An electro-optical (E-O) imaging Fourier-transform spectrometer (IFTS), now under development, is a prototype of improved imaging spectrometers to be used for hyperspectral imaging, especially in the infrared spectral region. Unlike both imaging and non-imaging traditional Fourier-transform spectrometers, the E-O IFTS does not contain any moving parts. Elimination of the moving parts and the associated actuator mechanisms and supporting structures would increase reliability while enabling reductions in size and mass, relative to traditional Fourier-transform spectrometers that offer equivalent capabilities. Elimination of moving parts would also eliminate the vibrations caused by the motions of those parts.
Figure 1 schematically depicts a traditional Fourier-transform spectrometer, wherein a critical time delay is varied by translating one the mirrors of a Michelson interferometer. The time-dependent optical output is a periodic representation of the input spectrum. Data characterizing the input spectrum are generated through fast-Fourier-transform (FFT) post-processing of the output in conjunction with the varying time delay.
In the E-O IFTS, the Michelson interferometer optics and the bulky, slow translation mechanism are replaced with a solid-state time-delay/interferometer assembly. Included in the assembly (see Figure 2) are an input polarizer, an input passive quarter-wave plate (phase shifter), a series of N liquid-crystal-based electro-optical achromatic half-wave switches (S1, S2, . . . SN) interspersed with a series of (N + l) passive birefringent wave retarders (Γ1, Γ2, . . . ΓN), and an output polarizer.
The assembly can be regarded as consisting largely of a series of overlapping building blocks, each consisting of two of the passive wave retarders and the achromatic half-wave switch between them. By electro-optically rotating the orientation of the switch to an angle of either 0° or 45° with respect to the input polarization, one can cause the total retardation of the waves passing through the unit to be either the difference or the sum, respectively, of the retardations introduced by the individual retarders. Each retarder following the first one is made twice as thick as (to introduce twice the retardation of) the one preceding it. Hence, by means of binary actuation of the switches among all combinations of sums and differences, it is possible to obtain 2N different retardation values in increments of the smallest such value and thereby to obtain an arithmetic progression of small time-delay steps.
This work was done by Tien-Hsin Chao and Hanying Zhou of Caltech for NASA’s Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
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Refer to NPO-42371.
This Brief includes a Technical Support Package (TSP).
Electro-Optical Imaging Fourier-Transform Spectrometer
(reference NPO-42371) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package for the Electro-Optical Imaging Fourier-Transform Spectrometer (EOIFTS), designated as NPO-42371, developed by NASA's Jet Propulsion Laboratory (JPL). It is part of NASA Tech Briefs, which disseminate information on aerospace-related innovations with broader technological, scientific, or commercial applications.
The EOIFTS is a cutting-edge instrument designed for hyperspectral imaging, which involves capturing and analyzing a wide spectrum of light across various wavelengths. This capability allows for detailed analysis of materials and environments, making it valuable in fields such as remote sensing, environmental monitoring, and various scientific research applications.
The document emphasizes the importance of compliance with U.S. export regulations, indicating that the information may contain proprietary data from Caltech/JPL. It serves as a resource for individuals and organizations interested in the technological advancements represented by the EOIFTS, providing insights into its potential applications and benefits.
Additionally, the Technical Support Package outlines the availability of further assistance through the NASA Innovative Partnerships Program and directs readers to the NASA Scientific and Technical Information (STI) Program Office for more information. The STI Program Office can be accessed online or through direct contact via phone or email, offering support for those seeking to explore the research and technology in this area.
The document also includes a notice clarifying that the U.S. Government and its representatives do not assume liability for the use of the information contained within, nor do they guarantee that such use will be free from privately owned rights. It highlights that any trade names or manufacturers' names mentioned are for identification purposes only and do not imply official endorsement by NASA.
In summary, the Technical Support Package for the EOIFTS provides a comprehensive overview of this innovative spectrometer, its applications in hyperspectral imaging, and resources for further exploration of related technologies. It underscores NASA's commitment to sharing advancements in aerospace technology and fostering partnerships that can leverage these innovations for broader societal benefits.
