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physica status solidi (b)

Lo‐phonon‐assisted two‐photon absorption of the first excited state of the biexciton in CuCl

Walter Ekardt, M. I. Sheboul

Published Mar 1, 1977• 5 citations
Publisher

Abstract

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.

DOI
10.1002/pssb.2220800105

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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.

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Direct Two-Photon Creation of Excitonic Molecule in CuCl

W. Ungier, P. Janiszewski, Maciej Suffczynski

The probability of direct excitation of excitonic molecule in the two-photon absorption process is calculated with an Hylleraas-Ore type biexciton envelope, which is variationally optimized.In the second order of perturbation, because of the resonance effect, only the exciton .r5intermediate state is taken into account.The band structure at band extrema due to spin-orbit interaction is assumed.The transition probability of two-photon absorption is expressed by matrix element between the free exciton and the biexciton envelopes.The obtained probability of two-photon absorption in CuCl is about three orders of magnitude smaller when compared to that obtained by Hauamura.

Acta Physica Polonica A•Oct 1, 2000•1 citation

Radiative and Two-Photon Resonance Raman Processes Associated with Excitonic Molecules in CuCl

N. Nagasawa, Tsuneyoshi Mita, Masayasu Ueta

Giant two-photon absorption spectrum for the direct generation of excitonic molecules is measured with using a frequency tunable dye laser, and absorption peak is found at 3.1870 eV. Emission spectrum with excitation at the giant two-photon absorption band depends on the spectral width, \(\varDelta\varOmega_{1}\), of excitation light. In the case of \(\varDelta\varOmega_{1}{=}0.25\) meV, the two-photon resonance Raman scattering is found to be predominant. The Raman process involves an excitonic molecule and a longitudinal exciton as the intermediate and final states, respectively. On the other hand, for the case of \(\varDelta\varOmega_{1}{=}2.3\) meV, the emission spectrum shows a very sharp line at 3.1649 eV, which has been previously ascribed to be due to the Bose-Einstein condensation of excitonic molecules. Discussions are made on the dependence of emission spectrum upon the energy band-width of excitation light.

Journal of the Physical Society of Japan•Sep 15, 1976•96 citations

Generation of Excitonic Molecules by Giant Two-Photon Absorption in CuCl and Their Bose Condensation

N. Nagasawa, Naotaro Nakata, Yoshiko Doi +1 more

Through the studies of excitation spectra of emissions in CuCl crystals by a frequency tunable dye laser, excitonic molecules have been found to be generated directly by the giant two-photon absorption at the photon energy of 3.187 eV, as suggested by Hanamura. Two-photon excitation of crystals at 1.6 K enhanced very narrow emission bands at 3.1647 eV and at 3.1709 eV. These photon energies coincide with those of the high energy edges of the M L and M T bands due to the radiative annihilation of excitonic molecules having K =0. From these facts the Bose condensation of excitonic molecules at K ∼0 has been suggested.

Journal of the Physical Society of Japan•Oct 1, 1975•76 citations
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.
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 Two different theoretical models of the giant two‐photon absorption due to excitonic molecules (xx) are examined experimentally. The conventional model (Hanamura, 1973) follows the sequence: photon + photon → exciton + photon → xx, while the self‐consistent model (Ivanov and Haug, 1993) gives the other scenario of the two‐photon absorption: photon + photon → exciton + exciton → xx. Our high‐precision measurement of the frequency dependence of the two‐photon xx absorption coefficient in CuCl allows us to discriminate these two models and supports the new self‐consistent model.
The probability of direct excitation of excitonic molecule in the two-photon absorption process is calculated with an Hylleraas-Ore type biexciton envelope, which is variationally optimized.In the second order of perturbation, because of the resonance effect, only the exciton .r5intermediate state is taken into account.The band structure at band extrema due to spin-orbit interaction is assumed.The transition probability of two-photon absorption is expressed by matrix element between the free exciton and the biexciton envelopes.The obtained probability of two-photon absorption in CuCl is about three orders of magnitude smaller when compared to that obtained by Hauamura.
Giant two-photon absorption spectrum for the direct generation of excitonic molecules is measured with using a frequency tunable dye laser, and absorption peak is found at 3.1870 eV. Emission spectrum with excitation at the giant two-photon absorption band depends on the spectral width, ΔΩ1\varDelta\varOmega_{1}ΔΩ1​, of excitation light. In the case of ΔΩ1=0.25\varDelta\varOmega_{1}{=}0.25ΔΩ1​=0.25 meV, the two-photon resonance Raman scattering is found to be predominant. The Raman process involves an excitonic molecule and a longitudinal exciton as the intermediate and final states, respectively. On the other hand, for the case of ΔΩ1=2.3\varDelta\varOmega_{1}{=}2.3ΔΩ1​=2.3 meV, the emission spectrum shows a very sharp line at 3.1649 eV, which has been previously ascribed to be due to the Bose-Einstein condensation of excitonic molecules. Discussions are made on the dependence of emission spectrum upon the energy band-width of excitation light.
Through the studies of excitation spectra of emissions in CuCl crystals by a frequency tunable dye laser, excitonic molecules have been found to be generated directly by the giant two-photon absorption at the photon energy of 3.187 eV, as suggested by Hanamura. Two-photon excitation of crystals at 1.6 K enhanced very narrow emission bands at 3.1647 eV and at 3.1709 eV. These photon energies coincide with those of the high energy edges of the M L and M T bands due to the radiative annihilation of excitonic molecules having K =0. From these facts the Bose condensation of excitonic molecules at K ∼0 has been suggested.