Experiments

Multi-dimensional spectroscopy

Our 10-50 kHz amplified laser system was designed for low noise operation, and this allows us to do pump-probe experiments with excellent S/N. The fundamental output of this amplifier has a shot to shot energy fluctuation that is < 0.1% RMS, we use it to pump a TOPAS -White, to get a broadband visual pulse (200nm bandwidth, 20 fs).As a consequence also after the many non-linear conversions that are required to generate broadband UV light the noise is <<1%. The output of the TOPAS is frequency doubled using Achromatic doubling, to get a 100 nm broad UV probe pulse .

Recent publications:

Ultrabroadband femtosecond two-dimensional ultraviolet transient absorption. G. Auboeck, C. Consani, F. van Mourik and M. Chergui. Optics Letters 37, p. 2337-2339, 2012.
Femtosecond pump/supercontinuum-probe setup with 20 kHz repetition rate. Gerald Auböck, Cristina Consani, Roberto Monni, Andrea Cannizzo, Frank van Mourik, and Majed Chergui
Rev. Sci. Instrum. 83, 093105 (2012)

Multi-dimensional coherent spectroscopy

To study ultrafast electronic coherences in molecular crystals, as well as biological systems, we developed a setup for ultra-broadband two-dimensional Fourier transform spectroscopy. The output of a 6 – 10 kHz Ti:Sa femtosecond laser is broadened by self-phase modulation inside an argon filled hollow core fiber, to produce continuum (500 – 1000 nm) laser pulses that are compressed to sub-10 fs, using a set of chirped mirrors (Ultrafast Innovations). We use the compressed laser pulses to perform photon echo spectroscopy in a passively phase stabilized BOXCARS geometry. Three excitations pulses with time delays τ and T stimulate a third order non-linear signal (the photon echo) that is emitted after a third time delay t (shown in the figure) and heterodyne detected with a local oscillator field (not shown). Fourier transformation along τ and t yields two dimensional correlation spectra of the excitation and detection frequencies at a certain population time T, allowing us to extract information that are “hidden” in classical transient absorption spectroscopy.

 

Recent publications:
A. Al Haddad, A. Chauvet, J. Ojeda, C. Arrell and F. van Mourik et al. Set-up for broadband Fourier-transform multidimensional electronic spectroscopy, in Optics Letters, vol. 40, num. 3, p. 312-315, 2015.
 

UV/vis/NIR Femtosecond Fluorescence experiments

The lay out of the upconversion set-up is shown above. A first femtosecond pulse excites the dye molecule and sets the time t=0 of the dynamics. The fluorescence emission from the dye is collected and focussed on a non-linear BBO crystal, where it is mixed with a second femtosecond pulse at 800 nm (called the gate pulse) which arrives at a given time delay. The mixing of the fluorescence light and with the gate pulse gives rise to the sum frequency of the two, which can be imaged with a spectrograph and a CCD camera. The delay of the gate with respect to the pump pulse can be continuously tuned which allows to record the temporal evolution of the dye fluorescence.

A special feature in our set-up is the polychromatic detection scheme. At each time-delay the BBO is rotated over the range of phase-matching angles to convert the whole fluorescence spectrum which is recorded with the CCD camera. In a single time-scan we obtain the whole 2D- (spectral and temporal) evolution of the fluorescence spectrum over a spectral range of >200nm with a temporal resolution of <100 fs.

Of special interest is  the combined coverage of a very wide spectral range with time-resolution we obtained in the UV spectral range

Time-resolved photoelectron spectroscopy