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physica status solidi (b)

Optical Nonlinearity Due to the Excitonic System in CuCl

N. Nagasawa

Published Dec 1, 1988• 2 citations
Publisher

Abstract

Abstract The optical nonlinearity associated with the giant two‐photon absorption, GTA, of excitonic molecules in CuCl is discussed. The metamorphoses of the four‐wave mixing spectra due to the generation of the exciton grating are demonstrated by the observation of their polarization characteristics. The propagation characteristics of the excitation around the GTA resonance are observed by micro‐Raman spectroscopy. The two‐photon Raman scattering light is used as a probe to monitor the spatial character of the excitation. The propagation characteristics show a drastic change in the very narrow spectral range around the GTA resonance energy.

DOI
10.1002/pssb.2221500273

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Relaxation Process of Excitonic Molecules in CuCl under the Two-Photon Resonant Excitation. I. Mutual Collision of Excitonic Molecules

Tadashi Itoh, 隆 上遠野, Masayasu Ueta

Line shapes of the giant two-photon absorption (GTA) band for the direct generation of excitonic molecules (EM) and the subsequent secondary emission of the EM resonantly generated have been studied in CuCl at various pump powers with the use of a high resolution spectroscopic method. The mutual collision of the EM, the rate of which is nearly proportional to their density, is found to be the main origin for causing the broadening of the GTA band, the decrease of the Raman yield and the rapid increase of the EM luminescence. The collision rate increases up to 10 12 /sec for the pump power of ∼1 MW/cm 2 . With the use of pump and probe method further evidence is obtained for the effectiveness of the mutual collision of the EM.

Journal of the Physical Society of Japan•Feb 1, 1984•27 citations
Abstract The optical nonlinearity associated with the giant two‐photon absorption, GTA, of excitonic molecules in CuCl is discussed. The metamorphoses of the four‐wave mixing spectra due to the generation of the exciton grating are demonstrated by the observation of their polarization characteristics. The propagation characteristics of the excitation around the GTA resonance are observed by micro‐Raman spectroscopy. The two‐photon Raman scattering light is used as a probe to monitor the spatial character of the excitation. The propagation characteristics show a drastic change in the very narrow spectral range around the GTA resonance energy.
The broadening of the excitonic molecule band in CuCl is studied from the giant two-photon absorption (GTA) measurements by a weak linearly polarized probe light beam under the simultaneous excitation around the same GTA by another strong pumping light beam of the orthogonal polarization to the probe beam. The width of the GTA line monitored by the probe light remains almost constant less than 0.3 meV under the strong irradiation of the pumping light. It is pointed out that the broadened width of the GTA band which have been observed by the strong one monochromatic beam experiments is not associated with the mutual collision between the really produced excitonic molecules.
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.
The three-wave mixing process has been studied as functions of incident photon energy and also of the geometrical configuration when incident photon energy lies around the two-photon resonance of excitonic molecule. Experiments indicate that the intensity of the third order nonlinear light beam is enhanced when the phase matching condition derived from the dispersion of excitonic polariton holds or when incident photon energy is equal to the two-photon resonance of excitonic molecule. The relation between this three-wave mixing process and two-photon resonant Raman scattering so far observed is discussed. It is shown that this three-wave mixing process is regarded as the two-photon resonant, coherent Raman scattering via excitonic molecules.
Line shapes of the giant two-photon absorption (GTA) band for the direct generation of excitonic molecules (EM) and the subsequent secondary emission of the EM resonantly generated have been studied in CuCl at various pump powers with the use of a high resolution spectroscopic method. The mutual collision of the EM, the rate of which is nearly proportional to their density, is found to be the main origin for causing the broadening of the GTA band, the decrease of the Raman yield and the rapid increase of the EM luminescence. The collision rate increases up to 10 12 /sec for the pump power of ∼1 MW/cm 2 . With the use of pump and probe method further evidence is obtained for the effectiveness of the mutual collision of the EM.