm directly from an all-solid-state laser oscillator is reported. Red pulses with pulse widths of the order of 170 fs were obtained with 24-mW average power at an 81-MHz repetition rate. They were achieved by intracavity frequency doubling of a mode-locked Cr(4+):forsterite laser with a 1-mm-thick beta-BaB(2)O(4) crystal. The process of laser mode locking was modified by surface coating the doubling crystal.     

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%.     

Laser-diode pumped passively Q-switched Nd3+:NaY(WO4)2 laser with Cr4+:YAG saturable absorber

A laser-diode pumped passively Q-switched new type crystal Nd³⁺:NaY(WO₄)₂ (known as Nd:NYW) laser with Cr⁴⁺:YAG saturable absorber has been realized. The dependence of pulse repetition rate, pulse energy, pulse width, and peak power on pump power for different small-signal transmission of Cr⁴⁺:YAG are measured. The coupled rate equations are used to simulate the Q-switched process of laser, and the numerical solutions agree with the experimental results.     

Comparison on performance of passively Q-switched laser properties of continuous-grown composite GdVO4/Nd:GdVO4 and YVO4/Nd:YVO4 crystals under direct pumping

The comparison on performance of passively Q-switched laser properties of continuous-grown composite GdVO(4)/Nd:GdVO(4) and YVO(4)/Nd:YVO(4) crystals under direct pumping to the emitting level was demonstrated. A Cr(4+):YAG crystal was used as saturable absorber. At an incident pump power of 10 W, the average output power, the pulse width, the repetition rate, the pulse energy, and the peak power for a GdVO(4)/Nd:GdVO(4) laser were 1.22 W, 48.1 ns, 121 kHz, 10.1 μJ, and 209.6 W, respectively. And for a YVO(4)/Nd:YVO(4) laser under the same conditions, these output characteristics were 1.26 W, 44.9 ns, 218 kHz, 5.8 μJ, and 128.7 W, respectively.     

Noise characteristics of a Nd:YVO(4) laser pumped by laser diode modulated at high frequency

We report, for the first time to our knowledge, on the noise characteristics of a Nd:YVO(4) laser pumped by a laser diode modulated at high frequency. We have investigated noise characteristics of a Nd:YVO(4) laser pumped by a laser diode that is oscillating in a stable multilongitudinal mode because of modulation by a high-frequency (several hundred megahertz) current. As a result, low-noise operations of -130 dB/Hz above frequencies of 1 MHz have been achieved. This noise level is comparable to the level obtained when pumping a Nd:YVO(4) laser with a laser diode that is oscillating in a single longitudinal mode. However, a noise peak corresponding to relaxation oscillations of the Nd:YVO(4) laser has appeared around a frequency of several hundred kilohertz.     

Periodic pulse oscillation in an intracavity-doubled Nd:YVO(4) laser

We report periodic pulse oscillation in an intracavity-doubled Nd:YVO(4) laser. The pulse oscillation is caused by alternate oscillation between two modes. We investigated improvement of green-light power with the pulse oscillation in a Nd:YVO(4) laser. The pulse oscillation gave a factor of approximately 2 higher average green-light power than that for cw oscillation at the same pumping power.     

Ultrabroadband operation of a cr(4+): forsterite laser by use of a spatially dispersed resonator

Ultrabroadband (half-width of 88 nm) nanosecond Cr(4+):forsterite oscillation was achieved simultaneously in the 1170-1340-nm range (1085 cm(-1)) by use of a spatially dispersed resonator with an intracavity prism pair. The laser demonstrates 4.8% real pump-to-laser efficiency. The oscillation build-up time for different spectral components is around 20 ns and varies by only 2.5 ns in the 1190-1260-nm region, which indicates that the ultrabroadband laser represents a complex multifrequency laser system with nonlinear spectral mode interaction.     

Diode-Pumped Er-Yb:Glass Laser Passively Q Switched by Use of Co(2+):MgAl(2)O(4) as a Saturable Absorber

We report on passively Q-switched operation of a diode-pumped Er-Yb:glass laser with a Co(2+):MgAl(2)O(4) plate as a saturable absorber. Optical pulses with peak power exceeding 2 kW and a pulse length of 2.3 ns have been generated. Single-longitudinal-mode Q-switched operation at 1.53 mum has been obtained by use of the Co(2+):MgAl(2)O(4) plate as an intracavity etalon. A discussion of the optimal Er(3+) concentration as well as optimization of the cavity design is included.     

Diode-laser-pumped 1.328-mum Nd:Sr(5)(PO(4))(3) F laser and its intracavity frequency doubling

Nd:Sr(5) (PO(4))(3) F, known as Nd:S-FAP, is a new material for efficient, miniature diode-pumped solid-state lasers. By using a laser-diode pump operating at 805.4 nm, we successfully lased Nd:S-FAP at 1.328 mum. A slope efficiency of 33.5% and a laser threshold of 18.5 mW have been measured. By using KTP as an intracavity doubling crystal, we also achieved an intracavity frequency Nd:S-FAP laser at 0.664 mum with a threshold power of 18.2 mW, a TEM(00) mode red laser output power of 20.7 mW at 250 mW incident pump power corresponding to an optical efficiency of 8.3%. In addition, we discuss ways to improve efficiency by use of this material.     

Comparative experimental investigation of thermal loading in continuous-wave cr(4 +):forsterite lasers

Results of a detailed experimental study aimed at reducing the thermal loading effects in room-temperature continuous-wave Cr(4+):forsterite lasers are presented. By using a Nd:YAG pump laser operated at 1.06 mum, the effect of the absorption coefficient and crystal cross-sectional area on the power performance of three crystals was compared between 12 and 36 degrees C. Experiments indicated that a low differential absorption coefficient significantly reduces the pump-induced thermal effects and cavity losses that would otherwise give rise to inefficient operation and increased temperature sensitivity. In particular, a Cr(4+):forsterite crystal with an absorption coefficient of 0.57 cm(-1) yielded as much as 900 mW of output power at 1.26 mum and a crystal temperature of 15 degrees C with an incident pump power of only 7.6 W. To the author's knowledge, the demonstrated slope efficiency of 30% represents the highest continuous-wave power performance reported to date from this laser system at elevated temperatures.     

Intracavity second-harmonic generation at 320 nm of an actively Q-switched Pr:LiYF4 laser

We demonstrate pulse laser operation of a Pr:LiYF(4) laser pumped by InGaN laser diodes (444 nm) using an acousto-optic modulator. We obtained a maximum laser peak power of 167 W (4 μJ/pulse) with a pulse width of 24 ns at an 11 kHz repetition rate for a 63 nm wavelength. Employing an 8 mm long lithium triborate nonlinear crystal in the laser cavity, we obtained a maximum peak power of 55 W (2.7 μJ/pulse) at 320 nm, which corresponds to a conversion efficiency of 69% with respect to the fundamental laser energy. The UV laser pulse width was 36 ns.