James B. Breckinridge

Polarization Properties of a Grating Spectrograph

The 13.7-m Czerny-Turner spectrograph at the McMath solar telescope is evaluated with regard to polarization properties. Let I || = the transmissivity of the spectrograph for incident light linear polarized parallel to the entrance slit and I perpendicular = transmissivity for light polarized perpendicular to the entrance slit. The ratio I ||/I perpendicular was measured photoelectrically as a function of wavelength in six diffraction orders. Values of this ratio vary from 0.3 to 20. It is shown that spectrograph transmission as a function of polarization may cause large photometric and radiometric errors. This fact is not unique to this particular instrument. Two mechanisms appear to contribute to the polarizance of the grating. These are: (1) the Rayleigh or Woods anomalies in which polarizance maxima and minima occur and (2) a vector wave interaction introduced because groove dimension is nearly the same as the wavelength. For lambda > groove depth it is found that the wavelength of a peak polarizance (lambda(p)) is given by lambda(p) = 0.7d costheta, where d is the ruling separation and theta is the grating angle. Photoelectric scans of the solar spectrum were made across several of the Woods anomalies to obtain their profiles.

Solar Speckle Interferometry

The technique of speckle interferometry was applied to solar photographs. Spatial frequencies as high as 4 cycles per arc second were detected in sunspots.

POLARIZATION EFFECTS IN REFLECTING CORONAGRAPHS FOR WHITE-LIGHT APPLICATIONS IN ASTRONOMY

The properties of metal thin films have been largely overlooked in discussions of the technical limitations and problems that arise in the field of direct detection of exoplanets. Here, polarization properties and anisotropy properties of highly reflecting thin metal films are examined within the context of the requirements for the ultra-low-scattered-light system performance of coronagraphs applied to space and ground-based high-contrast, white-light astronomy. Wavelength-dependent optical constants for highly reflecting thin metal films, taken from the literature, are used to calculate the polarization-dependent transmissivity of a typical coronagraph. The effects of degraded performance on the astronomical science are examined. Suggestions are made for future work.

System Concept For A Moderate Cost Large Deployable Reflector (LDR)

A study was carried out at the Jet Propulsion Laboratory during the first quarter of 1985 to develop a system concept for NASAs Large Deployable Reflector (LDR). This new system concept meets the primary scientific requirements and minimizes the cost and development time. The LDR requirements were investigated to determine whether or not the major cost drivers could be significantly relaxed without compromising the scientific utility of LDR. In particular, the telescope wavefront error is defined so as to maximize scientific return per dollar. Major features of the concept are a four-mirror, two-stage optical system; a lightweight structural composite segmented primary reflector; and a deployable truss backup structure with integral thermal shield. The two-stage optics uses active figure control at the quaternary reflector located at the primary reflector exit pupil, allowing the large primary to be passive. The lightweight composite reflector panels limit the short wavelength operation to approximately 30 pm but reduce the total primary reflector weight by a factor of 3 to 4 over competing technologies. System optical performance is calculated including aperture efficiency, Strehl ratio, and off-axis performance. On-orbit thermal analysis indicates a primary reflector equilibrium temperature of less than 200 K with a maximum gradient of =°C across the 20 m aperture. Weight and volume estimates are consistent with a single Shuttle launch and are based on Space Station assembly and checkout.

Measurement of the amplitude of phase excursions in the earth’s atmosphere

The maximum of the probability density distribution of phase fluctuations in the earth’s atmosphere, as a function of point separation, was measured visually in white light for starlight observed from the ground with a 1.5 m astronomical telescope. A wave-front folding interferometer was used.

The absorption spectrum of atmospheric water vapor in the vicinity of the He 10830 Å triplet

Wavelengths of clean atmospheric water lines, and some solar lines, in the wavelength interval 10750 Å to 10900 Å have been measured to an accuracy approaching ± 1 mÅ. Strengths and wavelengths have been measured for all atmospheric water lines with absorption coefficients > 5 × 10−4 cm−1 gm−1 cm−2 at ∼ 280K, that lie within 15 Å of the He I 10830 Å featur of the stronger He component is affected by a weak water line which reduces atmospheric transmission by nearly 1 % with 10 mm precipitable water in the line of sight.

Kitt Peak speckle camera

The speckle camera in regular use at Kitt Peak National Observatory since 1974 is described in detail. The design of the atmospheric dispersion compensation prisms, the use of film as a recording medium, the accuracy of double star measurements, and the next generation speckle camera are discussed. Photographs of double star speckle patterns with separations from 1.4 sec of arc to 4.7 sec of arc are shown to illustrate the quality of image formation with this camera, the effects of seeing on the patterns, and to illustrate the isoplanatic patch of the atmosphere.

Recent Progress In The Measurement Of Temperature And Salinity By Optical Scattering

Recent progress is described in the use of Brillouin and Raman scattering for the measurement of temperature and salinity in the ocean. The use of Brillouin scattering is described for the measurement of the sound velocity, and the use of Raman scattering is described for the independent measurement of the temperature and salinity. Coupling these techniques permits the assessment of both temperature and salinity. The experimental techniques are described together with the results of recent experiments and an assessment of the errors to be expected.

Reflecting Schmidt imaging spectrometers

A new very wide angle imaging spectrometer optical configuration which uses an all-reflecting Schmidt camera with a prism spectrometer to give a strip field of view is presented. Three complete systems (15 degrees, 8.5 degrees, 2.6 degrees FOV), including fore optics and spectrometer optics, were designed. These slit fields of view are pushbroomed across object space to create a 2-D image. The performance of each near diffraction-limited system and optical prescriptions is detailed. An all-reflecting Schmidt camera fore-optics system with a 60 degree field of view is also given.

Signal-to-noise limitations in white light holography

A simple derivation is given for the signal-to-noise ratio (SNR) in images reconstructed from incoherent holograms. Dependence is shown to be on the hologram SNR, object complexity, and the number of pixels in the detector. Reconstruction of involved objects becomes possible with high dynamic range detectors such as charge coupled devices. We have produced such white light holograms by means of a rotational shear interferometer combined with a chromatic corrector. A digital inverse transform recreated the object.