We developed a two-dimensional multispectral imager that exploits the extraordinary optical transmission of nanohole arrays (NHAs) in a metal film for color separation. The NHA device consisted of blocks in a tiled arrangement, where each block contained multiple metallic NHAs, each with unique feature geometry to enable separation of a mixture of colors into distinct spectral bands. The NHA device was integrated into an optical imaging system. The system was used to capture near video-rate images of a scene and then unmix the colors within the scene into 4 spectral bands in the nearinfrared regime.
We present a three dimensional (3D) metallic nanostructure, which has transmission resonance properties related to both localized surface plasmons and propagating surface plasmon polaritons. Various geometrical dimensions of the 3D metallic nanostructures were studied by means of simulation and experiment with respect to resonance position, resonance line width and bulk sensitivity. Narrower resonance line width and higher bulk sensitivity were achieved for the 3D nanostructure compared to conventional nanohole arrays. Finally, a 3D metallic nanostructure functionalized with a biotinylated thiol could detect streptavidin, suggesting the device may have potential as a bio-sensor.
The long anticipated deployment of nano-optics that can enable next generation computing has encountered several practical impediments that have delayed widespread adoption in commercial processes. However, the global market in nano-enabled products is expected to grow to over $80B USD within the next 3 years. In response, the research community is creating solutions to overcome challenging issues such as reliability and cost-effective fabrication. New approaches in sensing, continuous uptime powering, and post silicon manufacturing will maximize overall performance and allow unprecedented commercial applications. This paper reviews present limitations of nano-optics and then considers the new generation of devices and their manufacturing that may turn promises into reality. We highlight several recent innovations: high sensitivity/selectivity nano-optical sensing devices; sustainable power from polymer energy harvesting and storage; optical variable devices for visual authentication of secure documents; and nano-template masters for high-volume manufacturing.
The fabrication details to form large area systematically changing multishape nanoscale structures on a chip by laser interference lithography (LIL) are described. The feasibility of fabricating different geometries including dots, ellipses, holes, and elliptical holes in both x - and y - directions on a single substrate is shown by implementing a Lloyd’s interferometer. The fabricated structures at different substrate positions with respect to exposure time, exposure angle and associated light intensity profile are analyzed. Experimental details related to the fabrication of symmetric and biaxial periodic nanostructures on photoresist, silicon surfaces, and ion milled glass substrates are presented. Primary rat calvarial osteoblasts were grown on ion-milled glass substrates with nanotopography with a periodicity of 1200 nm. Fluorescent microscopy revealed that cells formed adhesions sites coincident with the nanotopography after 24 h of growth on the substrates. The results suggest that laser LIL is an easy and inexpensive method to fabricate systematically changing nanostructures for cell adhesion studies. The effect of the different periodicities and transition structures can be studied on a single substrate to reduce the number of samples significantly.
A metallic nano-hole array (NHA) structure with dynamic SP energy matching has been recently introduced, which benefits from a smaller resonance bandwidth, higher resonance transmission efficiency, and higher surface plasmon resonance (SPR) sensitivity compared to a structure without dynamic SP energy matching. Here, we present a more
comprehensive study on the effects of SP energy matching on SPR sensitivity of a NHA structure by numerical and
experimental means. Both experimental and numerical results were analyzed and compared and demonstrated that structures with dynamic SP energy matching had improved sensitivity over structures without the dynamic SP energy matching property.
We present a three-dimensional metallic nano-structure, which consists of a nano-hole array in a gold membrane and
a co-registered array of gold nano-disks situated on a substrate below the membrane. This structure provided a
transmission resonance due to a localized surface plasmon (LSP) interaction between each hole and co-registered
disk. Both numerical and experimental results demonstrated that the position of the LSP resonance transmission
depended greatly on hole and disk diameter. Enhanced electric field intensity between each hole and disk was
observed in the simulations. The device is expected to be well-suited for optical trapping applications.
The Radial Angular Filter Array (RAFA) is a novel optical filter consisting of a radially-distributed series of micromachined
channels with a focal length of a few millimeters. The RAFA filters photons passing through the focal point
according to the propagation direction and has proven to be capable of collecting the angular distribution and the spectral
information of photons simultaneously and non-invasively, which allows angle-resolved spectroscopic measurement of a
turbid medium. To explore the feasibility of using this device to characterize the optical abnormalities in human tissues,
we tested the performance of an angle-resolved RAFA-based spectroscopy system to detect absorption targets embedded
within a tissue-mimicking phantom. The body of the phantom was made of 0.1% IntralipidTM/agarose gel (7 mm in
thickness) and the targets were spherical (1.5 mm in radius) and contained 10 μM Indocyanine Green (ICG). The
illumination source was a broadband near infrared (NIR) collimated beam. Photons were angularly filtered by the RAFA
and spectrally resolved by a pushbroom spectrometer. The experimental results confirmed that the RAFA preferentially
filtered photons that carried absorption and scattering information of the embedded targets.
Angular Domain Spectroscopic Imaging (ADSI) is a novel technique for the detection and characterization of optical
contrast abnormalities in ex-vivo breast tissue samples based on spectral characteristics. The imaging system employs a
spatial filter called an angular filter array to reject scattered photons traversing a sample. The system employs an
imaging spectrometer to capture and discriminate the largely remaining quasi-ballistic photons based on spatial position
and wavelength. Spectral data were obtained from samples obtained from two patients, one sample contained invasive
mammary carcinoma, and the other one contained normal fat and fibrous tissue. Principal component analysis using
transmission absorption spectra obtained with ADSI was able to differentiate tumor versus normal tissue regions.
The Radial Angular Filter Array (RAFA) is a novel optical filter consisting of a radially-distributed series of micromachined
channels, which converge upon a focal point several millimeters away from the edge of the device. It is
designed to measure the angular distribution of light emitted from an object located at the focal point and is capable of
selecting ballistic and quasi-ballistic photons at specific angles out of strong background noise due to scattering. We
hypothesized that the device might be useful for examining optically absorbing features below the surface of a turbid
medium via a depth mapping approach. In order to validate this concept, experiments were performed with a focused
laser beam, a series of IntralipidTM solutions (0.1 wt% to 1.0 wt%), a 0.5 mm diameter graphite rod (absorber), and a
RAFA optically coupled to a line camera. By scanning the position of the rod and comparing the light scattering profiles
obtained by the RAFA at each scanning step, the location and the depth of the rod were successfully identified. Future
work will be directed toward studying the performance of the technique with a collimated broadband illumination beam
for spectroscopic applications.
We present a novel three-dimensional nano-hole array structure in an optically thick gold film, which benefits from
Surface Plasmon (SP) energy matching between the top and bottom of the gold film. We have experimentally
evaluated both a conventional and an SP energy-matched nano-hole array structure for Surface Plasmon Resonance
(SPR) sensing. Also, detection of various bulk refractive index liquids has been tested for both structures based on
the transmission intensity differences in a narrow detection band. We observed a 2-fold higher sensitivity during
SPR sensing with the new structure compared to a conventional nano-hole array.
Angular domain spectroscopic imaging (ADSI) is a novel technique for the detection and characterization of optical contrast in turbid media based on spectral characteristics. The imaging system employs a silicon micromachined angular filter array to reject scattered light traversing a specimen and an imaging spectrometer to capture and discriminate the largely remaining quasiballistic light based on spatial position and wavelength. The imaging modality results in hyperspectral shadowgrams containing two-dimensional (2D) spatial maps of spectral information. An ADSI system was constructed and its performance was evaluated in the near-infrared region on tissue-mimicking phantoms. Image-based spectral correlation analysis using transmission spectra and first order derivatives revealed that embedded optical targets could be resolved. The hyperspectral images obtained with ADSI were observed to depend on target concentration, target depth, and scattering level of the background medium. A similar analysis on a muscle and tumor sample dissected from a mouse resulted in spatially dependent optical transmission spectra that were distinct, which suggested that ADSI may find utility in classifying tissues in biomedical applications.
Angular Domain Spectroscopic Imaging employs an array of micro-channels to perform angular filtering of light that
traverses a turbid sample to reject moderately to highly scattered light. In this work, we experimentally characterized an
ADSI system by measuring transmission spectra and the first and second derivatives obtained from absorbing and
scattering targets. The derivative analysis was used to estimate the concentration of indocyanine green mixed in a
scattering liquid. The experimental results provided support for ADSI as a potential method for quantitative
spectroscopic imaging of ex vivo tissue samples.
In this paper, we present experimental analysis on the effect of composition of the adhesion layer (chromium or
titanium) between gold and a Pyrex substrate on the optical resonance transmission properties of nano-hole arrays in an
optically thick gold film. Nano-hole arrays of different hole periodicities in a square lattice arrangement were fabricated
with three types of adhesion layer (5 nm Cr, 5 nm Ti or 10 nm Ti). The optical transmission of each nano-hole array was
measured and the optical resonance transmission properties were analyzed and compared as a function of hole
periodicity and type of adhesion layer.
The Radial Angular Filter Array (RAFA) is a novel silicon micro-machined optical filter for real-time high resolution
measurement of the angular distribution of scattered photons. It includes a radially-distributed series of micro-channels
facing a focal point that is several millimeters away from the edge of the device. In this work, three RAFA designs were
devised to enhance the angular resolution, while lessening the complexity of the output coupling. These new RAFA
designs solved issues associated with a previous prototype device, including the signal loss in high angle channels and
light leakage beyond the acceptance angle. Typically, channels in the RAFA are 60 μm deep with a minimum length of
10 mm. To characterize the RAFA designs, we used an incoherent broadband source, collimation optics, turbid samples,
and a spectrometer. The tests identified which design features resulted in improved performance, including the preferred
output coupling structure, the recommended near specular direction blocking range, the choice of constant aspect ratio or
solid angle, and other geometrical parameters.
The miniaturization of nanostructure-based optical sensing devices requires integration of multiple nanostructure
patterns with smaller spacing. However, the effect of plasmonic cross-talk and its effect on spectral transmission are not
fully understood. In this paper, we experimentally fabricated different sets of nano-hole arrays (each with an area of 30
μm x 30 μm) of various hole diameter, hole spacing, and inter-array spacing. The spectral transmission of each nano-hole
array was measured and the effect of inter-array spacing on peak transmission and resonance wavelength was
determined.
In this paper, we present detailed experimental analysis on the optical resonance transmission properties of nano-hole
arrays in metallic films. Arrays of sub-wavelength holes with different periodicity (spacing between adjacent holes) in a
square lattice arrangement were fabricated in optically thick metal films (Au, Ag, and Al) on a Pyrex substrate using
Electron Beam Lithography. The optical transmission spectra of the nano-hole arrays were characterized in the visible
and near infrared regime. The optical resonance transmission properties were observed to depend on the type of metal
film and the periodicity in the lattice arrangement.
By employing high-aspect-ratio parallel microchannels as an angular filter, quasiballistic photons sensitive to internal structures in a turbid medium can be captured. Scattered photons exiting the turbid medium typically exhibit trajectories with random angles compared to the initial trajectory and are mostly rejected by the filter. However, angular filter arrays cannot differentiate between quasiballistic photons (early arriving) and photons that happen to attain a scattered trajectory that is within the acceptance angle (late arriving). Therefore, we have two objectives: (1) to experimentally characterize the angular distribution and proportion of minimally deviated quasiballistic photons and multiply scattered photons in a turbid medium and (2) to combine time and angular gating principles so that early and late arriving photons can be distinguished. From the angular distribution data, the angular filter with angular acceptance about 0.4 deg yields the highest image contrast for transillumination images. The use of angular domain imaging(ADI) with time-gating enables visualization of submillimeter absorbing objects with approximately seven times higher image contrast compared to ADI in a turbid medium with a scattering level of six times the reduced mean free path.
This paper presents a novel optical filter called the Radial Angular Filter Array (RAFA) for real-time measurement of
the angular and spectral distribution of diffuse light exiting a turbid medium. The RAFA consists of a radiallydistributed
series of 48 micro-channels micro-machined into a silicon substrate. To test the device, we constructed an
angle-resolved spectroscopy system by integrating a wideband light source, the RAFA, and an imaging spectrometer.
The collimated broadband light source was configured to trans-illuminate a turbid sample over a wide range of
wavelengths in the near infrared spectral region. The RAFA was used to collect the angular distribution of light exiting
the turbid sample. The imaging spectrometer decomposed the output of the RAFA into hyperspectral images
representative of scatter angle and wavelength. By scanning the RAFA and imaging spectrometer over the sample, the
intensity of the scattered light was acquired as a function of location on the sample surface, wavelength, and angle
relative to the surface normal. With angle resolved spectroscopy it will be possible to characterize the optical properties
of turbid samples in great detail.
We experimentally characterized a novel Angular Domain Spectroscopic Imaging (ADSI) technique for the detection
and characterization of optical contrast abnormalities in turbid media. The new imaging system employs silicon micromachined
angular filtering methodology, which has high angular selectivity for photons exiting the turbid medium. The
angular filter method offers efficient scattered light suppression at moderate levels of scattering (i.e. up to 6 reduced
mean free paths). An ADSI system was constructed from a broadband light source, an Angular Filter Array (AFA), and
an imaging spectrometer. The free-space collimated broadband light source was used to trans-illuminate a turbid sample
over a wide range of wavelengths in the near infrared region of the spectrum. The imaging spectrometer decomposed the
output of the AFA into hyperspectral images representative of spatial location and wavelength. It collected and angularly
filtered a line image from the object onto the CCD camera with the spatial information displayed along one axis and
wavelength information along the other. The ADSI system performance was evaluated on tissue-mimicking phantoms as
well as fresh chicken breast tissue. Collected images with the ADSI displayed differences in image contrast between
different tissue types.
In this paper, we present experimental and numerical analysis on Extraordinary Optical Transmission (EOT) through
various nano-hole arrays in a thick metal film within the visible and near infra-red spectrum of light. Large nano-hole
arrays with different spacing between adjacent holes in the square lattice arrangement were fabricated using Electron
Beam Lithography (EBL). Optical transmission properties (wavelength, peak, and spectral bandwidth of transmission
resonances) of the fabricated nano-hole arrays were characterized and validated by numerical analysis based on Finite
Difference Time Domain (FDTD). Finally, the dependencies and discrepancies between EOT properties of various nanohole
arrays were analyzed.
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