| Popis: |
Coherent anti-Stokes spectroscopy (CARS) can be considerably simpler than is suggested by literature analyses based on interactions of monochromatic waves. The simplification arises when the optical properties of real lasers are incorporated into the analysis. To incorporate these properties, it is necessary to recognize that the underlying nonlinear optical interaction has a previously ignored complexity and is dependent on the coherence properties of the fields as well as on their spectra. The coherence of the interaction, as described by the CARS linewidth parameter, is degraded by the imperfect coherence of the laser sources. The occurrence of the nonlinear interaction depends on the small size of laser mode widths, or more fundamentally, on the statistical degeneration of each incident field into a small number of independent fields, a property possessed only by optical fields from lasers. If the lasers' contributions to the linewidth parameter are made dominant, the degree of coherence becomes a fixed property of the apparatus, simplifying interpretation of CARS spectra and extending the range of usefulness of CARS well beyond what would otherwise be expected. Available numerical values plus considerations of effects such as mode frequency chirp suggest that domination of the coherence by the apparatus can be arranged or at least approached in most cases. |
