43 W picosecond laser and second-harmonic generation experiment

Combining the advantages of diode-end-pumped Nd: YVO₄ and diode-side-pumped Nd: YAG amplifiers, a high average power and high beam quality picosecond laser is designed. The system delivers a picosecond laser with average power of 43.4 W and good beam quality of M² < 1.7. By focusing the high power picosecond laser in LBO crystal, 532 nm green laser with maximal power of 20.8 W is generated and the conversion efficiency of second-harmonic generation reaches 56.4% when 17.7 W green laser obtained from the fundamental frequency laser with power of 31.4 W and beam quality of M² < 1.25.     

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.     

An 8.1 W diode pumped solid-state quasi-continuous-wave yellow laser at 589 nm by intracavity sum-frequency mixing generation

We report an L-shaped symmetrical co-folding-arm plane-plane diode pumped solid-state yellow laser at 589 nm by using intracavity sum-frequency mixing. By carefully designing the cavity and employing various techniques to optimize the laser’s specifications, a quasi-continuous-wave (QCW) free-oscillation yellow laser source, which has an average output power of 8.1 W, a beam quality factor of M² = 2.3, and a repetition rate of 1.1 kHz, is developed. The generation of yellow laser at 589 nm is achieved by intracavity sum-frequency mixing between the laser lines at 1319 nm and 1064 nm of an Nd:YAG laser in a KTP crystal. To the best of our knowledge, the 8.1 W output at 589 nm is higher than any other diode pumped solid-state yellow laser generated by intracavity sum-frequency generation so far.     

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.     

Picosecond laser amplification system with 93 W high average power

A high average power picosecond laser amplification system with diode-end-pumped Nd:YVO₄ and diode-side-pumped Nd:YAG is described. Laser with power up to 92.7 W, repetition frequency of 73.3 MHz, pulse duration of 26.5 ps, and beam quality of M² < 3.5 is generated in the amplification system. Thermal-birefringence-induced depolarization in the Nd:YAG rod laser head amplifier is measured to be 21.9 W though birefringence compensation is performed.     

Self-Q-switched and mode-locked 946 nm Cr,Nd:YAG laser

A simultaneous self-Q-switched and mode-locked diode-pumped 946 nm laser by using a Cr,Nd:YAG crystal as gain medium as well as saturable absorber is demonstrated for the first time as we know. The maximum average output power of 751 mW with a slope efficiency of 18.38% is obtained at an intra-cavity average peak power intensity of 4.83 × 10⁶ W/cm². Under this circumstance, the repetition rate of Q-switched envelopes is 9.63 kHz and the pulse width is about 460 ns. Almost 100% mode-locked modulation depth is obtained at all time in the experiment process whether the incident pump power is low or high. The repetition rate of mode-locked pulses within a Q-switched envelope is 135.13 MHz and the mode-locked pulse width is within 600 ps. The laser produces high-quality pulses in TEM₀₀-mode in the simultaneous self-Q-switched and mode-locked experiment.     

Intracavity frequency doubling of an active Q-switched Nd:YAG laser with 2.25 W output power at 473 nm

An active Q-switched diode-end-pumped Nd:YAG laser is reported with 2.9 W output power on the ⁴F_3/2 → ⁴I_9/2 transitions at a pump power of 24 W. With intracavity frequency doubling using a 20-mm-long LBO, a maximum blue output power of 2.25 W is achieved at a repetition rate of 23 kHz. The conversion efficiency from the corresponding Q-switched fundamental output to blue output is 96%. The peak power of the Q-switched blue pulse is up to 610 W with 160 ns pulse width. The fluctuation of the blue output power is less than 4.0% at the maximum output power.     

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.     

41 mW high average power picosecond 177.3 nm laser by second-harmonic generation in KBBF

We report on the generation of high average power, high repetition rate, and picosecond (ps) deep-ultraviolet (DUV) 177.3 nm laser. The DUV laser is produced by second-harmonic generation of a frequency-tripled mode-locked Nd: YVO₄ laser (<15 ps, 80 MHz) with KBBF nonlinear crystal. The influence of different fundamental beam diameters on DUV output power and KBBF-SHG conversion efficiency are investigated. Under the 355 nm pump power of 7.5 W with beam diameter of 145 μm, 41 mW DUV output at 177.3 nm is obtained. To our knowledge, this is the highest average power for the 177.3 nm laser. Our results provide a power scaling by three times with respect to previous best works.     

Repetition rate multiplication in figure-eight fibre laser with 3 dB couplers

The operation of a passively modelocked figure-eight laser with all fibre repetition rate multiplier is reported. Thirty two times the fundamental repetition rate is achieved with six conventional 3 dB couplers at a repetition rate of 182 MHz. The repetition rate 2^N times multiplication only requires (N + 1) passive fibre couplers and N fibre delay-lines. This method makes it possible to achieve high multiplication and is inexpensive when compared with conventional methods employing sub-ring cavity or special fibre Bragg grating to control repetition rate.     

Frequency stabilization of a Q-switched Nd:YAG laser oscillator with stability better 300 kHz following an rf-sideband scheme

A frequency stabilization scheme following the Pound-Drever-Hall technique modified with a sample and hold circuit has been applied to a Q-switched diode-pumped Nd:YAG ring oscillator. The high-power ring is injection seeded by a monolithic non-planar ring laser oscillator (NPRO). The slave oscillator emits pulses of 23 ns duration and 20 mJ pulse energy with almost diffraction limited beam quality (M² = 1.2) at a repetition rate of 400 Hz. The short-term fluctuation of the center frequency from pulse to pulse is 290 kHz. The oscillator is designed for applications within lidar measurements.     

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%.     

532 nm laser based on V-type doubly resonant intra-cavity frequency-doubling

LD side-pumped dual interconnected V-type quasi-continuous wave green laser has been demonstrated. The two Nd:YAG modules were placed in a plane-concave V-type resonator and a plane-concave straight cavity formed two stable operation beam of the 1064-nm fundamental frequency laser. Through acousto-optic Q-switched and frequency doubling crystal, two double-frequency laser beams arrived at the folded flat mirror, which were unidirectional output by the folded flat mirror at the end. As the pumped current was 50 A, the 532 nm green laser maximum average output power of 206 W at a repetition of 22.4 kHz was achieved with a pulse width of 201 ns and the largest single pulse energy of 9.2 mJ, corresponding to a peak power of 45.8 kW and a double frequency efficiency of 60.2%.     

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.     

Lasing at 1065 nm in bulk Nd-doped telluride-tungstate glass

We have achieved, for the first time to our knowledge, lasing in a new type of telluride-tungstate glass host doped with neodymium: Nd³⁺:(0.8)TeO₂-(0.2)WO₃. Lasing was obtained at 1065 nm with two samples containing 0.5 mol% and 1.0 mol% Nd₂O₃. During gain-switched operation, slope efficiencies of 12% and 10% were obtained with the 0.5 mol% and 1.0 mol% doped samples, respectively, at a pulse repetition rate of 1 kHz. Judd-Ofelt analysis was further employed to determine the emission cross section σ_e at 1065 nm from the absorption spectra and lifetime data. The emission cross section from the Judd-Ofelt analysis came to 3.23 ± 0.09 × 10⁻²⁰ cm², in reasonable agreement with the value of 2.0 ± 0.13 × 10⁻²⁰ cm² obtained from the analysis of laser threshold data.     

Laser fluence, repetition rate and pulse duration effects on paint ablation

The efficiency (mm³/(J pulse)) of laser ablation of paint was investigated with nanosecond pulsed Nd:YAG lasers (λ = 532 nm) as a function of the following laser beam parameters: pulse repetition rate (1-10,000 Hz), laser fluence (0.1-5 J/cm²) and pulse duration (5 ns and 100 ns). In our study, the best ablation efficiency (η ≅ 0.3 mm³/J) was obtained with the highest repetition rate (10 kHz) at the fluence F = 1.5 J/cm². This ablation efficiency can be associated with heat accumulation at high repetition rate, which leads to the ablation threshold decrease. Despite the low thermal diffusivity and the low optical absorption of the paint (thermal confinement regime), the ablation threshold fluence was found to depend on the pulse duration. At high laser fluence, the ablation efficiency was lower for 5 ns pulse duration than for the one of 100 ns. This difference in efficiency is probably due to a high absorption of the laser beam by the ejected matter or the plasma at high laser intensity. Accumulation of particles at high repetition rate laser ablation and surface shielding was studied by high speed imaging.     

Generation of high average power 1 kHz shaped THz pulses via optical rectification

Generation of near single-cycle THz pulses from lithium niobate with 3.3 μJ energy, 3.3 mW average power, 1.2 THz central frequency and 4 MW peak power was demonstrated by tilting the intensity front of the pump pulses from a 1 kHz Ti:sapphire laser. THz pulse intensity as high as 200 MW/cm² was achieved. The energy conversion efficiency was 7 × 10⁻⁴. The capability of the present scheme to generate high energy shaped THz pulses was also demonstrated by using a sequence of optical pump pulses.     

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%.     

Low threshold, actively Q-switched Nd:YVO4 self-Raman laser and frequency doubled 588 nm yellow laser

We reported an actively Q-switched, intracavity Nd³⁺:YVO₄ self-Raman laser at 1176 nm with low threshold and high efficiency. From the extracavity frequency doubling by use of LBO nonlinear crystal, over 3.5 mW, 588 nm yellow laser is achieved. The maximum Raman laser output at is 182 mW with 1.8 W incident pump power. The threshold is only 370 mW at a pulse repetition frequency of 5 kHz. The optical conversion efficiency from incident to the Raman laser is 10%, and 1.9% from Raman laser to the yellow.     

100 W Kinetically enhanced copper vapor laser at 10 kHz repetition-rate, high (∼1.5%) efficiency with low (∼1.6 kW/l) specific input power and performance of new resonator configurations

It is established here that kinetically enhanced copper vapor lasers (KE-CVLs) based on large-bore discharge tubes can provide high (>1.4%) efficiency at ∼9-10 kHz rep-rate with very low (<2 kW/l) specific input power. Comparative performance of various large-bore kinetically enhanced copper vapor lasers in the range 45-70 mm is presented for most suitable discharge tube. Maximum output power of ∼100 W was achieved with efficiency of about 1.55% at 10 kHz rep-rate from the 60 mm bore KE-CVL. The pulse to pulse efficiency of the KE-CVL was ∼2%, tube efficiency ∼2.1%, and laser pulse energy was about ∼10 mJ. These results show significant advancement in the laser system as an elemental high temperature CVL due to volumetric scaling and KE-effects combined with very low specific input power of ∼1.65 kW/l as compared to 8-9 kW/l normally required in other kinetically enhanced copper vapor lasers to generate ∼100 W output power. Performance of the KE-CVL with 3 new cavity configurations namely, (1) CAT-EYE resonator (2) hybrid resonator, and (3) modified diffraction coupled resonator with dot mirrors are presented for the first here. CAT-EYE resonator was demonstrated to achieve high misalignment tolerance without significant loss of power. A typical drift in power of ∼5% was observed with misalignment responsible for 40% decline in power in case of standard plane-plane cavity. Effect of resonator misalignment on amplifier output drift was also investigated using CAT-EYE resonator in oscillator-amplifier configuration. In case of using stable-unstable hybrid resonator, high magnification of M ∼ 1500 was realized resulting in extremely low divergence (∼0.08 mrad) beam with modest (∼20%) loss in average power. In case of modified DCR cavity, record power of about 48 W was achieved with beam divergence of about 0.1 mrad on using intra-cavity 2 × 2 array of 4 dot mirrors.