Time-resolved Photoelectron Imaging Using Ultrashort VUV Pulses

A photoexcited molecule is deactivated through a variety of photo-physical/chemical processes, and ultimately relaxes to the ground electronic state (S0) or further undergoes chemical reactions in S0. Time-resolved photoelectron imaging (TRPEI) [1] enables full observation of these photoinduced dynamics, because photoionization can be induced from any part of the potential energy surfaces (PESs). However, observation of low-lying electronic excited states and S0 requires probe pulses in the vacuum ultraviolet (VUV) region, and it has been difficult to generate intense ultrashort VUV laser pulses. Following the generation of sub-20 fs deep UV (DUV) pulses at 4.7 and 6.3 eV by cascaded filamentation four-wave mixing (FWM) [2], we have succeeded in generating ultrashort DUV and VUV (7.8 and 9.3 eV) pulses simultaneously [3,4]. While this light source is simple and easily implemented (Fig. 1), it provides multiple colors with ultrashort time-duration (<20 fs) without any dispersion control (Fig. 2). Thus, it is an ideal light for TRPEI. In this talk, we present TRPEI using ultrashort VUV pulses to obtain a “global reaction map” of photoinduced dynamics of an isolated molecule.