Noncollinear optical parametric amplification of a supercontinuum

University essay from Lunds universitet/Atomfysik; Lunds universitet/Fysiska institutionen

Abstract: During this thesis, work has been done towards realizing a short-wave infrared (SWIR) laser source based on optical parametric amplification. It is planned that this setup should be able to produce few-cycle laser pulses at 2μm with a stable carrier-envelope phase (CEP). This will be done by using various nonlinear processes to convert the output from a 1030-nm, 200 kHz laser source, based on Yb-doped rod-fiber amplifiers. During my work, the first part of the envisioned SWIR source has been implemented: A super- continuum has been generated, to provide a broadband seed for a non-collinear optical parametric amplifier (NOPA). The NOPA also requires a pump beam, which was produced using second-harmonic generation to obtain light at 515 nm. Finally, the NOPA was implemented using the supercontinuum seed and the pump beam. The supercontinuum was generated through spectral broadening in a YAG crystal. The focusing conditions and the length of the crystal were adjusted to obtain a flat and stable spectrum in the wavelength range of interest (620 - 750 nm). The NOPA utilized a BBO crystal as a nonlinear medium. Phase-matching simulations of the NOPA process was carried out to design an optimal geometry for the amplification of the white light in the range of 640 - 750 nm. The NOPA was subsequently implemented using the optimal parameters obtained from the simulations. The resulting NOPA produced an output of 440 mW, using an input of approximately 5 - 6 mW of supercontinuum power. The spectrum of the amplified supercontinuum stretched between 640 - 695 nm. The gain of the NOPA is satisfying, however, the bandwidth is narrower than desired. Further improvements can be done to the amplifier such as removing residual chirp from the supercontinuum to further increase the bandwidth. In future work, a stage performing difference frequency generation will be implemented, which will provide CEP-stable SWIR pulses.

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