Two-photon absorption and nonlinear polariton effects in organic crystals
Two-photon excitation (TPE) and second harmonic generation (SHG) were studied in phenanthrene crystals at low temperatures (2 to 6/sup 0/K). Polarized TPE spectra of the 350 nm /sup 1/A/sub 1/ reverse arrow /sup 1/A/sub 1/ absorption system in phenanthrene crystals are supplemented using a nitrogen laser-pumped dye laser. Analysis of vibronic structure reveals that the dominant intermediate states for TPA are those of B/sub 2/ (L axis) symmetry. TPE spectra principally associated with intermediate states of A/sub 1/ (M) symmetry exhibit strong intramolecular vibronic coupling by totally symmetric vibrations. Polarized TPE spectra of mixed crystals of phenanthrene in fluorene confirm the predominance of the long-axis mechanism in TPA and the participation of states of A/sub 1/ symmetry by vibronic coupling. Position of the upper Davydov component of the origin depends on photon propagation direction and polarization in both TPE and SHG. The appearance of the dipole-forbidden lower Davydov component in these spectra is discussed in terms of misalignment and excitation of a longitudinal exciton. Similarity of TPE and SHG spectra indicates that both result from polariton fusion. The calculated polariton dispersion curve accounts for the energy shifts of the upper component in TPE and SHG. Phase matching on the a*b face leads to creation of a polariton on the upper polariton branch, above the one-photon absorption frequency, for a*- and b-polarized light.
- Research Organization:
- Ames Lab., IA (USA)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 5679600
- Report Number(s):
- IS-T-962; ON: DE82005623
- Resource Relation:
- Other Information: Thesis
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE
MOLECULAR CRYSTALS
POLARONS
PHENANTHRENE
SPECTRA
CRYSTALS
DISPERSION RELATIONS
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
EXCITONS
FLUORENE
HARMONICS
MIXTURES
SPECTROSCOPY
ULTRALOW TEMPERATURE
VIBRATIONAL STATES
AROMATICS
CONDENSED AROMATICS
DISPERSIONS
ENERGY LEVELS
HYDROCARBONS
ORGANIC COMPOUNDS
OSCILLATIONS
QUASI PARTICLES
400301* - Organic Chemistry- Chemical & Physicochemical Properties- (-1987)
360603 - Materials- Properties