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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Beam Shape Effects on Grating Spectrometer Resolution

The collimated optical beam in a grating spectrometer may be circular or elliptical in cross section, so that different parts of the beam illuminate different numbers of grooves on the grating. Here we estimate the consequent loss in spectral resolution relative to that obtained with a beam which illuminates a fixed number of grooves. For representative diffraction resolution functions, the effect is to reduce the intrinsic resolving power of the spectrometer by about 13%, exclusive of other contributions such as finite entrance slit width.

Erickson, Edwin F.↗
DOE OSTI2024

Excitation and detection of coherent nanoscale spin waves via extreme ultraviolet transient gratings

The advent of free electron lasers has opened the opportunity to explore interactions between extreme ultraviolet (EUV) photons and collective excitations in solids. While EUV transient grating spectroscopy, a noncollinear four-wave mixing technique, has already been applied to probe coherent phonons, the potential of EUV radiation for studying nanoscale spin waves has not been harnessed. Here we report EUV transient grating experiments with coherent magnons in Fe/Gd ferrimagnetic multilayers. Magnons with tens of nanometers wavelengths are excited by a pair of femtosecond EUV pulses and detected via diffraction of a probe pulse tuned to an absorption edge of Gd. The results unlock the potential of nonlinear EUV spectroscopy for studying magnons and provide a tool for exploring spin waves in a wave vector range not accessible by established inelastic scattering techniques.

Science & Technology - Other Topics↗
DOE OSTI2026

Polarization Control via Artificial Optical Nonlinearity in Dielectric Metasurfaces

Nonlinear optical phenomena are generally governed by geometry in matter systems, as they depend on the spatial arrangement of atoms within materials or molecules. Metasurfaces, through precisely designed geometries on a subwavelength scale, allow the optical response of a material to be tailored far beyond its natural properties. Therefore, metasurfaces are highly appealing for enabling the engineering of nonlinear optical interactions. Current studies of nonlinear metasurfaces predominantly focus on the phase control of the generated light. Nonetheless, investigating the tensorial nature of the nonlinearity of metasurfaces and its effect on the polarization of the generated light is critical to fully unlocking a range of applications, such as nonlinear vector beam generation and nonlinear polarization imaging. Here, we study the artificial optical nonlinearity of a dielectric metasurface originating from its meta-atom symmetry and describe the third-order nonlinear behavior by considering the polarization degree of freedom. We establish an effective nonlinear medium model that serves as a design toolbox for developing amorphous silicon-based geometric metasurfaces with customizable features for third-harmonic generation. We further extract quantitative values of the artificial nonlinear susceptibility tensor elements related to the investigated nonlinear process and geometry. The implemented functional devices demonstrate the versatility of dielectric metasurfaces in shaping the emitted light in terms of amplitude, phase, and polarization for the precise engineering of advanced nonlinear architectures targeting applications in nonlinear imaging and complex light generation.

Diffraction↗
NASA NTRS1989

AlGaAs phased array laser for optical communications

Phased locked arrays of multiple AlGaAs diode laser emitters were investigated both in edge emitting and surface emitting configurations. CSP edge emitter structures, coupled by either evanescent waves or Y-guides, could not achieve the required powers (greater than or similar to 500 mW) while maintaining a diffraction limited, single lobed output beam. Indeed, although the diffraction limit was achieved in this type of device, it was at low powers and in the double lobed radiation pattern characteristic of out-of-phase coupling. Grating surface emitting (GSE) arrays were, therefore, investigated with more promising results. The incorporation of second order gratings in distribute Bragg reflector (DBR) structures allows surface emission, and can be configured to allow injection locking and lateral coupling to populate 2-D arrays that should be able to reach power levels commensurate with the needs of high performance, free space optical communications levels. Also, a new amplitude modulation scheme was developed for GSE array operation.

Carlson, N. W.↗
NASA NTRS2006

Achromatic shearing phase sensor for generating images indicative of measure(s) of alignment between segments of a segmented telescope's mirrors

An achromatic shearing phase sensor generates an image indicative of at least one measure of alignment between two segments of a segmented telescope's mirrors. An optical grating receives at least a portion of irradiance originating at the segmented telescope in the form of a collimated beam and the collimated beam into a plurality of diffraction orders. Focusing optics separate and focus the diffraction orders. Filtering optics then filter the diffraction orders to generate a resultant set of diffraction orders that are modified. Imaging optics combine portions of the resultant set of diffraction orders to generate an interference pattern that is ultimately imaged by an imager.

Stahl, H. Philip↗
NASA NTRS1998

Systems Issues Pertaining to Holographic Optical Data Storage in Thick Bacteriorhodopsin Films

The optical data storage capacity and raw bit-error-rate achievable with thick photochromic bacteriorhodopsin (BR) films are investigated for sequential recording and read- out of angularly- and shift-multiplexed digital holograms inside a thick blue-membrane D85N BR film. We address the determination of an exposure schedule that produces equal diffraction efficiencies among each of the multiplexed holograms. This exposure schedule is determined by numerical simulations of the holographic recording process within the BR material, and maximizes the total grating strength. We also experimentally measure the shift selectivity and compare the results to theoretical predictions. Finally, we evaluate the bit-error-rate of a single hologram, and of multiple holograms stored within the film.

Downie, John D.↗
NASA NTRS1998

Long Holographic Lifetimes in Bacteriorhodopsin Films

The D85N genetic variant of bacteriorhodopsin displays a nearly permanent lifetime of the photochromic P490 state. We present pump-probe measurements that demonstrate this behavior. However, experimental diffraction efficiency measurements made from holograms recorded in a hydrated D85N film show markedly different decay behavior, suggesting a molecular diffusion process occurring in the film. Holograms recorded with different grating frequencies display correspondingly different decay times which support this hypothesis. A thin D85N film was then fabricated which was chemically crosslinked, resulting in the elimination of diffusion of BR molecules within the polymer matrix. This film exhibits a grating lifetime on the order of weeks or more, thus allowing the long term holographic storage of information in a BR film.

Downie, John D.↗
NASA NTRS2005

Submillimeter Spectroscopy with SOFIA

Four submillimeter spectrometers are being developed for use on SOFIA, the Stratospheric Observatory for Infrared Astronomy. They will be nearly diffraction limited by SOFIA'S 2.5 m telescope, giving for example images of 8.5 arc seconds FWHM at 100 microns. The instruments are FlFI LS, an integral-field imaging grating spectrometer (MPE) covering 40-210 microns with ~150 km/s resolution; SAFIRE an imaging Fabry-Perot spectrometer covering 100-'650 microns with resolution ~200 km/s, and two heterodyne receivers with resolving powers up to ~0.03 km/s: GREAT covering bands from 158-187 um, 110-125, and 62-65 microns, and CASIMIR, operating from 150-264 and 508-588 microns. These instruments will enable a variety of studies including topics relating to the origins of stars, planets, and biogenic materials in the interstallar medium of our own and other galaxies. Opportunities for observing with these and the other SOFIA instruments will be available to general investigators. SOFIA is a joint project of NASA in the U.S. and DLR in Germany.

Erickson, E.↗
NASA NTRS1989

Optomechanical design of the grating laser beam combiner (GLBC) laser diode header

A laser diode header has been fabricated for a grating laser beam combiner (GLBC). The laser diode header provides the thermal control, the drive electronics, and the optical system necessary for proper operation of the beam combiner. The diode header is required to provide diffraction limited optical performance while providing correction for worst case defocus aberration, 0.6 mrad excess divergence, and worst case decenter aberration, 1.0 mrad pointing error. The design of the header considered the mechanical design and the optical design together resulting in a small, self-contained header with 0.7 mrad range for focus correction and +/- 2.5 mrad of beam steering. The complete diode header is currently undergoing optical and mechanical performance testing.

Rall, Jonathan A. R.↗
NASA NTRS2001

Stitching-error reduction in gratings by shot-shifted electron-beam lithography

Calculations of the grating spatial-frequency spectrum and the filtering properties of multiple-pass electron-beam writing demonstrate a tradeoff between stitching-error suppression and minimum pitch separation. High-resolution measurements of optical-diffraction patterns show a 25-dB reduction in stitching-error side modes.

Integrated optics semiconductor lasersgratings↗
NASA NTRS1996

Design considerations for AIRES, an airborne infrared echelle spectrometer for SOFIA

The airborne infrared echelle spectrometer (AIRES) was proposed as a facility instrument for the stratospheric observatory for infrared astronomy (SOFIA) project. The preliminary AIRES design uses multiple two dimensional detector arrays and a 1.2 m long, 76 deg blaze angle echelle to combine high spectral resolution with diffraction limited imaging in the cross-dispersion direction. A preliminary optical design and the mechanical architecture are presented together with the analysis and prototyping of lightweight aluminum echelles. Instrument efficiencies are calculated and compared for different gratings, and the associated mechanical design tradeoffs are discussed.

Haas, Michael R.↗
NASA NTRS2000

Optical Performance Modeling of FUSE Telescope Mirror

We describe the Metrology Data Processor (METDAT), the Optical Surface Analysis Code (OSAC), and their application to the image evaluation of the Far Ultraviolet Spectroscopic Explorer (FUSE) mirrors. The FUSE instrument - designed and developed by the Johns Hopkins University and launched in June 1999 is an astrophysics satellite which provides high resolution spectra (lambda/Delta(lambda) = 20,000 - 25,000) in the wavelength region from 90.5 to 118.7 nm The FUSE instrument is comprised of four co-aligned, normal incidence, off-axis parabolic mirrors, four Rowland circle spectrograph channels with holographic gratings, and delay line microchannel plate detectors. The OSAC code provides a comprehensive analysis of optical system performance, including the effects of optical surface misalignments, low spatial frequency deformations described by discrete polynomial terms, mid- and high-spatial frequency deformations (surface roughness), and diffraction due to the finite size of the aperture. Both normal incidence (traditionally infrared, visible, and near ultraviolet mirror systems) and grazing incidence (x-ray mirror systems) systems can be analyzed. The code also properly accounts for reflectance losses on the mirror surfaces. Low frequency surface errors are described in OSAC by using Zernike polynomials for normal incidence mirrors and Legendre-Fourier polynomials for grazing incidence mirrors. The scatter analysis of the mirror is based on scalar scatter theory. The program accepts simple autocovariance (ACV) function models or power spectral density (PSD) models derived from mirror surface metrology data as input to the scatter calculation. The end product of the program is a user-defined pixel array containing the system Point Spread Function (PSF). The METDAT routine is used in conjunction with the OSAC program. This code reads in laboratory metrology data in a normalized format. The code then fits the data using Zernike polynomials for normal incidence systems or Legendre-Fourier polynomials for grazing incidence systems. It removes low order terms from the metrology data, calculates statistical ACV or PSD functions, and fits these data to OSAC models for the scatter analysis. In this paper we briefly describe the laboratory image testing of FUSE spare mirror performed in the near and vacuum ultraviolet at John Hopkins University and OSAC modeling of the test setup performed at NASA/GSFC. The test setup is a double-pass configuration consisting of a Hg discharge source, the FUSE off-axis parabolic mirror under test, an autocollimating flat mirror, and a tomographic imaging detector. Two additional, small fold flats are used in the optical train to accommodate the light source and the detector. The modeling is based on Zernike fitting and PSD analysis of surface metrology data measured by both the mirror vendor (Tinsley) and JHU. The results of our models agree well with the laboratory imaging data, thus validating our theoretical model. Finally, we predict the imaging performance of FUSE mirrors in their flight configuration at far-ultraviolet wavelengths.

Saha, Timo T.↗
NASA NTRS1999

Three-Dimensional Displacement Measurement Using Diffractive Optic Interferometry

This paper introduces a powerful new optical method which utilizes diffractive optic interferometry (DOI) to measure both in-plane and out-of-plane displacement with variable sensitivity using the same optical system. Sensitivity is varied by utilizing various combinations of the different wavefronts produced by a conjugate pair of binary Optical elements; a transmission grating is used to produce several illumination beams while a reflective grating replicated on the surface of a specimen, provides the reference for the undeformed state. A derivation of the equations which govern the method is included along with a discussion Of the experimental tests conducted to verify the theory. Overall, the results are excellent, with experimental data agreeing to within a few percent of the theoretical predictions.

Gilbert, John A.↗
NASA NTRS1999

Application of Novel Nonlinear Optical Materials to Optical Processing

We describe wave mixing and interactions in nonlinear photorefractive polymers and disodium flourescein. Higher diffracted orders yielding forward phase conjugation can be generated in a two-wave mixing geometry in photorefractive polymers, and this higher order can be used for image edge enhancement and correlation. Four-wave mixing and phase conjugation is studied using nonlinear disodium floureschein, and the nature and properties of gratings written in this material are investigated.

Banerjee, Partha P.↗
NASA NTRS1992

Integrated device with diffractive polarization components for a magneto-optical disk head

The optical components in the detection train of a conventional magneto-optical (MO) disk head include a half-wave plate and a polarization beamsplitter. These polarization components are bulky and require specialized mounting hardware. In order to realize a more compact head, we propose that these elements be replaced by an integrated device composed of cascaded volume and surface-relief gratings. Herein, the proposed system is described in detail for the individual elements, theoretical and prototype element performance are compared, and the operational tolerances of these elements are discussed.

Haggans, Charles W.↗
NASA NTRS1986

Diffraction effects and special advantages in electronic heterodyne moire deflectometry

Effects of diffraction on the performance of electronic heterodyne readout of moire fringes are investigated. The sensitivity, accuracy, and resolution of the system are calculated, and it is shown that these features are significantly improved compared with the conventional intensity moire readout technique. The sensitivity of the system can be tripled without changing the distance between gratings. The system was evaluated experimentally by measuring the refractive-index derivatives of a weak phase object consisting of a large KD(asterisk)P crystal. Effects of nonlinear fringe modulation were studied both theoretically and experimentally. It is shown that in this case the electronic phase is not linearly related to the fringe shift, and calibration of the system is necessary.

Stricker, J.↗
NASA NTRS2014

Micro-Spec: An Ultracompact, High-sensitivity Spectrometer for Far-Infrared and Submillimeter Astronomy

High-performance, integrated spectrometers operating in the far-infrared and submillimeter ranges promise to be powerful tools for the exploration of the epochs of reionization and initial galaxy formation. These devices, using high-efficiency superconducting transmission lines, can achieve the performance of a meter-scale grating spectrometer in an instrument implemented on a 4 inch silicon wafer. Such a device, when combined with a cryogenic telescope in space, provides an enabling capability for studies of the early universe. Here, the optical design process for Micro-Spec (micron-Spec) is presented, with particular attention given to its two-dimensional diffractive region, where the light of different wavelengths is focused on the different detectors. The method is based on the stigmatization and minimization of the light path function in this bounded region, which results in an optimized geometrical configuration. A point design with an efficiency of (is) approximately 90% has been developed for initial demonstration and can serve as the basis for future instruments. Design variations on this implementation are also discussed, which can lead to lower efficiencies due to diffractive losses in the multimode region.

cryogenic telescope↗