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Funding Information: This work was supported by Villum Fonden (Villum Investigator grant 00037822), National Natural Science Foundation of China (61905065), Natural Science Foundation of Jiangsu Province (BK20210276), and the State Scholarship Fund of China. Publisher Copyright: © 2022 The Author(s) Controlled flexible ultrafast pulses are of great importance in many application fields, such as metrology. Here, we report a compact pulse width tunable passively harmonic mode-locked fiber laser by exploiting the combination effect of spectral filtering and gain management. The spectral filtering is achieved by adopting a bandwidth tunable filter, resulting in pulse width tunable and changing the harmonic order (i.e., repetition rate). On the other hand, gain management can tune the harmonic order, while the emission pulse width typically remains the same. Thus, a combination of these two effects can make the pulse width tunable in a broad range at a fixed repetition rate. At the 6th-order harmonic mode-locking (76.8 MHz), the pulse width can be tuned from ∼ 0.8 ps to 4.3 ps by adjusting the bandwidth and pump strength. The development of pulse width tunable laser sources at a high-repetition rate would find potential applications in fields such as optical sensing and biomedical imaging.

The lead halide perovskite material shows its unique photoelectric properties, the resulting conversion efficiency of perovskite solar cells. However, the efficiency comes to a bottleneck owing to that mechanism research fall behind the device research. Multiple excitons dynamics play an important role, especially in the lifetime and binding energy of multiple excitons. A long multiexciton lifetime is beneficial to the application for light-emitting devices and photovoltaic devices. Large multiexciton binding energy means a large Stokes shift in exciton absorption, thus avoiding the loss of linear absorption. To conclude, discussions are presented regarding views of current multiple excitons research in terms of the biexciton lifetime and biexciton binding energy that should be considered for further advances in materials and devices.

Stimulated Brillouin scattering (SBS) is a non-linear process which has the capacity to improve the beam quality and pulse characteristics of laser beams. In this paper, we theoretically and experimentally study the process of SBS in fused silica. In particular, we examine the energy reflection and pulse compression of input laser pulses as functions of focus position, pump energy and beam diameter. We utilized coupled wave equations and a distributed noise model to simulate the reflected energy and time waveform under different gain parameters. An experimental system is constructed and used to qualify the numerical simulations. The results reveal that the threshold for the SBS process and the energy reflectivity significantly change with laser focus position under the same pump and focusing parameters. Ultimately, the gain characteristics of the SBS material is the primary factor that influences the SBS output. This work presented here offers insight into the operation of short-length solid-state SBS lasers and serves as a basis for the design and optimization of such systems.

All-solid-state passively Q-switched lasers have advantages that include simple structure, high peak power, and short sub-nanosecond pulse width. Potentially, these lasers can be applied in multiple settings, such as in miniature light sources, laser medical treatment, remote sensing, and precision processing. Cr4+:YAG crystal is an ideal Q-switch material for all-solid-state passively Q-switched lasers owing to its high thermal conductivity, low saturation light intensity, and high damage threshold. This study summarizes the research progress on all-solid-state passively Q-switched lasers that use Cr4+:YAG crystal as a saturable absorber and discusses further prospects for the development and application of such lasers.

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.

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.

We present the second harmonic generation (SHG) of a low power and of both Q-switched mode-locked (QML) and CW (CWML) mode-locked picosecond (ps) laser at 1064 nm based on a single-pass frequency-doubling configuration of an end-pumped passively mode-locked Nd:YVO4 laser in a 3-mm periodically poled MgO-doped lithium-niobate (MgO:PPLN). The maximum SHG conversion efficiency is 27.4% when the laser is operated in the QML mode at an averaged pumping power of 895 mW and the conversion efficiency is reduced to 24.1% in the CWML mode with a maximum averaged pumping power of 1.37 W. The corresponding pulse width of the SHG output is estimated to be 15.5 ps. The repetition rates of the laser are 137 kHz for QML and 78.7 MHz for CWML. The theoretical efficiencies of SHG are calculated in both QML and CWML and the results agree very well with the experiments especially in the QML. This work provides a useful method for efficient frequency conversion for low power mode-locked lasers.

We report a 166 W burst mode pulse fiber amplifier seeded by a Q-switched mode-locked all-fiber laser at 1064 nm based on a fiber-coupled semiconductor saturable absorber mirror. With a pump power of 230 W at 976 nm, the output corresponds to a power conversion efficiency of 74%. The repetition rate of the burst pulse is 20 kHz, the burst energy is 8.3 mJ, and the burst duration is ∼ 20 μ s, which including about 800 mode-locked pulses at a repetition rate of 40 MHz and the width of the individual mode-locked pulse is measured to be 112 ps at the maximum output power. To avoid optical damage to the fiber, the initial mode-locked pulses were stretched to 72 ps by a bandwidth-limited fiber bragg grating. After a two-stage preamplifier, the pulse width was further stretched to 112 ps, which is a result of self-phase modulation of the pulse burst during the amplification.

We demonstrated a high efficiency and high average power picosecond green light source based on SHG (second harmonic generation) of an unpolarized ytterbium-doped fiber amplifier chain. Using single-pass frequency doubling in two temperature-tuned type-I phase-matching LBO crystals, we were able to generate 46 W, >70 ps pulses at 532 nm from a fundamental beam at 1064 nm, whose output is 96 W, 4.8 μJ, with a repetition frequency of 20 MHz and nearly diffraction limited. The optical conversion efficiency was ∼48% in a highly compact design. To the best of our knowledge, this is the first reported on ps green source through SHG of an unpolarized fiber laser with such a high output and high efficiency.

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.

Lasers with emission wavelengths of 1.5 μm are suitable for the eye-safe band and transparency region of the atmosphere. During extremely bad weather conditions, the penetration is stronger than the traditional 1 μm and visible band; thus, they are extensively employed in remote sensing, ranging, and imaging. In recent years, Er:Yb:glass has been widely used for generating 1.5 μm lasing, particularly for the generation of passively Q-switched pulses. Herein, different types of saturable absorbers (SAs) for Er:Yb:glass Q-switching have been reviewed, and the development of passively Q-switched Er:Yb:glass lasers based on these SAs has been discussed.

We demonstrate a compact dual-wavelength operation of Nd:LuVO 4 laser with a power-ratio adjustable between 1064 nm and 1342 nm lines in a compound cavity configuration. The output power at two wavelengths of the laser indicates that it depends not only on pumping-power and but also on the controllable polarization loss in the cavity. Also, the power-ratio, defined as ratio between the output power at 1064 nm and that at 1342 nm, can be adjusted from 0 to 8 or higher accurately by rotating a quarter-wave plate (QWP) in the cavity.

We report a frequency-doubled green picosecond (ps) laser based on K3B6O10Br (KBB) nonlinear optical crystal with cutting angle of θ = 34.7° and φ = 30°. Through intracavity frequency doubling using a type I phase-matched KBB crystal with dimensions of 4 mm × 4 mm × 13.2 mm, the average output power of 185.00 mW green ps laser was obtained with a repetition rate of 80 MHz and pulse width of 25.0 ps. In addition, we present external frequency doubling using KBB crystal. The average output power of 3.00 W green ps laser was generated with a repetition rate of 10 kHz and pulse width of 38.1 ps, which corresponds to a pulse energy of 0.30 mJ and a peak power 7.89 MW, respectively. The experimental results show that KBB crystal is a promising nonlinear optical material.

High brightness laser sources with different wavelengths play an important role in the fields such as defense, industrial, and life sciences etc. However, due to the intrinsic spectral and thermophysical properties of current available laser gain materials, it is difficult to take into account the wavelength and output power of the traditional inversion lasers, which even leads to the decrease of beam brightness. To overcome this problem, beam cleanup by using nonlinear optical technology has been carried out in recent years, which is directly transferring the low beam quality generated from inversion lasers into the high through the effects such as stimulated Raman or Brillouin scattering. Among them, with excellent properties such as high Raman gain coefficient, high thermal conductivity and wide spectral transmission range, diamond exhibits excellent beam brightness enhancement characteristics while realizing high efficiency Raman conversion, which provides a new technical path to generate high power and high brightness laser beam. Here, the development of brightness enhancement based on first-order and cascaded Raman conversion of diamond was reviewed, and its future applications were discussed.

The characteristics of fiber amplifiers of burst pulses envelope during the propagation are comprehensively studied under the conditions of pulsed pump with low repetition rate. The variation of signal envelopes, pump power and upper-level population distribution are discussed in this paper. The impacts of linear varied and exponential varied pump to the raising edge and tailing edge of the output pulses' envelope, are mainly emphasized. Finally, the genetic algorithm is employed to reshape the pulses' envelopes.

In recent years, 589 nm lasers have attracted much attention in the fields of laser sodium guide star, laser radar, and adaptive optics. Therefore, the sodium guide star technology at 589 nm has been particularly topical. The sodium guide star technology requires that the average power should be Watt-level for the continuous-wave yellow laser which having narrow-linewidth and are capable of being tuned to match transition lines accurately. According to the generation method, the sodium guided star laser can be divided into four types: dye lasers, solid-state lasers, optically pumped semiconductor lasers, and fiber lasers. Solid-state laser includes sum-frequency generation, stimulated Raman scattering and optical parametric amplifier. Among them, sum-frequency generation lasers are used mostly. The development history and state of the art of them are expatiated, which is useful reference for the future research in this field.

We demonstrate an all-fiber sub-nanosecond passively mode-locked Tm-Ho co-doped fiber laser. With 1.1-km single-mode fiber (SMF) inserted into the cavity, the laser system can generate 183.4-kHz and 720-ps pulses based on a GaAs saturable absorber (SA). The output spectrum is presented with three wavelengths, which are at 1858.5, 1861.3, and 1864.2 nm, respectively. In addition, with the adjustment of the polarization controller and pump power, the multiple-pulse operation, such as the harmonic mode-locking operation, can also be observed. Higher order of harmonic mode locking is promising but limited by the damage threshold of the SA.

An electro-optical modulator (EOM) and Cr4＋:YAG saturable-absorber-based doubly Q-switched Nd:YAG laser at 1. 06 μ m with single-longitudinal-mode (SLM) output was demonstrated. The spatial-hole-burning suppression and cavity axial-mode selection were provided by a twisted-mode technique and resonant-reflector-mediated SLM operation. The Cr4＋:YAG initial transmittance ( T 0 ) affected the pulse profile, pulse energy, and laser spectra, which were analyzed theoretically and experimentally. Consequently, the laser output obtained an SLM rate of 96.2% with a symmetry factor of 0.64 when T 0 was 6.2%. The results indicate that symmetric and SLM laser pulse can be obtained in a double Q-switched laser by adjusting the cavity loss according to T 0 . Compared with a solely Q-switched laser, the double Q-switches of EOM and Cr4＋:YAG provide a practical route toward the generation of a symmetric temporal profile and SLM operation.

We report a compact 85-W burst-mode pulse fiber amplifier seeded by a Q-switched mode-locked laser at 1064 nm. At a repetition rate of 154 kHz, the pulse duration of the burst is 4 μs containing 280 of 20-ps pulses with temporal space of ∼14 ns, and the total burst energy is about 552 μJ per pulse. The pulse number and the burst repetition frequency can be adjusted from 121 to 154 kHz through increasing the pump power of the seed laser. To the best of our knowledge, this is the first time to observe this type burst pulse amplifier based on the Q-switched mode-locked seed laser. No significant amplified spontaneous emission and stimulated Raman scattering were observed in our experiment when the output power is less than 85 W.

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.

We demonstrated a Q-switched Nd:LuVO 4 laser with fundamental mode at 1064 nm using BaB2O4 electro-optic Q-switching. High-efficiency operation of Q-switched laser with dynamic to static ratio of 91.4% was realized. When the absorbed pump power was 6.59 W, the maximum average output power of 2.88 W was achieved with a repetition rate of 50 kHz. The optical conversion efficiency and slope efficiency were 43.7% and 55.5%, respectively. The minimum pulse width of 17.8 ns was achieved. Meanwhile, the pulse energy and peak power were 57.6 μ J and 3.2 kW, respectively. To the best of our knowledge, this study is the first to demonstrate about the electro-optically Q-switched laser in Nd:LuVO 4 crystal.