Molecular Physics seminar

Realization of ultraviolet 2-dimensional spectroscopy in the collinear pump-probe geometry

by Nils Krebs (Uppsala University)

FA31 ()


2-dimensional Fourier transform spectroscopy additionally resolves the excitation-frequency when compared to conventional pump-probe spectroscopy. The measured excitation-detection frequency correlation resolves congested spectra and provides ultrafast structural and dynamical information like intra- or interchromophoric couplings. Despite successful applications in the IR and VIS, the spectral bandwidth of both the excitation and the probe pulses is the major challenge in 2D-UV spectroscopy. In our experimental setup, UV pulses tuneable between 295 – 370 nm are broadened to 25 nm by self-phasemodulation in bulk material. An acousto-optical pulse shaper (Dazzler, Fastlite) is used to compress and generate the phase-locked double pump pulses needed for 2D spectroscopy. Correct consideration of the spatio-temporal coupling of the pulse shaper is necessary to achieve nearly Fourier limited pulses. For probing, a supercontinuum spanning 250 – 720 nm is used. To achieve high signal-to-noise ratios and short acquisition times, referencing of the probe intensity fluctuations was used. The potential of the 2D-UV setup is demonstrated by unraveling the excitation-frequency dependent molecular dynamics of representative UV absorbing molecules.