7 research outputs found
Mueller matrix polarimetry of plasmon resonant silver nano-rods: biomedical prospects
Fundamental understanding of the light-matter interaction in the context of
nano-particles is immensely bene- fited by the study of geometry dependent
tunable Localized Surface Plasmon Resonance (LSPR) and has been demonstrated to
have potential applications in various areas of science. The polarization
characteristics of LSPR in addition to spectroscopic tuning can be suitably
exploited in such systems as contrast enhancement mech- anisms and control
parameters. Such polarization characteristics like diattenuation and retardance
have been studied here using a novel combination of Muller-matrix polarimetry
with the T-matrix matrix approach for silver nano-rods to show unprecedented
control and sensitivity to local refractive index variations. The study carried
out over various aspect ratios for a constant equal volume sphere radius shows
the presence of longitu- dinal (dipolar and quadrupolar) and transverse
(dipolar) resonances; arising due to differential contribution of
polarizabilities in two directions. The overlap regions of these resonances and
the resonances themselves exhibit enhanced retardance and diattenuation
respectively. The spectral and amplitude tunability of these polarimetric
parameters through the aspect ratios to span from the minimum to maximum ([0,
1] in the case of diattenuation and [0, {\pi}] in the case of retardance)
presents a novel result that could be used to tailor systems for study of
biological media. On the other hand, the high sensitivity of diattenuation dip
(caused by equal contribution of polarizabilities) could be possibly used for
medium characterization and bio-sensing or bio-imaging studies.Comment: 8 pages, 6 figures, Proceedings of the Saratov Fall Meeting, 201
Differing self-similarity in light scattering spectra: A potential tool for pre-cancer detection
The fluctuations in the elastic light scattering spectra of normal and
dysplastic human cervical tissues analyzed through wavelet transform based
techniques reveal clear signatures of self-similar behavior in the spectral
fluctuations. Significant differences in the power law behavior ascertained
through the scaling exponent was observed in these tissues. The strong
dependence of the elastic light scattering on the size distribution of the
scatterers manifests in the angular variation of the scaling exponent.
Interestingly, the spectral fluctuations in both these tissues showed
multi-fractality (non-stationarity in fluctuations), the degree of
multi-fractality being marginally higher in the case of dysplastic tissues.
These findings using the multi-resolution analysis capability of the discrete
wavelet transform can contribute to the recent surge in the exploration for
non-invasive optical tools for pre-cancer detection.Comment: 13 pages, 14 figure
Swelling-Induced Optical Anisotropy of Thermoresponsive Hydrogels Based on Poly(2-(2-methoxyethoxy)ethyl methacrylate): Deswelling Kinetics Probed by Quantitative Mueller Matrix Polarimetry
Thermodynamically favored polymer–water interactions
below
the lower critical solution temperature (LCST) caused swelling-induced
optical anisotropy (linear retardance) of thermoresponsive hydrogels
based on polyÂ(2-(2-methoxyethoxy)Âethyl methacrylate). This was exploited
to study the macroscopic deswelling kinetics quantitatively by a generalized
polarimetry analysis method, based on measurement of the Mueller matrix
and its subsequent inverse analysis via the polar decomposition approach.
The derived medium polarization parameters, namely, linear retardance
(δ), diattenuation (<i>d</i>), and depolarization
coefficient (Δ), of the hydrogels showed interesting differences
between the gels prepared by conventional free radical polymerization
(FRP) and reversible addition–fragmentation chain transfer
polymerization (RAFT) and also between dry and swollen state. The
effect of temperature, cross-linking density, and polymerization technique
employed to synthesize hydrogel on deswelling kinetics was systematically
studied via conventional gravimetry and corroborated further with
the corresponding Mueller matrix derived quantitative polarimetry
characteristics (δ, <i>d</i>, and Δ). The RAFT
gels exhibited higher swelling ratio and swelling-induced optical
anisotropy compared to FRP gels and also deswelled faster at 30 °C.
On the contrary, at 45 °C, deswelling was significantly retarded
for the RAFT gels due to formation of a skin layer, which was confirmed
and quantified via the enhanced diattenuation and depolarization parameters