PUBLICATIONS
September 2015
OPTICS OF A GRANULAR IMAGING SYSTEM (I.E. “ORBITING RAINBOWS”)
Proc. SPIE, Vol. 9602,UV/Optical/IR Space Telescopes and Instrumentation: Innovative Technologies and Concepts VII, 9602E, September 22, 2015
In this paper, we present some ideas regarding the optics and imaging aspects of granular spacecraft. Granular spacecraft are complex systems composed of a spatially disordered distribution of a large number of elements, for instance a cloud of grains in orbit. An example of this application is a space-borne observatory for exoplanet imaging, where the primary collecting aperture is a cloud of small particles instead of a monolithic aperture.
March 2002
OBSERVED SCATTERING INTO A DARK OPTICAL VORTEX CORE
PHYSICAL REVIEW LETTERS, Vol. 88, No. 10, March 11 2002
The dark core of an optical vortex was used to detect on-axis, forward-scattered light from a colloidal solution in the single and multiple scattering regimes. Using no adjustable parameters we obtain good agreement with a concentration-dependent scattering model.
April 2004
SPATIAL CORRELATION SINGULARITY OF A VORTEX FIELD
PHYSICAL REVIEW LETTERS, Vol. 92, No. 14, 9 April 2004
Experimental and numerical techniques allowed us to predict and verify the existence of a robust phase singularity in the spatial coherence function when a vortex is present. Though observed in the optical domain, this phenomenon may occur in any partially coherent vortex wave.
July 2010
HOLOGRAPHIC VORTEX CORONAGRAPH
NASA Tech Briefs, July 2010
A holographic vortex coronagraph (HVC) has been proposed as an improvement over conventional coronagraphs for use in high-contrast astronomical imaging for detecting planets, dust disks, and other broadband light scatterers in the vicinities of stars other than the Sun. Because such light scatterers are so faint relative to their parent stars, in order to be able to detect them, it is necessary to effect ultra-high-contrast (typically by a factor of the order of 10^10) suppression of broadband light from the stars. Unfortunately, the performances of conventional coronagraphs are limited by low throughput, dispersion, and difficulty of satisfying challenging manufacturing requirements. The HVC concept offers the potential to overcome these limitations.
October 2006
LOW-ORDER ABERRATION SENSITIVITY OF AN OPTICAL VORTEX CORONAGRAPH
OPTICS LETTERS, Vol. 31, No. 20, October 15, 2006
We describe a high-contrast imaging technique capable of directly measuring light from a terrestrial planet by using a vortex mask of topological charge m=5. We demonstrate that this technique is relatively insensitive to low-order aberrations and compare its performance to that of a band-limited Lyot coronagraph.
December 2008
ASTRONOMICAL DEMONSTRATION OF AN OPTICAL VORTEX CORONAGRAPH
Optics & Photonics News, Vol. 19, No. 12,
2008
Direct optical detection of faint planets is exceedingly difficult, owing to the extraordinary glare of the parent star. The optical vortex coronagraph (OVC) provides an elegant solution by taking advantage of the unique diffraction properties of an optical vortex lens. Here we report on the first astronomical demonstration of an OVC to enhance the contrast between a bright star and its faint companion star.
July 2008
ASTRONOMICAL DEMONSTRATION OF AN OPTICAL VORTEX CORONAGRAPH
Optics Express, Vol. 16, No. 14, 7 July 2008
Using an optical vortex coronagraph and simple adaptive optics techniques, we have made the first convincing demonstration of an optical vortex coronagraph that is coupled to a star gazing telescope. We suppressed by 97% the primary star of a resolvable binary system, Cor Caroli. The stars had an angular separation of 1.9λ/D at our imaging camera. The secondary star suffered no suppression from the vortex lens.
November 2004
SPATIAL CORRELATION VORTICES IN PARTIALLY COHERENT LIGHT: THEORY
J. Opt. Soc. Am. B, Vol 21, No. 11, November 2004
Spatial correlation vortex dipoles may form in the four-dimensional mutual coherence function when a partially coherent light source contains an optical vortex. Analytical and numerical investigations are made in near- and far-field regimes.
September 2007
ADVANCEMENTS OF THE OPTICAL VORTEX CORONAGRAPH
Proc. SPIE 6693, Techniques and Instrumentation for Detection of Exoplanets III, 669311 (19 September 2007)
The optical vortex coronagraph is a promising scheme for achieving high contrast low loss imaging of exoplanets as close as 2λ / D from the parent star. We describe results using a high precision vortex lens that was fabricated using electron-beam lithography. We also report demonstrations of the coronagraph on a telescope employing a tip-tilt corrector.
June 2008
CONTRAST ENHANCEMENT OF BINARY STAR SYSTEM USING AN OPTICAL VORTEX CORONAGRAPH
arXiv: Optics, 2008
Using an optical vortex coronagraph and simple adaptive optics techniques we have made the first convincing demonstration of an optical vortex coronagraph that is coupled to a star gazing telescope. In particular we suppressed by 97% the primary star of a barely resolvable binary system, Cor Caroli, having an effective angular separation of only 1.4!/D. The secondary star suffered no suppression.
September 2005
AN OPTICAL VORTEX CORONAGRAPH
Proc. SPIE 5905, Techniques and Instrumentation for Detection of Exoplanets II, 59050N September 14, 2005
An optical vortex may be characterized as a dark core of destructive interference in a beam of spatially coherent light. This dark core may be used as a filter to attenuate a coherent beam of light so an incoherent background signal may be detected. Applications of such a filter include: eye and sensor protection, forward-scattered light measurement, and the detection of extra-solar planets. Optical vortices may be created by passing a beam of light through a vortex diffractive optical element, which is a plate of glass etched with a spiral pattern, such that the thickness of the glass increases in the azimuthal direction. An optical vortex coronagraph may be constructed by placing a vortex diffractive optical element near the image plane of a telescope. An optical vortex coronagraph opens a dark window in the glare of a distant star so nearby terrestrial sized planets and exozodiacal dust may be detected. An optical vortex coronagraph may hold several advantages over other techniques presently being developed for high contrast imaging, such as lower aberration sensitivity and multi-wavelength operation. In this manuscript, I will discuss the aberration sensitivity of an optical vortex coronagraph and the key advantages it may hold over other coronagraph architectures. I will also provide numerical simulations demonstrating high contrast imaging in the presence of low-order static aberrations.
August 2006
THE HIGH-CONTRAST PERFORMANCE OF AN OPTICAL VORTEX CORONAGRAPH
Proc. SPIE 6288, Current Developments in Lens Design and Optical Engineering VII, 62880B, August 31 2006
The goal of the Terrestrial Planet Finder Mission is to detect and characterize Earth-like planets. Detection of these faint objects, which appear very close to their parent stars, requires a coronagraph capable of achieving better than 10-10 starlight suppression within a few Airy rings of the stellar image. The coronagraph is also required to maintain this high stellar extinction over a 100nm spectral bandwidth. To ease requirements on the telescope, a high planet light throughput and low sensitivity to wave front aberrations are also desirable features. An optical vortex coronagraph is a promising candidate architecture, which makes use of a spiral phase plate placed in an intermediate image plane to null out the stellar signal. This architecture has the advantage of high stellar extinction, high planet light throughput, and low sensitivity to wave front aberrations. Here we report the high contrast performance of an optical vortex coronagraph limited by the manufacturability of the spiral phase plate.
July 2006
THE TERRESTRIAL PLANET FINDER CORONAGRAPH OPTICAL SURFACE REQUIREMENTS
Proc. SPIE 6265, Space Telescopes and Instrumentation I: Optical, infrared, and millimeter, 62651L, July 6, 2006
We derive the requirements on the surface height uniformity and reflectivity uniformity of the Terrestrial Planet Finder Coronagraph telescope and instrument optics for spatial frequencies within and beyond the spatial control bandwidth of the wave front control system. Three different wave front control systems are considered: a zero-path difference Michelson interferometer with two deformable mirrors at a pupil image; a sequential pair of deformable mirrors with one placed at a pupil image; and the Visible Nuller spatially-filtered controller. We show that the optical bandwidth limits the useful outer working angle.
