Four-wave mixing scheme

Fig. 1. Four-wave mixing scheme to produce radiation at Lyman-a in mercury vapor...

The majority of femtosecond time-resolved PP experiments is performed in the condensed phase and is based on the detection of photons. For these experiments, the calculation of the nonlinear electric polarization represents the central task of the theoretical description. While femtosecond time-resolved measurements with detection of photons are possible also in the gas phase, e.g. by the detection of laser-induced fluorescence (LIF) or with background-free four-wave-mixing schemes, the detection of charged particles (i.e. photoelectrons or ions) has the advantage of the extremely high collection efficiency. By mass-selected detection of the ions, additional information on the photoinduced fragmentation... 

The integration in Equation [4] considers the existence of several frequency combinations matching the condition = Ey cOy, within the bandwidth of the applied field. A single laser whose bandwidth is large enough to include frequency components that match 0) -0) = O) can drive the nonlinear response. However, more frequently the laser bandwidth is smaller than o) and different beams with distinct centre frequencies at needed to match the Raman resonance. Let us now consider a field composed of a superposition of quasi-monochromatic beams, i.e. the amplitude at a carrier frequency is modulated by a complex envelope that defines its spectral shape. The central frequencies are chosen to match the Raman resonant four-wave mixing scheme (see Table 1), which can be later adapted to other colour choices. Three laser beams are present of frequencies o)q, cOp, cOg, with 0) -0) = 0) as the only resonant frequency combination. 

Fig, 1. Pump-probe photoionization (PPI) and time-resolved degenrate four-wave mixing (TRDFWM) schemes for rotational coherence spectroscopy (RCS). 

Kinetics of an intramolecular proton-transfer cycle of 2-(2 -hydro-xyphenyl)benzothiazole (HBT) was investigated by the degenerative four wave mixing [47] (Scheme 2). After a preexcitation of the enol form to the... 

There are many schemes for detecting the arrival of the vibrational wavepacket at a specifiable position on the excited state potential energy curve. These include one-color and two-color schemes, with detection by absorption, fluorescence, ionization, four-wave mixing, and many other methods. Two simple schemes are discussed here. 

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