SURFACE PLASMON RESONANCE AT SILVER-AIR INTERFACE

HOME THEORY APPARATUS DATA ACQUISITION RESULTS AND CONCLUSIONS

Data Acquisition

For each of 21 wavelengths of light between 450 and 650 nm, two images were taken. The two images were identical besides the presence or absence of resonance. The background image was subtracted from the resonance image to produce a noise-free image containing the resonance band (and no fluctuations in background intensity).

The subtracted image was averaged along paths parallel to the resonance band to produce intensity profile along y-axis pixel number (shown in the figure below).

However, these pixel values had no inherent meaning, as they relate only to the positioning and orientation of the camera. To associate these values with a physical quantity, a "zero pixel," from which all other pixels could be measured, was determined. As shown in the background image above, the intensity of light followed a somewhat Gaussian distribution; the highest intensity point in this image corresponds to direct reflection off of the surface of the silver and therefore to the center of the light beam shown in APPARATUS .

To find this point, the background images for all wavelengths of light were averaged in the same manner as described above to produce an intensity profile against y-axis pixel number. The pixel corresponding to the maximal intensity for each wavelength of light was found, and the average of these values was taken to be the zero pixel.

This allowed the intensity profiles of the subtracted images to be plotted against y-axis pixel relative to this zero pixel, as shown in the top axis of the figure below for three representative wavelengths.

The system geometry shown in APPARATUS was used to convert pixel relative to the zero pixel to internal angle Θ_int, yielding the lower axis in the figure above. The point of lowest reflectivity was chosen as Θplasmon.

Jesse Grindstaff & Molly Andersen

References:

[1] Pluchery O., Vayron R., and Van K., 2011 “Laboratory experiments for exploring the surface plasmon resonance.” Eur. J. Phys. 32 585–99.

[2] Haes A.J. and Van Duyne R.P., 2002 “A Nanoscale Optical Biosensor: Sensitivity and Selectivity of an Approach Based on the Localized Surface Plasmon Resonance Spectroscopy of Triangular Silver Nanoparticles.” J. ACS 124 (35), 10596-10604.

[3] Barnes W.L., Dereux A. and Ebbesen T.W., 2003 “Surface plasmon subwavelength optics.” Nature 424 824-830.

[4] Drescher, D. G., Ramarkrishnan, N. A., and Drescher, M. J., 2009 “Surface plasmon resonance (SPR) analysis of binding interactions of proteins in inner-ear sensory epithelia.” Meth. Mol. Biol. (493) 323-343.

[5] Yang, H.U., D’Archangel, J., Sundheimer, M.L., Tucker, E., Boreman, G.D., Raschke, M.B., 2015 “Optical dielectric function of silver” Physical Review B 91 234137.

[6] Griffiths, D.J. “Introduction to Electrodynamics.” (Pearson Education, Inc.) 4^th ed. 2013.

[7] Novotny, L., and Hecht, B. “Principles of nano-optics.” (Cambridge University Press, New York, New York). 2006.