An imager based upon an etched liquid-crystal Fabry-Perot (LCFP) dispersive element is able to simultaneously sample
four distinct resolution elements in the region 800 nm - 1100 nm, and tune in milliseconds to any one of 30,661 possible
four-color scene images with a spectral resolution of 0.67 nm. Independently tunable quadrants of a single LCFP etalon
are created by etching a transparent conducting layer on the etalon substrate, and one image from each quadrant is
formed on a focal-plane array detector. Designed to weigh less than 20 lbs. in production, the portable, solid-state
camera system is designed to provide fast RGB images of transient spectral phenomena, but many applications are
possible. The fourth image in each four-element image is intended to be a background channel for contrast
enhancement in bright background environments.
The LCFP hyperspectral imager provides high-spectral resolution, allowing detection of short-lifetime atomic spectral
line emissions characteristic of excited or ablating constituents against a bright, broadband, greybody background. High
luminosity via the characteristic Fabry-Perot étendue advantage and an f/0.9 optical system accommodate the tactical
need for a lightweight device with a small footprint. The LCFP dispersive element is tuned with battery-pack power, 0-
10V DC and mA current.
The LCFP hyperspectral technology is easily adapted to Doppler imaging by enhancing the etalon gap and sampling
over a narrower instrument passband. Operation in the MWIR and LWIR is also possible. The camera design creates
multi-spectral images with a small but simultaneously sampled data-cube of narrow bandwidth.
Microstructures built into the surfaces of an optic or window, have been shown to suppress the reflection of broad-band
light to unprecedented levels. These antireflective (AR) microstructures form an integral part of an optic component,
yielding an AR property that is as environmentally robust, mechanically durable, and as radiation-hardened as the bulk
material. In addition, AR microstructures built into inexpensive glass windows, are shown below to exhibit a threshold
for damage from high energy lasers of nearly 60 J/cm<sup>2</sup>, a factor of 2 to 4 increase over published data for conventional
thin-film dielectric material AR coatings.
Three types of AR surface relief microstructures are being developed for a wide variety of applications utilizing light
within the visible to very long wave infrared spectrum. For applications requiring broad-band operation, Motheye AR
textures consisting of a regular periodic array of cone or hole like structures, are preferred. Narrow-band applications
such as laser communications, can utilize the very high performance afforded by sub-wavelength structure, or SWS AR
textures that consist of a periodic array of simple binary, or step profile structures. Lastly, Random AR textures offer
very broad-band performance with a simple manufacturing process, a combination that proves useful for cost sensitive
applications such as solar cells, and for complex devices such as silicon and HgCdTe sensor arrays.
An update on the development of AR microstructures is discussed for many specific applications. Data from SEM
analysis, reflection and transmission measurements, environmental durability testing, and laser damage testing, is shown
for AR microstructures fabricated in silicon, fused silica, borofloat glass, ZnGeP, AMTIR, As<sub>2</sub>Se<sub>3</sub>, As<sub>2</sub>S<sub>3</sub>, and GaAs.
A solar photovoltaic energy collection system using a reflection hologram is described herein. The system uses a single-axis tracking system in conjunction with a spectral- splitting holographic element. The hologram accurately focuses the desired regions of the solar spectrum to match the bandgaps of two ro more different solar cells, while diverting unused IR wavelengths away. Other applications for solar holography include daylighting and greenhouses.
Holographic nonspatial filters designed to clean up the output of a laser have been shown to be a great improvement over conventional spatial filters. This paper successfully addresses several major problems or shortcomings of the nonspatial filter. The problems were in the use of two filters together for cleaning up a laser beam in both dimensions. Polarization and orientation effects made the system complicated an inconvenient. A simple compound element consisting of a sandwich of two identical holograms is shown to solve these problems.
The present paper deals with new results ont he development of a holographic nonspatial filter to be used for laser beam clean up. An analysis of thick holographic materials suitable for recording of such elements is carried out. The experimental setups for hologram recording and evaluation are described. The results on measurements of angular selectivity contour of such holographic filters are presented.
Daylighting techniques are an effective means of reducing both lighting and cooling costs; however, many of the standard techniques have flaws which reduce their effectiveness. Daylighting holograms are an efficient and effective method for diffracting sunlight up onto the ceiling, deep in a room, without diffracting the light at eye-level. They need only cover the top half of a window to produce significant energy savings. They may be used as part of a new glazing system or as a retrofit to existing windows. These holograms are broadband and are able to passively track the movement of the sun across the sky, throughout the day and year.
Recently, at the University of Massachusetts Lowell, promising Thermophotovoltaic (TPV) experimental results have been produced utilizing an experimental system that incorporates holographic optical elements and tubular geometry thermal sources. The results and concepts presented in this paper bring to light a unique merging of combustion and solar energy sources. The holographic elements provide a mechanism for spectral splitting, as well as concentration, while the tubular thermal source provides a flexible TPV photon emitter geometry that is capable of utilizing various thermal sources. The work reported here details the experiments as well as the concepts that indicate that such a TPV system could readily produce electricity utilizing 'dual' thermal sources. A tubular photon source was located in the focus of parabolic assembly to 'collimate' the photons emitted by a lamp simulating a TPV photon emitter. The collimated photons were directed onto the holographic element and spectrally redirected as a function of the photon energy. Components of a system constructed in this geometry can be readily converted to produce a highly concentrating solar photovoltaic electrical power source.
A novel technique is described for laser beam cleanup, the nonspatial filter, which is based on the Bragg selectivity of thick holograms. Unlike pinhole and fiber spatial filters, which employ lenses and apertures in the transform plane, nonspatial filters operate directly on the laser beam. This eliminates the need for laser beam focusing, which is the source of many of the alignment instabilities and laser power limitations of spatial filters. Standard holographic materials are not suitable for this application because differential shrinkage during processing limits the maximum Bragg angle selectivity attainable. This paper describes a new technology which eliminates the problem of differential shrinkage. This technology is based on the use of a rigid porous substrate material, such as porous gas, filled with a light sensitive material, such as holographic photopolymers or dichromated gelatin. We report preliminary results of holographic nonspatial filtering of a laser beam in one dimension, with an angular selectivity of less than 1 milliradian.
The main goal of the present paper is the study of opportunities of solar energy conversion into electricity in space by the systems including holographic concentrators. A maximal efficiency of such systems was analyzed. The emphasis is made on the analysis of dichromated gelatin emulsion layers to be used for hologram recording.
The Index Interferometer is a novel instrument being developed by Northeast Photosciences. The instrument is a breakthrough in the high-accuracy measurement of the index of refraction, the dispersion, and the index profile of materials. The instrument accurately measures the index of refraction of materials to one or two more significant figures than previous instruments. Material slices polished moderately flat are sufficient, without any requirement for special or complicated material shapes, such as prisms. The index profile at any chosen wavelength can be measured using a simple color filter. No special laser sources or carefully collimated parallel beams are required. The index profile over an entire sample can be directly obtained at any desired wavelength. This instrument is remarkable in that it greatly increases the accuracy of measurement, eliminates the need for high-quality, extremely narrow sources and for fabrication of special-geometry samples, and adds additional features, such as index profile measurements. The technique compares the fringe pattern from the top surface with that from a reference mirror to determine the thickness. Then, with the aid of a filtered white light source, the interference pattern from the back surface is compared with that from the front to yield the optical thickness of the sample. The combination of the two measurements gives the index. The back surface fringe pattern itself gives the index profile.
A holographic device has been developed that greatly improves the efficiency of solar energy conversion. The single-element hologram focuses light to the side and also spectrally splits it. The output appears as a thin concentrated line, focused perpendicular to the hologram and displaced to the side. Different wavelengths are diffracted, concentrated, and dispersed to different locations on the line which resembles an elegant rainbow in the visible. The hologram lets each of two or more different solar cells absorb only those wavelengths which can efficiently convert to electric power. The device also prevents overheating by diffracting unwanted infrared radiation away from the cells. The side focus eliminates shadow effects, and cooling is easy, since the cells are not cascaded and the heat load is minimal. This novel system is ideal for concentrated, split-spectrum, high efficiency solar power generation.