Coherent laser control of molecules

Abstract In Chapters 9–11, we have considered methods for incoherent control of atoms and molecules, whose realization relies on differences in their spectra. Of course, coherent effects inevitably manifest themselves in these methods, especially in the case of atoms, but with rare exceptions, they play no crucial role here. Noncoherent control was quite natural for the first stage of laser control, when the duration τ  p of the laser pulses used is much longer than the coherence time T  2 of the quantum system being controlled. A typical case is that of polyatomic molecules (Chapter 11) in highly excited vibrational states and molecules in condensed media, where the relaxation time of the coherence induced by a coherent laser pulse falls within the subpicosecond range. The progress in the development of nanosecond, picosecond, and femtosecond pulsed lasers has led to the corresponding development of new avenues of noncoherent and coherent laser control of molecules (Fig. 12.1). The first wave of successful applications of lasers for the purpose of effecting noncoherent laser control of polyatomic molecules was associated with the development in the early 1970s of the relatively simple CO2 laser, generating high-power IR pulses in the range 9–11 μm with a duration of the order of 100 ns. The use of these lasers to excite vibrations in polyatomic molecules gave birth to multiphoton photoselective IR laser photochemistry, providing intermolecular selectivity, isotopic selectivity in particular (Chapter 11).