We reported a simple and compact Yb-doped fiber femtosecond oscillator, which is based on a dispersion management and nonlinear polarization evolution (NPE) technique. Here, 84 fs, 4 nJ at 1030 nm pulses were generated directly from the mode-locked fiber oscillator by optimization of the net dispersion of the cavity. Only a pair of gratings was used to compensate the positive dispersion caused by the fibers and other optics in the cavity. This is, to our knowledge, the shortest pulse duration directly from a fiber oscillator without any extra compressor outside the cavity.

We present an adaptive optics (AO) system for a 1.94-µm laser source. Our system consists of a home-made Shack–Hartmann wavefront sensor and silver-coated bimorph deformable mirror operating in a closed-loop control scheme. The wavefront sensor used an uncooled vapor phase deposition PbSe focal-plane array for the actual light sensing. An effect of thermal afterimage was found to be reducing the centroid detection precision significantly. The effect was analyzed in detail and finally has been dealt with by updating the background calibration. System stability was increased by reduction of control modes. The system functionality and stability were demonstrated by improved focal spot quality. By replacing some of the used optics, the range of the demonstrated mid-IR AOS could be extended to cover the spectral range of 1–5 µm. To the best of our knowledge, it is the first AO system built specifically for mid-IR laser wavefront correction.

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The fluctuation-magnification effect on the peak intensity of a laser pulse caused by the nonlinear Kerr effect in the chirped volume Bragg grating (CVBG) compressor is investigated experimentally for a high-energy, thin-disk, chirped pulse amplification system. The nonlinear Kerr effect occurs at the blue end, and the accumulated nonlinear phase shift (B-integral) in the CVBG rises with the increase of laser pulse energy. Experiments show that small fluctuations in peak power of uncompressed pulses cause increasing of the temporal fluctuation and spatial fluctuation due to high Kerr-nonlinearity in the CVBG when B-integral is larger than π. Thus the initial fluctuation would be magnified by the CVBG compressor.

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