Dynamical symmetries and harmonic generation

Ceccherini, F. and Bauer, D. and Cornolti, F. (2001) Dynamical symmetries and harmonic generation. Journal of physics B, Atomic, molecular and optical physics, 34 . p. 5017. ISSN 1361-6455

Abstract

SUMMARY We discuss harmonic generation in the case of laser field-dressed Hamiltonians that are invariant under so-called dynamical symmetry operations. Examples for such systems are molecules which exhibit a discrete rotational symmetry of order N (e.g. benzene with N=6) interacting with a circularly polarized laser field and single atoms in a bichromatic field, with the two lasers having circular polarizations. Within a general group theory approach we study the harmonics one obtains from the interaction of a laser pulse and a circular molecule. When the system is in a pure field-dressed state the known selection rule kN \pm 1, k=1,2,3, ... results. However, other lines are observed when recombinations with states of a symmetry different from the initial one become important. This is the case for realistic laser pulses (i.e., with a finite duration). In particular when the fundamental laser frequency (or one of its multiples) is resonant with a transition between field-dressed states. Numerical ab initio simulations, confirming our analytical calculations and illustrating the power of the group theory approach, are presented.

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