The high-power narrow-linewidth fiber laser has become the most widely used high-power laser source nowadays. Further breakthroughs of the output power depend on comprehensive optimization of stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS) and transverse mode instability (TMI). In this work, we aim to further surpass the power record of all-fiberized and narrow-linewidth fiber amplifiers with near-diffraction-limited (NDL) beam quality. SBS is suppressed by white-noise-signal modulation of a single-frequency seed. In particular, the refractive index of the large-mode-area active fiber in the main amplifier is controlled and fabricated, which could simultaneously increase the effective mode field area of the fundamental mode and the loss coefficient of higher-order modes for balancing SRS and TMI. Subsequent experimental measurements demonstrate a 7.03 kW narrow-linewidth fiber laser with a signal-to-noise ratio of 31.4 dB and beam quality factors of Mx2 = 1.26, My2 = 1.25. To the best of our knowledge, this is the highest reported power with NDL beam quality based on a directly laser-diode-pumped and all-fiberized format, especially with narrow-linewidth spectral emission.

In this paper, we have experimentally demonstrated a high-power and high-brightness narrow-linewidth fiber amplifier seeded by an optimized fiber oscillator. In order to improve the temporal stability, the fiber oscillator consists of a composite fiber Bragg grating-based cavity with an external feedback structure. By optimizing the forward and backward pumping ratio, the nonlinear effects and stimulated Raman scattering-induced mode distortion of the fiber amplifier are suppressed comprehensively, accompanied with the simultaneous improvement of beam quality and output power. The laser brightness is enhanced further by raising the threshold of transverse mode instability by approximately 1.0 kW by coiling the gain fiber with a novel curvature shape. Finally, a 6 kW narrow-linewidth laser is achieved with beam quality (M2) of approximately 1.4. The laser brightness doubled compared to the results before optimization. To the best of our knowledge, it is the highest brightness narrow-linewidth fiber laser based on a one-stage master oscillator power amplification structure.

This study analyzes the linewidth narrowing characteristics of free-space-running Brillouin lasers and investigates the approaches to achieve linewidth compression and power enhancement simultaneously. The results show that the Stokes linewidth behavior in a free-space-running Brillouin laser cavity is determined by the phase diffusion of the pump and the technical noise of the system. Experimentally, a Stokes light output with a power of 22.5 W and a linewidth of 3.2 kHz was obtained at a coupling mirror reflectivity of 96%, which is nearly 2.5 times compressed compared with the linewidth of the pump (7.36 kHz). In addition, the theorical analysis shows that at a pump power of 60 W and a coupling mirror reflectivity of 96%, a Stokes output with a linewidth of 1.6 kHz and up to 80% optical conversion efficiency can be achieved by reducing the insertion loss of the intracavity. This study provides a promising technical route to achieve high-power ultra-narrow linewidth special wavelength laser radiations.

We report here the first hundred-watt continuouswave fiber gas laser in H2-filled hollow-core photonic crystal fiber (PCF) by stimulated Raman scattering. The pump source is a homemade narrow-linewidth fiber oscillator with a 3 dB linewidth of 0.15 nm at the maximum output power of 380 W. To efficiently and stably couple several-hundred-watt pump power into the hollow core and seal the gas, a hollow-core fiber end-cap is fabricated and used at the input end. A maximum power of 110 W at 1153 nm is obtained in a 5 m long hollow-core PCF filled with 36 bar H2, and the conversion efficiency of the first Stokes power is around 48.9%. This work paves the way for high-power fiber gas Raman lasers.

In this work, an all-fiberized and narrow-linewidth fiber amplifier with record output power and near-diffraction-limited beam quality is presented. Up to 6.12 kW fiber laser with the conversion efficiency of approximately 78.8% is achieved through the fiber amplifier based on a conventional step-index active fiber. At the maximum output power, the 3 dB spectral linewidth is approximately 0.86 nm and the beam quality factor is Mx2 = 1.43, My2 = 1.36. We have also measured and compared the output properties of the fiber amplifier employing different pumping schemes. Notably, the practical power limit of the fiber amplifier could be estimated through the maximum output powers of the fiber amplifier employing unidirectional pumping schemes. Overall, this work could provide a good reference for the optimal design and potential exploration of high-power narrow-linewidth fiber laser systems.

Bottom-up assembly of nanomaterials using solution-processed methods is ideally suited for use in fabrication of large-area optoelectronic devices. Tailorable visible and near-infrared absorption in shaped nanostructured noble metals is strongly influenced by localized plasmon resonance effects. Obtaining sharp and selective absorption with solution-processed methods is a challenge and requires suitable control on the growth kinetics, which ultimately results in appropriate size and morphology of the final product. In this work, a photo-assisted multigenerational growth process for synthesis of silver nanotriangle ink with narrow linewidth absorbance is developed. This technique combines photochemical and seed-mediated growth approaches. The resulting ink exhibits a sharp absorption at 700 nm with full width at half maximum of ∼170 nm, verified by absorption as well as dynamic light scattering, transmission electron microscopy, and field emission scanning electron microscopy measurements. Numerical modeling using finite-difference time-domain calculations yields a close match with observed absorption and is used to examine electric field distribution and enhancement factor resonating at 720 nm. The synthesis technique is potentially useable for production of highly selective absorbers in solution phase.

High-peak-power transform-limited narrow-linewidth nanosecond all-fiber lasers are desired in a range of applications. However, their linewidths will be broadened by self-phase modulation (SPM). We propose a novel concept that generates transform-limited laser pulses by temporally shaping the pulse seed. The impact of the pulse shape on SPM-induced spectral broadening was studied numerically and experimentally. It was found theoretically that the square-shape pulsed laser is immune to SPM-induced spectral broadening. Based on this principle, we built a high-peak-power, linearly polarized, square-shape nanosecond all-fiber laser in a master oscillator power amplifier (MOPA) configuration. Stimulated Brillouin scattering (SBS) limited peak powers of 4.02 kW, 5.06 kW, 6.52 kW and 9.30 kW were obtained at pulse widths of 8 ns, 7 ns, 6 ns and 5 ns. Thanks to the square-shape pulsed seed, the linewidths at maximum peak power remained at 129.5 MHz, 137.6 MHz, 156.2 MHz and 200.1 MHz, respectively, close to the transform-limited values of 110.8 MHz, 126.6 MHz, 147.7 MHz and 177.3 MHz.

An all-fiberized and narrow-bandwidth master oscillator power amplification (MOPA) system with record output power of 4 kW level and slope efficiency of 78% is demonstrated. Tandem pumping strategy is tentatively introduced into the narrow-bandwidth MOPA system for thermally induced mode instability (TMI) suppression. The stimulated Brillouin scattering (SBS) effect is balanced by simply using one-stage phase modulation technique. With different phase modulation signals, SBS limited output powers of 336 W, 1.2 kW and 3.94 kW are respectively achieved with spectral bandwidths accounting for 90% power of ${\sim}$0.025, 0.17 and ${\sim}$0.89 nm. Compared with our previous 976 nm pumping system, TMI threshold is overall boosted to be ${>}$5 times in which tandem pumping increases the TMI threshold of ${>}$3 times. The beam quality ($M^{2}$ factor) of the output laser is well within 1.5 below the TMI threshold while it is ultimately saturated to be 1.86 with the influence of TMI at maximal output power. Except for SBS and TMI, stimulated Raman scattering (SRS) effect will be another challenge for further power scaling. In such a high power MOPA system, multi-detrimental effects (SBS, SRS and TMI) will coexist and may be mutual-coupled, which could provide a well platform for further comprehensively investigating and optimizing the high power, narrow-bandwidth fiber amplifiers.

An all-fiberized high-average-power narrow linewidth ns pulsed laser with linear polarization is demonstrated. The laser system utilizes a typical master oscillator power amplifier (MOPA) configuration. The stimulated Brillouin scattering (SBS) is effectively suppressed due to the short fiber length and large mode area in the main amplifier, combined with the narrow pulse duration smaller than the phonon lifetime of SBS effect. A maximal output power of 466 W is obtained with a narrow linewidth of ${\sim}$203.6 MHz, and the corresponding slope efficiency is ${\sim}$80.3%. The pulse duration is condensed to be ${\sim}$4 ns after the amplification, corresponding to the peak power of 8.8 kW and the pulse energy of $46.6~\unicode[STIX]{x03BC}\text{J}$. Near-diffraction-limited beam quality with an $M^{2}$ factor of 1.32 is obtained at the output power of 442 W and the mode instability (MI) is observed at the maximal output power. To the best of our knowledge, this is the highest average output power of the all-fiberized narrow linewidth ns pulsed fiber laser with linear polarization and high beam quality, which is a promising source for the nonlinear frequency conversion, laser lidar, and so on.

We report here a high-power, wavelength tunable and narrow linewidth $1.5~\unicode[STIX]{x03BC}\text{m}$ all-fiber laser amplifier based on a tunable diode laser and Er-Yb co-doped fibers. The laser wavelength can be precisely tuned from 1535 nm to 1580 nm, which covers many absorption lines of mid-infrared laser gases, such as $\text{C}_{2}\text{H}_{2}$, HCN, CO, and HI. The maximum laser power is ${>}$11 W, and the linewidth is about 200–300 MHz, which is close to the absorption linewidth of the above-mentioned gases. This work provides a suitable pump source for high-power wavelength tunable mid-infrared fiber gas lasers based on low-loss hollow-core fibers.

In this manuscript, we demonstrate high-power, narrow-linewidth linearly polarized fiber laser with excellent beam quality through compact one-stage amplification scheme. By employing a single-mode–multimode–single-mode structure seed laser, a linearly polarized Yb-doped fiber laser with narrow linewidth and high output power is achieved. This laser, when used as a master oscillator, can be capable of suppressing the ASE in the process of power amplification. Thus, only one-stage amplification structure is used to scale up the laser power, and linearly polarized output with a polarization extinction ration of 14 dB, a narrow linewidth of 0.3 nm and an output power of 1018 W are achieved. Moreover, due to the good beam quality of seed laser and the well-designed amplifier stage, the beam quality of the output laser is near-diffraction-limited with $M_{x}^{2}\sim 1.18$ and $M_{y}^{2}\sim 1.24$ at the maximum power, and without mode instability occurring.

A high power narrow-linewidth nanosecond all-fiber laser based on the master oscillator power amplifier (MOPA) configuration is demonstrated. A pulsed seed with high repetition rate of 10 MHz was generated by modulating a continuous-wave (CW) single-frequency fiber laser at $\sim $1064 nm by using an electro-optic intensity modulator (EOIM). After multi-stage cascaded power amplification, the average power was boosted to be kilowatt level. The pulses from the main amplifier had a pulse width of $\sim $3 ns and an average/peak power of 913 W/28.6 kW. Further power scaling of the pulses was limited by stimulated Raman scattering (SRS) for the moment, method for SRS suppression and further power scaling was briefly discussed.