Prism and grating coupling to long-range coupled-surface exciton–polaritons

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Abstract
Long-range surface exciton–polaritons are optically excited on thin chromium films deposited on quartz glass substrates and covered by a matching fluid. Both prism coupling and grating coupling are examined at a wavelength of 1.52 μm. Comparing the results obtained for prism coupling with predictions from Fresnel theory confirms that the dielectric constant of chromium at this wavelength is excitonic in character. In the case of prism coupling the influence of both the chromium thickness and the matching fluid thickness on coupling strength is examined. For grating coupling the influence of grating groove depth is examined as well as the influence of changing the refractive index of the covering fluid, which alters the asymmetry of this coupled-surface-mode system. All the results confirm the fundamental proposition that a thin layer that has a dielectric constant with a large imaginary component is capable of supporting an extremely long-range coupled-surface mode.