YAG Modules Research Articles

Power scaling of intra-cavity Nd:YAG/LBO laser at 532 nm by birefringence compensation

We report an effective method to reduce the impact of polarization state changes caused by thermal birefringence in intra-cavity frequency-doubled laser. The laser consists of a diode side pumped Nd:YAG module, an acousto-optic modulator Q-switch, and an LBO crystal used for SHG generation in 532 nm laser. The effect of thermal birefringence originated by the Nd:YAG rod with concave-shape end surfaces on SHG efficiency is compensated by the insertion of a λ/8 plate into the cavity. At the repetition frequency of 9 kHz, the 532 nm laser achieves a maximum output power of 23.8 W, a pulse duration of 60 ns (FWHM), and a beam quality factor of Mx 2 × My 2 = 1.52 × 1.43. Compared with the λ/4 plate and without plate, the maximum average power of the laser with the λ/8 plate has increased by 22.7% and 66.4%, respectively, the beam quality factor has also been greatly improved correspondingly. This method provides a new solution for lasers to compensate thermally induced birefringence.

High-power dual-wavelength intracavity diamond Raman laser

Diamond crystals have garnered significant attention for applications in photonics, owing to their characteristics of ultra-high thermal conductivity, extremely broad spectral transmission range, and high Raman gain coefficient. These characteristics are particularly advantageous for the development of high-power, multi-wavelength lasers. In this work, we utilize single crystal diamond as a Raman gain medium, for intracavity wavelength-conversion of emission from a side-pumped, electro-optically Q-switched Nd:YAG module. Cascaded Raman conversion is demonstrated and dual-wavelength, pulsed laser emission at wavelengths of 1.2 μm (first-Stokes wavelength) and 1.5 μm (second-Stokes wavelength) is achieved (with a maximum combined pulse energy of 6.19 mJ). The relative ratio of output energy at the two Stokes orders could be varied by tuning the characteristics of the output coupling mirror and the length of the laser resonator. When operating at maximum pump power, the pulse width of the second-Stokes field was approximately half that of the first-Stokes field (second-Stokes ∼10 ns, first-Stokes ∼18 ns), resulting in maximum peak powers of 174 kW (at 1.2 μm) and 220 kW (at 1.5 μm). To the best of our knowledge, this is the highest reported peak power generated from a dual-wavelength, intracavity diamond Raman laser. This work highlights the diversity and utility of diamond as an effective wavelength-conversion component in high-power lasers, and stands as the current state-of-the-art in high pulse-energy, high peak-power, multi-wavelength intracavity Raman lasers.

High stability 500 Hz MOPA system for planar laser-induced fluorescence

A high pulse energy laser diode-pumped Nd:YAG master oscillator power amplifier (MOPA) laser is demonstrated. The maximum energy of 68 mJ, 9.6 ns, 1064 nm laser at a pulse repetition frequency of 500 Hz is achieved by utilizing the amplifier composed of three LD side-pumped Nd:YAG modules. Moreover, the maximum laser energy of 35.6 mJ is obtained at 532 nm by employing a KTP crystal as a frequency doubler. When ambient temperature ranges from 5 °C to 45 °C, the master oscillator has a pulse energy jitter of <5%. During the shake-environment test, the maximum-pulse-energy jitter of the MOPA laser is less than 2%. The developed MOPA laser has been used in a laser-induced fluorescence system and the variation of the flow field is obtained at a repetition rate of 500 Hz.

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.

Dynamically stable single frequency ring resonator from diode pumped Nd:YAG modules with 55.6 W of output power

A Nd:YAG rod single-frequency ring laser based on side-pumped commercial modules is presented. Thermally induced birefringence compensation was applied in a dynamically stable resonator providing 55.6 W of continuous, linearly polarized, TEM00 output. The particular case of a symmetric ring resonator containing one or two focusing rods and a pair of curved mirrors was analyzed and a design technique is presented, allowing for easy, continuous shaping of the stability limits by changing only the distances in the resonator.

A picosecond laser at 1 kHz with dual-length of regenerative amplifier for the SLR in the daytime

An average power of 3 W green picosecond laser at a pulse repetition frequency of 1 kHz was reported. At the Shanghai satellite laser ranging (SLR) station, many satellites were measured with this laser and a narrow spectrum filter in the daytime. Satellites of the Beidou satellite navigation system for the Chinese, Global navigation satellite system for the Russian and Galileo satellite navigation system for the Europe were measured respectively. Especially ranging precision root mean square was up to 19.4 mm for the satellite of compassi5 about 37,000 km far from the earth. A Nd:YVO4 mode-locked laser with an etalon, a dual-length of Nd:YAG regenerative amplification cavity, single-pass two Nd:YAG modules amplifier and nonlinear optical materials LiB3O5 frequency doubling were designed. An average power of 3 W in 532 nm was obtained with pulse width of 30 ps, and angle of divergence was 0.8 mrad. Using the dual-length of regenerative cavity would greatly decrease the laser's volume and improve stability of picosecond laser. A narrow spectrum filter can reduce a lot of optics noise from the sun, and so all the satellites were almost be measured with this laser in the daytime at the Shanghai SLR station.

Dynamically stable Nd:YAG resonators with beam quality beyond the birefringence limit and pumping of a singly resonant optical parametric oscillator.

A simple, reliable, linearly polarized laser source with very high beam quality is demonstrated using standard diode-side-pumped Nd:YAG modules. The laser produced 30W of output power with beam quality factor M2<1.15 over the entire range of input powers and beam quality of 1.02 at the laser operation point. This is, to our knowledge, the highest beam quality for a dynamically stable high-power laser that uses an optically isotropic crystal. The laser was used as a pump source for an optical parametric oscillator based on a periodically poled lithium niobate, producing wavelength in the 1.5-3.8μm range.

Investigation on LD-pumped acousto-optically Q-switched pulse burst 1064 nm laser

Pulse-burst lasers with high pulse energy and high repetition rate are widely applied in the fields of laser diagnostics, such as Planar Laser-Induced Fluorescence (PLIF). In this paper, we reported a pulse-burst Nd:YVO4/Nd:YAG Maser Osillator Power Amplifier. The laser oscillator operates at 1064nm with a YVO4/Nd:YVO4 crystal end-pumped by an 808nm laser diode (LD). During the pumping duration of 1ms the pulse-burst laser contains 10, 50 and 100 pulses with the burst energies of 6mJ, 6.7mJ and 6.9mJ, when repetition rates are 10kHz, 50kHz and 100kHz, respectively. After amplification by a LD-side-pumped Nd:YAG module, the burst-pulse energies reach 64‍ ‌mJ, 61mJ and 62mJ, corresponding to single pulse energies of 6.4mJ, 1.2mJ and 0.6mJ, at repetition rates of 10kHz, 50kHz and 100kHz.

100 W continuous linearly polarized, high beam quality output from standard side-pumped Nd:YAG laser modules

Dynamically stable operation with joined stability zones of a linearly polarized resonator is shown for a laser containing two diode side-pumped Nd:YAG rods. The unpolarized resonator generated 115W of output. When polarized by a Brewster plate, it reached 100.5W of output power at a beam quality M2<2. Best measured beam quality was of 1.1 and 1.3 in the x and y directions respectively, with 76W of 95% polarized output. The output power achieved is, to our knowledge, the highest reported for continuous polarized, fundamental-mode lasers using standard side-pumped Nd:YAG modules.

18 W pulse-bursts 532 nm picosecond laser system with four equal amplitude and spacing pulses at 1 kHz

An average power of 18 W pulse-burst 532 nm picosecond laser was obtained with four pulses in a burst at 1 kHz. A mode-locked laser and beam splitter mirrors were used to obtain seed pulse-bursts, that one single pulse was divided into four pulses and each pulse in bursts can be controlled. The pulses were broadened from 23.5 to 135 ps by single-pass volume Bragg gratings. After Nd:YAG regenerative amplifier and single-pass two Nd:YAG modules amplifier, 31.2 W in 1064 nm was got. The four pulses had equal amplitude and pulse spacing of 800 ps. Then, 18 W in 532 nm was obtained with nonlinear optical materials of LiB3O5 frequency doubling, the beam quality of the M2 factor was 1.24, and the pulse width was 50 ps. It is a very nice way to obtain high-power pulse-burst picosecond laser with equal pulse spacing and amplitude.

High-energy, high-repetition-rate picosecond pulses from a quasi-CW diode-pumped Nd:YAG system

We report on a high-power quasi-CW pumped Nd:YAG laser system, producing 130 mJ, 64 ps pulses at 1064 nm wavelength with a repetition rate of 300 Hz. Pulses from a Nd:YVO(4) oscillator are first amplified by a regenerative amplifier to the millijoule level and then further amplified in quasi-CW diode-pumped Nd:YAG modules. Pulsed diode pumping enables a high gain at repetition rates of several hundred hertz, while keeping thermal effects manageable. Birefringence compensation and multiple thermal-lensing-compensated relay-imaging stages are used to maintain a top-hat beam profile. After frequency doubling, 75 mJ pulses are obtained at 532 nm. The intensity stability is better than 1.1%, which makes this laser an attractive pump source for a high-repetition-rate optical parametric amplification system.

Generation of radially polarized beams based on thermal analysis of a working cavity

The laser oscillation and polarization behavior of a side-pumped Nd:YAG laser are studied theoretically and experimentally by a thermal model for a working cavity. We use this model along with the Magni method, which gives a new stability diagram, to show important characteristics of the resonator. High-power radially and azimuthally polarized laser beams are obtained with a Nd:YAG module in a plano-plano cavity. Special regions and thermal hysteresis loops are observed in the experiments, which are concordant with the theoretical predictions.

Segmented circular LD arrays side-pumped a Nd:YAG laser rod

We design a Nd:YAG module with symmetrical LD side-pumped structure in a periodical arrangement between circular LD arrays and holders. This novel design has great potential to be used in compact and miniature laser systems. Design optimization and simulation on thermal effects have been performed. An experiment has also been carried out. The experiment results indicate the all-solid-state laser with the-Nd:YAG module can stably operate in the range of 10–30 Hz with no controlling temperature by TE cooler. The laser beam had a divergence angle less than 3.8 mrad and a maximum output pulse of 174 mJ has been obtained at the pump current of 50 A and working frequency of 23 Hz, corresponding to optical-optical conversion efficiency of 40.2%.

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 average power Q-switched green beam generation by intracavity frequency doubling of diode-side-pumped Nd:YAG/HGTR-KTP laser

To obtain high power and high beam quality second harmonic generation, a Q-switched system has been demonstrated by intracavity frequency doubling of two diode-side-pumped Nd:YAG modules with double AO-modulators in an astigmatism compensated cavity geometry. A maximum average frequency doubled power of 185 W is obtained when the pumping power is 600 W for each module. The corresponding optical-to-optical conversion efficiency is 15.4% and the pulse width is 180 ns at a repetition rate of 10 kHz. An instability of 2.5% was measured over a period of 2 h and the beam quality factors were measured to be M x 2 = 9.52 , M y 2 = 9.86 the maximum output power.

Diode-side-pumped intracavity frequency-doubled Nd:YAG/BaWO_4 Raman laser generating average output power of 314 W at 590 nm

We report a linear-cavity high-power all-solid-state Q-switched yellow laser. The laser source comprises a diode-side-pumped Nd:YAG module that produces 1064 nm fundamental radiation, an intracavity BaWO(4) Raman crystal that generates a first-Stokes laser at 1180 nm, and a KTP crystal that frequency doubles the first-Stokes laser to 590 nm. A convex-plane cavity is employed in this configuration to counteract some of the thermal effect caused by high pump power. An average output power of 3.14 W at 590 nm is obtained at a pulse repetition frequency of 10 kHz.

Multiwatt high-repetition-rate 2-µm output from an intracavity KTiOPO_4 optical parametric oscillator

We have obtained 6.5 W of 2-mum output from a near-degenerate, type II KTiOPO(4) (KTP) optical parametric oscillator (OPO) pumped within the cavity of a Q-switched diode-pumped Nd:YAG laser that operates at 3 kHz. We adopted the simplest configuration with a compact diode-pumped Nd:YAG module pumping the doubly resonant KTP OPO in its randomly polarized resonator with an acousto-optic Q switch. Attempts to increase the 2-mum output power by pumping this intracavity KTP OPO with a polarized laser beam by use of thermal birefringence compensation configurations are discussed.