Fiber Preamplifier Research Articles

High-gain Ho:YLF sub-nanosecond system seeded by a gain-switched laser diode

We demonstrate a high-gain Ho:YLF sub-nanosecond laser system utilizing a gain-switched laser diode as the seed source. The 1.0 kHz pJ-level seed from the gain-switched laser diode is first amplified to 1.1 mJ by a Ho-doped fiber preamplifier with a gain of 30 dB and a regenerative amplifier (RA) with a gain of 60 dB. By adding a single-pass amplifier, the pulse energy is further extended to 7.5 mJ. A pulse duration of 518.5 ps was achieved, which is symmetrical with no tail or sub-peaks. The root mean square (RMS) stability of the output energy of the entire system over a 0.5 h period is 2.11%. This method provides a reliable and simple way to directly obtain high-energy 2.05 µm sub-nanosecond lasers.

2.09 µm high-gain, high-energy sub-nanosecond laser amplification system and its application to a millijoule-level mid-infrared ZnGeP2 optical parametric generator.

In this Letter, we report for the first time to our knowledge a 2 mJ-level 2.09 µm Ho:YAG regenerative amplifier (RA) seeded by the first-stage Ho-doped fiber (HDF) preamplifier of a gain-switched laser diode (GSLD). After the single-pass power amplifier (SPPA), the output of a 2.09 µm pulse laser with 1 kHz, 570 ps, and >10 mJ was achieved. The overall gain of the whole amplifier system was greater than 90 dB, providing a novel, stable, and reliable sub-nanosecond (sub-ns) pump source operating at a pulse repetition frequency (PRF) of 1 kHz for an optical parametric generator (OPG) based on ZnGeP2 (ZGP). Specifically, for the ZGP OPG structure, a maximum pulse energy of 1.82 mJ at 3-5 µm had been achieved with an injected pump pulse energy of 5.47 mJ, corresponding to a slope efficiency of 39.5% and an optical-to-optical conversion efficiency (OOCE) of 33.27%.

Sub-50 fs pulses generation from an all-fiber monolithic gain-managed nonlinear amplifier with CFBG-based pre-compressor

We demonstrate an all-fiber monolithic laser source from a gain-managed nonlinear (GMN) fiber amplifier with a CFBG-based pre-compressor that generates high-contrast pulses with a repetition rate of 80 MHz, average power of 1.6 W, and pulse duration of sub-50 fs. The compressed pulse quality can be optimized by tuning the parameters of the seed pulses injected into the GMN amplifier by controlling the pump power of the fiber pre-amplifier. This compact and cost-effective laser system is a simplified design of the GMN amplification-based femtosecond fiber laser systems. With alignment-free characteristics in the amplifiers and clean compressed pulses, it is easy to assemble and use in applications such as multi-photon microscopy.

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.

Millijoule 265 fs Tm:YAP regenerative amplifier for driving ultrabroad band collinear mid-infrared optical parametric amplifiers.

Generation of 265-fs millijoule pulses at 1940 nm from a solid-state regenerative amplifier has been demonstrated. The amplification chain consists of a thulium-doped fluoride (Tm:ZBLAN) fiber oscillator, a two stage Tm:ZBLAN fiber preamplifier, and a regenerative amplifier with a thermoelectrically cooled thulium-doped yttrium aluminium perovskite crystal. The newly developed light source is used for pumping an ultra broadband mid-infrared optical parametric amplifier based on a gallium selenide crystal. The 2.5-4 µm range of a multioctave supercontinuum, generated in a polarization-maintaining ZBALN fiber, is used as the MIR seed. The amplified signal in combination with the corresponding idler pulses spread from 2.5 to 10µm in a collinear geometry.

An All-Fiberized Chirped Pulse Amplification System Based on Chirped Fiber Bragg Grating Stretcher and Compressor

We report an all-fiberized chirped pulse amplification system without any bulk devices. The stretcher and compressor are chirped fiber Bragg gratings inscribed in a 6/125 μm single-mode fiber and a 30/250 μm large-mode-area fiber. The fabrication system of chirped fiber Bragg gratings was designed and built by ourselves. The width of the linear exposure spot was controlled according to the different fiber sizes to improve the fabrication quality, and the parameters of chirped fiber Bragg gratings were fine-tuned during the fabrication to achieve the overall system’s spectral matching. Two fiber circulators with the same fiber sizes as the chirped fiber Bragg gratings were employed to auxiliarily achieve the pulse stretching and compression. The dispersion accumulations provided by the stretcher and compressor are 129.8 ps and 90.8 ps. The power amplifiers were composed of the two-stage 10/130 μm fiber pre-amplifier and the 30/250 μm fiber main amplifier. The proposed chirped pulse amplification system with no spatial light is the true sense of an all-fiberized chirped pulse amplification structure and shows the main trend in development of ultrashort pulse fiber lasers.

High power, single-frequency, long pulse width 1064 nm laser source

We present a high power, long pulse width, high pulse repetition rate (PRR), single-frequency 1064 nm master oscillator power amplifier (MOPA). The MOPA system consists of a single-frequency 1064 nm seed laser, ytterbium-doped fiber preamplifier, and two stages of rod Nd: YVO4 amplifier. The MOPA delivers a maximum average output power up to 122.3 W with a spectral linewidth of 24.15 fm, operating at a PRR of 50 kHz with a pulse width of 10 μs. The average beam quality factor is measured to be M2=1.375, exhibiting a Gaussian TEM00 mode. The output power fluctuation of the MOPA system is less than 0.96% over one hour. Such a high power, single-frequency laser source with long pulse width and high PRR is expected to be utilized for long-distance, high-precision laser imaging.

Development and Demonstration of Australian First Working Sodium Guide Star Laser

The Australian first working sodium guide star laser system has been designed and developed for various astronomical and space-related applications. A completely diode-pumped pulsed system was developed initially followed by a largely fiber-based continuous wave (CW) system operating at 589 nm achieved through a unique wavelength conversion scheme by combining 1342 and 1050 nm through a sum frequency generation process. For the CW system, single-mode laser beams at both 1342 and 1050 nm are achieved from fiber-based seed oscillators and fiber amplifiers. The output power of ~25 W at 1342 nm is achieved from a single frequency fiber Raman amplifier. Output power up to 70 W at 1050 nm is achieved from a Yb-doped fiber pre-amplifier followed by a Yb-doped fiber power amplifier. For the sum frequency generation process, optimum focusing parameters are evaluated and determined. The CW system has generated more than 20 W output power at 589 nm, a circularly polarised beam with a good beam quality, spectral linewidth ≤ 2 MHz, and the laser output locked on the sodium D2 line at 589.159 nm. The system has been successfully demonstrated at EOS Space Research Centre, Mt Stromlo, Canberra, and become the Australian first working sodium guide star laser system.

Adaptive Nonlinear Phase Compensation in a Femtosecond Hybrid Laser with Varying Pulse Repetition Rate

In this manuscript, an implementation of a tunable nonlinear phase compensation method is demonstrated on a typical femtosecond hybrid laser consisting of a fiber pre-amplifier and an additional solid-state amplifier. This enables one to achieve constant laser pulse parameters over a wide range of pulse repetition rates in such a laser. As the gain in the solid-state amplifier is inversely proportional to the input power, the shortfall in the solid-state gain at higher repetition rates must be compensated for with fiber pre-amplifier to ensure constant pulse energy. This increases the accumulated nonlinear phase and consequently alters the laser pulse parameters such as pulse duration and Strehl ratio. To overcome this issue, the nonlinear phase must be compensated for, and what is more it should be compensated for to a different extent at different pulse repetition rates. This is achieved with a tunable CFBG, used also as a pulse stretcher. Using this concept, we demonstrate that constant laser pulse parameters such as pulse energy, pulse duration and Strehl ratio can be achieved in a hybrid laser regardless of the pulse repetition rate.

The 266-nm ultraviolet-beam generation of all-fiberized super-large-mode-area narrow-linewidth nanosecond amplifier with tunable pulse width and repetition rate

We report on a compact, stable, all-fiberized narrow-linewidth (0.045 nm) pulsed laser source emitting laser beam with a wavelength of 266 nm, and tunable pulse width and repetition rate. The system is based on all-fiberized nanosecond amplifier architecture, which consists of Yb-doped fiber preamplifiers and a super-large-mode-area Yb-doped fiber power amplifier. The fiber amplifier with a core of 50 μm is used to raise the threshold of the stimulated Brillouin scattering (SBS) effect and to obtain high output power and single pulse energy. Using lithium triborate (LBO) crystal and beta-barium borate (BBO) crystal for realizing the second-harmonic generation (SHG) and fourth-harmonic generation (FHG), we achieve 17 μJ (1.73 W) and 0.66 μJ (66 mW), respectively, at wavelengths of 532 nm and 266 nm and a repetition rate of 100 kHz with pulse width of 4 ns. This source has great potential applications in fluorescence research and solar-blind ultraviolet optical communication.

270 μJ subnanosecond hybrid MOPA system operating at the wavelength of 539.5 nm

The hybrid laser system based on the picosecond fiber ring laser with a two fiber preamplifiers and terminal bulk amplifier was demonstrated. The cavity length of the master oscillator was 200 meters, the mode-locking regime was realized by the effect of nonlinear polarization evolution. After amplification and conversion of radiation to the second harmonic while using the lithium niobate crystal, the laser system emitted bursts of pulses at a wavelength of 539.5 nm with a duration of 70 μs at the half of maximum. The energy in a single pulse with a duration of 100 ps was up to 270 μJ and short pulses repetition rate inside bursts was 1 MHz.

Hybrid CPA system comprised by fiber-silicate glass fiber-single crystal fiber with femtosecond laser power more than 90 W at 1 MHz

A high power and hybrid chirped pulse amplification (CPA) system comprised by fiber-silicate glass fiber-single crystal fiber amplifier is demonstrated in this work. In this hybrid system, the high gain compact silicate glass fiber amplifier is used to boost the power, amplified power more than 92 W is obtained with the injected power of 400 mW at 1 MHz, corresponded amplification gain as high as 23.6 dB. To our best knowledge, this is the highest power obtained in CPA amplification with silicate glass fiber. The single crystal fiber amplifier is used to boost the energy with low nonlinearity in high pulse energy amplification. Amplified power of 122 W at 1 MHz is obtained, corresponding to a pulse energy of 122 μJ. After amplification, the laser pulses are compressed by chirped volume Bragg grating (CVBG), the total compression efficiency greater than 73% is obtained by control the spectrum width with a fiber filter with pass band of 5 nm in the fiber pre-amplifier to match the reflected bandwidth of the CVBG compressor. To match the dispersion between the chirped fiber Bragg grating (CFBG) stretcher and the CVBG compressor, the self-made temperature tuning device of CFBG is employed to make precision dispersion match. The optimized pulse width of 660 fs at compressed power of 90 W is obtained. This compact and high power ultrafast laser will find various applications in scientific research and industrial applications.

High gain fiber-solid hybrid double-passing end-pumped Nd:YVO4 picosecond amplifier with high beam quality**Project supported by the National Natural Science Foundation of China (Grant Nos. 61675009 and 61325021) and Key Program of Beijing Municipal Natural Science Foundation, China (Grant No. KZ201910005006).

We propose a fiber-solid hybrid system which consists of a semiconductor saturable absorber mirror (SESAM) mode-locked fiber seed with a pulse width of 10.2 ps and a repetition rate of 18.9 MHz, a two-level fiber pre-amplifier and a double-passing end-pumped Nd:YVO4 amplifier. In the solid-state amplifier, to enhance the gain and the extraction efficiency, a specially designed structure in which the seed light passes through the gain medium four times and makes full use of population inversion is used as the double-passing amplifier. Besides, the beam filling factor (the ratio of the seed light diameter to the pump light diameter) and the thermal lens effect of the double-passing amplifier are considered and its optical-to-optical conversion efficiency is further improved. To preserve the beam quality of the double-passing amplifier, a new method of spherical-aberration self-compensation based on the principles of geometrical optics is used and discussed. Our system achieves a maximum average power of 9.5 W at the pump power of 28 W, corresponding to an optical-to-optical efficiency of 27%. And the beam quality factor M2 reaches 1.3 at the maximum output power.

30 W single-frequency continuous-wave master oscillator power amplifier laser at 1342 nm.

We present a power-scalable high-power single-frequency continuous-wave 1342 nm master oscillator power amplifier (MOPA) system that consists of a polarized single-frequency 1342 nm LD seed laser, a Raman fiber preamplifier, and a three-stage ${\rm Nd}:{{\rm YVO}_4}$Nd:YVO4 power amplifier. The single-frequency output power of 30 W at 1342 nm is achieved with the beam quality factors ${{\rm M}^{2\:}} = {1}.{26}$M2=1.26, and the power stability for 1 h is better than ${\pm }\;{0}.{5}\% $±0.5%.

Powerful ultrafast hybrid PM Yb:fiber–Nd:GdVO4 master oscillator power amplifier

We demonstrated an ultrafast hybrid fiber — Nd:GdVO4 master oscillator power amplifier (MOPA) system at 1063 nm without the chirped pulse amplification (CPA) technique for the first time. The fiber oscillator delivered a pulse duration of 1.8 ps at a repetition rate of 22.4 MHz. The pulse energy from the fiber oscillator was 0.2 nJ. The beam went through a fiber preamplifier and was boosted to 8.1 mW, corresponding to a pulse energy of 0.36 nJ. Then the seed was further amplified by the solid-state MOPA system. As a consequence, the output power of 4.8 W at 1063.2 nm was obtained with a pulse duration of 4.7 ps and a peak power of 45.5 kW. The long term operation revealed the MOPA system was very stable and robust.

Radiation Effects on WDM and DWDM Architectures of Preamplifier and Boost-Amplifier

We investigated the X-ray [40 keV, 700 Gy(SiO2), ~80 mGy/s] radiation effects on the performances (gain) of Er-doped fiber preamplifier (EDFA) and Er/Yb codoped fiber boost amplifier (EYDFA). Various EDFA and EYDFA architectures have been designed to operate either in wavelength division multiplexing (WDM) or dense WDM (DWDM) schemes. We compare the performances of amplifiers based on conventional or radiation-hardened (RH) versions of the active Er-doped or Er/Yb-codoped fibers. Our results show that for all amplifier architectures, the various channels undergo similar gain degradation levels and kinetics, as expected from the measured spectral dependence of the radiation-induced attenuation of the phosphosilicate (ErYb-doped) and aluminosilicate (Er-doped) glass matrixes of these fibers. This degradation remains very limited for the amplifiers based on RH fibers, with a gain decrease of less than 0.3 mdB.Gy−1 for the EDFA (~30 dB initial gain) and less than 0.8 mdB.Gy−1 for the EYDFA (~18 dB initial gain) in the DWDM architecture.

25 W 2 μm broadband polarization-maintaining hybrid Ho- and Tm-doped fiber amplifier.

We report the design, evaluation, and performance of a polarization-maintaining (PM) fiber amplifier with a CW output power of >25 W at 2051nm and a high input signal dynamic range of 34dB at 25W. To improve both the output power and dynamic range performance of previous amplifiers, we propose a PM hybrid design with a single-clad Ho-doped preamplifier (HDFA) followed by a double-clad Tm-doped power amplifier (TDFA). The role of the Ho-doped fiber preamplifier is to provide large input signal dynamic range, low noise figure, and moderate output power over an operating bandwidth from ≈2-2.1 μm. The role of the Tm-doped fiber power amplifier is to offer power amplification with good efficiency, taking full advantage of 2-for-1 ion-ion interactions, with the possibility of scaling up the output power to values much higher than 25W. Our hybrid Ho-Tm-doped design provides a PM fiber amplifier with a combination of large input signal dynamic range, low noise figure, broad operating bandwidth, and high output power. Simulations of the hybrid HDFA/TDFA performance agree relatively well with experimental data.

Direct Amplification of High Energy Pulsed Laser in Fiber-Single Crystal Fiber with High Average Power

A laser master oscillator power amplifier (MOPA) system consisting of a fiber amplifier and a two-stage Yb:YAG single crystal fiber (SCF) is experimentally studied. The nonlinear stimulated Raman scattering (SRS) is avoided by limiting the output power of the fiber preamplifier to 600 mW. Due to the benefit from the low nonlinearity and high amplification gain of the SCF, a laser pulse duration of 16.95 ps and a high average power of 41.7 W at a repetition rate of 250 kHz are obtained by using a two-stage polarization controlled double-pass amplification of Yb:YAG SCF, corresponding to an output energy of 166.8 μJ and a peak power of 9.84 MW, respectively. The polarization controlled SCF amplification scheme achieved a gain as high as more than 69 times. During the amplification, the spectra gain narrowing effect and the polarization controlled four-pass amplification setup are also studied. The laser spectrum is narrowed from over 10 nm to less than 3 nm, and the pulse width is also compressed to hundreds of femtosecond by dechirping the laser pulse. This compact-sized, cost-effective laser source can be used in laser micromachining, or as the seeder source for generating much higher power and energy laser for scientific research. For some applications which need femtosecond laser, this laser source can also be compressed to femtosecond regime.

High-Energy Single-Frequency Millisecond 1336.630-nm Nd:LGGG Amplifier (April 2017)

We demonstrate a high-energy, single-frequency, and millisecond (ms) 1336.630-nm amplifier with high beam quality and narrow-linewidth simultaneously based on the Nd3+:(LuxGd1-x)3Ga 5O12 (Nd:LGGG) disordered crystal for the first time. The amplifier system consists of a polarized single-frequency 1336.630-nm LD oscillator, two-stage Raman fiber preamplifier, and four-stage Nd:LGGG main amplifier. The seed laser pulse energy is amplified up to a record high pulse energy of 2.05 J at a repetition rate of 5 Hz and a pulse duration of 1 ms with linewidth as narrower as 0.5 pm. The beam quality factor is ${\rm{M}}^{2}\,= \,1.46$ . The wavelength of the single-frequency amplifier can be tuned from 1336.600 to 1336.660 nm. All results indicate that the Nd:LGGG is high performance 1.3-μm laser amplification medium, especially for generating the specific wavelength at 1336.630 nm. Moreover, such laser source with the specific wavelength at 1336.630 nm is promising for the development of a high accuracy 27Al+ ion optical clock.

A Unified Approach to Achieving High Power and High Energy in Chirally Coupled-Core Ytterbium-Doped Fiber Amplifier Systems

An approach based on a comprehensive, unified model for fiber laser and amplifier systems is used in the design of high-power, high-energy systems. With guidance from the model, a chirally coupled-core Yb-doped fiber amplifier system is constructed. We use a two-stage system comprised of a 2.5-m long fiber preamplifier and a 3.0-m long fiber booster amplifier to illustrate the method. This compact system is capable of generating outputs of up to 1.2 mJ for 25-ns pulses at a repetition rate of 100 kHz, with average power of up to 121 W, and a slope efficiency of 82%.