Nils-Oliver Schütz

Setup for the generation of ultrashort pulses in the deep UV through achromatic phase matching

The generation of ultrashort pulses via phase matching in a BBO crystal is limited by the wavelength dependence of the phase-matching condition. This results in either efficient conversion of only a fraction of the broad spectral bandwidth or, an overall low conversion efficiency when very short BBO crystals are used. This inherent compromise between pulse duration and conversion efficiency can be addressed by second-harmonic generation (SHG) using achromatic phase matching (ACSHG). By laterally separating the spectral components of the beam and tightly focusing each individual component into the BBO crystal at its respective phase-matching angle, efficient SHG can be achieved across the entire spectral bandwidth. This enables the efficient generation of ultrashort pulses in the deep UV. The setup is combined with a compression stage.

Inteferometry via acousto-optic phase modulation

Pump–probe spectroscopic experiments investigate the dynamics of molecules following electronic excitation. To resolve ultrafast dynamics, the pulses must be sufficiently short. However, short pulse durations inherently limit the spectral resolution, as the spectral bandwidth remains constant with time. To overcome this limitation, a monochromator is introduced into the reference arm of the
interferometer. This allows wavelength selection and therefore dynamic adjustment of the temporal pulse length to achieve maximum spectral resolution. Temporal phase modulation of both pulses with two acousto-optic modulators enables the detection of even very weak signals via electronic lock-in to the signal of the wavelength selected reference arm. The setup was tested by recording an
interferogram of the caesium fluorescence. Both setups will be used as a pump source in time-resolved photo electron spectroscopy experiments.