Control noncoherent

Acid-base cements are formed at room temperature but exhibit properties like those of ceramics. They are formed by reaction of an acid with a base. Normally this reaction produces a noncoherent precipitate. If, however, the reaction rate is controlled properly between certain acids and bases, coherent bonds can develop between precipitating particles that will grow into crystalline structures and form a ceramic. The acidic and alkaline components neutralize each other rapidly, and the resulting paste sets rapidly into products with neutral pH. 

The situation with molecules is much more involved for several reasons. First, for polyatomic molecules, the intramolecular relaxation processes that occur on a subpicosecond timescale are essential. It was for exactly this reason that the first successful experiments were conducted on the noncoherent laser control of polyatomic molecules with intermolecular selectivity. Second, the phase relaxation time in a condensed medium is also on a subpicosecond scale because of the interaction between the quantum system and its surroundings. Therefore, it was only the creation of relatively simple and inexpensive femtosecond lasers that made it possible to set about realizing the ideas of the coherent laser control of unimolecular processes (Tannor and Rice 1985 Brumer and Shapiro 1986 Judson and Rabitz 1992), particularly the... 

Fig. 1.5 Main methods for the laser noncoherent and coherent control of molecules by lasers (Chapters 9-12).

Fig. 12.1 Three waves of evolution of laser noncoherent and coherent control of molecules over a quarter of a century from nanosecond to femtosecond laser pulses. The next wave is the development of attophysics. (Modified from Letokhov 1997a.) Integrated activity (funding, number of experiments, and number of publications) in arbitary units.

Let us emphasize that noncoherent laser control of molecules depends on differences in the absorption spectrum between different molecular species, for example isotopic molecules. Coherent laser control is distinguished by its nontrivial manipulation of the phase coherence of excited states in molecules that can be similar in their absorption spectra but different in their phase coherence properties (Brixner et al. 20016). 

Letokhov, V. S., and Ryabov, E. A. (2004). Laser infrared multiphoton noncoherent control of intermolecular (isotope) selectivity for polyatomic molecules on a practical scale. Israel Journal of Chemistry, 44, 17. 

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