Master Oscillator Power Amplifier Laser System Research Articles

Pulse-shaped high-energy and high-average-power fiber laser in the nanosecond regime.

A high-energy and high-average-power pulsed fiber laser has been investigated in a master oscillator power amplifier (MOPA) configuration seeding with a diode laser at a programmed pulse duration of ∼250ns. The fiber amplifier successfully demonstrates the pulse with 21.4 mJ at the repetition rate of 50 kHz and a maximum average output power of 1535 W with a slope efficiency of 81.6% at 250 kHz. To overcome fiber nonlinearities such as stimulated Raman scattering (SRS) and self-phase modulation (SPM), extra-large mode area ytterbium (Yb)-doped step-index dual cladding fiber has been utilized as gain fiber in the MOPA laser system. The gain saturation effect in the power amplifier was greatly mitigated by the programmed seed signal. This pulse-shaped MOPA system can provide practical applications in many fields such as laser cleaning, paint stripping, and other applications requiring special pulse shapes.

High-stability, high-pulse-energy MOPA laser system based on composite Nd:YAG crystal with multiple doping concentrations

In this paper, a high-stability, high-pulse-energy laser at a repetition rate of 2 kHz was presented from an electro-optically Q-switched Nd:YAG master oscillator power amplifier (MOPA) system. A multi-segment composite Nd:YAG crystal was utilized as the gain medium of the electro-optically Q-switched laser, yielding a pulse energy of 8.6 mJ and a pulse width of 7.8 ns at 2 kHz. By using two laser diode (LD) end-pumped Nd:YAG amplifiers, the single pulse energy was amplified to 28.6 mJ, corresponding to a peak power of 3.7 MW. By frequency doubling with a LiB3O5 (LBO), 13.2 mJ and 6.4 ns laser pulses were achieved at 532 nm. With the temperature varying from −40℃ to 55℃, the coefficient of variation (CV) of the pulse energy was 2.6%. Besides, the laser system also presented high stability under the typical vibration condition of the airborne platform. This MOPA laser system is a promising laser source for airborne remote sensing.

High peak/average power picosecond pulsed MOPA system with tapered large mode area double-clad Yb-doped fiber

In this paper, a high peak/average power picosecond pulsed master‑oscillator power‑amplifier (MOPA) system utilizing tapered large mode area double-clad fiber (T-DCF) is presented. In a high average power regime, we report a pulsed MOPA laser system with average power up to 613 W at 20 MHz repetition rate with 50 ps pulse duration (613 kW of peak power and 30.6 μJ pulse energy). In high peak power regime, over 3MW of peak power pulses (at seed source bandwidth) at 1 MHz repetition rate (310 μJ pulse energy and 310 W average) was demonstrated. The outstanding properties of T-DCF for amplification of laser signals to high power/energy levels with maintaining the excellent beam quality open a new horizon for advanced laser material processing.

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.

Utilizing phase-shifted long-period fiber grating to suppress spectral broadening of a high-power fiber MOPA laser system

Abstract Suppressing nonlinear effects in high-power fiber lasers based on fiber gratings has become a hotspot. At present, research is mainly focused on suppressing stimulated Raman scattering in a high-power fiber laser. However, the suppression of spectral broadening, caused by self-phase modulation or four-wave mixing, is still a challenging attribute to the close distance between the broadened laser and signal laser. If using a traditional fiber grating with only one stopband to suppress the spectral broadening, the signal power will be stripped simultaneously. Confronting this challenge, we propose a novel method based on phase-shifted long-period fiber grating (PS-LPFG) to suppress spectral broadening in a high-power fiber master oscillator power amplifier (MOPA) laser system in this paper. A PS-LPFG is designed and fabricated on 10/130 passive fiber utilizing a point-by-point scanning technique. The resonant wavelength of the fabricated PS-LPFG is 1080 nm, the full width at half maximum of the passband is 5.48 nm, and stopband extinction exceeds 90%. To evaluate the performance of the PS-LPFG, the grating is inserted into the seed of a kilowatt-level continuous-wave MOPA system. Experiment results show that the 30 dB linewidth of the output spectrum is narrowed by approximately 37.97%, providing an effective and flexible way for optimizing the output linewidth of high-power fiber MOPA laser systems.

High-beam-quality sealed-off laser system oscillating in middle infrared spectral range on strontium atomic transitions

High-beam-quality laser oscillation is obtained at two Sr+ and several Sr atom lines in the middle infrared spectral region with average output power of about 1 W in a sealed-off laser tube. Using the same laser tube construction and enhancing the active volume in bore and length, average output power of about 3 W is also achieved in a sealed-off regime. Based on these laser tubes, master oscillator–power amplifier laser system is also developed and investigated.

Pulse amplification in a Cr4+:forsterite single longitudinal mode (SLM) multi-pass amplifier

An efficient multi-pass Cr:forsterite master oscillator-power amplifier laser system operating in the single-longitudinal mode was demonstrated and characterized. A significant increase in energy was obtained in a six-pass amplifier configuration giving a maximum value of up to 10.8 mJ, with a good beam quality and without significantly broadening the linewidth or increasing the M2. The amplifier performance was evaluated as a function of the pump energy and the number of passes. A Fourier transformation of the laser pulses was performed to confirm the linewidth value measured using a Fabry–Perot etalon.

Efficient picosecond traveling-wave Raman conversion in a SrWO4 crystal pumped by multi-Watt MOPA lasers at 1064 nm

Raman conversion with a 50-mm-long SrWO4 crystal in a single-pass, traveling-wave setup has been investigated in both purely steady-state and transient stimulated Raman scattering (SRS) regimes. For steady-state SRS experiment, we employed as a pump source a Q-Switched master oscillator power amplifier (MOPA) laser system at 1064 nm, delivering 325 μJ, 550-ps-long pulses with diffraction limited beam quality and high spectral purity. At 2-kHz repetition rate, we obtained up to 90 μJ pulse energy and 250 ps pulse duration at 1180 nm, with a conversion slope efficiency close to quantum limit. To approach the transient SRS regime, we pumped the same crystal with 16-ps-long pulses from a hybrid MOPA laser system based on a mode-locked Yb-fiber oscillator followed by a diode-pumped bulk Nd:YVO4 power amplifier. At the maximum incident pump average power of 3.75 W, we obtained 1.4 W at the first Stokes Raman-shifted wavelength of 1180 nm (37 % optical-to-optical conversion efficiency), with 15 ps pulse duration and 70 % conversion slope efficiency.

200 ps pulse generation at 1180 nm with a SrWO4 Raman crystal pumped by a sub-nanosecond MOPA laser system

We are reporting Raman conversion experiments with a SrWO4 crystal in a single-pass traveling-wave setup. As a pump source we employed a master oscillator power amplifier (MOPA) laser system at 1064 nm, delivering 200 µJ, 500 ps long pulses at a 9 kHz maximum repetition rate with limited diffraction beam quality. At 2 kHz we obtained up to 45 µJ pulse energy and 200 ps pulse duration at 1180 nm, with a conversion efficiency of 22%. Up to the maximum incident average pump power of 1.35 W no serious beam quality degradation was observed, and we measured a factor M2 ⩽ 1.5 for the Raman shifted beam.

High power diode-side-pumped 1 112-nm Nd:YAG laser based on master-oscillator power-amplifier system

We demonstrate a high power high beam quality diode-pumped 1 112-nm Nd:YAG master-oscillator poweramplifier (MOPA) laser system. To increase the extraction efficiency and output power, a four-pass amplifier scheme is employed. Finally, the injected laser output power is amplified from 26 to 64 W with beam quality factor M2=2.85. Furthermore, a theoretical model that takes the temporal overlap inversion number dynamics into account is employed to analyze the performance of the MOPA laser system, and a good agreement with the experimental data is obtained.

Narrowband, mid-infrared, seeded optical parametric generator based on non-critical CdSiP2 pumped by 120-ps, single longitudinal mode 1,064 nm pulses

In this work, we present low-threshold, efficient optical parametric generation in CdSiP2 pumping at 1,064 nm with 120-ps-long, single longitudinal and transverse mode pulses at 230-kHz repetition rate provided by a microchip passively Q-switched master-oscillator power amplifier laser system. Seeding at the signal wavelength with a laser diode, we generated bandwidth-limited idler pulses at 6,100 nm.

Single-frequency linearly-polarized 1083 nm all fiber nanosecond laser

Single-frequency linearly-polarized 1083 nm all fiber nanosecond master-oscillator power amplifier laser system is demonstrated. A ring laser, whose key components are one saturable absorber and two polarization controllers, delivers a single-frequency continuous wave laser. Using an electro-optic modulator as the modulator, the pulse laser seed is obtained by modulating the CW laser. By amplifying the pulse seed to the average power of 61.6 W in three stages, a single-frequency linearly-polarized laser with pulse duration of 16 ns, repetition rate of 10 MHz and pulse energy of 6.16 μJ is obtained. No nonlinear effect is observed in our experiment. Higher output power can be obtained by increasing LDs of the main amplifier.

High-energy Ho:LLF MOPA laser system using a top-hat pump profile for the amplifier stage

Numerical simulations show the advantage of using a top-hat intensity profile pumping the amplifier stage in an Ho:LuLiF4 (Ho:LLF) master oscillator power amplifier (MOPA) configuration over a Gaussian pump profile: higher pulse energies could be generated simultaneously with reduced peak fluence in Q-switched operation. In the experimental implementation, the top-hat beam was realized with a coherent beam transformation of the non-absorbed pump beam transmitted by the oscillator to pump the amplifier stage. The Ho:LLF MOPA produced 103.6 mJ at a repetition rate of 100 Hz with a pulse duration of 30 ns at a wavelength of 2053 nm, which corresponds to an optical-to-optical efficiency of 12.9 %. The beam quality was nearly diffraction limited (M 2 = 1.03).

90.4-W all-fiber single-frequency polarization-maintained 1 083-nm MOPA laser employing ring-cavity single-frequency seed oscillator

A high-power all-fiber single-frequency polarization-maintained (PM) laser operating at 1 083 nm is demonstrated using a master oscillator power amplifier (MOPA) structure. The seed source of this MOPA laser system is an in-house-built ring-cavity fiber oscillator. Four-stage amplification configuration is employed, in which the maximal output power of the main amplifier is 90.4 W, corresponding to a conversion efficiency of 72.5%. The polarization extinction ratio of the output light is 13 dB. The amplified spontaneous emission is suppressed by a factor of over 25 dB, and no stimulated Brillouin scattering effect is observed when a large-mode-area and high absorption coefficient PM gain fiber is employed.

Fifteen terawatt picosecond CO_2 laser system

The generation of a record peak-power of 15 TW (45 J, 3 ps) in a single CO(2) laser beam is reported. Using a master oscillator-power amplifier laser system, it is shown that up to 100 J of energy can be extracted in a train of 3 ps laser pulses separated by 18 ps, a characteristic time of the CO(2) molecule. The bandwidth required for amplifying the short injected laser pulse train in a 2.5 atm final CO(2) amplifier is provided by field broadening of the medium at intensities of up to 140 GW/cm(2). The measured saturation energy for 3 ps pulses is 120 mJ/cm(2) which confirms that energy is simultaneously extracted from six rovibrational lines.

High power high beam quality diode-pumped 1319-nm Nd:YAG oscillator-amplifier laser system

This paper demonstrated a high power and high beam quality diode-pumped 1319-nm Nd:YAG master oscillator-power amplifier laser system. A thermally near-unstable resonator with four-rod birefringence compensation flat-flat cavity was adopted as the master oscillator. A solid etalon was inserted in the unidirectional ring resonator to compress the laser linewidth. Under a repetition rate of 500 Hz and pulse width of 160 μs, the master oscillator delivers an average output power of 16.8 W at 1319 nm with linear polarisation, beam quality factor M2 = 1.16 and linewidth of 3.2 GHz. A double-pass power amplifier with two amplifier stages was employed for higher power scaling and the output power was amplified to be 25.9 W with M2 = 1.43.

Double-pass copper vapor laser master-oscillator power-amplifier systems: generation of flat-top focused beams for fiber coupling and percussion drilling

In this paper, a compact master-oscillator power-amplifier laser system incorporating telescopic beam expansion in a high-gain double-pass amplifier is presented. A miniature (0.5 W) master-oscillator copper vapor laser is used to efficiently extract over 37 W of high-beam-quality (full transverse coherence) output power from a kinetically enhanced nominally 35-W copper vapor laser at 12-kHz pulse repetition frequency. By configuring the oscillator for low coherence output and using a multimode optical fiber between the oscillator and the double-pass amplifier, a high-power (34 W) low-divergence output beam having a well-defined flat-top far-field beam profile was also produced. The flat-top farfield beam profile arises from control of the spatial coherence of a flat-top near-field beam, rather than the usual techniques for producing flattened Gaussian beams from coherent Gaussian beams. Use of the flat-top focused beam for high-speed percussion drilling of high quality 100-/spl mu/m diameter holes in metals was demonstrated, as well as high-power (34-W average power, 80-kW peak power) damage-free power transmission through 100-/spl mu/m core diameter step-index optical fibers.