2 Experimental Set-Up
Apparatus
The experimental setup is as follows: a platform with an arm which is allowed to rotate about the center of the platform was used as the base of the apparatus. A rail section mounted to this arm served as the connection for a 625 nm (15 nm Bandwidth FWHM) 17.5 mW Diode laser (Class 3B) directed through a fiber optic cable into an aligned polarizer, iris, and convex lens (focus at 25.4 mm). Once mounted to the arm, this assembly is locked perpendicular to a screen positioned 60 cm away from the base. The lens provides a window of beam angles to be incident on the hypotenuse of the prism, which allows multiple angles to be sampled at the same time. The polarizer is used to change the orientation of polarization to allow coupling between the beam and the surface plasmons.
from the rail section reflects out the other side of the prism (as seen in figure ), exiting the prism and projecting onto a screen. A camera is mounted on a linear translational stage oriented parallel to the screen which allows the camera to be moved in order to detect the projected dark band.
A sample of thin silver foil is deposited onto a glass microscope cover slip, using Vacuum Evaporation Deposition. Then the sample is mounted onto the hypotenuse of a BK7 glass prism using index matching solution. The prism and thin silver foil sample are mounted on the platform using prism clamps such that the laser beam
Data Collection
Due to limitations in the window of the camera used, intensity and angle data was collected separately using two different methods and later combined in analysis. Angle was collected by projecting the dark band onto a screen and measuring it's horizontal distance from a point of known angle marked on the screen. this point of known angle was calibrated by coupling a HeNe laser into a fiber optic cable and attaching that to the cage section of the base's rotational arm. The beam was focused to a point and passed through the prism as indicated in figure to the right. Using the 45 and 90 degree angles and the geometry of the system, a scale of angles was calculated for the horizontal axis of the screen.
To measure the intensity of the reflected light, a video camera was directed at the prism was used to collect intensity data. The data collected by the camera was later calibrated with the angular data collected from the screen so each pixel corresponded to an angle of incidence of the laser on the thin silver foil sample.
