Multilayer
interference filters operate by causing constructive (or destructive, depending
on spacing and wavelength) multiple reflections from a series of interfaces
between otherwise transparent planar media. Thus, a sequence of alternating
high and low index layers are deposited --- more layers means that more
reflections are coupled together and thus give more distinct color effects.
In most of our published work we have deposited sol-gel coatings that yield
either pure SiO2 (low refractive index) or a 90:10 mixture of
TiO2/SiO2 (high refractive index). In one case we
had deposited 11-layer stacks having alternating layers (at matched quarter-wave
optical thicknesses for the respective materials) with slightly thicker
bounding layers onto a fused silica substrate as required by the optical
design. Our design was targeted for most reflectance near the middle of
the optical spectrum. This filter had spectral characteristics as shown
in the adjacent figure.
Our goal in
early studies was to modify the spectral characteristics of these interference
filters locally by using laser irradiation. Although this was partially
successful, we were not able to push the color differences far enough to
make the technique interesting from a practical aspect. Further information
about these interference filter fabrication tests can be found in these
references:
B. D. Fabes, D. P. Birnie, B. J. J. Zelinski, S. M. Melpolder, and M.
J. Hanrahan, "Laser Processing of Multilayer Interference Filters," in
Sol-Gel Processing and Applications, Y. A. Attia, Ed., Plenum Press,
N.Y., 81-95 (1994).
D. P. Birnie, III, S. M. Melpolder, B. D. Fabes, B. J. J. Zelinski,
and M. J. Hanrahan, "Laser Processing of Chemically Derived Dichroic Filters,"
Optical Engineering, 32, 2960-2965 (1993).
D. P. Birnie, III, S. M. Melpolder, B. D. Fabes, B. J. J. Zelinski,
M. J. Hanrahan, D. J. Taylor, and L. Weisenbach, "Laser processing of sol-gel
derived multilayer interference filters", Proc. SPIE 1758, Sol-Gel
Optics II, 630-637 (1992).
Page last edited February 2005.
(c) 1998, 1999, 2000, 2005 Dunbar
P. Birnie, III,
Department of Materials Science and Engineering
Rutgers, The State University of New Jersey
In most of our published work we have deposited sol-gel coatings that yield
either pure SiO2 (low refractive index) or a 90:10 mixture of
TiO2/SiO2 (high refractive index). In one case we
had deposited 11-layer stacks having alternating layers (at matched quarter-wave
optical thicknesses for the respective materials) with slightly thicker
bounding layers onto a fused silica substrate as required by the optical
design. Our design was targeted for most reflectance near the middle of
the optical spectrum. This filter had spectral characteristics as shown
in the adjacent figure.