A new method of laser photobiology and photochemotherapy is considered. It consists in producing, by two-step laser excitation, an irreversible modification in a chromophore attached to a given biomolecule. The excitation may lead to the ionization, dissociation, or other irreversible chemical modifications of the chromophore. The resulting photoproducts may then induce a chemical change on the biomolecule. This phenomenon is to be contrasted with the photodynamic action where the chemical change in the biomolecule is produced by the surrounding oxygen molecules raised to the first excited singlet state by energy transfer from the excited chromophore.

© 1984 Optical Society of America

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