Optical selection rule and oscillator strength of confined exciton system in CuCl thin films

Abstract

Transmission and absorption spectra of CuCl epitaxial films are studied. Many structures are observed over the ${\mathit{Z}}_{3}$ exciton region, corresponding to the quantization condition ${\mathit{K}}_{\mathit{n}}$=n\ensuremath{\pi}/L with odd n (${\mathit{K}}_{\mathit{n}}$: wave number). The absence of the states with even n is interpreted in terms of the parity selection rule in the confined exciton system. The value of the oscillator strength for the nth exciton is found to be proportional to L/${\mathit{n}}^{2}$ for odd n and zero for even n, in accordance with theoretical expectation. As a polariton system, this belongs to a simple regime of long wavelength approximation.