Compact fibre-laser-pumped Ho:YLF oscillator–amplifier system

We developed a compact Ho:YLF oscillator–amplifier system in a novel setup to utilise the unpolarised pump power from a fibre laser efficiently, and produced 21.3 mJ at 1 kHz, with an M ² better than 1.1. The amplified energies agreed well with the predicted values from a two dimensional rotational symmetric amplifier model that we developed. The model considers upconversion losses and ground-state depletion, as well as the spatial distribution of the pump beam.     

High-power master-oscillator power-amplifier with optical vortex output

A high-power master-oscillator power-amplifier with optical vortex output is reported. The master oscillator for an optical vortex seed beam is a simple two-mirror Nd:YAG laser using a fiber-based pump beam conditioning scheme. The seed is amplified in a double-clad multimode fiber amplifier end-pumped by a high-power diode laser at 975 nm yielding 10.7 W of continuous-wave output at 1064 nm in the first-order Laguerre–Gaussian beam with M ² ≈ 2.11 for an absorbed pump power of 17.5 W, corresponding to a slope efficiency of ~59 %. The ring-shaped intensity profile and the wave front handedness of the seed beam were well preserved in the fiber amplifier. The prospects of power scaling via this approach are discussed.     

120 W high repetition rate Nd:YVO<Subscript>4</Subscript> MOPA laser with a Nd:YAG cavity-dumped seed laser

A master oscillator power amplifier (MOPA) system in which the output from an end-pumped Nd:YAG oscillator cavity dumped at 500 kHz is scaled up by a four-stage Nd:YVO₄ amplifier is reported. Decrease in extraction efficiency of the amplifier chain with crystals different from that in the oscillator was analyzed. With the 5.4 W seed output, 118 W of power was extracted from the amplifier chain at the pump power of 345 W, with an extraction efficiency of 34.2% and an overall optical–optical efficiency of 30.9% for the MOPA system. The beam quality factors were measured as M _x ²=1.45 and M _y ²=1.59 in two orthogonal directions, respectively.     

High-beam-quality, 5.1 J, 108 Hz diode-pumped Nd:YAG rod oscillator-amplifier laser system

A high efficiency, high beam quality diode-pumped Nd:YAG master oscillator power-amplifier (MOPA) laser with six amplifier stages is demonstrated. The oscillator with two-rod birefringence compensation was designed as a thermally determined near hemispherical resonator, which presents a pulse energy of 223 mJ with a beam quality value of M² = 1.29 at a repetition rate of 108 Hz. The MOPA system delivers a pulse energy of 5.1 J with a pulse width of 230 μs, a M² factor of 3.6 and an optical-to-optical efficiency of 38.5%. To the best of our knowledge, this is the highest pulse energy for a diode-pumped Nd:YAG rod laser operation with a high beam quality and a pulse width of hundreds of microseconds at a repetition rate of over 100 Hz.     

A comparison of resonantly pumped Ho:YLF and Ho:LLF lasers in CW and Q-switched operation under identical pump conditions

Singly 0.5 at.% Ho doped crystals of YLiF₄ (YLF) and LuLiF₄ (LLF) are studied under identical pump conditions in continuous-wave (CW) and Q-switched operation. Longitudinal end-pumped CW laser performance shows Ho:LLF to have a slightly lower threshold and a slightly higher slope efficiency with respect to absorbed pump power than Ho:YLF. Both lasers were operated on π-polarization. At a cavity output coupling of 20% and a crystal length of 30 mm, the Ho:LLF (Ho:YLF) laser yielded 18.8 W (18 W) of CW output at a wavelength of 2067.8 nm (2064.0 nm) for 41.4 W (42.2 W) of absorbed pump power with a slope efficiency of 67.1% (65.6%) and an optical-to-optical efficiency of 45.4% (42.6%) with respect to absorbed pump power. With the same output coupling and a crystal length of 40 mm, the Ho:LLF (Ho:YLF) laser yielded 20.5 W (18.1 W) of CW output at a wavelength of 2067.7 nm (2064.3 nm) for 51.5 W (50.0 W) of absorbed pump power with a slope efficiency of 58.4% (55.4%) and an optical-to-optical efficiency of 39.8 (36.1%) with respect to absorbed pump power. The influence of the temperature of the cooling mount on CW laser performance was studied and showed very similar results for both laser materials. At full pump power, a slope of −155 mW/°C (−149 mW/°C) was observed for the Ho:LLF (Ho:YLF) laser with a crystal length of 30 mm. In Q-switched operation, the Ho:LLF (Ho:YLF) laser produced 37 mJ (38.5 mJ) at a repetition rate of 100 Hz with a pulse duration of 38 ns (35 ns) at a wavelength of 2053.1 nm (2050.2 nm) with a slope efficiency of 30.3% (31%) and an optical-to-optical efficiency of 14.2% (13.9%) with respect to absorbed pump power. The beam quality was nearly diffraction limited (M ²<1.1).     

Injection-Seeded 500 Hz Repetition Rate High Peak Power Single-Frequency Nd:YAG Laser for Mid-Infrared Generation

We develop an injection-seeded single-frequency neodymium-doped yttrium aluminum garnet (Nd:YAG) laser with 500 Hz repetition rate and high peak power. The laser construction is designed as seed injection and master oscillator power amplifier (MOPA) including single-frequency master oscillator, extra-cavity frequency doubling crystal, and round-trip power amplifier. The master oscillator can emit 1,064 nm laser of 8.4 mJ with 6.8 ns pulse width at the pump energy equal to 23 mJ. A green laser energy of 1.1 mJ is obtained by setting the proper temperature of the LBO crystal. The pulse energy of 1,064 nm laser decreases to 6.5 mJ after passing through the LBO crystal and rises to 25.3 mJ after a round-trip power amplifier corresponding to the extraction efficiency of 29%. The final output pulse width is 6.5 ns, representing a peak power of 3.9 MW. The 1,064 nm laser beam quality factor M² of the master oscillator and the amplified one are 1.3 and 1.5, respectively. The laser will be used to generate mid-infrared where the 532 nm laser with narrow pulse width is to pump sheet optical parametric oscillator (OPO) and the 1,064 nm laser with high peak power to pump the OPO.     

Theory of Pr:ZBLAN ultraviolet upconversion fiber master oscillator power amplifier

A theoretical study for ultraviolet upconversion fiber master oscillator power amplifier (MOPA) based on the transition from the 4f5d state to the ³H₄ ground state in Pr³⁺:ZBLAN fiber is performed by using steady population rate equations and propagation equations. The variation of the output power with the fiber length of master oscillator and MOPA and the launched pump powers, the dependence of the slope efficiency on the fiber length of master oscillator and MOPA, and the optimum fiber length of MOPA as a function of the launched pump powers, are calculated. Both the output power and the slope efficiency of MOPA are 2-3 times those of the simplex oscillator. It is found that the UV upconversion fiber MOPA system can effectively improve the output power and the slope efficiency of laser.     

AOM fourfold pass for efficient Q-switching and stable high peak power laser pulses

We report on a scheme for efficient acousto-optical Q-switching. A flash lamp pumped Nd:YAG oscillator with an acousto-optic modulator (AOM) fourfold pass configuration is presented. The setup combines two important advantages: enhancement of the diffraction efficiency by additional AOM passes and a compact oscillator design in spite of an extension of the optical path length. A flash lamp pumped oscillator with an average output power of 7 W and a beam quality of M² = 1.2 is developed. The system operates with a 100 Hz repetition rate for the flash lamps. In each pumping pulse a pulse train of 1 up to 40 Q-switched laser pulses is generated. The pulse duration is from 15 to 120 ns. In comparison to a former setup (AOM double pass) the AOM fourfold pass configuration allows single pulses with energy above 20 mJ and a pulse peak power of more than 1 MW. In addition, the beam profile is improved due to a better separation of the incident and diffracted beam caused by the AOM. The laser is dedicated as master oscillator in a master oscillator power amplifier (MOPA) system where pulse peak powers in the MW range should be achieved.     

Amplification of a <Emphasis Type="Italic">Q</Emphasis>-Switched Ho:GdVO<Subscript>4</Subscript> Oscillator in Thulium-Doped Large-Mode-Area Fiber

We report a high peak power, narrow linewidth, stable pulsed Ho:GdVO₄ amplifier based on thuliumdoped fiber, which produces 6.65 W average output power at 2,048 nm and 56.8 kW peak power with 11.7 ns pulse width at 10 kHz repetition rate. We use a simple Q-switched Ho:GdVO₄ laser as a seed laser and a thulium-doped fiber pumped by a 792 nm laser diode as an amplifier. The fiber amplifier provided 6.5 dB gain to the input signal. The spectral linewidth of the Ho:GdVO₄ amplifier remains < 0.5 nm with an M² beam quality of 1.36.     

QCW diode-pumped 654 W AO Q-switched Nd:YAG rod oscillator-amplifier laser

A diode laser-pumped acoustic-optic Q-switched Nd:YAG master-oscillator power amplifier laser is presented. The laser is quasi continuously pumped at 1.1 kHz with a pulse width of 172 μs, and the ultrasonic frequency of the AO Q-switcher is set at a higher value (53 kHz). The master oscillator is designed as a thermally near-unstable-resonator, which presents an average output power of 48 W with a beam quality value of M² = 1.41 and a Q-switching pulse duration of 121 ns. The maximum average power of the MOPA system is 654 W, and the beam quality is M² = 6.     

Diode-pumped single-frequency-Nd:YGG-MOPA for water–vapor DIAL measurements: design, setup and performance

A diode-pumped Q-switched and injection-seeded single-frequency laser, generating tunable laser radiation at 935 nm, is presented. Using Nd:YGG (Y₃Ga₅O₁₂) as the active medium, the laser that was developed to serve as a transmitter for water–vapor lidar measurements. The configuration consists of a stable resonator in rod geometry that is injection seeded by a narrowband diode laser and stabilized by the ramp-and-fire technique. Energy scaling was done in a power amplifier in slab geometry. Both oscillator and amplifier crystal were diode pumped at 806 nm. More than 30 mJ pulse energy at 100 Hz repetition rate with a beam propagation factor of M²<1.4 and pulse duration of 52 ns in single-frequency mode were generated. To our knowledge this is the first direct generation of 935 nm Q-switched pulses from Nd:YGG suitable for water–vapor measurements. The reported results show great promise of this laser in applications where high efficiency and reduced complexity is indispensable, such as for spaceborne or airborne water–vapor lidar instruments.     

Diode-pumped 250-W zigzag slab Nd:YAG oscillator amplifier system

A laser-diode-pumped zigzag slab Nd:YAG master oscillator power amplifier (MOPA) system featuring high pulse energy and high average power was developed for pumping of an ultrashort-pulse laser system. The MOPA system consists of an oscillator, a preamplifier, two postamplifiers, and image-relay telescopes. The postamplifiers have an angle-multiplexed ring-type double-pass configuration. A pulse energy of 1.26 J and an average power of 251 W were obtained at a repetition rate of 200 Hz. The frequency-doubled power when a LiB(3)O(5) crystal was used was 105 W at a repetition rate of 170 Hz. The intensity profiles of the fundamental and the second harmonic are nearly top-hat shaped and are suitable for pumping.     

Idler-resonant optical parametric oscillator based on KTiOAsO4

An idler-resonant KTiOAsO₄ (KTA) optical parametric oscillator is demonstrated within a diode-end-pumped acousto-optically Q-switched Nd:YAG laser. With an X-cut KTA crystal, idler wave at 3467 nm and signal wave at 1535 nm are generated. Under an incident diode pump power of 15.4 W, the idler output power of 105 mW and signal power of 720 mW are obtained at a pulse repetition rate of 40 kHz. The pulse widths of the idler and signal waves are 7.2 and 3.1 ns, respectively. The beam quality factors (M²) of the idler wave are within 1.2 in both horizontal and vertical directions.     

Highly efficient,kW peak power, 1.55 µm all-fiber MOPA system with a diffraction-limited laser output beam

We report a high-efficiency, single-mode, all-fiber pulsed laser system built in a master oscillator power amplifier format, operating in the eye-safe (λ ~1,549 nm) spectral range, providing over 1.5 W of average output power with up to 51 dB of total signal gain. It comprises the flexibility of smooth pulse duration control from single ns to 260 ns with independently tunable repetition rate ranging from 40 kHz to 1 MHz. Pulses as short as 4 ns with up to 20 μJ energy and corresponding peak power of 5 kW are demonstrated. The laser system delivered a nearly diffraction-limited beam with M ² ~1.     

Yb3+-doped 200 μm diameter core, gain guided index-antiguided fiber

The lasing in an end-pumped gain guided index-antiguided (GG-IAG) Yb³⁺-doped silicate glass fiber with a 200 μm diameter core is demonstrated. Laser beams with similar beam propagation factors M ² and mode field diameters W ₀ (>160 μm) were observed at the output end of the GG-IAG fibers under different pump powers, which indicated that single mode behavior and excellent beam quality were achieved during propagation. Furthermore, the laser amplifier characteristics in the present Yb³⁺-doped GG-IAG fiber were also evaluated.     

1 mJ, 500 kHz Nd:YAG/Nd:YVO<Subscript>4</Subscript> MOPA laser with a Nd:YAG cavity-dumping seed laser

We report a high-repetition-rate, high-pulse-energy master oscillator power amplifier (MOPA) laser system, in which the seed laser from the Nd:YAG rod-based oscillator cavity dumped at 500 kHz, was scaled up consecutively by a four-stage Nd:YVO₄ preamplifier and a two-stage Nd:YAG zigzag slab main amplifier. The laser pulsed output with the average power of 510 W was achieved, with the efficiency extraction of 26.6% at the main amplifier stage and the single-pulse energy of 1.02 mJ.     

Study of gain dynamics and temporal jitter effects in copper vapor laser oscillator-amplifier chain

Effect of temporal jitter on the performance of copper vapor laser (CVL) master oscillator power amplifier (MOPA) chain using Monte-Carlo techniques was studied. The MOPA chain comprised an oscillator and five amplification stages. Amplification of CVL signal in each amplifier stage was modeled using rate equation based optical model. The effect of temporal jitter on the pulse energy stability in CVL MOPA chain was estimated for various jitter values. Our studies show that the pulse energy spread and the pulse energy instability increases with increase in jitter which in turn depends on the gain pulse width and the jitter considered. Pulse to pulse gain variation in CVL MOPA chain was studied along with temporal jitter. The acceptable tolerance limit on temporal jitter is ±4 ns for a pulse energy stability of 5% of CVL MOPA chain.     

A ring ZnGeP2 optical parametric oscillator pumped by a Ho:LuAG laser

We have demonstrated that we believe to be the first ring ZnGeP₂ (ZGP) optical parametric oscillator (OPO) pumped by a pulsed Ho:LuAG laser. The maximum output power of the ring ZGP OPO laser was 5.51 W at 13.1 W incident Ho pump power, corresponding to a slope efficiency of 59.0 %. The ZGP OPO laser produced 14 ns mid-infrared pulses in the 3.72–4.01 and 4.37–4.75 μm spectral regions simultaneously. In addition, the continuous wave Ho:LuAG laser generated 26.5 W of linearly output at 2,094.4 nm at the absorbed Tm pump power of 49.9 W.     

500 W Nd:YAG zigzag slab MOPA laser

A MOPA Nd:YAG laser with end-pumped zigzag slab architecture has been developed. 277 W laser output is obtained from the master-oscillator stage, corresponding to the average slope efficiency of 35.9% and the optical conversion efficiency of 34.6%, which emits the maximum power of 402 with 1163 W of pump power. Furthermore, the amplifier stage produces 505 W with the slope efficiency of 24% and the extraction efficiency of 25%. The beam quality is estimated as M _x ² ≈ 10, M _y ² ≈ 50 in the orthogonal directions respectively.     

High-repetition-rate high-beam-quality 43 W ultraviolet laser with extra-cavity third harmonic generation

High-power, high-repetition-rate extra-cavity third harmonic generation of 355 nm with high beam quality has been developed. The acoustic-optical Q-switched Nd:YVO₄ MOPA laser including 2- and 4-stage amplifiers was used as the IR source. With the extra-cavity frequency conversion of LBO crystals, 30.2 W TEM₀₀-mode 355 nm UV laser was obtained with a 2-stage amplifier MOPA laser, and the optical-to-optical (1064 nm to 355 nm) conversion efficiency was up to 30%. Enhanced 43 W TEM₀₀ UV laser at 60 kHz was achieved with a 4-stage amplifier MOPA IR laser, and pulse duration was 10.7 ns corresponding to the peak power as high as 67 kW, with single pulse energy of 0.72 mJ. The optical–optical efficiencies from IR and diodes to UV were 28% and 10% respectively.