Measurement and stabilization of carrier-envelope phase of 1kHz amplified femtosecond laser pulses using spectral interferometry

Abstract

This thesis is devoted to an investigation of a technique to monitor and actively stabilize the carrier-envelope phase (CEP) of high-power femtosecond laser pulses. The carrier-envelope phase stabilization and electronic control of the CEP of amplified femtosecond laser pulses, generated in a grating-based chirp-pulse amplification (CPA) kHz Ti-sapphire laser, has been demonstrated. The CEP of a femtosecond laser oscillator was stabilized using the direct locking technique developed in our group. The CEP of amplified laser pulses was monitored using a self-referencing spectral interferometry. The modulation of fringe patterns provided the information on CEP variation. The measurements revealed a very slow CEP drift, at about 0.1 Hz. This slow CEP drift was stabilized by applying an electrical feedback to the acousto-optic modulator controlling the pump power input of the oscillator, adding a slow feedback loop to the fast feedback loop used in the direct locking electronics. The technique to compensate the slow variation in the CEP of the amplified pulses was successfully demonstrated. In the experiments performed, the average CEP drift of the amplified laser pulses was reduced below 0.2 radians. Long term stabilization up to 180 seconds was demonstrated, which will be further extended to several tens of minutes as the oscillator could be stabilized for two hours. In addition, the characterization of femtosecond laser mirrors, necessary for the generation of few-cycle laser pulses, has also been investigated. A compact and practical white-light interferometer was developed for rapid evaluation of the group delay dispersion (GDD) of femtosecond optics. GDD is obtained from the Fourier transform of the cross-correlation interferogram with femtosecond time resolution. The GDD characterization of broadband dielectric mirrors, broadband chirped mirrors and output couplers of different reflectivities has been performed. This study was used to select appropriate mi...