A growing number of commercial products such as displays, solar panels, light emitting diodes (LEDs and OLEDs),
automotive and architectural glass are driving demand for glass with high performance surfaces that offer anti-reflective,
self-cleaning, and other advanced functions. State-of-the-art coatings do not meet the desired performance characteristics
or cannot be applied over large areas in a cost-effective manner. “Rolling Mask Lithography” (RML™) enables highresolution
lithographic nano-patterning over large-areas at low-cost and high-throughput. RML is a photolithographic
process performed using ultraviolet (UV) illumination transmitted through a soft cylindrical mask as it rolls across a
substrate. Subsequent transfer of photoresist patterns into the substrate is achieved using an etching process, which
creates a nanostructured surface. The current generation exposure tool is capable of patterning one-meter long substrates
with a width of 300 mm. High-throughput and low-cost are achieved using continuous exposure of the resist by the
cylindrical photomask.
Here, we report on significant improvements in the application of RML™ to fabricate anti-reflective surfaces. Briefly,
an optical surface can be made antireflective by “texturing” it with a nano-scale pattern to reduce the discontinuity in the
index of refraction between the air and the bulk optical material. An array of cones, similar to the structure of a moth’s
eye, performs this way. Substrates are patterned using RML™ and etched to produce an array of cones with an aspect
ratio of 3:1, which decreases the reflectivity below 0.1%.
We validate a molecular imaging technique called Nonlinear Interferometric Vibrational Imaging (NIVI)
by comparing vibrational spectra with those acquired from Raman microscopy. This broadband coherent
anti-Stokes Raman scattering (CARS) technique uses heterodyne detection and OCT acquisition and design
principles to interfere a CARS signal generated by a sample with a local oscillator signal generated
separately by a four-wave mixing process. These are mixed and demodulated by spectral interferometry. Its
confocal configuration allows the acquisition of 3D images based on endogenous molecular signatures.
Images from both phantom and mammary tissues have been acquired by this instrument and its spectrum is
compared with its spontaneous Raman signatures.
Coherent anti-Stokes Raman scattering (CARS) can be used to identify biological molecules from their vibrational
spectra in tissue. A single double-chirped broadband optical pulse can excite a broad spectrum of resonant
molecular vibrations in the fingerprint spectral region. Such a pulse also excites nonresonant CARS, particularly
from water. We describe a theoretical technique to design an optical pulse to selectively excite coherent vibrations
in a target molecular species so that the CARS signal generated is increased. The signal from other molecules
is reduced, since the incident pulse does not excite them to have coherent vibrations. As an example, we apply
the technique to design pulses to elicit increased CARS signal from a mixture of one or more of the alcohols
methanol, ethanol, and isopropanol. We also show how such pulse designs can be used to selectively excite one
member of closely related complex biological species. As measured interferometrically, the CARS signal from
three phosphodiester stretch modes of DNA can be increased to more than ten times that of the analogous signal
from RNA when the pulse design technique is used.
We demonstrate imaging with the technique of nonlinear interferometric vibrational imaging (NIVI). Experimental
images using this instrumentation and method have been acquired from both phantom and biological tissues. In our
system, coherent anti-Stokes Raman scattering (CARS) signals are detected by spectral interferometry, which is able to
fully restore high resolution Raman spectrum on each focal spot of a sample covering multiple Raman bands using
broadband pump and Stokes laser beams. Spectral-domain detection has been demonstrated and allows for a significant
increase in image acquiring speed, in signal-to-noise, and in interferometric signal stability.
We studied trends in three measures of both duration and average speed of optical videopulses transmitted
through chiral sculptured thin films (STFs). The films, a class of nanoengineered materials which consist of
parallel helical nanowires grown on a substrate, were taken to be linear or nonlinear with an intensity-dependent
refractive index. We used a finite-difference algorithm to compute the evolution of the pulse shapes in the
time domain. The durations of videopulses transmitted through chiral STFs tended to decrease with increasing
carrier wavelength, while the average speeds tended to increase or remain roughly constant with increasing
carrier wavelength. The durations and average speeds were similar irrespective of whether the incident pulse
possessed a left or right circularly polarized carrier plane wave. That is, the circular Bragg phenomenon−due
to a circular polarization dependent photonic bandgap exhibited by chiral STFs over a bandwidth called the
Bragg regime−did not affect the results to any meaningful extent, in contrast to previous work. We attribute
this finding to the wide bandwidth of the incident pulses swamping the Bragg regime.
We computed three measures each of the durations and average speeds of ultrashort optical pulsed plane waves transmitted through linear and nonlinear chiral sculptured thin films (STFs). The durations tended in general to decrease with increasing carrier wavelength (save for an exception involving the circular Bragg phenomenon), while average speeds tended to increase under the same conditions. Durations tended to increase with increasing nonlinearity displayed by the chiral STF, while average speeds tended to decrease. The results quantify some aspects of ultrashort optical pulse shaping by chiral STFs, which heretofore had only been studied qualitatively.
Decreasing feature sizes due to advances in nanotechnology place a premium on careful treatment of phase, length, and time in optics. All three quantities are intermeshed due to morphology at the nanometer length scale. After examining the characteristics of the responses of columnar thin films and chiral sculptured thin films to optical pulses and beams, we put forward the thesis that nanotechnology for optics is a phase-length-time sandwich.
We study the shaping of pulsed two-dimensional optical beams by chiral sculptured thin films (STFs) in the time domain, so that the spatiotemporal evolution of the light is elucidated as it propagates through the film. The time-domain manifestation of the circular Bragg phenomenon is examined in two dimensions, and we comment on its implications for pulsed beam shaping by STF devices. Several crucial differences separate the time-domain manifestation of the circular Bragg phenomenon for pulsed plane waves and pulsed beams. Specifically, the beam waist is an important parameter for prediction of how reflection from or transmission through a chiral STF will shape the edges of a pulsed beam with respect to its central portion. In addition, control of the position of chiral STFs with respect to pulsed beam sources is important for proper pulse shaping. We expect that further advances in STF fabrication will allow for the development of STF-based pulsed beam shaping devices.
Sculptured thin films (STFs) comprise parallel bent nanowires that are 30-100 nm in diameter. Using a finite-difference algorithm, we solved the time-domain Maxwell equations to investigate the reflection of optical narrow-extent pulses from both linear and nonlinear chiral STFs. Although he axial component of the Poynting vector -- the pulse shape -- is invariant to changes of carrier wave phase in the incident pulse, we determined that the reflected pulse shape is affected by those changes.
We report numerical time-domain simulations that reveal the continued reflection of an axially propagating optical pulse as it travels through a dielectric thin-film helicoidal bianisotropic medium (TFHBM) half- space, when the handedness of the pulse is the same as that of the medium. This phenomenon is dubbed pulse bleeding, and is a central feature of the spatio-temporal anatomy of the circular Bragg phenomenon.
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