A combination of sub-nanosecond photoexcitation and femtosecond supercontinuum probing is used to extend femtosecond transient absorption spectroscopy into the nanosecond to microsecond time domain. Employing a passively Q-switched frequency tripled Nd:YAG laser and determining the jitter of the time delay between excitation and probe pulses with a high resolution time delay counter on a single-shot basis leads to a time resolution of 350 ps in picosecond excitation mode. The time overlap of almost an order of magnitude between fs and sub-ns excitation mode permits to extend ultrafast transient absorption (TA) experiments seamlessly into time ranges traditionally covered by laser flash photolysis. The broadband detection scheme eases the identification of intermediate reaction products which may remain undetected in single-wavelength detection flash photolysis arrangements. Single-shot referencing of the supercontinuum probe with two identical spectrometer/CCD arrangements yields an excellent signal-to-noise ratio for the so far investigated chromophores in short to moderate accumulation times.
Received 08 April 2013Accepted 18 June 2013Published online 11 July 2013
The authors gratefully acknowledge stimulating discussions with and technical help by Benjamin Frisch and Stefan Gundacker from CERN and thank Gerhard Stresing for the helpful assistance in interfacing the CCD cameras, as well as Marcel Dubey, formerly GMP SA, for stimulating the initial idea of the project. We thank Arnulf Rosspeintner for the suggestion of and help with the measurement of the magnetic field effect. We would also like to thank one of the referees for the helpful suggestions to improve the quality of the paper. This work was supported by the Fonds National Suisse de la Recherche Scientifique through Project No. 200020-124393 and the NCCR MUST, and by the University of Geneva.
Article outline: I. INTRODUCTION II. EXPERIMENT A. Optical setup B. Timing measurements C. Measurement procedure and data treatment III. RESULTS AND DISCUSSION A. Signal to noise B. Time resolution IV. APPLICATION EXAMPLES A. Electron transfer and triplet recombination B. Magnetic field effect V. CONCLUSIONS AND OUTLOOK
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