Masayasu Ueta

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

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.

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

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.

Exciton spatial dispersion determined through the two-photon Raman scattering via excitonic molecule state at large wave vectors in CuCl

Abstract With simultaneous excitation of two dye laser beams the Raman scattering is studied in which the intermediate state is the excitonic molecule and the final states are the longitudinal and transverse excitons. The L-T splitting shows a large k-dependence. The effective masses are determined to be (2.3 ± 0.1)m0 and (3.1 ± 0.1)m0 for the transverse and longitudinal excitons, respectively.

The Effect of High Density Excitons on the Exciton Bands in CuCl

The effect of the strong laser irradiation on the exciton bands of CuCl has been studied. The Z 3 and Z 1,2 exciton bands are found to shift to high energy side linearly with the laser intensity. The fact is explained in terms of Hanamuras theory which describes the increase of the exciton formation energy due to the interaction between excitons. The ratio of the peak shift of the Z 1,2 band to that of the Z 3 band is 0.89. From the ratio and the reduced mass of the Z 3 exciton, the effective masses of the electron and hold are deduced to be 0.44 m 0 and 3.6 m 0 , respectively.

Resonant Raman Scattering under Two-Photon Excitation of Excitonic Molecules in CdS

Two-photon-resonant Raman scattering under the giant two-photon excitation of excitonic molecule has been observed from various scattering directions, and two types of Raman scattering, M T and M M are found. The transverse and mixed modes of the \(A(\varGamma_{5})\) exciton state are left behind in the M T and M M Raman processes, respectively. These Raman scatterings reflect the characteristic dispersions of their respective exciton states, and conform to the geometrical selection rules derived on the assumption that the excitonic molecule state has the \(\varGamma_{1}\)-symmetry. A non-linear absorption peak due to the giant two-photon absorption is found at 2.5506 eV (λ=486.10 nm) with the use of intense probe light. The binding energy of excitonic molecule is found to be 4.4 meV for two \(A(\varGamma_{6})\) triplet excitons.

Giant Two-Photon Absorption and Two-Photon Resonance Raman Scattering in CdS

Giant two-photon absorption for the direct generation of excitonic molecule is found at 2.5507 eV in CdS. Two-photon resonance Raman scattering is found which has an excitonic molecule and a transverse exciton as the intermediate and final states, respectively.

Anomalous Dispersion of Excitonic Polariton Due to the Giant Two-Photon Absorption into Excitonic Molecule in CuCl

The energy dependence of excitonic-polariton Raman lines upon the exciting laser energy has been found to show anomalous behavior when the excitation energy crosses the giant two-photon absorption band responsible for the direct generation of excitonic molecules. The anomalous behavior is ascribed to the non-linear change of the incident polariton dispersion.

Two-Photon Resonance Raman Scattering with Recoiling Excitonic Polariton in CuCl

Two-photon resonance Raman scattering associated with the giant two-photon absorption into the excitonic molecule state has been measured in near-forward scattering geometry, and a new type of Raman lines has been observed whose energies depend on the direction of observation. These Raman lines can well be explained as the Raman processes in which the excitonic molecule and excitonic polariton are the intermediate and final states, respectively.

Energy Level Scheme of Excitonic Molecule and Exciton in CuBr

Giant two-photon absorption for the direct generation of excitonic molecue is measured. Three absorption peaks are found at 2.9540, 2.9561 and 2.9576 eV, which are responsible for the two-photon transitions to the \(\varGamma_{1}(J{=}0)\), Γ 5 ( J =2) and \(\varGamma_{3}(J{=}2)\) states, respectively, of the excitonic molecule.

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