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Stimulated Brillouin scattering (SBS) is an effective method for compensating wavefront aberrations in high-energy lasers due to its phase conjugation property. However, SBS phase conjugate mirrors (SBS-PCMs) under high-power pumping often suffer from significant spatial aberrations and decreased energy reflectivity, indicating instability in the nonlinear gain. Here, a nonlinear gain modulation method is proposed to realize the stable output. Experiments show that the energy reflectivity of SBS decreased due to the thermal effect in high-repetition-rate pumped SBS-PCMs. The nonlinear gain modulation was accomplished with simultaneous adaptation of radial and axial focusing parameters resulting in a higher SBS gain under short-focus conditions. The feasibility of the method was experimentally confirmed by obtaining SBS energy reflectivity stabilized at 60%, while the root mean squares of steady-state Stokes energy and pulse time delay enhanced to 1.97% and 1.81%, respectively, in an HT-230 medium. This scheme ensures stable and efficient SBS output under high-power pumping, which is of great significance for expanding the application of SBS-PCMs in high-repetition-rate laser systems. [ABSTRACT FROM AUTHOR]

A high-efficiency Nd:LuVO4 laser, pumped by a fiber-coupled laser diode at 916 nm, was successfully demonstrated. Employing a recycling-pumping architecture, an output power of 12.1 W at 1,343.2 nm was achieved with an incident pump power of 20 W, resulting in a slope efficiency of 62.1% and an optical conversion efficiency of 60.5%. Furthermore, the beam quality factor was measured to be approximately 1.1 at the maximum output level. [ABSTRACT FROM AUTHOR]

We present a numerical investigation of the bound-state pulse formation mechanism and evolutionary dynamics based on the pump strength and spectral filtering bandwidth in the all-fiber Mamyshev oscillator. Through the numerical simulation and analysis, the different mode-locked pulses' (such as single pulses, bound-state pulses, and chaotic multi-pulses) regime transformation conditions are quantified. The results suggest that with an increase in the pump strength, the sub-pulse energy and output coupler of the Mamyshev oscillator show an inverse proportion trend, which plays an important role in increasing the number of sub-pulses in the bound-state pulses' state. Furthermore, optimization schemes, such as adjusting the filter bandwidth and slowing down the accumulation of nonlinear effects, are proposed to achieve a high-energy pulse output in the Mamyshev oscillator. [ABSTRACT FROM AUTHOR]

The generation of optical vortex beams with user-configurable topological charge and spatial profile is a topic of intense research due to the numerous potential applications for these types of laser beams. In this work, we demonstrate the direct generation of vortex laser beams with controllable topological charge and tunable spatial profile from a Pr3+:YLF laser cavity using a spot-defect technique. A theoretical model is established to examine the relationship between the topological charge of the generated vortex beam and how this relates to laser cavity parameters. Experimentally, the selective operation of first- and second-order vortex beams and tunable optical vortex lattices with one to four singularities at 607 nm can be achieved by adjusting the position of the defect spot. This work offers insight into methods for the generation of visible optical vortex beams with controllable topological charge and tunable singularities for a range of applications. [ABSTRACT FROM AUTHOR]

The cascade operation of Brillouin lasers (BLs) is an identified obstacle to single-frequency power scaling and further compression of the fundamental linewidth. In this study, we reveal the relationship between the maximum cascade order and system parameters, starting from the phase-matching conditions of the Stokes cascade. The second Stokes is suppressed for modes that fall away the Brillouin gain linewidth (ΓB), which is heightened for Brillouin gain media with high sound velocity, large refractive index, and narrow linewidth. Diamond, with its extremely high product of speed of sound and refractive index, satisfies these requirements and is found to achieve cascade-free intramode scattering (TEM00) without manipulating cavity mode structures. This study elucidates a route to single-frequency, narrow-linewidth BLs via Brillouin material selection. [ABSTRACT FROM AUTHOR]

Free-space Brillouin lasers (BLs) generate high-power narrow-linewidth laser outputs at specific wavelengths. However, despite these impressive results, further compressing the Stokes linewidth while maintaining a high-power output remains a challenge. This study was conducted to investigate the design of BLs, starting from the phase-matching conditions and stability of a Brillouin cavity, for media with different phonon frequencies. A high-power and narrow-linewidth output can be realized using large-size, wide-gain-bandwidth Brillouin media. We experimentally demonstrated a BL using fused silica and diamond with the same cavity parameters. Stokes powers of 21.6 and 18.9 W were obtained with fused silica and diamond, respectively, at an available pump power of 58 W. Using fused silica, a Stokes linewidth of 1.2 kHz was obtained, which is two times narrower than that obtained using the diamond BL. Such BL design routes for various Brillouin media provide a path for achieving high-power, ultra-narrow-linewidth laser radiation at specific wavelengths. [ABSTRACT FROM AUTHOR]

With high‐temporal coherence and low‐phase noise, narrow‐linewidth lasers have important applications in spectroscopy, holography, and coherent detection. At present, ultra‐narrow‐linewidth lasing is generated by solid‐state, optical fiber, and semiconductor lasers, which serve as a good light source for scientific research and industrial applications. In this article, we summarize the fundamental techniques and review recent developments in narrow‐linewidth lasers. Moreover, typical applications of narrow‐linewidth lasers are discussed to provide reliable and easy‐to‐use references for comparing the performance of narrow‐linewidth lasers. [ABSTRACT FROM AUTHOR]

An all‐solid‐state pulse width adjustable Nd:YAG nanosecond laser at 1064 nm is demonstrated based on the bidirectional voltage supplied Q‐switched technology. Continuously adjustable pulse‐width from 4.6 to 32.3 ns is generated in a linear cavity, which is laser diode side‐pumped at 808 nm at 100 Hz repetition rate. With 27 ns Q‐switch duration, the shortest pulse width of 4.6 ns with single pulse energy of 0.77 mJ and a near‐Gaussian beam quality (M2 < 1.6) is obtained. Our results suggest an approach to generating pulse‐width adjustable nanosecond lasers for applications in LIDAR. [ABSTRACT FROM AUTHOR]

Delayed self-heterodyne/homodyne measurements based on an unbalanced interferometer are the most used methods for measuring the linewidth of narrow-linewidth lasers. They typically require the service of a delay of six times (or greater) than the laser coherence time to guarantee the Lorentzian characteristics of the beat notes. Otherwise, the beat notes are displayed as a coherent envelope. The linewidth cannot be directly determined from the coherence envelope. However, measuring narrow linewidths using traditional methods introduces significant errors due to the 1/f frequency noise. Here, a short fiber-based linewidth measurement scheme was proposed, and the influence of the noise floor on the measurement of the laser linewidth using this scheme was studied theoretically and experimentally. The results showed that this solution and calibration process is capable of significantly improving the measurement accuracy of narrow linewidth. [ABSTRACT FROM AUTHOR]

• This study utilized fused silica as the gain medium and conducted theoretical and experimental investigations into key factors affecting Brillouin amplification. • A maximum amplification factor of 17.3 for the Stokes beam using a non-collinear Brillouin amplifier with fused silica as the gain medium was achieved. • The experimental setup demonstrated an energy extraction efficiency of up to 41.5 %, with a maximum extracted energy of 151 mJ. • The experimental results closely aligned with theoretical predictions, confirming the benefits of double-pass Brillouin amplification technology in improving amplification efficiency and system stability. Brillouin amplification is a crucial technique for overcoming power limitations in modern particle number inversion lasers, facilitating efficient laser power scaling. Non-collinear Brillouin amplifiers, operating in free space, offer superior adaptability and effectively address challenges such as pulse width matching, gain saturation, and limited beam count that are common in traditional collinear Brillouin amplifiers. This study utilized fused silica as the gain medium and conducted theoretical and experimental investigations into key factors affecting Brillouin amplification, such as interaction angle, energy, and polarization. The Stokes beam was amplified by a factor of 17.3, resulting in an extracted energy of up to 151 mJ and achieving an energy extraction efficiency of 41.5 %. [ABSTRACT FROM AUTHOR]

Lasers with narrow linewidths and single frequencies are widely used in fields such as radar detection, nonlinear optics, and precision measurements. The demand for such lasers has promoted the rapid development of single-longitudinal-mode (SLM) selection technology. Here, we highlight the working principles of current mainstream SLM selection technologies and the recent advances in the field. We compare the characteristics of different SLM selection methods and list the challenges faced by these technologies. [ABSTRACT FROM AUTHOR]

Stimulated Raman-scattering-based lasers provide an effective way to achieve wavelength conversion. However, thermally induced beam degradation is a notorious obstacle to power scaling and it also limits the applicable range where high output beam quality is needed. Considerable research efforts have been devoted to developing Raman materials, with diamond being a promising candidate to acquire wavelength-versatile, high-power, and high-quality output beam owing to its excellent thermal properties, high Raman gain coefficient, and wide transmission range. The diamond Raman resonator is usually designed as an external-cavity pumped structure, which can easily eliminate the negative thermal effects of intracavity laser crystals. Diamond Raman converters also provide an approach to improve the beam quality owing to the Raman cleanup effect. This review outlines the research status of diamond Raman lasers, including beam quality optimization, Raman conversion, thermal effects, and prospects for future development directions. [ABSTRACT FROM AUTHOR]

Brillouin lasers providing extremely narrow-linewidth are emerging as a powerful tool for microwave photonics, coherent communications, quantum processors, and spectroscopy. So far, laser performance and applications have been investigated for a handful of select materials and using guided-wave structures such as micro-resonators, optical fibers, and chip-based waveguides. Here, we report a Brillouin laser based on free-space laser action in an extreme optical material. Continuous-wave lasing 167 GHz from a 532 nm pump is demonstrated in diamond using a doubly resonant ring cavity, generating a pump-limited output power of 11 W. The Brillouin gain coefficient is measured to be 79 cm GW−1 with a linewidth of 12 MHz. These properties, along with an exceptionally high Brillouin frequency and wide transmission range, make diamond Brillouin lasers a promising high-power source of narrow-linewidth output and mm-wave beat notes. [ABSTRACT FROM AUTHOR]

Laser gain materials possessing high thermal conductivity and robust mechanical properties are key prerequisites for high power lasers. We show that diamond, when configured as a Raman laser, enables access to these and other extreme properties, providing an important new route to high power and high brightness beam generation. Recent achievements in pulsed and continuous wave oscillators, beam combining amplifiers, and single longitudinal mode oscillators are summarized, along with wavelength extension of these concepts through adaption to other pumps, use of Raman cascading, and intracavity harmonic generation. To date, diamond laser powers have attained 750 W with efficiency and beam quality so far unperturbed by nonlinear or thermally induced side-effects. Large factor brightness enhancement of low coherence inputs is demonstrated using multiple pump beams (via Raman beam combination) or highly multimode pumps for oscillator and amplifier configurations. Future directions for direct diode pumping, and for realizing extraordinary power and power density through reduced temperature operation and isotopically enriched diamond, are also discussed. Our results indicate that diamond is emerging as a generic high-power laser technology with advantages in terms of brightness (high average power and high beam quality) and wavelength range. [ABSTRACT FROM AUTHOR]

The power scaling of an all-solid-state visible laser is limited by the mode-to-pump ratio related to the thermal effect based on the spatial rate equation. The mode-to-pump ratio is also known as the overlap efficiency factor (OEF). We investigated the thermal effect as a function of pump power, the waist radius of pump beams, and the waist position of pump beams and have simulated the three-dimensional distribution of the OEF as a variable of the waist position and size of pump beams. Also, it is seen that the calculated optimal OEF under a plane–concave cavity is a decreasing function of input pump power, and it is less than unity in the case of high pump power. The practical example of a Pr:YLF laser pumped by 9-W fiber-coupled laser diodes confirms our theoretical analysis. The output power instability was < ± 1. 625 % (RMS) within 1 h. In addition, by changing the cavity length to 38 mm, the output power of 607 nm is up to 103 mW with an OEF of 0.741. [ABSTRACT FROM AUTHOR]

The nonlinear effect of fiber limits the further increase in pulse energy, and Mamyshev oscillator shows outstanding advantages in managing nonlinearity in waveguide medium, which is now associated with high peak power and high pulse energy. The potential applications of these laser sources based on Mamyshev mechanism have facilitated aggressive research and innovative ideas by researchers around the world. Here, we focus on the mode-locked principle and starting dynamics of Mamyshev oscillator. The review of Mamyshev technology is summarized from two starting modes of seed source injection and self-starting. Initial research and significant progress in this field, plus new insights and challenges of Mamyshev oscillator for ultrafast fiber laser technology are analyzed. [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]

This study demonstrated the use of a highly compact nanosecond laser system operating at 532 nm and producing a maximum output power of 70 W with a pulse width of 5 ns at 0.5 kHz, for space debris tracking. To improve the ranging accuracy while minimizing the influence of the pulse noise, a bidirectional Q-switch was adopted in the oscillator to generate a short pulse width with less tailing. The laser was applied for low-Earth-orbit space debris tracking, and space debris with the farthest distance of 1701.9 km at the minimum radar cross-section of 1 m2 could be detected with a ranging precision of up to 26.90 cm. • A highly compact all-solid-state nanosecond laser with a maximum output power of 70 W at 532 nm was developed. • The bidirectional voltage supplied Q-switch was introduced in the oscillator, which delivered the adjustable pulse-width output in the range of 5–21 ns without tailing. • Space debris with the minimum radar cross-section of 1 m2 was tracked. [ABSTRACT FROM AUTHOR]

• A novel L-band tunable multi-wavelength mode-locked EDFL was presented operating at ∼ 1.6 μm. • The novel device we used, known as MMF-FMF, serves as both an SA and a wavelength selection filter. • We achieved switchable lasing outputs with single-, dual-wavelength, and triple-wavelength modes. • The wavelength tuning range for single- and dual-wavelength outputs is 31 nm and 24 nm, respectively. 1.6 μm tunable mode-locked fiber laser are mainly used in the biomedical field, laser processing, and other aspects, have excellent application prospects. We propose a novel MMF-FMF-based device, which acts both as a saturable absorber and a wavelength selection filter. The reduction of insertion loss caused by FMF affects the laser gain competition process, leading to changes in gain allocation and bandwidth allocation. The laser generated stable mode-locked pulses with a repetition frequency of 23.23 MHz at pump powers exceeding 51 mW. By adjusting the angle of the fiber optic squeezer with the PC, successfully achieved switchable single-, dual-, and triple-wavelength lasing outputs, as well as tunable single- and dual-wavelength lasing outputs. The wavelength-tuning ranges for the single- and dual-wavelength lasing outputs were 31 nm (1570 nm-1601 nm) and 24 nm, respectively. The accurately adjustable L-band novel mode-locked fiber laser exhibits enormous potential for application. [ABSTRACT FROM AUTHOR]

A continuous-wave narrow linewidth diamond Raman laser based on an intracavity frequency doubling structure was demonstrated. Linewidth narrowing and power enhancement were realized by tuning the phase matching in the second-harmonic generation element through temperature control. A maximum output power of 5 W at 592 nm with a linewidth of 72 MHz was obtained using a Yb doped fiber laser with a power of 40 W and a linewidth of >4 GHz, an enhancement of the linewidth by a factor of about 65. The results indicate that high-power and narrow linewidth lasers can be produced utilizing diamond Raman conversion combined with the phase matching in the second-harmonic generation element. [Display omitted] • A linewidth compressed CW diamond Raman laser with 5 W at 592 nm laser output is proposed. • A temperature-power model of diamond frequency doubling laser is established. • Phase matching and nonlinear process in SRS and SHG conversion has been analyzed by linewidth changes. [ABSTRACT FROM AUTHOR]

• This research explores a 1.5 μm passively Q-switched pulse burst microchip laser, which is end-pumped by a 940 nm laser diode. • The laser utilizes Er:Yb:glass as the gain medium and Co:MALO as the passively Q-switched component. The performance of this pulse burst laser was exhaustively examined and optimized across a range of parameters. • A pulse train of up to 12 pulses, with a total pulse burst energy of 2 mJ was achieved. • A single pulse energy of 272 μJ was realized, featuring a pulse width of 6.2 ns, corresponding to a peak power of 43.9 kW. Burst mode lasers, characterized by a sequence of high-intensity pulses, are integral to applications such as the examination of turbulent flows and optical metrology. This study investigates a 1.5 μm passively Q-switched pulse burst microchip laser, end-pumped by a 940 nm laser diode. Utilizing Er:Yb:glass as the gain medium and Co:MALO for passive Q-switching, delivering a pulse width of 5.5 ms and a repetition rate of 10 Hz. When the initial transmittance of the saturable absorber was 93 % and the maximum absorbed pump energy reached 85 mJ, we successfully generated up to 12, 8, and 4 pulses within a burst at 1.5 μm. These results corresponded to cavity lengths of 12 mm, 13 mm, and 14 mm, respectively. By using a saturable absorber with an initial transmittance of 90.5 %, a higher single pulse energy and a narrower pulse width were realized. The narrowest pulse width was reduced to 6.2 ns, with a corresponding single pulse energy of 272 μJ. The peak power in the Er:Yb:glass/Co:MALO pulse burst laser reached an estimated 43.9 kW. This research provides valuable experimental and theoretical insights for the development of human eye-safe lasers with adjustable pulse sequences. [ABSTRACT FROM AUTHOR]

• Order controllable cascaded diamond Raman laser has been established. • The first-order to fifth-order output with wavelengths of 573.0, 620.3, 676.1, 743.0 and 824.7 nm has been achieved. Controllable multi-wavelength gets worse efficiency and quality at high orders and high energy, remaining cascade Raman laser a challenge. Here, we establish an order controllable multi-wavelength cascaded diamond Raman laser to achieve the first-order to fifth-order Raman lasers output with wavelengths of 573.0, 620.3, 676.1, 743.0 and 824.7 nm. At a 532.8 nm pump energy of 1.60 mJ, the total Stokes output energy of 0.51 mJ with a slope efficiency of 36.5% has been achieved. Meanwhile, a Stokes output threshold model of all order is proposed under short pulse pumping for the first time. The threshold energy of the first-order to fifth-order was 256, 298, 320, 494, 1100 μJ separately, which is in consistent with the simulation results perfectly. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a spatial beam shaping method to achieve high-quality near-field for a high-power frequency tripling laser system by using a liquid crystal spatial light modulator (SLM). Considering the nonlinear relationship between the output 3 ω intensity and the input 1 ω intensity of the frequency conversion system and the transmittance nonuniformity of the whole laser system, we introduce an efficient spatial beam shaping method that improves the output near-field beam quality of frequency tripling laser dramatically. Results show that the near-field peak-to-mean value of the frequency tripling laser improves from 1.83:1 to 1.42:1 after spatial beam shaping within four shots. This method provides effective guidance for spatial beam shaping of high-power frequency tripling laser systems. [ABSTRACT FROM AUTHOR]

• SESAM mode-locked fiber laser achieving repetition rate about 1 MHz with ps pulses. • Pulses stretches from 33 ps to 102 ps employing different FBGs. • Pulse dynamics and behavior with low repetition rates are discussed. • The effect of gain on pulse evolution at different repetition rates was simulated. We demonstrated a SESAM mode-locked Yb-doped fiber laser with pulse duration of 57 ps, bandwidth of 41 pm at repetition rate of 1.04 MHz. In addition, we numerically investigated the effect of the gain on pulse evolution of passively mode-locked fiber laser at different repetition rates. Experimentally, pulses stretches from 33 ps to 102 ps and linewidth ranges from 60 pm to 25 pm employing different bandwidth-limited FBGs under different repetition rates. The experiment results were nearly in agreement with simulation but further showed the pulse formation and evolution related to the decreasing repetition rate. [ABSTRACT FROM AUTHOR]