CW and quasi-CW diode-laser-pumped Nd:SSGM

Fiber-coupled laser diodes were used to pump a Nd-doped SGGM slab (Nd: 4at.%) in the Continous Wave (CW) and Quasi-CW (Q-CW) modes of operation. The optical-to-optical and slope efficiencies were determined in both cases.     

Diode end-pumped high-efficiency Nd:YAG laser

A close-coupled scheme has been developed to end-pump the Nd:YAG rod using diode lasers tuned to 808 nm. By using a single diode laser, an optical-to-optical conversion efficiency of about 40% has been demonstrated in the multimode operation at 1064 nm.     

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.     

High-average-power flashlamp-pumped Nd:Glass fiber-bundle laser

Flashlamp-pumped high-gain fiber-bundle lasers consisting of multimode phosphate glass fibers have been investigated. By optimizing the fiber number and the outcoupling reflectivity in dependence on the pump conditions, high single-pulse energies in excess of 1 J as well as high-average-power extraction up to 100 W at a pulse repetition frequency of 100 Hz could be obtained from slim fiber-bundle lasers. Fiber numbers in the range of 150–250 and reflectivities between 35% and 50% have been found to provide reliable performance.     

Pulse shortening to 25 ps in a cw mode-locked Nd: YAG laser by introducing an intracavity etalon

The gain spectrumG(v) of a cw mode-locked Nd:YAG laser is flattened by a properly designed intracavity etalon. The increase in amplification bandwidth allows the generation of very stable trains of pulses shorter than that of standard systems. A reduction of the pulse width from 70 to 25 ps is observed by incorporating a BK 7 platelet of 420 m thickness in the resonator. The properties of the laser are investigated as a function of the thickness and the orientation angle of the etalon. The laser performance is found to be considerably influenced by the fact that the Nd³⁺ laser transition at 1.064 m consists of a line doublet.     

A flashlamp-pumped 946 nm Nd:YAG laser

Generation of 946 nm radiation from a commercially available, flashlamp-pumped Nd:YAG laser was investigated. By suppression of the high-gain 1.064 m transition and with a specially designed cooling system, a stable emission at 946 nm was achieved in the temperature range 300–240 K. At a repetition rate of 10 Hz laser output powers of 100mW and 500 mW were obtained at room temperature and 240 K respectively. The temperature dependence of unsaturated gain, slope efficiency and pumping threshold were determined.S. Dimov is supported by a fellowship from the Alexander von Humboldt Foundation     

Investigation on amplitude and frequency noise of injection-locked diode-pumped Nd:YAG lasers

Amplitude and frequency stability of an injection-locked diode-pumped miniature Nd:YAG ring laser were measured. The mechanism of amplitude-noise transfer to the injection-locked slave laser was experimentally investigated and consequences for the injection locking of solid-state lasers operating at high output powers are discussed.     

Q-switched and continuous-wave mode-locking of a diode-pumped Nd:Gd0.64Y0.36VO4−Cr4+:YAG laser

We report on a diode-pumped passively mode-locked Nd:Gd_0.64Y_0.36VO₄ laser with a Cr⁴⁺:YAG saturable absorber. Q-switched mode locking (QML) with 90% modulation depth was obtained. The peak power of the mode-locked pulse near the maximum of the Q-switched envelope was estimated to be about 1.7 MW at the pump power of 12 W. Besides QML, continuous-wave mode locking was also experimentally realized, for the first time to our knowledge, in the laser under a strong intracavity pulse energy fluence. The mode-locked pulse width is about 2.96 ps at a repetition rate of 161.3 MHz.     

Tunable and high-energy Q-switched operation of an alexandrite slave ring laser

Narrow bandwith tunable Q-switched operation of an alexandrite oscillator was used for injection-locking of a high-energy alexandrite slave ring laser. Pulses with up to 600 mJ in energy over a 600 cm^–1 tuning range were obtained.     

Diode-pumped Nd:YAG laser using reflective pump optics

We have examined the performance of a diode-laser side-pumped Nd:YAG laser using elliptical mirrors to focus the output of 6 × 10 W laser-diode arrays into the Nd: YAG rod. The multimode cw output power was 14 W with an optical to optical efficiency of 29%. With a resonator designed for TEM₀₀ mode operation 12 W of output was achieved.     

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.     

Cr4+:YAG as passive Q-switch for a Nd:YALO oscillator with an average repetition rate of 2.7 kHz,TEM00 mode and 13 W output

A conventional pulsed Nd:YALO oscillator was passively Q-switched with a Cr⁴⁺:YAG crystal. During each of the flashes, with a repetition rate of 100 Hz, a burst of 27 Q-switch pulses with a half width (FWHM) of 140 ns was generated. The minimal pulse-to-pulse time interval within the burst was about 5 µs. The average repetition rate of these Q-switch pulses was 27 × 100 Hz. Nd: YALO as active material does not show any thermally induced birefringence and therefore a good TEM₀₀ mode was realized despite the high thermal load of the crystal. The 4 × 79 mm laser rod produced 13 W average output power at 1080 nm with an efficiency of 0.5%. In contrast to earlier used LiF:F ₂ ^– absorbers as passive Q-switch the Cr⁴⁺:YAG-crystals did not bleach and therefore the system operated very stable and reliable.     

Additive pulse mode-locked Nd: YAG laser

Additive pulse mode locking applied to lamppumped Nd: YAG lasers results in an attractive source of picosecond pulses at 1.06 m or 1.32 m with average powers at the Watt level. We provide detailed information on construction and operation and give data on performance. A modified active stabilization scheme allows not only improved stability of operation but also insight into the dynamics of pulse formation.     

A High-Energy Good-Beam-Quality Krypton-Lamp-Pumped Nd：YAG Solid-State Laser with One Pump Cavity

We investigate a high-energy good-beam-quality krypton-lamp-pumped pulsed Nd： YA G solid-state laser with one pump cavity. The symmetrical resonator laser is developed and is rated at 80 J with beam parameter product 12mm mrad. The total system electro-optics efficiency of the lamp-pumped YAG laser is as high as 3.3% and the stability of output energy is ±2% with pulse width tunable between 0.1 ms and 10ms. The experimental results are consistent with the theoretical analysis and simulation.     

Three-Rod Resonator for Krypton Lamp Pumped 1.8 kW Continuous-Wave Nd：YAG Laser

A three-rod series resonator cw Nd:YAG laser suitable for the industrial applications is presented. The symmetrical resonator laser has been developed and is rated at 1820-W output power with beam parameter product 24 mm.mrad. By utilizing the symmetrical resonator design, the characteristic of beam with multi-rod is not obviously decreased compared with that of a single one. The system total electro-optics efficiency of lamp pumped YAG crystal is as high as 4.0%. The main factors, which affect output power and beam quality of high power solid-state laser module, are theoretically analysed.     

Temperature dependence of efficiency and thermal lensing of diode-laser-pumped Nd:YAG lasers

Efficiencies, lasing thresholds and thermal lensing of a Nd:YAG rod side-pumped with two 10 W diode-laser-arrays are measured for various rod temperatures between 80 K and 380 K. The threshold is reduced by a factor of 2.5–4 on cooling from room temperature to about 100 K, while the slope efficiency is increased by between 0% and 50% depending on the reflectivity of the outcoupling mirror. Extrapolation to a 240 W pumped laser gives an increase in optical efficiency of 25% to 30%. The thermal lensing measured with a beam deflection and an interferometric method is reduced by a factor of 10.     

Spectroscopic characterization and laser performance of diode-laser-pumped Nd: GdVO4

We have carried out a detailed spectroscopic characterization of Nd: GdVO₄, a new laser crystal with high effective absorption and emission cross sections. The accidental degeneracy of the upper⁴ F _3/2 laser level decreases the number of emission lines and creates -together with the anisotropic crystal field - high emission cross sections (7.6 × 10^–19 cm² at 1.06 µm and 300 K). In addition, the lines are strongly homogeneously broadened (1.6 nm for the 808.4 nm diode-laser pump transition). The temperature dependences of lifetime, linewidths, and cross sections have been determined. Slope efficiencies up to 57% with respect to the absorbed diode-laser pump power and output powers up to 0.8 W have been achieved at 1.06 µm from a 2 mm long crystal. Intracavity second-harmonic generation, using a KTP crystal, is demonstrated.     

A new 3D multipass amplifier based on Nd:YAG or Nd:YVO4 crystals

We report on new, simple and efficient multipass amplifiers using prisms or corner cubes to perform several passes in different planes of incidence. This scheme provides an optimised overlap between the signal passes and the pumped volume. We investigated our amplification geometry with Nd:YAG and Nd:YVO₄ crystals: the use of a low-doped (0.3%) Nd:YVO₄ crystal allowed better thermal behaviour and higher performance. We amplified a pulsed microlaser (110 mW of average power at 1064 nm) and obtained a diffraction-limited output beam with an average power of 5.7 W for 15 W of pump power and a small-signal gain of 56 dB in a six-pass configuration. Received: 5 March 2002 / Revised version: 6 June 2002 / Published online: 25 September 2002 RID="*" ID="*"Corresponding author. Fax: +33-1/6935-8700, E-mail: Sebastien.forget@iota.u-psud.fr     

High power single-longitudinal-mode operation in a twisted-mode-cavity laser with a c-cut Nd:GdVO4 crystal

A twisted-mode-cavity laser was established by using a piece of c-cut Nd:GdVO₄ crystal as the lasers active material. Output spectra were scanned by a scanning Fabry–Perot interferometer, which demonstrated that the single-longitudinal-mode laser operation was realized in the twisted-mode-cavity laser configuration. A maximum single-longitudinal-mode laser output power of 2.1 W was obtained when the pump power was 11.5 W. The pump slope efficiency was about 20.0%. A passively Q-switched single-longitudinal-mode laser was also achieved in a twisted-mode cavity by inserting a piece of Cr⁴⁺:YAG as an intracavity saturable absorber. The Q-switched single-longitudinal-mode laser pulse duration was measured to be 100 ns and the single-pulse energy was about 40.0 J.     

Q-switched and mode-locked diode-pumped Nd:YAG laser with an LT-GaAs

Simultaneous Q-switching and mode-locking (QML) is accomplished in a diode-pumped Nd:YAG laser using low-temperature GaAs (LT-GaAs) as the saturable absorber, which also acts as an output coupler at the same time. The repetition rate of the Q-switched envelope increased from 25 to 40 kHz as the pump power increased from 2.2 to 6.9 W. The mode-locked pulses inside the Q-switched pulse envelope had a repetition rate of 714 MHz. A maximum average output power of 770 mW was obtained.