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physica status solidi (b)

Phonon‐Assisted Two‐Photon Absorption of the Excitonic Molecule in CuCl I. Bare‐Exciton Approach

Walter Ekardt, H.-J. Brocksch

Published May 1, 1979• 1 citation
Publisher

Abstract

Abstract Phonon‐assisted two‐photon absorption of biexcitonic levels in CuCl is considered including damping of the nearly resonant excitonic intermediate state. A pronounced structure of the line shape due to resonance effects, threshold effects, and structure in the Fourier transform of the envelope of the excitonic molecule is predicted. A detailed discussion of both temperature and damping effects is given. Large cross sections are predicted. The most favourable energetic range to observe the effects derived here is the low energy tail of the line, on the left of the Γ⅕ exeiton.

DOI
10.1002/pssb.2220930124

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Soviet Journal of Quantum Electronics•Apr 30, 1988•0 citations
Abstract Phonon‐assisted two‐photon absorption of biexcitonic levels in CuCl is considered including damping of the nearly resonant excitonic intermediate state. A pronounced structure of the line shape due to resonance effects, threshold effects, and structure in the Fourier transform of the envelope of the excitonic molecule is predicted. A detailed discussion of both temperature and damping effects is given. Large cross sections are predicted. The most favourable energetic range to observe the effects derived here is the low energy tail of the line, on the left of the Γ⅕ exeiton.
Abstract LO‐phonon‐assisted two‐photon absorption of the first excited level of the excitonic molecule in CuCl is considered on the basis of the previously derived symmetry properties of this state. A giant cross‐section for this process is predicted mainly due to the “resonant” intermediate state Γ 1/5 of the single exciton. The process under consideration overcomes the difficulties of pure two‐photon absorption (TPA) of p‐type envelope states of the excitonic molecule as stated by Hanamura.
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Abstract In CuCl at 1.7 K optical gain/absorption spectra are recorded in the spectral range of bound exciton and biexciton emission. Energy, effective temperature, and oscillator strength of biexcitons are determined. The observed kinetics indicates that the total pair density in the exciton‐biexciton system is pinned at about 1.6 × 1016 cm−3 for all excitation densities above 10 kW/cm2. At intense excitation, a Fano‐interference is observed between a discrete impurity absorption line and a continuum absorption tail. The latter is followed by a band of positive gain towards lower photon energies.
Abstract Two‐photon resonant Raman scattering processes are studied in different scattering configurations in CuCl. Observation of Raman lines from the front face of the crystal (backward scattering) yields new information on the energy of the transverse T5 exciton and on the biexciton damping. In transmission (forward scattering), two new emission lines can be identified as due to the Raman effect. They show a strong angular dependence because of the polariton nature of the particles involved. Their characteristic features contradict an interpretation in terms of Bose‐Einstein condensed biexcitons.