Master Oscillator Power Amplifier System Research Articles

High-energy, low-jitter, narrowband ps probe laser for kHz-rate fs/ps coherent anti-Stokes Raman scattering.

Hybrid fs/ps coherent anti-Stokes Raman scattering (CARS) thermometry often utilizes ps probe pulses derived from pulse shaping or spectrally filtering the primary laser source or by synchronization with a low repetition rate external laser. This results in limited energy, spectral resolution, and/or repetition rate of the ps probe. In this work, a master-oscillator power-amplifier (MOPA) laser was synchronized to the oscillator of a Ti:sapphire regenerative amplifier to achieve high-energy (600 µJ), narrowband (58 ps) probe pulses at kHz repetition rates. Temporal filtering allows the pulse characteristics to be adjusted for each application. At 25 Torr, relevant to high-speed flows, the kHz-rate MOPA system generated signal-to-noise ratios 3× higher in nitrogen and had improved precision relative to a 10 ps probe derived from spectral filtering and the power-amplifier. The MOPA system also enabled single-shot ro-vibrational hybrid fs/ps CARS thermometry in 650 K heated air.

A 71 mJ, 300 Hz mid-infrared source based on ZnGeP2 MOPA system

We demonstrated a 71 mJ mid-infrared ZnGeP2 (ZGP) master oscillator power amplifier (MOPA) system that operated at the pulse repetition frequency of 300 Hz. A 2090.6 nm electro-optical Q-switched holmium:yttrium–aluminum-garnet MOPA system with a total energy of 138.3 mJ was used as the pump source of the ZGP-MOPA system. First, based on a ZGP optical parametric oscillator, a mid-infrared laser output of 1.3 mJ was obtained in the state of low-energy pumping. The corresponding beam quality factor M2 was 2.01 × 2.10 (horizontal directions × vertical directions). After two-stage amplification, a mid-infrared laser of 71 mJ was obtained. The pump energy and seed energy of the second ZGP optical parametric amplifier were 92.7 mJ and 23 mJ, the corresponding slope efficiency was 70.3 %. At the maximum output energy level, the pulse width of the mid-infrared laser was 14.6 ns, and the beam quality factor M2 was 3.96 × 3.75.

Single-frequency high-energy pulses from an Er:Yb glass planar waveguide amplifier with good beam quality

We demonstrate a master oscillator power amplifier system that emits single-frequency, high-energy optical pulses at 1539 nm using an Er, Yb:glass planar waveguide amplifier with a normalized frequency of the waveguide of 4.4. A maximum pulse energy of 9.7 mJ is observed at a repetition frequency of 500 Hz. The signal to noise ratio is 25 dB and is independent of the repetition frequency from 100 to 500 Hz. The beam quality factor M2 of the output is 1.03 thanks to the small normalized frequency of the planar waveguide.

High-repetition-frequency, high-energy mid-wave infrared ZnGeP2 MOPA system

A high-repetition-frequency and high-energy ZnGeP2 master oscillator power amplifier (ZGP-MOPA) system was demonstrated. The pump source was a 2097 nm Ho:YAG laser with maximum average power of about 140 W and repetition frequency of 2 kHz. Using this pump source, the ZGP-MOPA system obtained a mid-wave infrared laser with a maximum average power of 58.9 W and pulse width of 20.1 ns, corresponding to the pulse energy and peak power of 29.5 mJ and 1.5 MW. By adjusting the divergence of seed source to match the divergence of pump source, the beam quality factor M 2 of the ZGP-OPA was 3.9 × 3.7 (horizontal directions × vertical directions), the M 2 of the signal was 2.7, and the M 2 of the idler was 2.8. The corresponding maximum average power and pulse energy were 53.3 W and 26.7 mJ.

Widely Tunable Pulse Duration 100 mJ Single-Mode MOPA System Based on Yb-Doped Tapered Double-Clad Fiber and Nd:YAG Solid-State Amplifiers

We report on a 1064 nm master oscillator power amplifier (MOPA) system based on pulse-modulated laser diode seed sources combined with fiber preamplifiers and a Yb-doped tapered double-clad fiber (T-DCF) amplifier used as an all-fiber master oscillator and a two-stage side-pumped solid-state power amplifier. The combination of two master oscillators and a single power amplifier allowed us to obtain pulses with a duration ranging from 10 ns to 10 μs with energy up to 137 mJ at 100 Hz. For the first time, we demonstrate a widely tunable pulse duration and a solid-state MOPA system with over 100 mJ energy based on a T-DCF fiber seed laser.

High-power, highly efficient, all-fiber wavelength-tunable polarization-maintaining Tm-doped fiber MOPA system

A 2 μm all-fiber wavelength-tunable polarization-maintaining Tm-doped fiber master oscillator power amplifier (MOPA) system is presented. We demonstrate an all-fiber ring cavity Tm-doped fiber master-oscillator (MO) with a tuning range of 60 nm (1959.9–2020.1 nm). The maximum output power of 82.4 mW is obtained at 1991 nm with the launched pump power of 16 W at 793 nm, corresponding to a slope efficiency of 10.8 % concerning launched pump power. Finally, through the first stage amplification, the power is successfully amplified to 38.92 W, the slope efficiency is about 31.4 %, and the polarization extinction ratio (PER) reaches 21.4 dB. Then a theoretical simulation is carried out to calculate the influence of different fiber lengths on the slope efficiency and output power of the amplifier stage when the pump power is increased to 420 W, which provides theoretical guidance for the subsequent experiments. Through the simulation, it is found that the output power will be greatly improved by choosing the appropriate fiber length and increasing the pump power.

1064 nm laser pumped optical parametric oscillator based on BaGa4Se7 crystal at 1 kHz repetition rate

In this work, a tunable mid-infrared optical parametric oscillator based on type I phase-matching BaGa4Se7 was demonstrated. Using a Nd:YAG master oscillator power amplifier system as pump source, we firstly achieve the 1064 nm pumped BGSe-OPO at 1 kHz repetition rate. With pump double-pass single resonant oscillator configuration, the maximum output power at 4.18 μm was 483 mW and the corresponding conversion efficiency is 8.78 %. Both temperature and angle tuning of BGSe-OPO were studied and widely tunable output in the range of 3.36–5.16 μm was obtained. The average power fluctuation measured within 30 min was 0.98 % root mean square. This study has unveiled the great potential of BGSe crystal in highly stable, widely tunable, high repetition rate mid-infrared pulse generation.

Single frequency pulsed Er,Yb co-doped fiber amplifier with 2 mJ of output energy

High-energy single-frequency pulsed light with low noise is generated from a master oscillator power amplifier (MOPA) system at 1.55 μm eye-safe wavelength using an ultra large mode area Er-Yb gain fiber. At a pulse repetition rate of 2 kHz, the maximum pulse energy without stimulated Brillouin scattering (SBS) reaches 2.07 mJ with 375 ns pulse duration for a pump power of 56.4 W. The pulse energy fluctuation is approximately 0.72 % within 21.5 min. The signal noise ratio (SNR) from the single-frequency fiber amplifier, at the highest pulse energy, centered at 1551.1 nm, is approximately 30 dB. The spectral half width of the signal light is calculated to be 1.28 MHz, which is close to the transform limit.

1.36 J nanosecond laser at 1 kHz repetition based on a slab amplifier chain.

A high beam quality diode-pumped Nd:YAG master oscillator power-amplifier (MOPA) laser with three end-pumped slab amplifiers is developed. The Q-swtiched side-pumped rod oscillator presented a pulse energy 3.1mJ with beam quality factors of M x2=1.17 and M y2=1.15 at a repetition of 1kHz. The MOPA system delivered a pulse energy of 1.36J with a pulse width of 48.2ns and an extraction efficiency of 44.8%. The beam quality factors of M x2=1.72 and M y2=3.85 are measured without any phase-conjugators or adaptive optics.

Backscattered Background Noise of the Lidar Ceilometer Influence Imposed by ASE in Single-Frequency Nanosecond Pulsed Laser at 1.5 μm

In this work, we demonstrate a three-stage all-fiber master oscillator power amplifier (MOPA) system emitting over 1 W of the linearly polarized narrow-linewidth pulse output power with 10 kHz pulse repetition frequency and 400 ns pulse width without the amplified spontaneous emission (ASE) at ~1.5 µm. Initially, we analyze the effect of the ASE on the first derivative of backscatter intensity via a contrast experiment. The experiment results show that the noise intensity with angle of inclination is affected by the ASE of the amplifier, thereby decreasing the signal-to-noise ratio of the output power. The laser is characterized by a very low or no ASE level of the output signal when acquiring the first derivative of backscatter intensity with low noise. This condition provides a reference for improving the properties of the laser used for cloud detection.

A high-energy Ho: YLF MOPA system pumped by Tm: YAP lasers

This paper introduces a high-energy Q-switched Ho: YLF master oscillator power amplifier (MOPA) system pumped using linearly polarized Tm: YAP lasers. In this system, the pulse repetition frequency was 100 Hz, and an 84.7 mJ Ho laser was generated with a total pump power of 102.3 W, corresponding to a total optical conversion efficiency of 8.3%. The oscillator yielded a maximum output energy of 20.0 mJ and pulse width of 19.0 ns, corresponding to a peak power of 1.05 MW. Moreover, the amplifier delivered a maximum output energy of 84.7 mJ and pulse width of 18.0 ns, corresponding to a peak power of 4.70 MW. In addition, the system exhibited an excellent beam quality in both directions, with the M2 factors better than 1.1 and 1.3 at the oscillator and amplifier, respectively.

Watt-level 1.6 μm dissipative soliton ultrafast laser and external generation of ∼70 fs noise-like pulses for supercontinuum generation

Here, we propose a high power dissipative soliton (DS) laser with a central wavelength of ∼1612 nm. The whole laser system includes the mode-locking oscillator and the corresponding master oscillator power amplifier (MOPA). The mode-locking oscillator is a nonlinear amplifier loop mirror (NALM) cavity, which has a net normal dispersion enabling the generation of nJ-level DS pulses. To further enhance the output power of the 1.6 μm DS pulses, the specially-designed MOPA system consisting of multiple-stage single-pass amplifier is constructed, which can amplify the output power to watt level and meanwhile keeps a high suppression ratio to C-band amplified spontaneous emission (ASE). This high power 1.6 μm DS laser will have further applications in biomedical research and material processing. In the amplifier, we observe the automatic evolution of the DS pulses into the noise-like (NL) pulses under high pumping strength. At the maximum pump power, the MOPA system delivers the NL pulses with an output power of over 2 W. The narrowest spike duration is ∼70 fs (fs). This 1.6 μm fs-scale NL laser is a good pump source for generating the mid-infrared supercontinuum without short wavelength region loss. To demonstrate the superiority of this NL laser, a broad supercontinuum from ∼0.87 μm to ∼3.75 μm waveband is achieved with a piece of highly germanium-doped (Ge-doped) fiber.

Improving performance prediction of diode end-pumped solid-state Nd:YAG rod amplifiers by incorporating pump mode evolution.

Master Oscillator Power Amplifier (MOPA) systems find extensive use in laser development to increase the optical power of laser emissions from a Master Oscillator (MO). Commonly used are the cylindrical rod MOPAs that are optically excited using a multimode fiber-coupled (FC) diode laser emission in an end-pumped configuration. Current analytical 3D models that incorporate thermal effects, gain saturation, and iterative Fourier beam propagation methods, collectively, rely on static approximations of the evolution of the FC pump beam profile over the longitudinal volume of the amplifier crystal. Furthermore, in general, the spectral behavior of the FC diode emission is assumed to be static, and the thermal wavelength shift is not accounted for in the simulation. In this work, we demonstrate a novel approach for accurate modeling of the multimode FC pump beam emission as a complex field using a phase-only Gaussian to flat-top (FT) diffractive optical element, thus allowing for the inclusion of the pump beam into the iterative propagation method. Additionally, we present a method for precise calibration of the model using simple experimental measurements of the diode emission spectrum. The theoretical model is experimentally validated using an end-pumped Nd:YAG crystal rod to perform single-pass amplification of a Gaussian beam, showing excellent agreement with predicted output powers over the calibrated range of pump powers. Furthermore, we provide experimental data that exhibits a strong correlation between the Gaussian to FT phase-only transformation and the multimode FC diode evolution in free-space propagation.

Widely-tunable all-fiber Tm doped MOPA with > 1 kW of output power.

In this paper, we report on a high-power and widely tunable thulium-doped fiber laser (TDFL) based on a monolithic master oscillator power amplifier (MOPA) system. The master oscillator is a Tm fiber ring laser incorporating a tunable bandpass filter to realize narrow linewidth and wavelength tunable operation. The MOPA generated 1010 W ∼1039 W of output power over a tuning range of 107 nm from 1943 to 2050nm with slope efficiencies of more than 51% and spectra linewidth of ∼0.5 nm. Power stability (RMS) in ∼10 min scale is measured to be ∼0.52%. A diffraction-limited beam quality factor M2 of ∼1.18 is measured at 920 W of laser output. Output power is pump-limited without the onset of parasitic oscillation or amplified spontaneous emission (ASE) even at the maximum power level. This is the first demonstration, to the best of our knowledge, on an all-fiber integrated wavelength-tunable TDFL at 2 µm with output power exceeding 1 kW.

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.

Amplification of higher-order Laguerre-Gaussian modes using a dual-pass MOPA system.

Structured light beams that are tailored for purpose have found a myriad of applications, from improved efficiency of laser-based industrial manufacturing processes to enhanced bandwidth in optical communication. While the selection of such modes is readily achievable at low powers (<100 mW) with external shaping devices, creating and controlling structured light at higher powers (>1 W) has proven to be a non-trivial task, particularly if dynamic control is required. Here we demonstrate the power amplification of low-power higher-order Laguerre-Gaussian modes using a novel in-line dual-pass master oscillator power amplifier (MOPA). The amplifier, operating at a wavelength of 1064 nm, consists of a polarization-based interferometer that alleviates parasitic lasing effects. Through our approach we demonstrate a gain factor of up to 17×, corresponding to an overall enhancement of 300% in amplification compared to a single-pass output configuration while preserving the beam quality of the input mode. These findings are confirmed computationally using a three-dimensional split-step model and show excellent agreement with the experimental data.

Spectrally flat mid-infrared supercontinuum pumped by a high power 2 µm noise-like pulse.

We demonstrate spectrally flat high-power mid-infrared supercontinuum (MIR SC) generation with record-breaking power of 33.1 W and power conversion efficiency of 75.06%. It is pumped by a 2 µm master oscillator power amplifier system consisting of a figure-8 mode-locked noise-like pulse seed laser and dual-stage Tm-doped fiber amplifiers with repetition rate of 4.08 MHz. Through cascading a piece of ZBLAN fiber with 13.5 µm large core diameter by direct-low-loss fusion splicing, SCs with spectral ranges of 1.9-3.68 µm, 1.9-3.84 µm, 1.9-4.02 µm and average powers of 33.1 W, 29.8 W, 25.9 W are generated. To the best of our knowledge, all of them have achieved the highest output power under the same condition of MIR spectrum range. This high-power all-fiber MIR SC laser system has relatively simple architecture, high efficiency and flat spectrum, demonstrating the advantages of 2 µm noise-like pulse pump in high-power MIR SC generation.

All-fiber 3.4-W 2.8-µm ultra-short pulse MOPA system seeded by the soliton self-frequency shift of 2-µm pulses.

We report an all-fiber 2.8-µm ultra-short pulse master oscillator power amplifier (MOPA) system seeded by a soliton self-frequency shift from a mode-locked thulium-doped fiber laser. This all-fiber laser source delivers 2.8-µm pulses with an average power of 3.42 W, a pulse width of 115 fs, and a pulse energy of 45.4 nJ. We demonstrate, to the best of our knowledge, the first femtosecond watt-level all-fiber 2.8-µm laser system. A 2.8-µm pulse seed was obtained via the soliton self-frequency shift of 2-µm ultra-short pulses in a cascaded silica and passive fluoride fiber. A novel, to the best of our knowledge, high-efficiency and compact home-made end-pump silica-fluoride fiber combiner was fabricated and used in this MOPA system. Nonlinear amplification of the 2.8-µm pulse was realized, and soliton self-compression was observed accompanied by spectral broadening.

Single-frequency 45-mJ pulses from a MOPA system using an Er,Yb:glass planar waveguide amplifier and a large mode area Er-doped fiber amplifier.

We demonstrate a master oscillator power amplifier (MOPA) system that emits single-frequency high-energy optical pulses at 1540 nm using an Er,Yb:glass planar waveguide amplifier and a large mode area Er-doped fiber amplifier. A double under-cladding and a 50-µm-thick core structure are employed for the planar waveguide amplifier to increase the output energy without degrading the beam quality. A pulse energy of 45.2 mJ with a peak power of 27 kW is generated at a pulse repetition rate of 150 Hz with a pulse duration of 1.7 µs. Moreover, the beam quality factor M2 of the output beam is 1.84 at the highest pulse energy thanks to its waveguide structure.

Stimulated Brillouin scattering induced mode degradation in high-power narrow-linewidth linearly polarized fiber amplifiers

In our high-power continuous-wave (CW) narrow-linewidth linearly polarized master oscillator power amplifier (MOPA) system, the mode degradation (MD) induced by stimulated Brillouin scattering (SBS) was observed. In the experiments, the beam quality maintained LP01 mode until the onset of SBS, and significantly deteriorated with the surging of SBS. Once the method of suppressing SBS was implemented, such as linewidth broadening and polarization extinction ratio (PER) weakening of the seed laser, the output laser mode recovered to fundamental mode, revealing the MD effect was evidently mitigated. Meanwhile, the associated relationship between MD and SBS was also investigated based on the analysis of spectrum, oscilloscope, and beam quality.