Chiral sculptured thin films (STFs) produced by substrate rotation during physical vapor deposition exhibit the circular Bragg phenomenon, whereby normally incident left- and right-circularly polarized plane waves are discriminated in a spectral regime called the circular Bragg regime. Theory had predicted that substrate rocking, in synchrony with substrate rotation, during deposition could suppress the propensity to exhibit the circular Bragg phenomenon. Therefore chiral STFs of a dielectric material were fabricated with/without substrate rocking, and their transmittance spectrums for incident linearly and circularly polarized plane waves were measured. With sufficient rocking amplitude, the discrimination between incident left- and right-circularly polarized light nearly vanished, whereas a Bragg phenomenon for all normally incident plane waves was observed. Thus, chiral STF technology can be used to produce both ordinary and circular-polarization Bragg filters.
Chiral sculptured thin films (STFs) produced by substrate rotation during physical vapor deposition exhibit
the circular Bragg phenomenon, whereby normally incident left- and right-circularly polarized plane waves are
discriminated in a spectral regime called the circular Bragg regime. Theory had predicted that substrate rocking,
in synchrony with substrate rotation, during deposition, could suppress the propensity to exhibit the circular
Bragg phenomenon. Therefore, ZnSe chiral STFs were fabricated with/without substrate rocking, and their
transmittance spectrums for incident linearly and circularly polarized plane waves were measured. With sufficient
rocking amplitude, the discrimination between incident left- and right-circularly polarized light nearly vanished,
whereas a Bragg phenomenon for all normally incident plane waves was observed. Thus, chiral STF technology
can be used to produce both ordinary and circular-polarization Bragg filters.
We developed ratiometric optical oxygen sensors to probe the oxygen consumption during epileptic events
in rat brain slices. The oxygen sensors consist of the sensing part of phosphorescence dyes (Platinum (II)
octaethylporphine ketone) and reference part of nanocystal quantum dots (NQDs) embedded in polymer blends,
with pre-designed excitation through fluorescence resonance energy transfer (FRET) from NQDs to the oxygen
sensitive dyes (OSDs). The ratiometric FRET sensors with fast temporal response and excellent bio-compatibility
are suitable for real time quantitative dissolved oxygen (D.O.) probes in biological microenvironment. Coating the
sensors onto the micro-pipettes, we performed simultaneous oxygen probes at pyramidal and oriens layers in rat
hippocampal CA1. Different spatiotemporal patterns with maximum D.O. decreases of 9.9±1.1 mg/L and 4.9±0.7
mg/L during seizure events were observed in pyramidal and oriens layers, respectively.
We report direct measurement of spectrally selective absorption properties of PbSe and PbS colloidal quantum
dots (CQDs) in Si nanomembrane photonic crystal cavities on flexible polyethylene terephthalate (PET) substrates.
Enhanced optical absorption was obtained when CQD absorption overlaps with photonic crystal Fano resonances.
On the other hand, no absorption was observed when the Fano resonance has no spectral overlap with the CQD
absorption bands. The measurement results agree well with the simulation results obtained based on 3D FDTD and
RCWA simulation techniques. Measured angular and polarization properties also agree well with Fano resonance
transmission properties, which were obtained experimentally and, theoretically based on simulated dispersion
properties and transmission properties. Bending induced spectral shifts were characterized for potentially flexible
photonic device applications.
We report theoretical and experimental investigations of infrared absorption characteristics for PbSe colloidal
quantum dots in defect-free photonic crystal (PC) cavities, via Fano resonances. Angle and polarization independent
transmission and absorption are feasible for surface normal incident beams with dispersion engineered modal
design. Experimental demonstration was done on patterned single crystalline silicon nanomembranes (SiNMs)
transferred on glass and on flexible PET substrates, with PbSe QDs backfilled into the air holes of the patterned
SiNMs. These findings enable the design of spectrally selective photodetectors at near infrared regime with the
desired angle and polarization properties.
We construct an external cavity diode laser (ECDL) comprising structurally left-handed chiral sculptured-thin-film
(STF) mirrors for pure circular-polarized (CP) emission, and observed single mode, left-handed CP lasing performance.
The extinction ratio of CP output was found to increase rapidly near the threshold of the injection-current for the laser
diodes.
When a sculptured thin film (STF), made of a metal and ≤ 50 nm thick, is used in lieu of a dense layer
of metal in the Kretschmann configuration, experimental data for a STF comprising parallel tilted nanowires
shows that a surface plasmon resonance (SPR) can still be excited. As the porosity of the chosen STF increases,
experimental data and numerical simulations indicate the SPR dip with respect to the angle of incidence of the
exciting plane wave widens and eventually disappears, leaving behind a a vestigial peak near the onset to the
total-internal-reflection regime.
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