Focused-beam attenuated total-reflection technique on absorptive film in Kretschmann's configuration

The conventional algorithm for obtaining the p-ray reflectance (R) of a metal in an attenuated total-reflection (ATR) experiment is to normalize the p-ray reflecting power of the metal (I(p)) with its s-ray reflecting power (I(s)). We found that for these ATR experiments in Kretschmann's configuration, two conditions will make I(s) less than I(p). In the first condition the film itself is absorptive; in the second the film is weakly absorptive but has thin thickness. When I(p) < I(p), the conventional algorithm is not applicable anymore; otherwise, the measured reflectance will be greater than one. With a modified focused-beam ATR experiment, we demonstrated that the above hindrance can be overcome by taking the intensity distribution of the incident p ray as the normalizing signal. The reflectance of the bare prism at incident angles greater than the critical angle is also suggested to be taken as a proper normalization factor.