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In this paper, we have demonstrated a narrow linewidth high power fiber laser emitting at a short wavelength of ~1050 nm. The fiber laser is based on a structure of master oscillator power amplification (MOPA) with an optimized fiber Bragg-grating-based laser cavity as the seed. Both stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) effects have been effectively suppressed by using a long passive fiber between the seed and the amplifier. Based on the fiber amplifier, we have ultimately boosted the narrow linewidth laser from ~40 W to 3.2 kW with a slope efficiency of 85.1% and a 3-dB linewidth of ~0.1 nm. The SRS suppression ratio of the laser is ~29.7 dB at maximum power. Due to our fiber mode control strategies, the beam quality always stays near-diffraction-limited while amplifying, and the measured M2 factor is ~1.4 at the maximum power. Further increase in output power is limited by the SBS effect. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, we have demonstrated a narrow linewidth high power fiber laser emitting at a short wavelength of ~1050 nm. The fiber laser is based on a structure of master oscillator power amplification (MOPA) with an optimized fiber Bragg-grating-based laser cavity as the seed. Both stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) effects have been effectively suppressed by using a long passive fiber between the seed and the amplifier. Based on the fiber amplifier, we have ultimately boosted the narrow linewidth laser from ~40 W to 3.2 kW with a slope efficiency of 85.1% and a 3-dB linewidth of ~0.1 nm. The SRS suppression ratio of the laser is ~29.7 dB at maximum power. Due to our fiber mode control strategies, the beam quality always stays near-diffraction-limited while amplifying, and the measured M2 factor is ~1.4 at the maximum power. Further increase in output power is limited by the SBS effect.

We present the module of booster amplifier for coherent beam combining Master Oscillator Power Amplifier (MOPA) system to operate with a text narrow-linewidth seed laser. The goal was to achieve a highly modular system, manifested in the ease of changing the number of Coherent Beam Combining (CBC) channels. It uses a frequency tagging phase control scheme performed at acoustical frequencies, enabling a simple piezo fiber stretcher as actuating and tagging element and a cheap microcontroller to perform all the signal processing. The text four-channel CBC system with the proposed booster module was built to verify our assumptions and the whole system’s performance.

A high-power, narrow-linewidth, continuous-wave, thulium-doped fiber laser (TDFL) based on a master-oscillator power-amplifier (MOPA) was experimentally demonstrated. The main oscillator (seed source) yielded 0.64 W of narrow-linewidth laser output at a central wavelength of 1940.32 nm and a 3 dB spectral bandwidth of 0.05 nm. The output narrow-linewidth laser from the main oscillator was amplified by two-stage, cladding-pumped, thulium-doped, all-fiber amplifiers. The main amplifier yielded 26 W of narrow-linewidth laser at a central wavelength of 1940.33 nm. The slope efficiency of the main amplifier was approximately 55.6%. Significant residual pumping light component in the output laser was not observed. During the amplification process, no stimulated Brillouin scattering (SBS) effect, strong amplified spontaneous emission (ASE) effect, and parasitic lasers were observed at the reverse monitoring end. Moreover, the output power was only limited by the incident pump power and the output power had a good stability in a 50 min monitoring period. [ABSTRACT FROM AUTHOR]

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.

This paper reports on the theoretical end experimental investigation of the output characteristics of a multisection master-oscillator power-amplifier (MOPA). It consists of a master oscillator (MO) composed by a gain section surrounded by two DBR sections monolithically integrated with a power amplifier (PA). We use a traveling wave equation model to calculate the optical output power in dependence on the current injected into the PA. The experimental results can be well explained with our theoretical analysis. For a finite front facet reflectivity of the PA the system is acting as a compound cavity.

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.

In this work, a narrow-linewidth linearly polarized fiber amplifier with a record output power of 3.2 kW was achieved based on a homemade polarization-maintaining Yb-doped fiber corresponding to a slope efficiency of 79% and a 3 dB linewidth of 0.2227 nm. By examining various numerical aperture (NA) PMYDFs, the experimental investigation on expanding mode instability (MI) threshold in PM fiber amplifiers was put on display. And the results reveal that the MI threshold is enhanced by more than 370 W for every 0.004 decrease in core numerical aperture. Increasing the seed linewidth from 0.0454 nm to 0.0976 nm by adding 200 m polarization maintaining Ge-doped fiber the stimulated Brillouin scattering threshold increased from 805 W to above 3.2 kW. By applying the MI suppression method, a double-eight-shaped aluminum plate was adopted to coil the gain fiber, and the MI threshold increased by more than 1100 W.

The 1.7 μm band eye-safe laser sources have recently received lots of attention thanks to the development of various applications. Although a variety of lasing configurations operating in this band have been demonstrated, one still needs to seek a good candidate for particular applications with a reasonable compromise between the relative performance targets (e.g., stability, output power, and spectral purity) and the construction cost. Here, we demonstrate a high-power 1694 nm random fiber laser (RFL) in a cost-effective structure pumped by a high-powered 1565 nm RFL. The maximum output power reached the 10 W level, and the output showed extremely low-intensity fluctuations for both the short-time and long-time regimes. Meanwhile, an excellent spectral purity as high as 26.9 dB was also realized. This work provides one of the most attractive approaches for constructing high-performance 1.7 μm band laser sources for practical applications. [ABSTRACT FROM AUTHOR]

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]

This paper deals with the birth and evolution of the civil service system of Bangladesh by segmentizing the entire period of Bangladesh's civil service into three epochs, i.e., The British-Indian Era (1601-1947), The East Pakistan Era (1947-1971), and The Bangladesh Era (1971-Present). The outline of the present Bangladesh Civil Service (BCS) system is also illustrated in this paper. There are 26 cadres in BCS under general and technical/professional cadres. The recruitment system is split into three segments; preliminary MCQ, written, and viva voce, except the special BCS, irregularly arranged in some years. This paper also demonstrates the marks distribution and overall recruitment system of BCS. This paper mentions the overall distribution of liabilities between the Bangladesh Civil Service Commission (BPSC), a quasi-judicial constitutional organization, and the Ministry of Public Administration (MoPA) from recruitment to management. This paper also discusses the organogram of the ministries and the significant changes in the administration system of Bangladesh. Above all, the Bangladesh government faces some critical challenges in personnel management, which are focused on in this paper, and possible remedies are also proposed. One of the goals of this review article is to provide material for academics outside Bangladesh (like those in Ukraine), so they may learn about, examine, and analyze Bangladesh's civil service system and personnel management, and then compare it to their own. [ABSTRACT FROM AUTHOR]

The master oscillator power amplifier (MOPA) pulsed laser, one of the popular topologies for high-power fiber laser systems, is widely applied in industrial machining laser systems. In MOPA, the low-power pulsed laser, stimulated from a seed laser diode, is amplified by the high- power optical energy from pump laser diodes via the gain fiber. Generally, the high-power pump laser diodes are driven by lossy linear current drivers. The switched mode current drivers boost the driver efficiency but suffer from pulse energy consistency due to the current switching ripple. In this paper, a laser driver system that varies the switching frequency of current source to synchronize with pulsed laser repetition rate is analyzed and implemented. Experimental results are demonstrated using a 20 W pulsed fiber laser system. [ABSTRACT FROM AUTHOR]

In this study, a 100-kHz narrow-linewidth burst-mode laser system combined with a master oscillator power amplifier (MOPA) structure was reported with a stable pulse burst profile over 2 ms duration. A theoretical model was established to characterize and compensate the variation characteristics of coefficient of variation (COV) within a burst envelope for the double-pass three-stage amplification system, in terms of different parameter factors. Simulated results yielded similar tendency with the measured ones. For a stable burst envelope with a COV of 2.72% and 2.93%, output pulse energy at a 100 kHz repetition rate was scaled up to 1.08 and 4.38 mJ in the case of an input average pulse energy of 8.6 and 116.51 nJ, respectively. Corresponding Mx2 and My2 values with 2.2 and 2.4 were endowed with 1.08 mJ output single-pulse energy and 2.7 and 2.1 for 4.38 mJ pulse energy. The spectral linewidth of amplified pulses was measured to be less than 83.1 and 67.9 MHz, with respect to output pulse duration of 10.3 and 96.1 ns, respectively.

A high-power, narrow-linewidth, continuous-wave, thulium-doped fiber laser (TDFL) based on a master-oscillator power-amplifier (MOPA) was experimentally demonstrated. The main oscillator (seed source) yielded 0.64 W of narrow-linewidth laser output at a central wavelength of 1940.32 nm and a 3 dB spectral bandwidth of 0.05 nm. The output narrow-linewidth laser from the main oscillator was amplified by two-stage, cladding-pumped, thulium-doped, all-fiber amplifiers. The main amplifier yielded 26 W of narrow-linewidth laser at a central wavelength of 1940.33 nm. The slope efficiency of the main amplifier was approximately 55.6%. Significant residual pumping light component in the output laser was not observed. During the amplification process, no stimulated Brillouin scattering (SBS) effect, strong amplified spontaneous emission (ASE) effect, and parasitic lasers were observed at the reverse monitoring end. Moreover, the output power was only limited by the incident pump power and the output power had a good stability in a 50 min monitoring period.

A multiplexed opsonophagocytosis assay (MOPA) was developed as a cost-effective, high-throughput biological assay to evaluate the efficacy of pneumococcal vaccines by in vitro measurement of opsonophagocytic activity of anti-capsular antibodies. Here, we report draft genomes of the 36 strains of Streptococcus pneumoniae developed for use in the reference pneumococcal MOPA., Competing Interests: The University of Alabama at Birmingham (UAB) has intellectual property rights to several opsonophagocytosis assay reagents developed in M.H.N.'s laboratory. All authors are affiliated with UAB.

Public administration has to compete with private sectors in terms of quality service delivery to citizens. In this context, civil service training, especially overseas training, has been considered the most significant requirement to increase the performance of the Bangladesh Civil Service. This article tries to explore the impact of overseas training on the performance of the Bangladesh Civil Service. To achieve this objective, this study interviewed Bangladesh Civil Servants who participated Asian Institute Training (AIT) Extension training programme from 2016 to 2018. A mixed-method was applied to analyse the collected data. It found that Bangladesh Civil Servants, who have received AIT Extension training, were satisfied with the training management of AIT. Participants believed that such overseas training positively contributes to enhancing the performance of the Bangladesh Civil Service. However, this study also disclosed that fewer overseas training opportunities for young civil servants, lack of need-based training, and poor management of overseas training policy are the main obstacles in Bangladesh Civil service management. This article strongly recommends that there must be a detailed overseas training policy management and more collaboration with international training institutes to get better performance from the government officers in Bangladesh.

The 1.7 μm band eye-safe laser sources have recently received lots of attention thanks to the development of various applications. Although a variety of lasing configurations operating in this band have been demonstrated, one still needs to seek a good candidate for particular applications with a reasonable compromise between the relative performance targets (e.g., stability, output power, and spectral purity) and the construction cost. Here, we demonstrate a high-power 1694 nm random fiber laser (RFL) in a cost-effective structure pumped by a high-powered 1565 nm RFL. The maximum output power reached the 10 W level, and the output showed extremely low-intensity fluctuations for both the short-time and long-time regimes. Meanwhile, an excellent spectral purity as high as 26.9 dB was also realized. This work provides one of the most attractive approaches for constructing high-performance 1.7 μm band laser sources for practical applications.

An all-diode laser-based master oscillator power amplifier (MOPA) configuration for the generation of ns-pulses with high peak power, stable wavelength and small spectral line width is presented. The MOPA emits alternating at two wavelengths in the spectral range between 964 nm and 968 nm, suitable for the detection of water vapor by absorption spectroscopy. The monolithic master oscillator (MO) consists of two slightly detuned distributed feedback laser branches, whose emission is combined in a Y-coupler. The two emission wavelengths can be adjusted by varying the current or temperature to an absorption line and to a non-absorbing region. The power amplifier (PA) consists of a ridge-waveguide (RW) section and a tapered section, monolithically integrated within one chip. The RW section of the PA acts as an optical gate and converts the continuous wave input beam emitted by the MO into a sequence of short optical pulses, which are subsequently amplified by the tapered section to boost the output power. For a pulse width of 8 ns, a peak power of 16.3 W and a side mode suppression ratio of more than 37 dB are achieved at a repetition rate of 25 kHz. The measured spectral width of 10 pm, i.e., 0.1 cm−1, is limited by the resolution of the optical spectrum analyzer. The generated pulses emitting alternating at two wavelengths can be utilized in a differential absorption light detection and ranging system. [ABSTRACT FROM AUTHOR]

The performance of seed laser source will have a great impact on the output pulse quality of the master oscillator power amplifier (MOPA) system. Here, we report the influence of the soliton vector features on the pulse uniformity in an all-fiber MOPA configuration. We demonstrated that, although the intensity of the dissipative soliton seed source is uniform, the intensity of the output pulse train from the MOPA will show fluctuations if the soliton polarization state is not locked, i.e., polarization-rotating vector soliton. It is found that the appearance of non-uniform pulse intensity is caused by the combination of the polarization instability and the polarization dependent gain in the polarization maintaining fiber amplifier. The obtained results indicate that the polarization evolution of seed pulsed source is critical to generation of stable pulse train from the MOPA, and also might be useful to the communities dealing with solitons and high-power pulsed fiber lasers.

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]

A nearly transform-limited, single-frequency $2~\mu \text{m}$ laser system with multi-stage of double-pass Tm:Ho:LuLiF4 slab amplifiers was demonstrated. An amplified pulse energy up to 5.6 mJ at central wavelength of 2051.9 nm was achieved successfully with around 429.7 ns pulse width at a repetition rate of 10 Hz. The line-width of the laser spectrum detected by a heterodyne technique was about 1.24 MHz. The M2 factors were less than 1.6 and 1.4 in the x and y directions, respectively. [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]

An all-diode laser-based master oscillator power amplifier (MOPA) configuration for the generation of ns-pulses with high peak power, stable wavelength and small spectral line width is presented. The MOPA emits alternating at two wavelengths in the spectral range between 964 nm and 968 nm, suitable for the detection of water vapor by absorption spectroscopy. The monolithic master oscillator (MO) consists of two slightly detuned distributed feedback laser branches, whose emission is combined in a Y-coupler. The two emission wavelengths can be adjusted by varying the current or temperature to an absorption line and to a non-absorbing region. The power amplifier (PA) consists of a ridge-waveguide (RW) section and a tapered section, monolithically integrated within one chip. The RW section of the PA acts as an optical gate and converts the continuous wave input beam emitted by the MO into a sequence of short optical pulses, which are subsequently amplified by the tapered section to boost the output power. For a pulse width of 8 ns, a peak power of 16.3 W and a side mode suppression ratio of more than 37 dB are achieved at a repetition rate of 25 kHz. The measured spectral width of 10 pm, i.e., 0.1 cm−1, is limited by the resolution of the optical spectrum analyzer. The generated pulses emitting alternating at two wavelengths can be utilized in a differential absorption light detection and ranging system.

The performance of seed laser source will have a great impact on the output pulse quality of the master oscillator power amplifier (MOPA) system. Here, we report the influence of the soliton vector features on the pulse uniformity in an all-fiber MOPA configuration. We demonstrated that, although the intensity of the dissipative soliton seed source is uniform, the intensity of the output pulse train from the MOPA will show fluctuations if the soliton polarization state is not locked, i.e., polarization-rotating vector soliton. It is found that the appearance of non-uniform pulse intensity is caused by the combination of the polarization instability and the polarization dependent gain in the polarization maintaining fiber amplifier. The obtained results indicate that the polarization evolution of seed pulsed source is critical to generation of stable pulse train from the MOPA, and also might be useful to the communities dealing with solitons and high-power pulsed fiber lasers. [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 compact and highly efficient 670.8-nm semi-conductor master oscillator power amplifier (MOPA) system, with a unique optical design, is demonstrated. The MOPA system achieves a continuous-wave (CW) output power of 2.2 W, which is much higher than commercial products using semi-conductor devices. By comparing solid state lasers and dye lasers, higher wall-plug efficiency (WPE) of 20 % is achieved. Our developed laser system also achieves spectral line-width of 0.3 pm (200 MHz) and mode-hop free tuning range of 49 pm (32.6 GHz), which is very suitable for experiments of lithium atomic physics at several-watt power levels, such as Bose-Einstein condensation (BEC) and isotope absorption spectroscopy. [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]

ABSTRACT Opsonophagocytic assays are used to measure functional antibodies important in protection against pneumococcal capsular antigens. There have been efforts to standardize these methods, as the assays are commonly used to measure vaccine immunogenicity. We report here the results from three international laboratories using their own methods, based on the recommended WHO standard method. We tested 30 pediatric sera, before and after administration of a 13-valent conjugate pneumococcal vaccine, against all 13 serotypes. The three laboratories demonstrated good agreement using their own standardized multiplex opsonophagocytosis assay protocols, particularly postimmunization for those serotypes in the vaccine. While serotype-specific IgG methods have already been internationally standardized and are currently used as a measure of vaccine immunogenicity, this report demonstrates that despite minor differences in methods and a minor variation in response to nonvaccine serotypes, the results from opsonophagocytic assays across the three laboratories may be compared with confidence. IMPORTANCE When measuring a functional antibody response to pneumococcal immunization, it is imperative that a specific, reproducible, accurate, and standardized assay with acceptable inter- and intra-assay variation be advocated internationally to allow for meaningful comparison of results between laboratories. We report here the results of a collaboration between 3 international laboratories testing 30 pediatric samples against the 13 serotypes in Prevenar13.

Bacterial manganese (Mn) oxidation is catalyzed by a diverse group of microbes and can affect the fate of other elements in the environment. Yet, we understand little about the enzymes that catalyze this reaction. The Mn oxidizing protein MopA, from Erythrobacter sp. strain SD-21, is a heme peroxidase capable of Mn(II) oxidation. Unlike Mn oxidizing multicopper oxidase enzymes, an understanding of MopA is very limited. Sequence analysis indicates that MopA contains an N-terminal heme peroxidase domain and a C-terminal calcium binding domain. Heterologous expression and nickel affinity chromatography purification of the N-terminal peroxidase domain (MopA-hp) from Erythrobacter sp. strain SD-21 led to partial purification. MopA-hp is a heme binding protein that requires heme, NAD+, and calcium (Ca2+) for activity. Mn oxidation is also stimulated by the presence of pyrroloquinoline quinone. MopA-hp has a K M for Mn(II) of 154 ± 46 μM and k cat = 1.6 min−1. Although oxygen requiring MopA-hp is homologous to peroxidases based on sequence, addition of hydrogen peroxide and hydrogen peroxide scavengers had little effect on Mn oxidation, suggesting this is not the oxidizing agent. These studies provide insight into the mechanism by which MopA oxidizes Mn. [ABSTRACT FROM AUTHOR]

A mode-locked fiber laser with pulse duration of 4.8 ps and repetition rate of 30 kHz is amplified by end-pumped Nd:YVO4 amplifiers and side-pumped Nd:YAG amplifiers. The output power is amplified up to 31.8 W, achieving a pulse peak power of more than 100 MW and a gain of 59 dB. The beam quality is well preserved with ${M^2}$ factor of 1.26, based on the method of aberration self compensation. The laser beam size in amplifiers is optimized to prevent the unwanted damage due to the high pulse peak power density by using two different types of pumping scheme. It is demonstrated to be an ideal laser source for higher harmonic generation due to high peak power and good beam quality. [ABSTRACT FROM AUTHOR]

A compact and highly efficient 670.8-nm semi-conductor master oscillator power amplifier (MOPA) system, with a unique optical design, is demonstrated. The MOPA system achieves a continuous-wave (CW) output power of 2.2 W, which is much higher than commercial products using semi-conductor devices. By comparing solid state lasers and dye lasers, higher wall-plug efficiency (WPE) of 20 % is achieved. Our developed laser system also achieves spectral line-width of 0.3 pm (200 MHz) and mode-hop free tuning range of 49 pm (32.6 GHz), which is very suitable for experiments of lithium atomic physics at several-watt power levels, such as Bose-Einstein condensation (BEC) and isotope absorption spectroscopy.

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]

For a high power 1064 nm nanosecond MOPA pulse fibre laser, the seeding pulse shape is distorted after amplified by pre-amplifier and power-amplifier stages under the effect of gain saturation. As the pulse shape is crucial for some industrial applications, the distortion of eight different shapes of seeding pulses is experimentally studied, and the Stimulated Raman Scattering (SRS) for several shapes is also investigated. [ABSTRACT FROM AUTHOR]