In 1996, the original HEIFTS paper described a totally new FT imaging spectrometer with no moving parts. Papers in 1997 and 2000 followed. In 1998 US US granted Patent #5,777,736, covering the device’s unique optical geometry and data reduction scheme.
Light interfering at the image plane need not come from a single aperture. Two new geometries are proposed. The first uses light from two separate but identical objectives. The second uses light from a single objective split by mirrors situated at a pupil image.
The physics of the original device will be reviewed and specific examples of the two new optical geometries.
This paper was published in error and has been withdrawn. A correct version of the paper can be found at https://doi.org/10.1117/12.857310. The Publisher regrets the error.
A new family of 2 mirror wide field unobscured telescopes have been designed. They are of compact "Schiefspiegler", off axis
Cassegrain geometry, incorporating aspheres, tilted and decentered secondary, and tilted focal surfaces. These additional
optimization variables allow control of the tilt of the focal surface. Designs range from f/5 to f/16, and provide fully baffled, all reflecting systems with no color, moderately wide diffraction limited fields of view with unobscured aperture MTF. The systems
are well suited for use as visual telescopes, CCD camera or high resolution wide field collimator and IR scene projector. The
nCUB designs provide a focal surface normal to the gut ray for visual use. The tCUB designs provide collimator telescopes with
focal surfaces tilted so that any light reflected from the reticle is eliminated and with it Narcissus. Instead, this reflection can be
used to provide a uniform "background" irradiance field. Simple interferometric tests allow straightforward element figuring and
system alignment. Examples will be described and compared to current designs. Manufacturing, testing and mounting of the
optical system will be briefly discussed.
The "Polarization Fidelity" Tracking Mount Optical Geometry describes an Az El tracking
mount and relay mirror geometry, which maintains a high degree of polarization fidelity for a
telescope image, passing through the gimbal, to a stationary sensor package outside the mount.
The paper models and compares this geometry to an standard Az El mount using ZEMAX.
The Magdalena Ridge Observatory (MRO) project is presently funded to design and build a facility including an optical/infrared imaging interferometer composed of up to 10 1.5 meter class telescopes and a single conventional 2.4 meter class telescope. The interferometer array will be arranged in a “Y” configuration and the use of movable telescopes will allow its reconfiguration from a very compact array with baselines up to tens of meters to a true long baseline configuration with baselines up to 400 meters. We plan to introduce adaptive optics systems on the array telescopes.
The Magdalena Ridge Observatory now being planned for a site within the Magdalena Mountains near Socorro, NM will have an optical/near infrared interferometric imaging array as its primary observing instrument. We are presently evaluating the use of array telescope apertures ranging from 1.2 to 2.0 m in diameter for this application. Telescopes in this size range are many times the size of Fried's coherence parameter r0 anywhere within the .6 to 2.2 μm wavelength range of interest and to be useful for interferometry will require the use of adaptive optics (AO) techniques to restore and maintain the spatial coherence of the telescope pupils. We review some of the practical limitations related to the use of AO systems on interferometer telescopes and discuss the enhanced interferometric performance that might thereby be attained.
KEYWORDS: Signal to noise ratio, Visibility, Interferometers, Mirrors, Camera shutters, Modulation transfer functions, Electronics, Data modeling, Diffraction, Spatial frequencies
At the Denver meeting in 1996 and at San Diego in 1997, we first presented the theory and later a demonstration of the operating Phase I HEIFTS, (High ?tendue Imaging Fourier Transform Spectrometer), laboratory device. The HEIFTS device forms the autocorrelation record image cube, (or ribbon), of a pushbroomed two dimensional image with no internal moving parts. This three dimensional autocorrelation record cube or ribbon can then be Fourier Transformed to obtain a ‘wavenumber’ hyperspectral data cube or ribbon.
The Phase II device has been demonstrated in the laboratory and results will be presented. Several areas, such as fringe visibility, spatial sampling rate and noise have been modeled, and the results of this modeling and the predicted effect on system performance will be discussed. We will also describe a compact IR HEIFTS system in current design, and modeled system performance will be discussed.
We present the Infrared Imaging Spatial Heterodyne Spectrometer (IRISHS) experiment. IRISHS is a new hyperspectral imaging spectrometer for remote sensing being developed by Los Alamos National Laboratory for use in identifying and assaying gases in the atmosphere when viewed against the Earth's background. The prototype instrument, which can operate between 8 and 11.5 micrometers (although the current IR camera operates from 8 - 9.5 micrometers), will be described. Imaging spatial heterodyne spectrometer technology is discussed in four companion papers also presented at this symposium.
At the Denver meeting, last year, we presented the High Etendue Imaging Fourier Transform Spectrometer, (HEIFTS), theory and optical design. This device uses a new 'image plane interferometer' geometry to produce 'autocorrelation function modulation' in the image plane of a 2D imaging array, such that the phase offset of the modulation varies linearly across the image. As a 2D image is pushbroomed across the imaging, array, the record of an individual scene pixel is recorded for each autocorrelation phase offset. The 3D array of this data is processed to yield an 'autocorrelation function' data cube, which is Fourier transformed to yield a 'wavenumber' hyperspectral data curve. A phase I device has been demonstrated in the laboratory and initial results are presented. The significant increase in signal to noise ratio, which the HEIFTS optical design promises over conventional hyperspectral imaging schemes, has been simulated, and results will be discussed. A Phase II system is being prepared for initial field deployment, and will be described.
Current hyperspectral imaging cameras are typically limited in throughput either by a slit or other optical geometries requiring small solid angle instantaneous fields of view. The high etendue imaging Fourier transform spectrometer optical design is a new optical geometry for the production of spectral autocorrelation fringe modulation over an image plane defined by a large CCD array. A throughput advantage approaching several hundred appears realizable, with an accompanying increase in signal to noise proportional to 'root N'. THe simple optical implementation of this design will be discussed along with initial experimental results.
The MSTI-3 sensor package is a three band imaging telescope for military and dual use sensing missions. The MSTI-3 mission is one of the Air Force Phillips Laboratory's Pegasus launched space missions, a third in the series of state-of-the-art lightweight sensors on low cost satellites. The satellite is planned for launch into a 425 Km orbit in late 1995. The MSTI- 3 satellite is configured with a down looking two axis gimbal and gimbal mirror. The gimbal mirror is an approximately 13 cm by 29 cm mirror which allows a field of regard approximately 100 degrees by 180 degrees. The optical train uses several novel optical features to allow for compactness and light weight. A 105 mm Ritchey Chretien Cassegrain imaging system with a CaF2 dome astigmatism corrector is followed by a CaF2 beamsplitter cube assembly at the systems first focus. The dichroic beamsplitter cube assembly separates the light into a visible and two IR channels of approximately 2.5 to 3.3, (SWIR), and 3.5 to 4.5, (MWIR), micron wavelength bands. The two IR imaging channels each consist of unity power re-imaging lens cluster, a cooled seven position filter wheel, a cooled Lyot stop and an Amber 256 X 256 InSb array camera. The visible channel uses a unity power re- imaging system prior to a linear variable filter with a Sony CCD array, which allows for a multispectral imaging capability in the 0.5 to 0.8 micron region. The telescope field of view is 1.4 degrees square.
We have explored a new family of 6 mm imaging endoscope designs for laparoscopes. These designs use a `solid' relay lens made up of plastic lens components bonded together in a repetitive fashion to form a long, monolithic relay element without air spaces. The lack of air spaces allows for the elimination of coatings and spacing elements. This simplifies construction and should considerably lessen cost. A four element objective lens is presented for the system which uses a plano-convex sapphire element as a combination window and lens element. The other three lens elements are plastic, and produce an image which is `buried' in the monolithic relay. Two designs are discussed, a relatively inexpensive, `single use' design, which incorporates easy-to-fabricate, low-temperature plastic lens elements, and a more expensive, `autoclavable' design, using high-temperature plastic lens elements. Both designs exhibit good optical resolution, and high optical throughput and contrast.
A method of phasing segmented-mirror systems using a new form of white-light radial-shear interferometer is presented. The device was used in a laboratory proof-of-concept demonstration to phase two elements of an annularly segmented mirror. This co-phasing was achieved both manually and with low-bandwidth closed-loop servo control using a new and perhaps simpler modulation technique than that proposed previously. The configuration used in the demonstration is described, together with some initial results.
This paper presents the optical description of a white light radial shear interferometer for use in the control of segmented mirror systems. White light from a segment of the mirror under control is caused to interfere with light from other segments. The resulting white light fringe position is modulated so that an error signal corresponding to wavefront offset may be generated.
The development of sophisticated Electro-Optical systems for use in a shipboard environment is somewhat hampered by the lack of reliable models of the optical turbulence effects in close proximity to the ship, caused by the ship itself. To this end, preliminary microthermal fluctuations were made on an operating aircraft carrier during July 1979, along with other optical and meteorological measurements. These microthermal fluctuation measurements are being studied to ascertain their value in the development of a suitable model. Three CONTEL model MT-2 Microthermal Probes were specially modified for shipboard measurements and remote data acquisition, and deployed at three deck level sites on the USS LEXINGTON. These sites included the forward port and starboard sponscns, and an aft starboard sponson. Data was logged once each second for nine to fourteen hour periods on three consecutive days. The measurements include periods of flight operations during which the launching of aircraft can be clearly observed as strong perturbations in the data. Analysis of the data, measurement techniques and other evidence, raises several cautions as to the application of the standard optical turbulence models. In this light, the value of the data set is discussed and the character of future measurements are suggested.
An 0.8 meter Cassegrain, reflecting relay and matching optics comprise a system which incorporates a Nike Hercules pedestal for an infrared tracking system. Optical design criteria and performance will be discussed.
From February to May 1977, extensive atmospheric transmission measurements were carried out over a 5.08 km, over-water path at Cape Canaveral Air Force Station using NRL's Infrared Mobil Optical Radiation Laboratory. This paper will report transmission measurements of 80 CO2 laser lines for three measurement periods. These periods were typified by high visibilities, (> 20 km), and 7.4, 15.7, and 18.4 torr atmospheric water vapor contents, respectively. The set of laser lines include the following transitions: 00°1 - 10°0 P4 to P44 and R4 to R42 00°1 - 02°0 P4 to P42 and R4 to R40 The Hitran calculations of atmospheric extinction were made using a computer code adapted by NRL for our DEC 11/40. The December 1975 AFCRL line compilation was augmented by a current H2O continuum model. A comparison points out possible problems with some H2O absorption lines as well as the shape of the water continuum absorption profile.
Long path atmospheric laser transmission measurements require the precise measurement of the radiant energy of laser beams after they have been turbled by the atmosphere. This requires a detector/integrator package with very uniform response and low speckle noise. A two scatter plate device has been fabricated for use with a lmm square cryogenic infrared detector. CO2 laser measurements have been made which verify the uniformity of response and low speckle noise. Absolute accuracies of better than 1% RMS are achieved with this device. The device is augmented with a Si Diode and allows atmospheric transmission measurements to be carried out for lasers in the wavelength range of 0.6 to 11.2 microns.
During the past several years the Optical Radiation Branch of the Naval Research Laboratory (NRL) has conducted extensive field experiments designed to validate high resolution atmospheric transmission codes for near-and mid-infrared wavelengths. The combined use of laser extinction data with Fourier transform spectrometer measurements over long atmospheric paths has produced several examples of high-quality, precisely calibrated transmission spectra. Instrumentation and procedures used in these experiments will be described and selected measurement results will be presented. Application of this information to current infrared atmospheric transmission problems will be discussed together with comparisons of the experimental data to high-resolution computer code calculations.
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