Master Oscillator Power Amplifier System Research Articles

Frequency noise suppression of the high-power pumping laser in the SERF atomic magnetometer

Abstract A high-sensitivity SERF atomic magnetometer based on a noise-suppressed master oscillator power amplifier (MOPA) system is demonstrated. The spectrum and frequency noise of the laser are measured and it is proved that the frequency noise in the MOPA system is affected by the amplified spontaneous emission (ASE) stimulated from the power amplifier. The frequency noise of the MOPA system is decreased by filtering out the ASE background in the spectrum through a bandpass filter. The sensitivity of the SERF atomic magnetometer is improved by using the frequency noise-suppressed MOPA system as a pumping laser. This method can also be applied to other precision measurement fields based on the MOPA systems that have high requirement for frequency noise of laser.

Figure-8 mode-locked Yb-doped fibre oscillator with a nonlinear amplifying loop mirror and power amplification

Abstract We report an all-polarization-maintaining Yb-doped fibre (YDF) femtosecond (fs) laser source at ∼1 µm comprising a figure-8 mode-locked oscillator and two YDF amplifier stages. By employing a nonlinear amplifying loop mirror, we could achieve dissipative soliton mode-locking with an output of 24.6 mW at a repetition rate of 6.2 MHz. In our experiments, a Raman signal of 16% in the pulse energy helps to obtain stable mode-locked operation in the figure-8 oscillator. The dissipative soliton pulse from the oscillator is stretched by a chirped fibre Bragg grating and is amplified by a two-stage YDF amplifier. After compression, the YDF master-oscillator power-amplifier system yields fs pulses with a pulse energy of 2.3 µJ and a pulse duration of 274.6 fs at a repetition rate of 0.52 MHz. The output pulse energy is limited by the third-order nonlinearity of the fibre amplifier chain. Prospects for further pulse energy scaling are discussed.

145 W single-frequency fiber laser at 1607 nm with the seed and MOPA configuration

In this paper, high Er3+ concentration erbium doped fiber (EDF) and erbium-ytterbium co-doped fiber (EYDF) were fabricated for the seed and master oscillator power amplifier (MOPA) system of the single-frequency fiber laser. An in-band pumping source with the wavelength of 1535 nm was proposed to improve the efficiency in the ring-cavity. A slope efficiency of 23.8% with an output power of 49 mW was achieved and the laser linewidth was measured to be 800 Hz. In the MOPA system, a piece of EYDF was used firstly to absorb the backward 1 µm amplified spontaneous emission (ASE) and amplified the signal from the seed. Based on the above methods, an output power of 145 W was achieved at 1607.75 nm. Because of the self-phase modulation, the laser linewidth was expanded to be 10.75 kHz at the output power of 132 W. To the best of our knowledge, this is the highest efficiency and output power of the seed and the highest output power of the 1.6 µm single-frequency fiber laser.

A >20-W, linearly polarized single-frequency continuous-wave all-fiber laser at ∼1540 nm

We have developed both theoretically and experimentally an all polarization-maintaining fiber-based master oscillator power amplifier (MOPA) system, which allows for amplifying the single-frequency continuous-wave (CW) fiber laser to >20 W without compromising the laser intensity noise (−110 dBc/Hz@ relaxation oscillation peak) at the specific wavelength of ∼1540 nm. The experimental results agree well with the simulated results. To the best of our knowledge, this is the first demonstration of a ∼1540-nm single-frequency all fiber laser and reaching such a high-power level. The amplified laser features a narrow linewidth of ∼1.4 kHz and a spectral side-mode-suppression ratio of >38 dB, even as the laser wavelength is tuned from 1538.216 nm to 1540.616 nm. It is believed to be the narrowest laser linewidth realized in the <1550-nm wavelength band of an Erbium-Ytterbium co-doped fiber MOPA system. The all polarization-maintaining configuration of the MOPA ensures the amplified laser linearly polarized with the polarization extinction ratio of >22 dB and power root mean square fluctuations of <0.2 %@1h. This high-performance single-frequency fiber laser is expected to be an ideal pump source in the spin-exchange relaxation-free (SERF)-based atomic sensors after second harmonic generation.

In-band pumped, Q-switched thulium-doped fiber laser system delivering 140 W and 7 mJ pulse energy.

We report on a highly efficient, in-band pumped, Q-switched, Tm-doped, rod-type master oscillator power amplifier (MOPA) system delivering up to 140 W average output power and 7 mJ pulse energy with a slope efficiency of 77% at 20 kHz repetition rate. The amplifier is pumped with Raman-shifted fiber lasers centered at 1692 nm. This in-band pump scheme for Tm-doped fiber lasers can significantly mitigate their quantum defect-related heat load limitations. At the same time, this pump wavelength yields a similar amount of storable and extractable energy to the state-of-the-art pumping at 793 nm. This approach has allowed for the development of highly efficient Tm-doped fiber laser systems combining a high average power and a high output pulse energy.

Modeling and analysis of single-mode widely tunable all-fiber Ho-doped CW master oscillator power amplifier system

We report the design of an all-fiber single-mode polarization maintaining widely tunable Ho-doped master oscillator power amplifier (MOPA) system operating in the wavelength range of 2005-2135 nm based on a pre-amplifier and two power amplification stages. The single clad Ho-doped active fibers in the ring cavity based master oscillator, pre-amplifier, and power amplifiers are pumped using 1950 nm semiconductor laser diode pump sources. The amplification of the MOPA system is investigated over the entire spectral range of 2005-2135 nm. The highest output power achieved by the continuous wave (CW) Ho-doped MOPA system is 43 W at a wavelength of 2028.6 nm using pump power of 20 W with power conversion efficiency (PCE) of 90% for second power amplifier while the total pump power of Ho-doped MOPA system is 45 W. Optical bandpass filters (OBPFs) are employed between different stages of MOPA system to enable amplification over the wider spectral range of 2005-2135 nm by suppressing the amplified spontaneous emission (ASE). Not using OBPFs results in amplification that is limited to the spectral range of 2045-2130 nm. Therefore, a penalty of 45 nm can be avoided at the expense of using the OBPFs between different stages of MOPA system. This flexible MOPA system can be used in multiple applications, especially for space-borne high power transmitters operating in atmospheric transmission windows.

Tailoring the visible light band of Watt-level SCs pumped via picosecond pulse with different Raman extent

We investigate the supercontinuum (SC) tailoring property by varying the transmission fiber length after the master oscillator power amplifier system. The conversion efficiency of the visible light band is effectively enhanced via tailoring the Raman extent of the injected 30 ps pulse into the nonlinear photonic crystal fiber (PCF). Experimentally, a 3.6 W all-fiber SC spanning from 414 nm to over 1750 nm (@20 dB) is accomplished by using a high duty cycle domestic PCF through precisely controlling the extent of Raman effect. The proposed method is instructive for the further realization of high power SC with an enhanced spectral intensity in the visible light band.

Towards high-power MOPA architectures in single-mode fibers for mid-IR mode-locked operation.

We report on a master oscillator power amplifier (MOPA) system at 2.8 µm to achieve an average power of 10.28 W with a pulse energy and peak power of 403 nJ and 5.76 kW, respectively. The seed, a semiconductor saturable mirror (SESAM) based mode-locked linear cavity source, delivers approximately 70 ps pulses at 28.16 MHz. Two amplifier stages are utilized in counter-pumping and dual-pumping configurations to enable high extraction efficiency and signal gain. To the best of our knowledge, this result is the highest average power and pulse energy obtained from a SESAM-based 2.8 µm mode-locked laser employing ZBLAN fiber MOPA architecture. It paves the way for achieving high average power in-fiber nonlinear amplification in single-mode fibers in the mid-infrared wavelength region.

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.