Measurement and minimization of angular chirp of stretcher in chirp pulse amplification laser

The measurement of the angular chirp by misalignment of the stretcher used for chirp pulse amplification (CPA) and optimization of the stretcher were studied. A misalignment in the optical system based on the CPA technique, which expands and compresses pulses using gratings, leads to angular chirps with different propagation directions depending on the wavelength. The angular chirp causes tilted pulse fronts in the near-field and reduces the intensity at the focus. The conventional method of correcting the grating misalignment by measuring the tilted pulse front mainly measures the laser beam after the compressor, and it is difficult to apply it to the measurement of the angular chirp generated by the stretcher. To overcome this, the wavelength of the laser was controlled by installing a slit inside the mode-lock oscillator, and the angular chirp was measured by direct measurement of the direction of the stretcher output according to each wavelength. This method measures the angular chirp in a simple manner without installing an additional light source or complex optical system and can be easily used for general ultrashort high-power lasers based on the CPA technique.