Abstract:
A system comprised of a Martin-Puplett type polarizing interferometer and a Helium-3
cryostat was developed to study the transmission of materials in the very-far-infrared
region of the spectrum. This region is of significant interest due to the low-energy excitations
which many materials exhibit. The experimental transmission spectrum contains
information concerning the optical properties of the material. The set-up of this system
is described in detail along with the adaptations and improvements which have been
made to the system to ensure the best results.
Transmission experiments carried out with this new set-up for two different varieties
of materials: superconducting thin films of lead and biological proteins, are discussed.
Several thin films of lead deposited on fused silica quartz substrates were studied.
From the ratio of the transmission in the superconducting state to that in the normal
state the superconducting energy gap was determined to be approximately 25 cm-1 which
corresponds to 2~/kBTc rv 5 in agreement with literature data. Furthermore, in agreement
with theoretical predictions, the maximum in the transmission ratio was observed to
increase as the film thickness was increased. These results provide verification of the system's
ability to accurately measure the optical properties of thin low-Tc superconducting
films.
Transmission measurements were carried out on double deionized water, and a variety
of different concentrations by weight of the globular protein, Bovine Serum Albumin, in
the sol, gel and crystalline forms. The results of the water study agree well with literature
values and thus further illustrate the reproducibility of the system. The results of the
protein experiments, although preliminary, indicate that as the concentration increases the samples become more transparent. Some weak structure in the frequency dependent
absorption coefficient, which is more prominent in crystalline samples, may be due to low
frequency vibrations of the protein molecules.
