Energy transfer between electromagnetic modes near the isotropic point in CdS

1994

Nuov Cim D

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(ricevuto il 12 Lugiio 1993; revisionato il 29 Gennaio 1994; approvato il 12 Febbraio 1994) Summary. --For photon energies below the absorption edge in CdS, CdSe and other II-VI crystals the polariton dispersion curves for E • c and E II c (c-axis in a wurtzite crystal) cross at some points called isotropic points (IP). The occurrence of isotropic points provides the possibility of mode coupling between ordinary and extraordinary waves. Since the consequences of mode coupling on the optical properties for photon energies near the lowest IP lying much below the f'u'st excitonic state were widely discussed in recent years, more attention is now paid to isotropic points lying near the band gap and related to the n = 2, 3, ... excitonic states (,,higher isotropic points,0. Making use of Stahrs real density matrix approach we derive the polariton dispersion relations k• (~o), and kl, (oJ), for CdS and CdSe bulk crystals and determine the positions of IP's due to the crossing of the B-polariton with higher A-excitonie resonances. By the method of multiple internal reflection we calculate the transmission spectra for various crystal thicknesses (between 3 ~m and 0.5 mm) and coupling mechanisms. The calculated transmission shows sharply peaked structures centred at the isotropic points. PACS 71.35 -Excitons and related phenomena (including electron-hole drops). PACS 71.36 -Polaritons (including photon-photon and photon-magnon interactions). PACS 78.20 -Optical properties of bulk materials.

“…3 indicate the influence of the increased slab thickness. We obtain oscillations very similar to that observed near IPl [2,11,13]. The transmission spectra shown in fig.…”

Section: ~M : Iomb/moxflb -~ Iomb/ioy • B Iomb = Iox • B : Ioylibsupporting

confidence: 76%

“…Their dependence on the coupling 72 can be easily seen from the formulae giving in a first approximation the transmittivities in both directions near an isotropic point [2,11,13]:…”

Section: ~M : Iomb/moxflb -~ Iomb/ioy • B Iomb = Iox • B : Ioylibmentioning

confidence: 99%

Transmission spectra of thin CdS and CdSe crystals near higher-order isotropic points

1994

Nuov Cim D

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“…Far from excitonic resonances one can neglect the q-dependence of q,L, • thus obtaining from (2.3) a biquadratie equation for q having the roots [16,17] ~,/( ~ 2)2 44]}~/z Far from excitonic resonances one can neglect the q-dependence of q,L, • thus obtaining from (2.3) a biquadratie equation for q having the roots [16,17] ~,/( ~ 2)2 44]}~/z…”

mentioning

confidence: 99%

Optical properties of Wurtzite-type semiconducting crystals near the isotropic point

1992

Nouv Cim D

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Using Stahrs coherent wave approach we calculated the linear interband susceptibility near the band gap. The starting point was the ,,MGM, formula with a smeared-out dipole density M(r) and the Green's function G for the effective-mass Hamiltonian with a screened Coulomb potential. The susceptibility so obtained was used for calculating transmission spectra of CdS platelets for energies near the so-called isotropic point lying far below the nearest excitonic resonance. By fitting experimental spectra we determined components of the residual dielectric tensor for polarization of the incident beam perpendicular and parallel to the c-axis, the mixed-mode dipole moment corresponding to B-exciton, and decay radii characterizing transition dipole densities. The established set of parameters determines the dielectric tensor for a quite wide energetic range.PACS 71.35 -Excitons and related phenomena (including electron-hole drops). PACS 71.36-Polaritons (including photon-phonon and photon-magnon interactions). PACS 78.20 -Optical properties of bulk materials.

“…The existence of the lowest isotropic point IP~ at the wavelength ---5100/~ (which energetically means far below the lowest excitonic resonance) is known and examined from very different points of view (cf., e.g., [1][2][3][4][5]). As is known, the optical susceptibility of the crystal depends on the polarization of the propagating wave: A wave with a frequency corresponding to energies below the fundamental gap and polarized perpendicular to the c-axis activates the A, B and C excitons.…”

Section: -Introductionmentioning

confidence: 99%

Higher-order isotropic points in CdS

1991

Il Nuovo Cimento D

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It is shown that the upper polariton branch for B.=I exciton (Etlc) crosses the n ---3, 4 .... branches for A-exciton (E • c). It indicates the possibility of energy transfer between ordinary and extraordinary modes near the crossing (~isotropic~0 points. PACS 71.35 -Excitons and related phenomena (including electron-hole drops). PACS 71.36 -Polaritons (including photon-phonon and photon-magnon interactions). PACS 78.20 -Optical properties of bulk materials.