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A novel method with single-wavelength light is developed to determine the optical constants and the thickness of a thin metal film. It bases on a new geometry which consists of a coupling prism, a transparent coating layer directly deposited onto the prism base, a thin metal film (most often gold or silver), and air. The attenuated total reflection technique is employed in our configuration to excite two different kind of surface plasma waves simultaneously. One is the conventional surface plasma wave which propagates along the metal-air interface. The other is a modified long-range surface plasma wave which propagates along the nonsymmetrical structure (coating layer-metal and metal-air interfaces). The reflectivity shows to obvious surface plasmon resonance dips in a single-scan measurement. Every dip can be characterized by three main parameters: the position of the minimum, the peak height at the minimum, and the width of the resonance dip. These parameters provide enough information to determine the thickness, real and imaginary part of the optical constant of the thin metal film. Compared to conventional double- wavelength method and the double-medium technique, the present single-scan method not only avoids of the ambiguity of different conditions caused by two-scan technique, but also the dispersion problem with different light wavelength.
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