A femtosecond stimulated raman spectrograph for the near ultraviolet

The design of a femtosecond stimulated Raman spectrograph (FSRS) optimized for measurements in the near UV is presented. It features a 387.5 nm Raman pump pulse causing a (pre-)resonance enhancement for molecular absorbing in the UV. As many photoreactive molecules absorb there, the set-up is particularly suited to study photochemical reactions. The 387.5 nm pulses are generated by frequency adding two femtosecond laser pulses with linear chirps, equal in magnitude but opposite in sign. This results in intense and spectrally narrow (∼10 cm^-1) Raman pump pulses which allow recording of Raman spectra with a good spectral resolution. The power of the spectrograph to trace ultrafast photoreactions is illustrated by measurements on the photochemistry of o-nitrobenzaldehyde. PACS 33.20.Fb; 39.30.+w     

Isotope selective ionization by optimal control using shaped femtosecond laser pulses

We report on selective optimization of different isotopes in an ionization process by means of spectrally broad shaped fs-laser pulses. This is demonstrated for (39,39)K2 and (39,41)K2 by applying evolution strategies in a feedback loop, whereby a surprisingly high enhancement of one isotope versus the other and vice versa is achieved (total factor approximately 140). Information about the dynamics on the involved vibrational states is extracted from the optimal pulse shapes, which provides a new spectroscopical approach of yielding distinct frequency pattern on fs-time scales. The method should, in principle, be feasible for all molecules.     

On an Extremal Scale of Approximation Spaces

This paper is concerned with an extremal scale of approximation spaces involving logarithmic weights. We give equivalent norms and study the behavior of this scale under reiteration and interpolation. Some applications to Lorentz-Zygmund operator ideals and Besov spaces with logarithmic weights are given.