Cavity-dumped burst-mode Nd:YAG laser master-oscillator power-amplifier system with a flat-top beam output realized by gain profile-controlled side pumping.

We report a compact cavity-dumped burst-mode Nd:YAG laser master-oscillator power-amplifier system with a flat-top intensity distribution across the output-beam section. Custom-designed gain profile-controlled diode side pumping modules providing flat-top and concave gain profiles were utilized to generate a uniform beam profile and suppress thermal lensing during amplification, respectively. Bursts with an energy of 2.0 J and duration of 1.6 ms were operated at 10 Hz. Within the bursts, single pulses with an energy of 12.7 mJ and pulse width of 3.3 ns were achieved at 100 kHz.

5 kHz, 4.2mJ, 900 ps end-pumped Nd:YVO4 MOPA laser system.

A 5 kHz sub-nanosecond master oscillator power amplifier (MOPA) laser system was reported in this paper. The master oscillator was an electro-optically Q-switched Nd:YVO4 laser directly pumped at 879 nm, yielding a pulse energy of 520 µJ and a pulse width of 900 ps at 5 kHz. With two Nd:YVO4 amplifiers directly pumped at 914 nm, the pulse energy was further scaled up. Under the absorbed pump energy of 11.0 mJ, the pulse energy was amplified to 4.2 mJ, corresponding to a peak power of 4.7 MW. The optical-to-optical efficiency of the amplifiers reached 33.5%.

High-pulse-energy passively Q-switched sub-nanosecond MOPA laser system operating at kHz level.

A passively Q-switched sub-nanosecond master oscillator power amplifier (MOPA) laser system at 1064 nm has been reported in this paper. The master oscillator was a passively Q-switched YAG/Nd:YAG/Cr4+:YAG microchip laser, yielding a pulse energy of 0.14 mJ and a pulse width of ∼490 ps at repetition rates of 500 Hz and 1 kHz. After passing a double-pass side-pumped Nd:YAG amplification system, the pulse energy reached 7.6 mJ and 1.7 mJ at 500 Hz and 1 kHz, respectively. The spatial beam deformation caused by the thermally induced birefringence was investigated numerically and experimentally.

Generation and amplification of a multi-beam sub-nanosecond laser.

In this paper, a methodology to produce a multi-beam sub-nanosecond laser is proposed. Laser pulses with a pulse energy of 0.14 mJ and a pulse width of 490 ps are generated in a YAG/Nd:YAG/Cr4+:YAG microchip laser at a repetition rate of 200 Hz. After amplification with a laser diode (LD) side-pumped Nd:YAG module, four laser beams are generated because of the thermally induced birefringence. With a double-pass LD side-pumped amplifier, the single pulse energy of the four laser beams is amplified to 5.23 mJ with a peak power of ∼10.67 MW, and air breakdown with four points is achieved with a 2 × 2 lens array.

Voxel-based spatial elongation filtering method for airborne single-photon LiDAR data.

A novel voxel-based spatial elongation filtering method is proposed, to reduce noise in airborne single-photon lidar (SPL) data. In this method, six additional points are generated adjacent to each point of interest in the SPL data. Then, we count the number of points within each voxel and discriminate signals from noise via a predefined threshold. A filter performance evaluation index (taking into account the false alarm and signal loss rates, and the average distance between the residual noise points and their nearest signal points) is introduced. We compare the proposed and voxel-based spatial filtering method. The average false alarm rate found with our method (3.5%) is 18.6% smaller than that of the voxel-based spatial filtering method (4.3%).

30 mJ, 1 kHz sub-nanosecond burst-mode Nd:YAG laser MOPA system.

We demonstrated a sub-nanosecond burst-mode MOPA Nd:YAG laser at 1.06 µm that consists of a cavity-dumped Q-switched master oscillator and a double-pass side-pumped amplification system. During the 1 kHz burst-mode operation, outputs with the single pulse energy of 29.8 mJ were obtained within the burst duration of 100 ms. The pulse width was 900 ps, which resulted in a peak power of 33.1 MW. During the 10 Hz operation, the single pulse energy reached 81 mJ with a pulse width of 900 ps, which resulted in a peak power of 90 MW.

Continuous-wave and pulsed 1,066-nm Nd:Gd0.69Y0.3TaO4 laser directly pumped by a 879-nm laser diode.

We demonstrated an 879-nm-diode-pumped Nd:Gd0.69Y0.3TaO4 laser in continuous-wave-(CW), pulse-pumped, pulse-reflection-mode Q-switched, and cavity-dumped burst-mode Q-switched operations for the first time. A maximum output power of 9.3 W at 1,066 nm was obtained in the CW operation with a slope efficiency of ~48%. The slope efficiency reached the value of ~68% in the pulse-pumped operation. A peak power of 150 kW and pulse width of 3.4 ns were obtained in the cavity-dumped burst-mode Q-switched operation at a Q-switching repetition rate of 20 kHz.

Investigation on 1.3 µm laser performance with Nd:Gd0.69Y0.3TaO4 and Nd:Gd0.68Y0.3NbO4 mixed crystals.

Laser performances around 1.3 µm are investigated in 879 nm laser diode (LD) end pumped Nd3+ doped mixed crystals with Nd:Gd0.69Y0.3TaO4 and Nd:Gd0.68Y0.3NbO4 crystals for the first time to our best knowledge. The maximum average power in LD end pumped Nd:Gd0.69Y0.3TaO4 1328 nm laser reaches 435 mW at 50 Hz with an optical-to-optical efficiency of 5.0% and a slope efficiency of 6.9%. In comparison, the highest average power of LD end pumped Nd:Gd0.68Y0.3NbO4 laser at 1337 nm is 190 mW at 50 Hz, corresponding to an optical-to-optical efficiency of 3.5% and a slope efficiency of 4.2%.

14 GHz broadband and continuously frequency-tuned Nd:YVO4 laser with an RTP etalon.

A laser-diode-pumped broadband and continuously frequency-tuned all-solid-state Nd:YVO4 laser at 1064 nm with an output power of 200 mW is demonstrated. A RbTiOPO4 (RTP) etalon and a piezoelectric-transducer (PZT) are utilized for coarse and fine frequency tuning, respectively. Dependence of the frequency excursion on the applied voltage to the RTP etalon and the displacement of the PZT is theoretically and experimentally investigated. A continuous frequency tuning of 14 GHz is conducted by synchronous adjustment of the RTP etalon and the PZT. The tuning covers more than 6 times the longitudinal mode spacing of a laser resonator without any mode hops.

2.4 THz/s continuously linearly frequency-modulated Nd:YVO4 laser.

We demonstrate a linearly frequency-modulated laser from a laser diode (LD) pumped Nd:YVO4 laser. A fast frequency tuning of 2.40 THz/s with a tuning range of 6 GHz is achieved in LD pumped Nd:YVO4 1064 nm laser by using RbTiOPO4 (RTP) crystals as the frequency modulator. The continuous tuning range is more than 3 times the longitudinal mode spacing of the resonator. The maximum output power of frequency-modulated laser reaches 160 mW at 1064 nm. Linewidth of the single frequency laser is measured to be 190 kHz by a delay self-heterodyne interferometer. A deviation lower than 60 MHz is obtained during linear modulation.

100 kHz, 3.1 ns, 1.89 J cavity-dumped burst-mode Nd:YAG MOPA laser.

We demonstrated a cavity-dumped burst-mode 1.06 µm side-pumped Nd:YAG laser and its dual-stage dual-pass amplified laser performance. The cavity dumping process has been theoretically studied and the output performance has been experimentally investigated. At the pumping duration of 2 ms and pumping frequency of 10 Hz, burst energy, peak power and pulse width of the amplified laser reached 1.89 J, 2.87 MW and 3.1 ± 0.3 ns, respectively, at the Q-switch repetition rate of 100 kHz. The maximum energy extraction efficiency reaches to 30%.

Linearly frequency-tuned LD-pumped Nd:YVO4 laser with an 18-GHz broadband tuning range.

A continuously frequency-tuned laser diode end-pumped Nd:YVO4 laser at 1064 nm is demonstrated. A coated etalon and a piezoelectric-transducer (PZT) are utilized for coarse and fine frequency tuning, respectively. Broadband and linear frequency tuning without mode hops is conducted by the synchronous adjustment of the etalon and the PZT. Dependence of the frequency excursion on the displacement of the PZT and the tilting angle of the etalon are theoretically and experimentally investigated. A linear frequency tuning range up to 18 GHz without mode hops or frequency overlaps in a one-way non-stopped scanning is obtained. The maximum output power is 930 mW at 1064 nm, and the average frequency tuning speed is 1.24 GHz/s. Standard deviation of the frequency variation to a linear frequency tuning is estimated to be 186 MHz, indicating a high tuning linearity.

Multiple-beam, pulse-burst, passively Q-switched ceramic Nd:YAG laser under micro-lens array pumping.

A novel four-beam (named laserI, laser II, laser III and laser IV, respectively), passively Q-switched, pulse-burst ceramic Nd:YAG laser under 2 × 2 micro-lens array pumping was demonstrated for the purpose of laser-induced plasma ignition (LIPI). Multiple-beam output together with pulse-burst mode in which both high repetition rate and high pulse energy can be realized simultaneously were obtained to greatly improve the performance of LIPI. The pulse-burst contained a maximum of 5 pulses, 3 pulses, 2 pulses and 3 pulses for laserI, laser II, laser III and laser IV, respectively, and the corresponding repetition rate of laser pulses in pulse-burst was 10.8 kHz, 7.2 kHz, 6.8 kHz and 5.2 kHz, respectively. The output energy for single laser pulse in pulse-burst was in the range of 0.12 mJ to 0.22 mJ.

A novel miniaturized passively Q-switched pulse-burst laser for engine ignition.

A novel miniaturized Cr4⁺:YAG passively Q-switched Nd:YAG pulse-burst laser under 808 nm diode-laser pulse-pumping was demonstrated for the purpose of laser-induced plasma ignition, in which pulse-burst mode can realize both high repetition rate and high pulse energy simultaneously in a short period. Side-pumping configuration and two different types of laser cavities were employed. The pumping pulse width was constant at 250 µs. For the plane-plane cavity, the output beam profile was flat-top Gaussian and the measured M² value was 4.1 at the maximum incident pump energy of 600 mJ. The pulse-burst laser contained a maximum of 8 pulses, 7 pulses and 6 pulses for pulse-burst repetition rate of 10 Hz, 50 Hz and 100 Hz, respectively. The energy obtained was 15.5 mJ, 14.9 mJ and 13.9 mJ per pulse for pulse-burst repetition rate of 10 Hz, 50 Hz and 100 Hz, respectively. The maximum repetition rate of laser pulses in pulse-burst was 34.6 kHz for 8 pulses at the incident pump energy of 600 mJ and the single pulse width was 13.3 ns. The thermal lensing effect of Nd:YAG rod was investigated, and an plane-convex cavity was adopted to compensate the thermal lensing effect of Nd:YAG rod and improve the mode matching. For the plane-convex cavity, the output beam profile was quasi-Gaussian and the measured M2 value was 2.2 at the incident pump energy of 600 mJ. The output energy was 10.6 mJ per pulse for pulse-burst repetition rate of 100 Hz. The maximum repetition rate of laser pulses in pulse-burst was 27.4 kHz for 6 pulses at the incident pump energy of 600 mJ and the single pulse width was 14.2 ns. The experimental results showed that this pulse-burst laser can produce high repetition rate (>20 kHz) and high pulse energy (>10 mJ) simultaneously in a short period for both two different cavities.

High-repetition-rate and short-pulse-width electro-optical cavity-dumped YVO4/Nd:GdVO4 laser.

In this paper, an electro-optical cavity-dumped 1.06 µm laser using YVO4/Nd:GdVO4 composite crystal under 808 nm diode-laser pumping was reported. Theoretical calculations showed that the temperature distribution in YVO4/Nd:GdVO4 crystal was lower than that in GdVO4/Nd:GdVO4 and Nd:GdVO4 crystals under the same conditions. A constant 3.8±0.3 ns pulse width was obtained and the repetition rate could reach up to 50 kHz with a maximum average output power of 5.6 W and slope efficiency of 40.7%, corresponding to a peak power of 31.1 kW.

High-efficiency Nd:LuVO4 quasi-three-level 916 nm laser under polarized pumping.

An efficient laser-diode-pumped Nd:LuVO4 916 nm laser by using the polarized pumping is reported. The maximum continuous-wave output power of 4.75 W is achieved at the incident pump power of 27.8 W, with an optical-to-optical efficiency of ~17.1% and a slope efficiency of ~29.5%. The slope efficiency is up to 45.4% with respect to the absorbed pump power and nearly 1.7 times higher than the previous results ever reported under the 808 nm diode laser pumping. The beam quality is measured to be M2 ~ 2.3 at the output power of 4.75 W.

High power 2 MHz passively Q-switched nanosecond Nd:YVO4/Cr4+:YAG 914 nm laser.

We report a high-power, high-repetition-rate end-pumped passively Q-switched Nd:YVO4/Cr4+: yttrium aluminum garnet 914 nm laser. The maximum output power of 3.8 W at 914 nm is achieved at 2 MHz with the absorbed pump power of 25.2 W. The highest single pulse energy of a pulsed 914 nm laser reaches 2.3 µJ with a pulse width of 27.1 ns.

Power scaling of directly dual-end-pumped Nd:GdVO4 laser using grown-together composite crystal.

Power scaling of end-pumped Nd:GdVO(4) laser was realized by direct pumping, grown-together composite crystal and dual-end-pumping. A maximum CW output power of 46.0W with M(2)<1.1 was achieved, corresponding to a slope efficiency of 71.1% to absorbed pump power. In A-O Q-switch operation, peak power of 304.1kW, 58.6kW and 23.8kW, pulse width of 7.2ns, 11.3ns and 16.2ns were obtained at the repetition rates of 10kHz, 50kHz and 100kHz, respectively.

High-repetition-rate, high-peak-power, linear-polarized 473 nm Nd:YAG/BiBO blue laser by extracavity frequency doubling.

We report on a high-repetition-rate, high-peak-power, linear-polarized 473 nm blue laser. A high-power 946 nm fundamental laser was obtained based on a diode-pumped acousto-optically (AO) Q-switched Nd:YAG laser using a thermal-compensating resonator and a microchannel heat sink for thermal dissipation. A pulsed 473 nm laser was generated using a BiB(3)O(6) (BiBO) crystal as an extracavity frequency doubler. The highest peak power of a 16.7 kW blue laser was obtained at a pulse repetition rate of 10 kHz with a pulse width of 9 ns. Stable operation of the pulsed blue laser can even reach 50 kHz.

Comparison on performance of acousto-optically Q-switched Nd:GdVO4 and Nd:YVO4 lasers at high repetition rates under direct diode pumping of the emitting level.

We detail the comparison on laser performance of Nd:GdVO(4) and Nd:YVO(4) lasers at high repetition rates operated at 1.06 microm under direct diode pumping of the upper laser level. The results reveal that Nd:GdVO(4) and Nd:YVO(4) are efficient laser crystals for solid-state lasers under direct pumping of the emitting level. However, Nd:YVO(4) crystal, compared with Nd:GdVO(4) crystal, is a more favorable gain medium when higher repetition rates and shorter pulse width are desired, owning to its larger stimulated emission cross-section.