Here r12 and r23 are the Fresnel reflection amplitudes at the dielectric-metal and the metal-air interfaces respectively, d is the film’s thickness while k, the exponential decay due to the absorption by the film, is given by the following expression. (2) Where n is the index of refraction for the dielectric, ε is the complex dielectric function for the metal film, and is the angle of incident at the dielectric-metal interface. EXPERIMENT Thin films of 80/20 Nichrome were grown using magnetron sputtering. A fused-silica prism was coated with a film thicknesses of 200±20 Å and a BK7 prism is coated with a film of 500±20 Å. For every prism coated with metal films, companion layers of the same nominal thickness and under the same growth conditions were also grown on glass substrate that were later used to carry out spectroscopic ellipsometry measurements. The experimental setup used to observe the SPR effects includes laser source of a chosen wavelength wavelengths followed by a polarization rotator and a linear polarizer as shown in figure 1. The coated prism was mounted on a rotational stage with 0.1 arc minute resolution which was computer controlled. Optical power meter was mounted on an independent rotational stage with 0.5 arc minute resolution. Each measurement was carried out with the light polarized in TM mode and then repeated in transverse electric (TE) mode. Both the reflected light as well as transmitted light through the film were measured. The ellipsometric measurements were carried out on Woollam spectroscopic ellipsometer for the determination of the ellipsometric parameters and over a wavelength range from 400 Figure 1. Schematic of experimental setup (left): (A) laser-diode, (D) polarization rotater, (E) linear polarizer, (F) coated prism on rotation stage and, (G) optical power meter. To model the actual experimental data one has to account for the fact that the metal film was deposited on the hypotenuse of a right angle face of the prism and light was refracted onto the glass side of the prism-metal interface in the TIR geometry and after reflection exited the prism. Fresnel losses at the first and last face of the prism were also accounted for along with the reflection (Eq. 1) that took place at the hypotenuse of the right angled prism. G A D E F – 900 nm. 224
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