Development of an interferometric auto-correlator for the temporal diagnosis of a mid-IR femtosecond laser

Abstract

Since the laser technique, chirped pulsed amplification(CPA), was invented in 1985, high power femtosecond lasers have been extensively developed due to wide applications in strong field physics, ultrafast optics, medicine, and defense. Femtosecond high power mid infrared lasers have been newly investigated due to their inherent property with large ponderomotive energy. In this thesis, the pulse duration of a mid-IR optical parametric amplifier operating at 1.9μm was measured using an interferometric auto-correlator without any nonlinear crystal which can induces group delay dispersion. A two photon absorption Si photodetector instead of a nonlinear crystal, was utilized to measure the auto-correlation of mid-IR pulses. A pulse with Fourier transform limited duration of 55 fs was measured as 61 fs. The several limiting factors were examined to improve the performance of pulse characterization in the time domain. This interferometric auto-correlator will be applied for the pulse duration measurement of a high power femtosecond laser to be developed in the coming years.