Pulses as short as 8.1 fs were generated from a blue laser-diode-pumped Kerr-lens mode-locked Ti:sapphire oscillator, with an average power of 27 mW and a repetition rate of 120.6 MHz. The full width at half-maximum exceeds 146 nm, benefitting from the dispersion management by a combination of a low-dispersion fused silica prism pair and a series of double-chirped mirrors. To the best of our knowledge, this is the first time to generate sub-10-fs pulses from a laser diode directly pumped Ti:sapphire oscillator.

A 21.2 kW, 1.94 times the diffraction-limit quasi-continuous-wave laser is presented in this Letter based on a multi-stage, power-scalable Yb:YAG master-oscillator-power-amplifier (MOPA) system under adaptive optics (AO) control. The output laser of the MOPA system is a rectangular beam with a length-width ratio of 2:1, a 200 μs pulse duration, and a 1000 Hz repetition rate. With the AO control system, the beam quality of the laser is improved from 4.20 to 1.94 times the diffraction limit. To our knowledge, this is the best quality laser in the 20 kW class except for combined lasers.

We address the power scaling issue in end-pumped laser rod amplifiers by studying, experimentally and numerically, the magnitude of thermal lensing in a high-energy diode-pumped Yb:YAG crystal. The spatio-temporal temperature profile of the gain medium and the focal length of the induced thermal lens are determined numerically. The influence of the repetition rate and pumping power on the temperature distribution is analyzed. Experimental measurements covered repetition rates between 1 and 10 Hz and up to 4 kW pumping power.

为了控制重频放大器的热致波前畸变，设计并加工了均匀冷却的背面水冷激活镜激光放大器，对放大器的热畸变特性开展了实验研究，实验发现在泵浦功率密度较高即重复频率达到10 Hz，平均功率密度达到200 W/cm²时，放大器的热畸变既影响远场分布又对近场产生显著的调制。近场的调制会给放大器带来较大的损伤风险。为了消除热畸变对近场的调制，首先对泵浦强度分布进行了匀化，然后对介质进行了边缘热平衡控制，消除了热畸变引起的近场调制。通过对上述因素的控制，采用水冷激活镜构型的四程放大器实现了在10 Hz频率下良好运行。在没有进行主动补偿的情况下，实现了远场焦斑优于5倍衍射极限的输出。

A power-scaled laser operation of Pr:YLiF₄ (YLF) crystal at 720.9 nm pumped by a 443.6 nm laser diode (LD) module was demonstrated. The 20 W module was used to pump the Pr:YLF crystal, and a maximum output power of 3.03 W with slope efficiency of 30.04% was obtained. In addition, a 5 W blue LD was also used to pump the Pr:YLF laser, and a maximum output power of 0.72 W was obtained at room temperature. The output power was limited by the wavelength mismatch between the single-emitter LD and the absorption peak of the crystal.

We report on the energetic and beam quality performance of the second to the last main amplifier section HEPA I of the PEnELOPE laser project. A polarization coupled double-12-pass scheme to verify the full amplification capacity of the last two amplifiers HEPA I and II was used. The small signal gain for a narrow-band continuous wave laser was 900 and 527 for a broadband nanosecond pulse, demonstrating 12.6 J of output pulse energy. Those pulses, being spectrally wide enough to support equivalent 150 fs long ultrashort pulses, are shown with an excellent spatial beam quality. A first active correction of the wavefront using a deformable mirror resulted in a Strehl ratio of 76% in the single-12-pass configuration for HEPA I.