USING OPTICAL COLLISION TO CONTROL THE TRANSITION-REGION DYNAMICS

We have developed the “optical collision (OC)” approach to reach and control the transition regions of atomic and molecular interactions. The approach is based on the photoabsorption by a collisional quasimolecule during a single binary collision. Here I present two different OC approaches; one is the time-domain approach based on the fs pump-probe technique, and the other is the frequency-domain approach based on what we call the “second-order optical collision (SOOC)”. The time-domain approach has been applied to the Hg−CO van der Waals (vdW) complex, which is regarded as the bound quasimolecule, to realize the first observation of wave packet motion associated with an intermolecular energy flow in the vdW interaction. Possibilities of chirped pump-pulse and double pump-pulse control of the relevant energy flow are discussed. For the frequency-domain approach, we have applied the “wing-wing double resonance” technique to the Hg−Ar collisional quasimolecule to observe an ultrafast SOOC, where two-color, two-photon absorption takes place during a single binary collision, with a pair of nanosecond laser pulses. This experiment serves as the optical switching of an ultrafast thermal atomic collision; a collision pathway is controlled by changing the frequencies of those laser pulses. It is also shown that an ultrafast pump/probe measurement can be carried out with sub-picosecond time resolution using nanosecond pulsed lasers.