YAG Oscillator Research Articles

Hundred-watt Ho:YAG oscillator pumped by high-power Tm:YLF laser with orthogonal cylindrical lenses spot shaping

A hundred-watt, linearly-polarized Ho:YAG oscillator, pumped by a 200 W, home-made and s-polarized Tm:YLF laser, was demonstrated. By utilizing a combination of a half-wave plate (HWP) and a thin-film polarizer (TFP), the Tm:YLF laser was split into two orthogonally polarized parts. Each part was significantly reshaped by a system of orthogonally arranged cylindrical lenses and subsequently used to dual-end pump the oscillator. With a total incident pump power of 183 W, a continuous wave (CW) output power of 101 W at 2.1 μm was achieved, with corresponding slope efficiency and optical-to-optical conversion efficiency (OOCE) of 61.6 % and 55.2 %, respectively. Additionally, the beam quality factors, measured in the x and y directions, were 1.59 and 1.35, respectively. Finally, under Q-switched operation at a repetition rate of 20 kHz, a maximum output power of 97 W was achieved, with a corresponding pulse width of less than 34 ns. The central wavelength of the laser was measured to be 2090.2 nm.

Generation of tunable vortex beams from a side-pumped Nd:YAG laser utilizing spot defect mirrors

High-order vortex lasers are important for high angular momentum quantum entanglement and high-resolution spatial detection. However, traditional spatial phase modulation for Gaussian beams have difficulties achieving high-order and continuously adjustable optical vortex output. In this study, a high-order vortex laser output of continuously adjustable topological charges between 1 and 9 was obtained by adjusting the cavity length in a side-pumped Nd:YAG oscillator with circular spot defects of different sizes etched on the surface of the cavity mirror. Its chirality was also controlled by slightly tilting the cavity mirror, and the mode changes under different cavity parameters and the factors limiting the output optical-vortex order in the side-pumping structure were analyzed. In addition, the generation of optical vortex lattice modes with multiple spatially separated OAMs was obtained based on the spot defect method by displacing the cavity mirror.

Externally pumped yellow laser source emitting at 577 nm

We demonstrated a 577 nm yellow laser source with a proper combination of Raman medium and frequency doubling medium, pumped externally. Cryogenic Yb:YAG oscillator acts as an external pump source, and it generates 1.2 mJ energy at 1 KHz emitting around 1029 nm. Using a Raman resonator with Ba(NO3)2 as Raman medium, stimulated Raman scattering around 1153.4 was generated. Finally, 577 nm yellow laser was generated using the frequency-doubling medium LBO. A maximum average output power of 65 mW with a pulse duration of 18 ns at 1 KHz was achieved.

Compact LD side-pumped Nd:YAG oscillator at 100 Hz without water-cooling

A high-repetition-frequency side-pumped electro-optical (E-O) Q-switched Nd:YAG laser without water cooling is reported. A 100 Hz laser module without water-cooling was designed and the related parameters of crystal are simulated. The crystal is annularly pumped in both ends and is conductively cooled in the middle. The heat generated by crystal and laser diode is dissipated by thermoelectric cooler (TEC), fins and fan. The 1064 nm maximum output energy is 68 mJ with a pulse width of 31 ns and a repetition rate of 100 Hz. The optical–optical conversion efficiency is 10.6%. To the best of our knowledge, this is the first report of 100 Hz repetition rate operation for a E-O Q-switched Nd:YAG rod laser without water-cooling.

Study on satellite pulse characteristics of LD-end pumped sub-nanosecond Nd:YAG/Cr4+:YAG oscillator

Miniaturized sub-nanosecond laser is critical to the applications such as medical treatment, Lidar and manufacturing. In this paper, a high repetition rate hundred picosecond pulse oscillator based on Nd:YAG/Cr4+:YAG bonded crystal is demonstrated, and its output pulse characteristics are studied. It is found that the stability of amplitude and frequency of Q-switched pulse can be improved effectively by pulsedpumping. A satellite-free sub-nanosecond laser with a pulse width of 663 ps and an average power of 80 mW at the repetition rate of 1 kHz was developed, while the 50 μs pulse width of the pump was employed. Meanwhile, the near-diffraction limit output beam (M2 =1.03 ± 0.02) with pulse energy instability of less than 2 % was obtained. This study provides a reference for the development of highly stable satellite-pulse-free passive Q-switched lasers with a high repetition rate.

High Pulse Energy 1319 nm Q-Switched Nd: YAG Laser

We describe a high-peak-power macro/micro pulse 1319 nm laser operation, which is produced by the acousto-optic Q-switched Nd:YAG oscillator that is side-pumped with quasi- continuous-wave laser diode. Under remaining a fixed macro pulse repetition frequency of 400 Hz, the lasing characteristics for different micro pulse schemes are investigated. To realize 1319 nm single wavelength oscillation, a birefringence-plate is employed to suppress the adjacent 1338 nm line. Under 390 W of pump power with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200 ~\mu \text{s}$ </tex-math></inline-formula> of pulse duration, an average Q-switched 1319 nm power is increased from 32.5 W to 51.5 W by increasing the repetition rate of micro pulse from 400 Hz to 1600 Hz, and the corresponding micro pulse width can be stretched from 124 ns to 154 ns. The calculated maximum peak power is 0.655 MW with a pulse energy of 81.2 mJ, which is the highest-result reported to date for Q-switched 1319 nm lasers.

Space-qualified, compact and lightweight pulsed DPSS UV laser for the MOMA instrument of the ExoMars mission

A space-qualified pulsed UV laser has been developed as an irradiation source for the Mars Organic Molecule Analyser (MOMA) instrument aboard the “Rosalind Franklin” rover of the ExoMars mission (ESA/Roscosmos). MOMA will search for signatures of extinct and/or extant life on Mars. Its advanced analytical capabilities arise from the combination of a pyrolysis gas chromatograph and an ion trap-based mass spectrometer. With the addition of a compact UV laser system enabling laser desorption/ionization mass spectrometry, MOMA can detect a wide variety of both volatile and non-volatile, organic and inorganic molecules within Martian soil samples of interest. The design of the MOMA Laser Head is based on a longitudinally diode-pumped, passively Q-switched Nd:Cr:YAG oscillator generating millijoule pulses with nanosecond pulse durations at a wavelength of 1064 nm. A subsequent two-stage frequency quadrupling converts the fundamental infrared emission of the oscillator into the deep UV at 266 nm. The Laser Head emits UV pulses with a duration of about 1.5 ns and an energy tunable between 12.5 and 125 µJ for optimum adaptation to varying ionization thresholds of different molecular species. The complex but highly compact opto-mechanical design, enclosed in a hermetically sealed housing, is realized within an envelope of 200 × 56 × 45 mm3 with a total mass of less than 220 g. In this paper, we present a comprehensive summary of our development efforts towards the delivery of the LH Flight Model, which has been integrated to the MOMA instrument and finally incorporated into the ExoMars rover.

Compact 200 W level linearly polarized microsecond-pulse Nd:YAG oscillator with nearly diffraction-limited beam quality.

A compact 200 W level diode-side-pumped microsecond (µs) pulse linearly polarized rod Nd:YAG laser oscillator was demonstrated with nearly diffraction-limited beam quality. The oscillator was based on a thermally near-unstable cavity design with two concave lenses in the cavity to enlarge the volume of the fundamental mode, leading to improvement of the laser efficiency and beam quality. Consequently, a record-high average power of 222 W was obtained at a repetition rate of 400 Hz with a 180 µs pulse width, corresponding to an optical-to-optical (o-o) conversion efficiency of 37%. The average beam quality factor was measured to be M2=1.32, resulting in a brightness value as high as of 11.25GW/sr⋅cm2. To the best of our knowledge, this represented the highest average power, the highest o-o efficiency, and the highest brightness for a µs pulse 1064 nm rod Nd:YAG laser oscillator.

High-energy Q-switched Nd:YAG oscillator and amplifier development for large-mode, low-alignment sensitivity applications

High pulse energy, low-alignment sensitivity master-oscillator power-amplifier (MOPA) systems enable portable long range laser devices. Comprehensive amplifier modelling is an essential tool in producing efficient, optimised amplfication capable of producing high pulse energies. This paper outlines the development of a large-mode, low-alignment sensitivity neodymium yttrium aluminium garnet (Nd:YAG) (MOPA) system, achieving a total output pulse energy of 265 mJ with an optical efficiency of 18%. A Q-switched diode-pumped Nd:YAG zig-zag oscillator is developed with an output pulse energy of 98 mJ and slope efficiency of 31%. Through the use of an intracavity aperture, the beam quality exhibited an M2 of 4.3 and 4.6 and far field divergence of 1.3 mrad and 1.2 mrad in the horizontal and vertical, respectively. The oscillator output is amplified within a diode-pumped Nd:YAG zig-zag amplifier with a system amplification of 2.8. Comprehensive amplifier modelling based on a Frantz-Nodvik analysis is demonstrated, with the saturation characteristics suggesting a route to further energy enhancement and highlighting the necessity for amplifier modelling in high energy system design.

Pulsed Diode Laser Minibars for Pumping Space-Borne Solid-State Lasers

Laser diode benches (LDBs) with lasing wavelength of 808 nm were developed, manufactured and endurance-tested for utilization as pump lasers for the Nd:YAG oscillator in the climate satellite MERLIN. The LDBs combine customized TE-polarized GaAs-based 5-mm minibars with fast axis collimation lenses to produce a reliable, space qualified component at optical power of 63 W per minibar. Accelerated life tests of 20 LDBs are presented. Except for a small increase in threshold current, no wear out in operating current or sudden failures were observed, and reliable operation over the full mission time of >4 gigashots was confirmed. The electro-optical characteristics remain in the specified ranges after exposure to the total operational load of the mission.

A 61-mJ, 1-kHz cryogenic Yb:YAG laser amplifier* *Project supported by the National National Science Foundation of China (Grant Nos. 12004262 and 62005184) and the Natural Science Foundation of Top Talent of SZTU (Grant No. 202024555101039).

We report a diode-pumped rod-type Yb:YAG laser amplifier operating at 1 kHz.Cryogenic cooling method was adopted to make the Yb:YAG crystal work with four-level behavior. A single-frequency fiber laser acts as the seed in an actively Q-switched Yb:YAG oscillator. The resonator delivers 5.75-mJ pulses at 1 kHz with a pulse duration of approximately 40 ns. The pulses were amplified to 61 mJ in a four-pass rod-type Yb:YAG amplifier with optical-to-optical efficiency of 24% in the main amplifier. The M 2 parameter of the output laser is < 1.4.

Frequency-doubled Nd:YAG MOPA laser system with programmable rectangular pulses up to 200 microseconds

A compact frequency-doubled diode-pumped Nd:YAG master-oscillator power-amplifier laser system with programmable microsecond pulse length has been developed. Analog pulse shaping of the output from a single-frequency continuous-wave Nd:YAG oscillator, and subsequent amplification, allowed the generation of rectangular pulses with pulse lengths on the order of the Nd:YAG fluorescence lifetime. Temporally flat-top pulses of 1064 nm light with 520 mJ pulse energy, 2.6 kW peak power, and 200 μs duration, with linewidth below 10 kHz, were obtained at a repetition rate of 2 Hz. Second harmonic generation in a LBO crystal yielded pulses of 262 mJ and 1.3 kW peak power at 532 nm. The peak power can be maintained within 2.9% over the duration of the laser pulse, and long-term intensity stability of 1.1% was observed. The spatially flat-top beam at 1064 nm used in the amplifier is converted to a Gaussian beam at 532 nm with beam quality factor M2 = 1.41(14) during the second harmonic generation. This system has potential as a pump source for Ti:sapphire, dye, or optical parametric amplifiers to generate tunable high-power single-frequency radiation for applications in precision measurements and laser slowing.

A 37 mJ, 100 Hz, high energy single frequency oscillator* *Project supported by the National Natural Science Foundation of China (Grant No. 11504389) and the Funds of Key Lab of Function Crystal and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences.

Ways on energy enhancement for single frequency oscillator are reported in this paper. By quantitative analysis on gain and loss coefficients for each cavity mode with inserted etalons, a 37 mJ, 100 Hz high energy single-frequency Nd:YAG oscillator is obtained. The pulse energy is promoted by enhancement of nearly 7 times for a single frequency oscillator reported. The result proves that this method does help for energy enhancement. It has attractive potential for high energy single frequency oscillator design, especially on condition of intensive side pumped or long cavity laser, where strong competitors exist and are hard to be suppressed.

5.4 W, 9.4 ns Pulse Width, Long-Wave Infrared ZGP OPO Pumped by Ho:YAG MOPA System

We demonstrated a narrow pulse-width long-wave infrared ZnGeP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (ZGP) optical parametric oscillator (OPO) pumped by a 2.1 μm Ho:YAG master oscillator power-amplifier (MOPA). By short-cavity structure, a minimum pulse width of ~12 ns was achieved at 1kHz, 2kHz and 3kHz in Ho:YAG oscillator. By employing a three-stage amplifier, a maximum average output power of 73.1 W with pulse width of ~17 ns at the pulse repetition frequency of 3 kHz was obtained. Then a ZGP OPO pumped by the Ho:YAG MOPA was demonstrated. The maximum average output powers of 5.48 W at 8.2 μm and 22.4 W at 2.8 μm were obtained, corresponding to the pulse width of <; 10 ns.

161 W middle infrared ZnGeP2 MOPA system pumped by 300 W-class Ho:YAG MOPA system.

We demonstrated a high-power Q-switched two-stage Ho:YAG master-oscillator power-amplifier (MOPA) system dual-end pumped by Tm:YLF lasers. A new method was introduced by rotating and swapping spatial axial directions of pump beams to improve the beam quality of the Ho:YAG oscillator and first-stage amplifier. Two parallel second-stage Ho:YAG amplifiers were employed to output high power. A total maximum average output power of 332 W at 2091 nm with pulse repetition frequency of 20 kHz was achieved. Then a ZnGeP2 MOPA system was demonstrated using the Ho:YAG MOPA as the pump source. A maximum average output power of 161 W at 3-5 µm was obtained with 290 W incident Ho pump power, corresponding to beam quality factors M2 of 3.42 and 3.83 for horizontal and vertical directions, respectively.

10.8 kW, 2.6 times diffraction limited laser based on a continuous wave Nd:YAG oscillator and an extra-cavity adaptive optics system.

In this Letter, a 10.8kW, 2.6times diffraction limited laser based on a continuous wave (CW) Nd:YAG oscillator using an unstable resonator and an extra-cavity adaptive optics system was presented. Two Nd:YAG slabs and a disk-laser configuration were used to make the laser compact and power scalable. The output was a rectangular annulus, which was further expanded to a square annulus and was adaptively corrected by an extra-cavity deformable mirror (DM). The DM was designed to be capable of correcting the square annular wavefront aberrations. In the experiment, the vertical beam quality was improved from 51.7 to 2.6times diffraction limited after correction. To the best of our knowledge, this is the highest power and brightness based on a CW Nd:YAG oscillator.

Kilohertz 1645 nm Cavity-Dumped Er:YAG Laser Pumped by a Broadband 1470 nm Laser Diode

A laser diode (LD) pumped cavity-dumped 1645 nm Er:YAG laser with a kilohertz pulse repetition rate is reported for the first time. Using a cost-efficient continuous wave 48 W fibre-coupled broadband 1470 nm LD as the pumping source, an average power of 7.7 W with a pulse width of ~10 ns was achieved at 9.5 kHz, which is the highest average power ever obtained from an LD-pumped Er:YAG pulsed laser. Moreover, a pulse peak power of ~0.16 MW (~1.6 mJ in energy) was reached at repetition rates of 3 kHz and lower, which is the highest pulse peak power ever obtained from an LD-pumped kilohertz Er:YAG oscillator, to the best of our knowledge. This laser has a variety of potential applications in eye-safe remote sensing and laser radars in both the near- and mid-infrared ranges.

High-power narrow-linewidth QCW diode-pumped TEM00 1319 nm Nd:YAG oscillator using twisted-mode technique

We demonstrated a high-average-power, narrow-linewidth, quasi-continuous-wave diode-side-pumped 1319 nm Nd:YAG twisted-mode laser oscillator with a linearly polarized TEM00 mode. The resonator is based on a symmetrical convex–convex structure with a two-rod configuration for birefringence compensation, working in a thermally near-unstable cavity. With an optimum cavity length of 940 mm, a 39.4 W linear polarized 1319 nm laser is obtained with a good beam quality of M2 = 1.21 and a linewidth of ~250 MHz, and the corresponding brightness is as high as 1.55 GW cm−2. The laser is operated at a repetition rate of 500 Hz and pulse duration of 150 µs. To the best of our knowledge, this is the highest output power 1319 nm laser with narrow-linewidth from diode-pumped Nd:YAG lasers, and is the first report on the twisted-mode laser operation at the 1.3 µm region.

193 fs from an Yb:YAG oscillator mode-locked using nonlinear polarization rotation via Type I SHG with intrinsic dispersion compensation.

The mode-locking technique using nonlinear polarization rotation via Type I second-harmonic generation (SHG) is demonstrated on the femtosecond timescale. The narrow spectral bandwidth of the loss modulation was broadened via a double crystal approach, which allows for mode-locking broadband gain media. We prove the predicted advantages of the technique to be correct utilizing intrinsic dispersion compensation and group-velocity mismatch management to produce 193 fs pulses. This eliminates the need for dispersion compensating elements. The technique can be applied to high-power lasers at any wavelength where a suitable SHG process is possible.

High-Power High Beam Quality Narrow-Linewidth Quasicontinuous Wave Microsecond Pulse 1064-nm Nd:YAG Amplifier

We demonstrated a high average power, high beam quality, narrow linewidth, quasicontinuous wave (QCW) diode-pumped 1064-nm Nd:YAG amplifier. A narrow-linewidth QCW pulse Nd:YAG oscillator was employed as the seed laser, providing a maximum average power of 53.4 W at a pulse repetition frequency of 500 Hz and pulse width of 108 μ s with a beam quality factor M2 = 1.21. After that, a two-stage double-pass Nd:YAG amplifier was performed. The amplifier delivers a maximum output power of 238 W with a linewidth of 0.4 pm and a tunable range of 119.3 pm. The beam quality was measured to be M2 = 1.65. To the best of our knowledge, this represents the highest average power and the highest brightness for a narrow-linewidth QCW microsecond pulse 1064-nm laser.