The interference of additional waves of forbidden polaritons excited by allowed polaritons in CuGaS2 Original Research Article

Additional waves of exciton polaritons are studied in thin (1.5–1.8 μm) CuGaS2 crystals at 9 K. The reflectivity spectra show a fine structure related to the interference of Fabry–Perot and additional waves which is a consequence of the polariton spatial dispersion. The main parameters of the exciton polaritons were determined from the spectra calculations. The Γ4 excitons of big oscillator strength are shown to excite the additional polariton waves of the Γ5 excitons of small oscillator strength, which interfere determining the fine structure in exciton resonance optical spectra.