A large-mode-area (LMA) ytterbium-doped photonic crystal fiber (PCF) with core NA of 0.034 and core diameter of 50 μm was made by the stack-and-draw technique. The core is formed by Yb³⁺/Al³⁺/F /P⁵⁺ co-doped silica glass containing 0.09 mol% Yb₂O₃ with an absorption coefficient at 976 nm up to 3.2 dB/m. The core glass with homogeneous distribution of Yb³⁺ ions and refractive index difference of 4 × 10 ⁴ compared with pure silica was prepared by the sol-gel method and heat homogenization at 2000°C. Laser power amplification of this LMA PCF was studied using a seed source of 21 ps pulse duration and 48.7 MHz repetition rate at 1030 nm wavelength. With pump power of 520 W, a maximum 272 W (266 kW peak power) quasi-single-mode laser output with M² of 2.2 was achieved in a 4.7 m fiber length bent at a diameter of 47 cm with slope efficiency of 52%, and no obvious mode instability, stimulated Raman scattering, or thermal damage on the end facet of the fiber were observed.

We report a hybrid femtosecond laser system based on a femtosecond Yb-doped fiber laser and a Yb-doped potassium gadolinium tungstate (Yb:KGW) regenerative amplifier. To match the central wavelength of the seed source, a Yb:KGW crystal is used in the regenerative amplifier for Np polarization. We study and optimize the dynamics of nonlinear amplification to alleviate the gain narrowing effect. With optimization, the system can output 270 fs pulses with 21 μJ pulse energy at a 60 kHz repetition rate.

In this work, non-isothermal bleaching of Yb–Li co-doped fiber was investigated. The Yb–Li co-doped fiber was beneficial to reduce the photodarkening-induced excess loss and had no bad effect on the temperature of thermal bleaching (TB). Photodarkened fibers were bleached with different temperature ramp rates. The higher the ramp rate, the higher the complete bleaching temperature. The activation energy of the bleaching of Yb/Al/Li fiber was calculated by fitting, which was similar to that of an Yb-doped fiber. These observations are helpful in revealing the relationship between the mechanism of Li ion co-doping and TB.

With the increasing output power of the monolithic fiber laser oscillators, the stimulated Raman scattering (SRS) effect becomes one of the main limitations of power scaling. Employing fiber with a larger mode area is an effective technique to mitigate the SRS, but, for the monolithic fiber laser oscillators, the difficulty of the inscription of the high-reflection fiber Bragg gratings (FBGs) increases with the fiber mode area. In this work, we demonstrated a high-power monolithic fiber laser oscillator based on the home-made large mode area FBGs and ytterbium-doped fiber (YDF) with 25 μm core diameters. A maximum output power of 4.05 kW is achieved at the central wavelength of ～1080 nm with a total 915 nm pump power of ～6.7 kW. At the operation of 4.05 kW, the intensity of the Raman Stokes light is ～25 dB below the signal laser, and the beam quality (M2-factor) is ～2.2. To the best of our knowledge, this is the first detailed report of the monolithic fiber laser oscillator with an output power beyond 4 kW.

Stable 68 fs pulses with the average power of 1.5 W is directly generated from a multimode diode-pumped Kerr-lens mode-locked Yb:CYA laser by separating the gain medium and Kerr medium. The repetition rate is about 50 MHz, resulting in a single pulse energy of 30 nJ and a peak power of 0.44 MW. To the best of our knowledge, this is the highest single pulse energy ever produced from a mode-locked Yb:CYA oscillator. Our experimental results show that Yb:CYA crystal is an excellent candidate for multiwatt, sub-100 fs pulse generation in diode-pumped all-solid-state lasers. It is believed that the output power can be scalable to multi-W while the pulse duration is maintained with this simple method.

We report on the design and performance of a fiber laser system with adaptive acousto-optic macropulse control for a novel photocathode laser driver with 3D ellipsoidal pulse shaping. The laser system incorporates a three-stage fiber amplifier with an integrated acousto-optical modulator. A digital electronic control system with feedback combines the functions of the arbitrary micropulse selection and modulation resulting in macropulse envelope profiling. As a benefit, a narrow temporal transparency window of the modulator, comparable to a laser pulse repetition period, effectively improves temporal contrast. In experiments, we demonstrated rectangular laser pulse train profiling at the output of a three-cascade Yb-doped fiber amplifier.

A high power continuous-wave single-frequency green fiber laser by second-harmonic generation of a Yb-doped fiber amplifier (YDFA) is developed. A linearly polarized single-mode fiber amplifier produces a 60 W infrared laser at 1064 nm with a 103 W incident diode pump laser at 976 nm, corresponding to an optical conversion efficiency of 58%. An external bow-tie enhancement cavity incorporating a noncritically phase-matched lithium triborate crystal is employed for second-harmonic generation. A 33.2 W laser at 532 nm is obtained with a 45 W incident 1064 nm fundamental laser, corresponding to a conversion efficiency of 74%.

A mode-locked (ML) picosecond ytterbium-doped thin disk laser using a monolayer MoS2 as the saturable absorber (SA) is demonstrated. The monolayer MoS2 is fabricated through the method of low-pressure chemical vapor deposition. The laser directly produces stable ML picosecond pulses at a slope efficiency of 9.71%. The maximum output power is approximately 890 mW, while the corresponding repetition, pulse energy, and pulse duration are 48.6 MHz, 18.3 nJ, and 13.1 ps, respectively. Results suggest that the monolayer MoS2 is a promising SA for ultrafast lasers system.

We report a 307 W 1018 nm Yb-doped fiber laser pumped by a single 976 nm laser diode. The cavity slope efficiency is up to 75.9% and the amplified spontaneous emission is suppressed by 54 dB. The beam quality of the output laser has an M2 factor of 1.17. Effective thermal management is considered to ensure the stable operation of our system. The power stability at the maximum output power level is measured during a period of 0.5 h and the power fluctuation is less than 0.8%. This architecture can be an effective high brightness pump source of core-pumping high-power fiber amplifiers.

The laser performance of a new Yb:germanophosphate (Yb:GP) glass is investigated. A maximum output power of 826 mW at 1063 nm is achieved with direct diode pumping at 976 nm. The wavelength is tuned from 1034.47 to 1070.83 nm, corresponding to a tuning range of 36.36 nm. Thermal lens effects are investigated to optimize the optical cavity.