A novel time-resolved mid-IR setup for the investigation of vibrational dynamics in aqueous nanoclusters

The ultrafast dynamics of the hydrogen bond network of liquid water remain a challenging field of research relevant to a plethora of disciplines, ranging from biology to geology. We present first results obtained with a newly developed optical setup, that allows mid-IR pump probe spectroscopy with a time resolution of 150 fs. The infrared pulses are generated via a recently proposed hybrid NOPA layout [1]. In order to achieve a selective excitation of the vibrational modes under investigation, the pump pulses are tunable in the range from 2000 to 4000 cm^-1, and their spectral widths are controlled by a spectral grating selector. The pulses generated in this way have a spectral bandwidth between 20 and 150 cm^-1 and pulse durations between 120 and 600 fs, with typical pulse energies of 3 μJ. The probe pulses are shorter than 50 fs (FWHM up to 600 cm^-1), yielding few-cycle mid-IR pulses with unprecedented spectral width. The Fourier limit for these pulses is below 30 fs. Fig. 1(a) shows a typical FROG measurement of the probe pulses. They are spectrally resolved to obtain both temporal and spectral information on the fast processes under investigation.