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We report theoretical results on the wavelength stability of a multisection master-oscillator power-amplifier emitting at 1064 nm. We use a traveling wave equation model to calculate the optical output power and spectral maps versus the currents injected into the different sections of the device. The numerical model explains quantitatively the experimental findings, particularly the collapse of the power if the current injected into a control section adjacent to the distributed Bragg reflector laser acting as master oscillator exceeds certain values. We investigate the influence of the reflectivity at the facet of the power amplifier on the laser behavior. [ABSTRACT FROM AUTHOR]

High energy, high repetition rates laser with excellent beam quality are fundamental components for LiDAR. In particular, high pulse energy is benefit for long distance range imaging. Narrow pulse width and high repetition rates are benefit for high resolution and high refresh rate operation of LiDAR. However, increasing the laser repetition rates will cause the pulse energy decreasing and the pulse width expanding. In order to achieve the requirements at the same time, we propose a 885 nm laser diode end‐pumped RTP Q‐switched Nd:YAG laser. Pulse pumping scheme was used to avoid heat accumulation. With a master oscillator power amplifier (MOPA) system, 40.5 mJ, 7.5 ns of 1064 nm pulses were obtained at 2 kHz. The beam quality factor M2 was measured as 1.60/1.51. Moreover, by frequency doubling with a LBO crystal, 16.4 mJ, 6.5 ns of 532 nm laser with the M2 factor of 1.52 and 1.50 was obtained. The 1064 and 532 nm pulses are suitable for avalanche photodiode arrays LiDAR and streak tube imaging LiDAR, respectively. The laser system is shown to accomplish high stability from temperature of −10°C to 30°C and vibration frequency of 10 to 100 Hz. [ABSTRACT FROM AUTHOR]

• Design and fabrication of a compact unstable positive branch multi-pass telescopic amplifier. • Assembly and operation of a homemade Q-Switched Nd:YAG oscillator coupled with multi-pass telescopic amplifier. • Output beam diagnosis. • Beam tuning study by investigating beam divergence control with mirror pair-separation in multi-pass telescopic amplifier. Here, an unstable positive branch multi-pass telescopic amplifier has been designed and fabricated. At first, a stable Q-switched Nd: YAG oscillator has been implemented operating in near fundamental mode. A well-designed pair of mirrors is elaborated for the multi-pass telescopic amplifier to extract the maximum energy from the gain medium within a compact volume. This configuration exhibits a small angular beam divergence (typically 0.06 mrad). Furthermore, the tuning of beam diameter at far field is investigated in terms of mirrors separation. Hence, it is feasible to tune the beam diameter during remote sensing not only to reduce the divergence but also to focus the beam at the target under certain conditions. The experimental arrangement gives out a near field donut-shaped profile with 1 J pulse energy, 10 ns, 1 Hz at 1064 nm. Systematic measurements are carried out to obtain the small-signal gain and saturation properties in terms of various pump energies and the correlation of those parameters are elucidated with the beam profile in near field configuration. The output beam profile is empirically recorded at different distances as far as 50 m to verify the theoretical model given by the physical optical propagation algorithm of the Zemax software. The latter simulates the laser beam intensity distribution in the far field. The measurements taken by the beam profiler are in good agreement with those given by Zemax simulation. [ABSTRACT FROM AUTHOR]

We demonstrated a master oscillator power amplifier (MOPA) based on Yb:KGW and Yb:YAG crystals at 1 MHz repetition rate without chirped pulse amplification (CPA) technique. The Yb:KGW oscillator delivered 1.28 W, 1.87 ps pulses with a repetition rate of 45 MHz. After an acousto-optic modulator (AOM) as the pulse picker, the repetition rate was reduced to 1 MHz. Subsequently, the seed was sent to Yb:YAG amplifiers and boosted to an average power of 8.2 W with a pulse duration of 4.66 ps, corresponding to a pulse energy of 8.2 μ J and a peak power of 1.76 MW. [ABSTRACT FROM AUTHOR]

Highlights • A burst-mode MOPA frequency-tripled Nd:YAG laser at 355 nm is presented. • Ultraviolet pulses with high energy and high repetition rate are achieved. • In-house designed 5-bar LD pump modules improve laser intensity distribution. • Suitable for plenty of applications like pumping dye lasers and PLIF imaging. Abstract We demonstrated a Nd:YAG based Q-switched burst-mode MOPA laser with frequency-tripled ultraviolet output by nonlinear harmonic generation. The individual pulse energy of 13.4 mJ with a repetition rate of 10 kHz at 355 nm was obtained. The short pulse width of ∼10 ns provides a high peak power up to 1.3 MW at 355 nm. This high-energy and high-repetition-rate ultraviolet source has the potential in applications such as pumping the dye laser systems for PLIF imaging. [ABSTRACT FROM AUTHOR]

We applied a multi-offset surface wave analysis (MOPA) to detect subsoil lateral heterogeneities at a dismissed industrial site along the coast of the city of Trieste (Italy). The site is heavily contaminated and is undergoing characterization in view of possible remediation and re-use. Sea/land interactions and massive anthropic interventions make the site particularly complex. The main lateral heterogeneities consist of an extended buried quay, which also divides continental and marine sediments. We used seismic surface waves to define this contact, while also using supporting data from boreholes and geo-electrical surveys. A multi-offset phase and attenuation analysis was conducted on a few seismic lines, and produced clear evidence concerning the sought heterogeneities. Field data interpretation was corroborated also by ancillary information, and by synthetic modeling, that produced seismograms totally consistent with the recorded ones. In summary, the case study demonstrates how MOPA can be applied in a straightforward manner to define heterogeneities even at a very small spatial scale, and in complex environments such as derelict industrial sites. • Multi-Offset phase analysis applied to an industrial site. • 2D surface wave processing • Comparison with ERT and borehole data • Synthetics seismograms computation [ABSTRACT FROM AUTHOR]

• A 100 mJ master oscillator power amplifier is reported. • A thermal lens Q-switched laser is used as an oscillator. • Thermal lens Q-switched is realized, generating 17.2 mJ of pulse energy. • High power pumping is achieved without water cooling of the gain medium. In this study, we report an Nd: YAG master oscillator power amplifier(MOPA) based on a thermal lens Q-switching oscillator and unilateral side-pumped power amplifier system. We first proposed the thermal lens Q-switching oscillator as a viable method for Q-switching solid-state lasers. Here, we discuss more technical theory and details, focusing mainly on the selection of operating frequency and methods for enhancing pulse energy. Further, a two-stage unilateral side-pumped solid-state power amplifier is proposed because it has high pumping power and a compact structure and does not require water cooling. Optimal unilateral side-pumping amplification was discussed based on the simulation of the pump light and gain distribution. An above Nd: YAG MOPA device was also constructed. When the oscillator's pump power, pump pulse width, and pump frequency are 415 W, 200 μs, and 5 Hz respectively, and the total pump power and pump pulse width of the two-stage amplifier are 4150 W, 3900 W, and 300 μs respectively, a pulse output of 85.2 mJ is generated, M2 = 5.6. The results demonstrate that the Nd: YAG MOPA, based on thermal lens Q-switching, offers a viable method for generating high-energy pulses without the need for water cooling. [ABSTRACT FROM AUTHOR]

We report on a high-energy high-repetition-rate nanosecond Nd:YAG main oscillator power amplifier (MOPA) system. Maximum output pulse energy of 2.36J with duration of 9.4ns at 50Hz has been achieved. The master oscillator was a LD side-pumped electro-optical Q-switched Nd:YAG rod laser adopting unstable cavity with variable reflectivity mirror (VRM). It delivered a pulse train with energy up to 180mJ and pulse duration of 10.7ns. The near-field pattern demonstrated a nearly super Gaussian flat top profile. In the amplification stage, the pulse was boosted via double-pass two Nd:YAG rod amplifiers. Maximum pulse energy was obtained at the peak pump power of 37.5kW, corresponding to an optical-optical conversion efficiency of 25.2%. The correlative peak power was deduced to be 251MW. We also presented the result of 100Hz nanosecond laser with average output power of >100W [ABSTRACT FROM AUTHOR]

We present the strict design parameters of the experiment for the 780 nm tunable continuous-wave second harmonic (SH) generation by the nonlinear resonator containing a MgO doped periodically poled LiNbO (MgO:PPLN) crystal. Optimization of such critical parameters, including focusing and impedance matching, more than 84% SH conversion efficiency and 3.1 W available output power at 780 nm were obtained from the fundamental wave at 1560 nm with two different input couplers. The thermal saturated behavior of the SH output power has been observed in the experiment. The beam quality factor M of the generated SH wave is 1.04 (1.03), and the RMS power stability is 1.29% in 3 h. The SH wave was further used to detect the D transitions of Rb atom, exhibiting a fine tunable characteristic. Such laser source can be a suitable candidate in the atomic physics and quantum optics. [ABSTRACT FROM AUTHOR]

Ultrafast photonics has become an interdisciplinary topic of great significance owing to the spectacular development of compact and efficient ultrafast pulse generation. Saturable absorbers (SAs) are the kernel for ultrafast pulse generation. However, the conventional SAs performance is plateauing owing to the complex preparation process, the diversification of demand for pulse width, and the relatively low laser output at mill watt level. Herein, high-quality comprehensive vertical Lead Sulfide (PbS) nanoflakes were synthesized by the physical vapor deposition (PVD), and a home-build handy dry-transfer system was used to simplify the fabrication process of PbS saturable absorbers device (PbS-SAs). Total-energy calculations by the density functional theory (DFT) were performed to further understand the saturable absorption characteristic of PbS. A time-domain flexible erbium-doped fiber pulse laser has obtained Q-switched, mode-locked, and highest 14th order harmonic mode-locked pulse. Based on a selected mode-locked operation, an all-fiber master oscillator power amplifier (MOPA) pulse laser system was proposed and demonstrated. The integrated system based on PbS-SAs achieved a time-domain flexible fiber pulse laser, high order harmonic mode-locked pulse, and a picosecond pulse (∼ 287 ps) with high average power of ∼ 57.5 W and peak power of ∼ 13.7 kW at the central wavelength of 1562 nm. This research not only provides a simple manufacturing process for high uniformity SAs devices but also greatly improves output power, which would attract interest in exploring the unique properties of nanocomposite SAs for photonic applications. • High quality of Lead Sulfide (PbS) via physical vapor deposition (PVD) method was prepared. • Time-domain flexible pulse outputs by using a PbS saturable absorber device. • The output power of ultrafast pulse laser can be amplified in one all-fiber MOPA system to 57.5 W. [ABSTRACT FROM AUTHOR]

• We report the generation of broadband spectroscopy using highly nonlinear dispersion-shifted fiber (HNL-DSF) in an all-fiber system without any free-space optics instruments. • The seed pulse used in this paper is a traditional soliton mode-locked pulse with low energy, which also produces an ultra-Broadband light source of more than 500 nm compared with other seed pulses with higher energy, which is a method for efficiently generating a broadband light source. • High efficiency of output power amplification after two stages of seed pulse amplification (from 2 mW to 600 mW). A compact and robust broadband light source is desirable for frequency combs, and broadband infrared microscopy. To address these demanding problems, we report the generation of broadband spectroscopy using highly nonlinear dispersion-shifted fiber (HNL-DSF) in an all-fiber system without any free-space optics instruments. However, due to the damage to the glass material by a large number of photons at high power, the ability of the fiber to widen will weaken over time. Therefore, the seed pulse used in this paper is the traditional soliton mode-locked pulse, which has lower energy than other types of mode-locked pulse. After two-stage amplification, the peak power, pulse width, and pulse energy of the soliton pulse are about 2 kW, 10 ps, and 18.79 nJ respectively. Amplifying the power of a low-energy pulse to pump the dispersion-shifted fiber, the ultra-wideband spectrum of more than 500 nm can be obtained without damaging the fiber, which is an efficient method to generate a wide spectrum. This method can be potentially used in astronomy, industry, medicine, etc. [ABSTRACT FROM AUTHOR]

A 1064 nm master oscillator power amplifier (MOPA) pulsed fiber laser is developed with flexible control over the pulse width, repetition frequency and peak power, and it is used to investigate the dependence of mono-crystalline silicon scribe depth on the laser pulse width, scanning speed and repeat times. Experimental results indicate that long pulses with low peak powers lead to deep ablation depths. We also demonstrate that the ablation depth grows fast with the scanning repeat times at first and progressively tends to be saturated when the repeat times reach a certain level. A thermal model considering the laser pulse overlapping effect that predicts the silicon temperature variation and scribe depth is employed to verify the experimental conclusions with reasonably close agreement. These conclusions are of great benefits to the optimization of the laser material processing with high efficiency. [ABSTRACT FROM AUTHOR]

• A high pulse energy Nd:YAG laser is demonstrated and environmental tested. • Stable mechanical structure of resonator is designed and stress simulated. • Experimental proved high stability of output energy at different operation conditions. • Potentially benefits applications like PLIF and laser remote sensing. A high pulse energy laser diode-pumped Nd:YAG master oscillator power amplifier (MOPA) laser is demonstrated. The maximum energy of 68 mJ, 9.6 ns, 1064 nm laser at a pulse repetition frequency of 500 Hz is achieved by utilizing the amplifier composed of three LD side-pumped Nd:YAG modules. Moreover, the maximum laser energy of 35.6 mJ is obtained at 532 nm by employing a KTP crystal as a frequency doubler. When ambient temperature ranges from 5 °C to 45 °C, the master oscillator has a pulse energy jitter of <5%. During the shake-environment test, the maximum-pulse-energy jitter of the MOPA laser is less than 2%. The developed MOPA laser has been used in a laser-induced fluorescence system and the variation of the flow field is obtained at a repetition rate of 500 Hz. [ABSTRACT FROM AUTHOR]

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: YVO 4 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 μ s. The average beam quality factor is measured to be M 2 = 1. 375 , exhibiting a Gaussian TEM 00 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. [ABSTRACT FROM AUTHOR]

• A high-power stable picosecond laser based on Nd:YVO 4 and Nd:YAG rod amplifiers was proposed. • A maximum average output power of 310 W at 4.27 MHz was obtained. • A maximum peak power of 86.6 MW at 300 kHz was generated with a pulse energy of 700 μJ and a pulse duration of 8.08 ps. Herein, a high-power picosecond laser system based on master oscillator power amplifier structure is demonstrated. The seed source is a SESAM mode-locked fiber oscillator; the pulse repetition frequency is selected by an acoustic optical modulator with a tunable range from 100 kHz to 4.27 MHz. The amplification system includes one fiber amplifier stage, four stages of end-pumped Nd:YVO 4 amplifiers, and two stages of side-pumped Nd:YAG amplifiers. Finally, the average output power of >300 W is achieved. The maximum peak power is 86.6 MW at 300 kHz with a pulse energy of ∼700 μJ and a pulse duration of ∼8.08 ps. [ABSTRACT FROM AUTHOR]

A 50.2W high pulse energy green laser system at 532 nm was demonstrated by extra-cavity second-harmonic generation (SHG). The fundamental laser was based on laser diode (LD) side-pumped MOPA Q-switched technology, producing 79W of average power at the repetition rate of 500 Hz, while the pulse width was 6 ns. Type-II angle phasematched KTiOPO (KTP) crystal was used as the nonlinear crystal. The 50.2W average power of 532 nm laser was obtained with the divergence angle less than 0.6 mrad and the corresponding peak power of 16.7MW. The optical frequency conversion efficiency from fundamental to green laser was up to 63.5%. The measured output power fluctuation was less than 0.38% in one hour operation. [ABSTRACT FROM AUTHOR]

Abstract: A narrow linewidth pulse and a broadband pulse were simultaneously operated in the master oscillator power amplifier (MOPA) of a self-seeded Ti:sapphire laser, and their intensity ratio was varied by increasing the incident pump energy. The broadband pulse from the independent free-running oscillation was preferentially amplified in the MOPA chain and replaced the narrow linewidth pulse. This explanation was confirmed by comparing the behavior with that of a bandpass filter inserted at the exit of the oscillator. The behaviors were well simulated by numerical calculations. From the results, a method to produce both narrow linewidth and broadband pulses was proposed with their ratio depending on the pump energy. [Copyright &y& Elsevier]

Abstract: We report a wide bandwidth (Δλ=8nm) optical pulsed MOPA (master oscillator power amplifier) source emitting 11.23mJ pulses (1.25MW peak power) in the wavelength centered at (λ=1064nm). Pulse duration and repetition rate were 9ns and from 10Hz to 100Hz, respectively. In order to suppress amplified spontaneous emission (ASE), multi-stage pulse pump technology is applied. And the large core diameter (90μm) and wide bandwidth ensures the high peak power and energy output. [Copyright &y& Elsevier]

We report on a reduced-complexity laser-diode-seeded master-oscillator-power-amplifier setup of a continuous wave fiber laser, with a single-stage ytterbium doped photonic crystal fiber amplifier. The laser is capable of generating up to 7.5 W single-transverse-mode, narrow-linewidth, polarized output suitable for second harmonic generation. The approach used possesses a further power scaling potential. [ABSTRACT FROM AUTHOR]

Due to the complex lateral structure of Distributed Feedback lasers (DFB) and Master Oscillator Power Amplifiers (MOPAs), one-dimensional methods like the classical Transfer Matrix Method (TMM) are not suitable for simulating the optical wave in these devices. Therefore, we applied Trigonometric Finite Wave Elements (TFWE) that generalize the TMM in two or three dimensions. By coupling the dynamic wave equation with simplified temperature and drift-diffusion models, we can simulate the dynamic behavior of DFB lasers and MOPAs. Furthermore, by Fourier transformation, we can calculate the modes of the laser cavity and the corresponding wavelengths. By this approach, the influence of injection current and temperature on the resulting modes and output power can be analyzed in detail. [ABSTRACT FROM AUTHOR]

Abstract: A diode-pumped Master Oscillator Power Amplifier (MOPA) laser system based on cryogenic cooled Yb:YAG has been designed, developed and its output performance characterised. The laser system consists of a fibre oscillator, an active mirror regenerative amplifier and a four pass main amplifier. 2.4mJ, 10ns, 100Hz seed pulses from the fibre oscillator/regenerative amplifier arrangement were amplified up to pulse energies of over 200mJ by using the four pass main amplifier arrangement. As a further study we have obtained an increased slope efficiency of 40% and an optical-to-optical efficiency of 30% using a pinhole vacuum spatial filter/image relay for laser mode control. With 1.8mJ input seed pulses, output pulse energies of around 150mJ were achieved. [Copyright &y& Elsevier]

• The common LMA fiber amplifier achieving peak power above 0.2 MW with ps pulses. • The maximum pulse energy of 12.36 μJ was achieved. • Output pulse spectra and temporal trace was simulated and agree with experiment. We demonstrated the generation of narrow spectral bandwidth, high energy picosecond pulses from a low repetition rate SESAM mode-locked laser seeded Yb-doped fiber MOPA system. A short large mode field diameter gain fiber (DCF-30/250) was adopted to efficiently reduce the influence of nonlinear effects. The maximum pulse energy of 12.36 μJ, ∼60 ps pulses with a narrow bandwidth was obtained at a repetition rate of 5 MHz, corresponding to the peak power of 0.2 MW and average output power of 64 W. The optical-to-optical conversion efficiency was ∼64% in such a low repetition rate all-fiber laser design. The output pulse spectra and temporal trace of the MOPA system for different output powers was investigated by simulation. The simulation results were in agreement with experiment but further showed that the spectral splitting would occur as output power increased. [ABSTRACT FROM AUTHOR]

A compact high peak power eye-safer optical parametric oscillator was constructed by pumping it with a master oscillator power amplifier consisting of a large-mode-area ytterbium doped fiber amplifier and a diode-pumped, passively Q-switched Nd:YAG microchip laser. The master oscillator power amplifier has the maximum output pulse energy of 570 μJ with a 3 nanosecond pulse width and a 3 kHz pulse repetition rate. The compact singly resonating optical parametric oscillator utilized a 50 mm periodically poled Lithium Niobate crystal and generated high peak power 1.5 μm eye-safe laser pulses with more than 140 μJ pulse energy, 3 nanosecond pulse width and 3 kHz repetition rate. [ABSTRACT FROM AUTHOR]

A new laser-wire has been installed in the extraction line of the ATF at KEK. It aims at demonstrating that laser-wires can be used to measure micrometre scale beam size. In parallel, studies have been made to specify a laser suitable for the ILC laser-wires. [ABSTRACT FROM AUTHOR]

Abstract: In the first part of this article we review the challenges associated with erbium–ytterbium doped fibre amplifiers and the design considerations to scale-up the output power and energy using cladding-pumped large-core fibre amplifiers in master-oscillator power-amplifier (MOPA) configuration. Previous results are also given to illustrate this rather successful approach. The second part consists of our latest experimental results with improvements in terms of linewidth and peak power using shorter pulses. Sub-hundred nanosecond pulses with millijoule energy and narrow linewidth were obtained using cascaded fibre amplifiers with large-core fibres. The energy level obtained with such short pulse duration and narrow spectral linewidth is the highest ever reported. System limitations and potential routes for further improvement are also discussed. To cite this article: C. Codemard et al., C. R. Physique 7 (2006). [Copyright &y& Elsevier]

Until recently, simple and reliable high repetition-rate laser sources with nanosecond pulses much shorter than from conventional A-O Q-switch lasers were not available. However over the past 2 years we have developed such lasers based on proprietary fast E-O switching technology, which allows designs delivering ∼1 ns pulses and subnanosecond jitter for good synchronisation. The technology provides pulses with multi-kW peak power and repetition-rates to >100 kHz.Most recently, the performance of these short pulse lasers has been developed further by implementing oscillator/amplifier (master oscillator and power amplifier, MOPA) technology which increases the output to >1 W average power. Here we report on a simple model that has been used to predict the performance of the CW pumped Nd:YVO4 amplifier used in the MOPA laser. The model is based on the well-known expressions for the saturated gain applying to laser pulses, but more usually applied to pulse-excited amplifiers. The model is shown to allow a good interpretation of the amplifier behaviour for kHz pulses and to be a useful tool for predicting the performance of the MOPA laser. [Copyright &y& Elsevier]

• The harmonic DSR is realized in an Yb-doped fiber laser with large normal dispersion. • Based on an PM MOPA system, the pulses are amplified up to 110 W output power with the PER of 18.7 dB. • A record pulse energy of 0.51 mJ at the frequency of 221 KHz for the pulses is achieved. The formation of harmonic dissipative soliton resonance (DSR) is experimentally investigated in an Yb-doped fiber laser operating in large normal dispersion regime. The DSR is observed at a fundamental frequency of 221 KHz, which delivered square-shaped with of 18.7–98.5 ns and single pulse energy of 0.25 μJ at 1056 nm. By adjusting the PCs, the DSR square pulses could be split into their harmonic mode-locked (HML) counterparts. These experimental results provide a new viewpoint for the further understanding of the mechanism and characteristics of HML square pulses. Based on a two-stage all-fiber PM master oscillator power amplifier (MOPA) system seeded by this oscillator, the pulses are amplified up to 110 W output power with the polarization extinction ratio (PER) of 18.7 dB at different frequencies ranging from 221KHz to 663 KHz and a record pulse energy of 0.51 mJ at the frequency of 221 KHz is achieved. [ABSTRACT FROM AUTHOR]

We report on an all-fiber single frequency pulsed laser at 1030 nm in a master oscillator power amplifier system. The pulsed seed was achieved through an acoustic-optic modulator driven by an arbitrary waveform generator. The seed pulse was pre-shaped to mitigate the SBS effect by balancing the dynamic gain saturation in the active fiber. With 30 μm core diameter PLMA fiber amplification, 206 μJ, 500 ns with a fixed repetition rate of 1 kHz was obtained. The linewidth was measured to be 1.73 MHz, which indicates a near transform-limited single frequency source. [ABSTRACT FROM AUTHOR]

We report on an all-fiber single frequency pulsed laser at 1030 nm in a master oscillator power amplifier system. The pulsed seed was achieved through an acoustic-optic modulator driven by an arbitrary waveform generator. The seed pulse was pre-shaped to mitigate the SBS effect by balancing the dynamic gain saturation in the active fiber. With 30 μm core diameter PLMA fiber amplification, 206 μJ, 500 ns with a fixed repetition rate of 1 kHz was obtained. The linewidth was measured to be 1.73 MHz, which indicates a near transform-limited single frequency source. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate the generation of a radially polarized beam (RPB) with a maximum average output power of 20 W by our self-developed nanosecond pulsed ytterbium (Yb)-doped fiber MOPA system. The method of spatial phase conversion was adopted for the system, and a liquid crystal polymer (LCP) vortex half-waveplate (LCP-WPV) was utilized to realize efficient conversion of the linearly polarized LP 01 mode to the radially polarized TM 01 mode. A narrow-linewidth, linearly polarized fundamental mode with an average power of 20.5 W was produced in the multistage all-fiber MOPA system consisting of a continuous-wave (CW) single-frequency fiber laser seed, an electro-optical intensity modulator, two-stage core-pumped amplifiers and three-stage cladding-pumped amplifiers. Afterwards, an RPB output with a 20 W maximum average output power, a 7.5 ns pulse width and a 10 kHz repetition rate was finally obtained after the LCP-WPV was adopted as the spatial mode converter. Then, the mode purity of the RPB was measured to be approximately 88.5 % with the PBS (polarization beam splitter) method. This work provides a reference for the generation of cylindrical vector beam sources with the advantages of high efficiency and high mode purity. [ABSTRACT FROM AUTHOR]

High-power all-solid-state lasers have received widespread attentions as the core component of space debris observing systems, however, the system's efficiency and thermal management constrain certain practical applications. A novel kind of master oscillator power-amplifier (MOPA) system with a high optical efficiency, compact structure and simple cooling system was proposed and demonstrated, which based on single-frequency seeder and diode bounce-pumped slab amplifier. By injecting a single frequency laser, the output pulse energy achieved is about 310 mJ (@532 nm, 200 Hz), which has excellent parameters including pulse duration of 4.8 ns, beam quality M2 of 3.0 and power stability (RMS) of 1.0% for 4 h. Most importantly, the proposed MOPA system has been successfully used for space debris observations for the first time, which strongly indicates that it is a promising solution. • The laser for space debris observations for the first time. • The novel method of ramp-fire with bias feedback. • Theoretical simulation and experiment of slab amplification. • Conductively cooled bounce-pumped slab amplifier with more reliable and efficient. [ABSTRACT FROM AUTHOR]

We demonstrated an ultrafast hybrid fiber — Nd:GdVO 4 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. [ABSTRACT FROM AUTHOR]

• A picosecond master oscillator power amplifier system was proposed. • A single-pass traveling-wave amplifier with the optic-optic efficiency 19.39% was demonstrated. • A maximum output power 35.7 W was generated through the system. We have demonstrated a high pulse energy single-pass picosecond (ps) master oscillator power amplifier (MOPA) system of 1064 nm at a pulse repetition rate of 500 kHz. A 500 kHz, 32.38 μJ picosecond laser was used as the signal laser. Through a single-pass traveling-wave amplifier, a maximum output power of 35.7 W at a pump power of 100.6 W was generated with the optic-optic efficiency of 19.39%. The output pulse duration was 16.9 ps, corresponding to the pulse energy of 71.4 μJ, while simultaneously the beam quality factor M 2 was measured to be 1.36 and 1.32 along the x, y axis direction, respectively. [ABSTRACT FROM AUTHOR]

• Supercontinuum source based on a simple architecture based on an all-silica Thulium MOPA. • Pulsed seed 1950 nm semiconductor laser, based on direct modulation. • A supercontinuum 10 dB bandwidth greater than 600 nm with up to 1.5 W output power. We report on mid-IR supercontinuum generation in an all-silica nanosecond pulsed fiber laser. The laser topology is a master oscillator power amplifier which consists of a two stage Thulium-doped fiber amplifier seeded with a directly modulated semiconductor laser at 1952 nm. The supercontinuum performance is investigated for repetition rate frequencies between 35 kHz and 100 kHz and pulse widths between 6 ns and 21 ns. Supercontinuum average output powers greater than 1.5 W and spectra ranging from 1.95 µm to 2.65 µm are demonstrated. [ABSTRACT FROM AUTHOR]