A coded aperture microscope for X-ray fluorescence full-field imaging.

The design and construction of an instrument for full-field imaging of the X-ray fluorescence emitted by a fully illuminated sample are presented. The aim is to produce an X-ray microscope with a few micrometers spatial resolution, which does not need to scan the sample. Since the fluorescence from a spatially inhomogeneous sample may contain many fluorescence lines, the optic which will provide the magnification of the emissions must be achromatic, i.e. its optical properties must be energy-independent. The only optics which fulfill this requirement in the X-ray regime are mirrors and pinholes. The throughput of a simple pinhole is very low, so the concept of coded apertures is an attractive extension which improves the throughput by having many pinholes, and retains the achromatic property. Modified uniformly redundant arrays (MURAs) with 10 µm openings and 50% open area have been fabricated using gold in a lithographic technique, fabricated on a 1 µm-thick silicon nitride membrane. The gold is 25 µm thick, offering good contrast up to 20 keV. The silicon nitride is transparent down into the soft X-ray region. MURAs with various orders, from 19 up to 73, as well as their respective negative (a mask where open and closed positions are inversed compared with the original mask), have been made. Having both signs of mask will reduce near-field artifacts and make it possible to correct for any lack of contrast.

Multiscale gigapixel photography.

Pixel count is the ratio of the solid angle within a camera's field of view to the solid angle covered by a single detector element. Because the size of the smallest resolvable pixel is proportional to aperture diameter and the maximum field of view is scale independent, the diffraction-limited pixel count is proportional to aperture area. At present, digital cameras operate near the fundamental limit of 1-10 megapixels for millimetre-scale apertures, but few approach the corresponding limits of 1-100 gigapixels for centimetre-scale apertures. Barriers to high-pixel-count imaging include scale-dependent geometric aberrations, the cost and complexity of gigapixel sensor arrays, and the computational and communications challenge of gigapixel image management. Here we describe the AWARE-2 camera, which uses a 16-mm entrance aperture to capture snapshot, one-gigapixel images at three frames per minute. AWARE-2 uses a parallel array of microcameras to reduce the problems of gigapixel imaging to those of megapixel imaging, which are more tractable. In cameras of conventional design, lens speed and field of view decrease as lens scale increases, but with the experimental system described here we confirm previous theoretical results suggesting that lens speed and field of view can be scale independent in microcamera-based imagers resolving up to 50 gigapixels. Ubiquitous gigapixel cameras may transform the central challenge of photography from the question of where to point the camera to that of how to mine the data.

Compressive sensing in the EO/IR.

We investigate the utility of compressive sensing (CS) to electro-optic and infrared (EO/IR) applications. We introduce the field through a discussion of historical antecedents and the development of the modern CS framework. Basic economic arguments (in the broadest sense) are presented regarding the applicability of CS to the EO/IR and used to draw conclusions regarding application areas where CS would be most viable. A number of experimental success stories are presented to demonstrate the overall feasibility of the approaches, and we conclude with a discussion of open challenges to practical adoption of CS methods.

Characterization of the AWARE 10 two-gigapixel wide-field-of-view visible imager.

System requirements for many military electro-optic and IR camera systems reflect the need for both wide-field-of-view situational awareness as well as high-resolution imaging for target identification. In this work we present a new imaging system architecture designed to perform both functions simultaneously and the AWARE 10 camera as an example at visible wavelengths. We first describe the basic system architecture and user interface followed by a laboratory characterization of the system optical performance. We then describe a field experiment in which the camera was used to identify several maritime targets at varying range. The experimental results indicate that users of the system are able to correctly identify ~10 m targets at between 4 and 6 km with 70% accuracy.

Development of a scalable image formation pipeline for multiscale gigapixel photography.

We report on the image formation pipeline developed to efficiently form gigapixel-scale imagery generated by the AWARE-2 multiscale camera. The AWARE-2 camera consists of 98 "microcameras" imaging through a shared spherical objective, covering a 120° x 50° field of view with approximately 40 microradian instantaneous field of view (the angular extent of a pixel). The pipeline is scalable, capable of producing imagery ranging in scope from "live" one megapixel views to full resolution gigapixel images. Architectural choices that enable trivially parallelizable algorithms for rapid image formation and on-the-fly microcamera alignment compensation are discussed.

High-throughput, multiplexed pushbroom hyperspectral microscopy.

We describe a high-throughput hyperspectral microscope. The system replaces the slit of conventional pushbroom spectral imagers with a static coded aperture mask. We present the theoretical underpinnings of the aperture coded spectral engine and describe two proof-of-concept experimental implementations. Compared to a conventional pushbroom system, the aperture coded systems have 32 times greater throughput. Both systems have about a 1 nm spectral resolution over the spectral range of 550-665 nm. For the first design, the spatial resolution for the system is 5.4 microm while the spatial resolution for the second system ranges from 7.7 microm to 1.54 microm. We describe experimental results from proof-of-concept applications of the imager to hyperspectral microscopy.

Multiple order coded aperture spectrometer.

We introduce a multiple order coded aperture (MOCA) spectrometer. The MOCA is a system that uses a multiplex hologram and a coded aperture to increase the spectral range and throughput of the system over conventional spectrometers while maintaining spectral resolution. This results in an order of magnitude reduction in system volume with no loss in resolution.

Longwave infrared (LWIR) coded aperture dispersive spectrometer.

We describe a static aperture-coded, dispersive longwave infrared (LWIR) spectrometer that uses a microbolometer array at the detector plane. The two-dimensional aperture code is based on a row-doubled Hadamard mask with transmissive and opaque openings. The independent column code nature of the matrix makes for a mathematically well-defined pattern that spatially and spectrally maps the source information to the detector plane. Post-processing techniques on the data provide spectral estimates of the source. Comparative experimental results between a slit and coded aperture for emission spectroscopy from a CO(2) laser are demonstrated.

Single-shot compressive spectral imaging with a dual-disperser architecture.

This paper describes a single-shot spectral imaging approach based on the concept of compressive sensing. The primary features of the system design are two dispersive elements, arranged in opposition and surrounding a binary-valued aperture code. In contrast to thin-film approaches to spectral filtering, this structure results in easily-controllable, spatially-varying, spectral filter functions with narrow features. Measurement of the input scene through these filters is equivalent to projective measurement in the spectral domain, and hence can be treated with the compressive sensing frameworks recently developed by a number of groups. We present a reconstruction framework and demonstrate its application to experimental data.

Coded aperture Raman spectroscopy for quantitative measurements of ethanol in a tissue phantom.

Coded aperture spectroscopy allows for sources of large étendue to be efficiently coupled into dispersive spectrometers by replacing the traditional input slit with a patterned mask. We describe a coded aperture spectrometer optimized for Raman spectroscopy of diffuse sources, (e.g., tissue). We provide design details of the Raman system, along with quantitative estimation results for ethanol at non-toxic levels in a lipid tissue phantom. With 60 mW of excitation power at 808 nm, leave-one-out and blind cross-validation of partial least squares (PLS) regression models achieve r(2) > 0.98. Leave-one-out cross-validation demonstrates prediction errors of <15% at the common legal limit for intoxication (17.4 mmol/L = 0.08% by vol) and the best blind cross-validation achieves <12% error at this concentration.

Calcium amelioration of aluminium toxicity effects on root hair development in soybean [Glycine max (L.) Merr.].

Low activities of the monomeric aluminium (Al) species, Al3+ , Al(OH)2 + and Al(OH)2+ in solution reduce root growth and root hair development in soybean [Glycine max (L.) Merr.]. Calcium (Ca) ameliorates to a certain extent the toxic effects of Al on root growth, but the interactive effects of Ca and Al on root hair development are not known. In the absence of added Al in solution culture, Ca concentration over the range 500-2000 µM had little effect on root growth or root hair development of soybean cv. Fitzroy. Where the sum of the activities of the monomeric Al species was 2 µM, taproot elongation and lateral root development of soybean was suppressed in solution with 500 µM Ca. The length of the root hair zone was only 10% of that in plants not exposed to Al, and scanning electron microscopy revealed a low density of root hairs. Increasing the Ca concentration to 2000 µM largely overcame these deleterious effects. The results are discussed in relation to the role of root hairs as infection sites for Bradyrhizobium, and the known effects of Al in suppressing nodulation in soybean.

Dispersion multiplexing with broadband filtering for miniature spectrometers.

We replace the traditional grating used in a dispersive spectrometer with a multiplex holographic grating to increase the spectral range sensed by the instrument. The multiplexed grating allows us to measure three different, overlapping spectral bands on a color digital focal plane. The detector's broadband color filters, along with a computational inversion algorithm, let us disambiguate measurements made from the three bands. The overlapping spectral bands allow us to measure a greater spectral bandwidth than a traditional spectrometer with the same sized detector. Additionally, our spectrometer uses a static coded aperture mask in the place of a slit. The aperture mask allows increased light throughput, offsetting the photon loss at the broadband filters. We present our proof-of-concept dispersion multiplexing spectrometer design with experimental measurements to verify its operation.

Control of spatial excitation patterns in two-level systems by use of time-domain fields.

Spatial structures created by pulsed field interactions with surface-bound two-level systems are considered. Superresolved pattern formation is possible by the use of extra degrees of freedom programmed in the time-domain field.

Real-time holography in azo-dye-doped liquid crystals.

When exposed to an Ar laser at 514 nm, azo-dye molecules in a nematic liquid-crystal host undergo photo-isomerization from trans-isomers to cis-isomers. The conformation change of the azo-dye molecules reorients liquid-crystal molecules. Reversible polarization holograms can be recorded dynamically by this effect, with a threshold intensity as low as 3.0 mW/cm(2) and a response time from a few hundred microseconds to 100 ms, depending on the spatial frequency of the recorded grating.

Surface-stabilized holography in an azo-dye-doped liquid crystal.

Holograms are recorded by a 514-nm laser polarized parallel to the molecular director in an azo-dye-doped nematic liquid crystal. For some surface treatments, the recorded holograms persist in the dark. For glass surfaces, exposure to light polarized normal to the molecular director erases the hologram. The hologram also vanishes when the sample is heated across the nematic to isotropic phase transition but reappears when the sample is cooled back to the nematic phase. The dynamics and strength of this effect depend strongly on the surface treatment of the sample cell.

Holographic interconnections in photorefractive waveguides.

An architecture for implementing large scale holographic interconnections in photorefractive waveguides is described. Methods for controlling the hologram using unguided light are considered and experimentally demonstrated.

Three-dimensional source reconstruction with a scanned pinhole camera.

We present a simple reconstruction algorithm for three-dimensional (3D) incoherent source distributions imaged by a laterally scanned pinhole camera. We consider digital sampling of multiple pinhole images for 3D reconstruction and implement an experimental demonstration with lateral resolution of 2x10(-3) rad and longitudinal resolution of approximately 0.14z(2) m , where z is the object-to-pinhole distance in meters.

Impulse responses of strong reflection holograms.

Strong scattering in broad spatial bandwidth reflection holograms is analyzed by using numerical techniques. Transfer functions and impulse responses for various index modulations are found, and techniques for constructing holograms for optical pulse shaping, coding, and dispersion compensation are discussed.

Pulse shaping in volume reflection holograms.

Ultrashort pulses are shaped by reflection from dynamic volume holograms recorded in azo-dye-doped epoxies. The spectral resolution and controllability of the reflection geometry are optimal for this application.