Phase control of absorption in large polyatomic molecules

Abstract

The phenomenon of interference of the amplitude for absorption of one photon of frequency 3ω and the amplitude for absorption of three photons of frequency ω was theoretically predicted by Shapiro, Hepburn, and Brumer. The interference was demonstrated experimentally by varying the relative phase between the tripled frequency photon and three photons with the fundamental frequency by the groups of Elliott and Gordon in atoms and small molecules. In order to see how general this phenomenon is, five compounds were studied, ammonia, trimethylamine, triethylamine, cyclooctatetraene, and 1,1-dimethylhydrazine. CH3I was used as the tripling gas for light in the range 604–600 nm. Interference was observed in all cases. The last four compounds have low ionization potentials and interference was observed between a 3+1 and a 1+1 ionization process with a maximum modulation of 22%. NH3 with a higher ionization potential requires absorption of 3+2 or 1+2 photons and exhibits a maximum modulation of 33%. We conclude that molecular size is no obstacle and that as long as a molecule has sufficiently strong absorption at the tripled frequency, and sufficient vapor pressure, and the laser fundamental beam is very strong, phase control of interference is observable.

Laser Control of Chemical Reactions

“…The relative yields are predicted to be a sinusoidal function of this phase difference and a function of the relative intensities of the fundamental and third harmonic of the light. Recently, Bersohn and co-workers (39,40) studied the interference between the 1Ј ϩ 2 and 3 ϩ 2 multiphoton ionization of methyl iodide (Fig. 3), ammonia, 2) and (1Ј ϩ 2) photoionization of methyl iodide.…”

Photodynamic control using field optimized initial state: A mechanistic investigation of selective control with application to IBr and HI photodissociation

“…In any case, treatment of rotational effects will increase the computational complexities by at least an order of magnitude 37 and we have therefore found it judicious to neglect rotational motion in this initial application. Photodissociation of IBr 21,26,[38][39][40][41][42][43] and HI [9][10][11][12][13][14][15][16]20 have been studied extensively and are our representative systems of choice. In the following section we analyze some representative max (0) for IBr and HI to investigate the mechanistic underpinning of photodynamic control of product selectivity and yield.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12] The different established theoretical approaches to control have been reviewed recently. 1 While the focus of these theoretical approaches has been on field design, the photodissociation yield has also been found to be extremely sensitive to the initial vibrational state from which photolysis is induced.…”

Coherent Control of Chemical Reactions

“…A second issue is the application of coherent control to large polyatomics. In this context, the bound-state control experiments of Wang et al 28 are encouraging. A third major challenge is the control of collisional processes.…”

“…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.…”