Coherent control in four-photon excitation schemes

Abstract

We report the observation of coherent control of the ionization rate in four-photon resonant, five-photon ionization schemes in Kr and Xe. The intermediate resonance is excited via different interfering channels involving four-photon absorption of the fundamental laser frequency ( ionization) as well as one third harmonic and one fundamental frequency photon absorption ( excitation), a particular aspect of the scheme being that interference occurs at a virtual level. By varying the relative phase of the two electromagnetic fields, a large modulation depth has been observed which is due to the chosen non-linear excitation scheme. In the Xe excitation experiment the interference between the different channels could be additionally probed through the modulation of the third-harmonic signal.

Coherent phase control in ionization of Magnesium by a bichromatic laser field of frequencies ωand 2ω

“…3. Four-photon generalized ionization cross section σ (4) , leading to 1 S e (full line), 1 D e (dotted line) and 1 G e (dashed line) continua from the ground state of Mg, as a function of the photoelectron energy.…”

“…The aspect in question is the possibility of altering the line shape of an autoionizing resonance through such phase control. The general features of phase control in photoabsorption have been discussed in the literature extensively [1,2,3,4,5,6,7]. The possibility of altering an autoionizing line shape has also been discussed [8] to some extent in theoretical work where it has been shown that one particularly intriguing feature, depending on parameters, is the possibility of turning off the transition to the "discrete" or the continuum part of the resonance [9,10].…”

Coherent Control of Chemical Reactions

“…25 Early experiments used coherent phase control to transfer population from one bound state to another. [26][27][28][29][30] More challenging, and of greater chemical interest, is the control over bound-to-continuum transitions. To date, coherent control has been demonstrated for the ionization of atoms 31 and molecules, 31,32 the photodissociation of molecules, 33,34 and the switching of photocurrents in semiconductors 35,36 and photocathodes.…”

Coherent control of frequency conversion toward short (picosecond) vacuum-ultraviolet radiation pulses

“…The latter corresponds to control of photoionization and photodissociation yields. There are only very few experiments dealing with coherent control of frequency conversion [5][6][7].…”