Quantum plane Confinement effect of Exciton as an example of Boson Confinement

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A study of quantized excitons in CuCl epitaxial thin films is reported. Film thickness (L) that are much smaller than the photon wavelength (lambda) is the medium (-160nm), but larger than the exciton Bohr radius a_B (-0.7nm), are considered here. Many structures have been observed in transmission and absorption spectra over the Z_3 exciton region. When L<30nm, these structures correspond well to the confined exciton levels with odd quantum number n. The oscillator strength for the nth quantized exciton is found to be proportional to L/n^2 for odd n and zero for even n. The absence of the states with even n in the optical spectra is interpreted in terms of the parity selection rule in the confined exciton system when the long-wavelength approximation holds. The measured optical spectra are compared with the additional-boundary condition-free response theory. Polariton-interference fringes given by the theory demonstrate a good agreement with the experimental results both for thick and thin films. By analyzing the absorption line shape, the dependence of nonradiative damping of the quantized exciton on quantum number n and film thickness L is discussed.