10^-7 contrast ratio at 4.5 lambda/D: New results obtained in laboratory experiments using nano-fabricated coronagraph and multi-Gaussian shaped pupil masks

Chakraborty, Abhijit; Thompson, Laird A.; Rogosky, Michael

doi:10.1364/opex.13.002394

Cited by 12 publications

(9 citation statements)

References 14 publications

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“…This multi-stage approach was also recently considered for coronagraphy with a combination of a classical Lyot coronagraph and a shaped pupil mask (Chakraborty et al 2005). Another way consists in combining nulling interferometry and coronagraphy (Nishikawa et al 2005).…”

Section: Approachmentioning

confidence: 99%

Removal of central obscuration and spider arm effects with beam-shaping coronagraphy

Abe

Murakami

Nishikawa

et al. 2006

A&A

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This paper describes a method for removing the effect of a centrally obscured aperture with additional spider arms in arbitrary geometrical configurations. The proposed method is based on a two-stage process where the light beam is first shaped to remove the central obscuration and spider arms, in order to feed a second, highly efficient coronagraph. The beam-shaping stage is a combination of a diffraction mask in the first focal plane and a complex amplitude filter located in the conjugate pupil. This paper specifically describes the case of using Lyot occulting masks and circular phase-shifting masks as diffracting components. The basic principle of the method is given along with an analytical description and numerical simulations. Substantial improvement in the performance of high-contrast coronagraphs can be obtained with this method, even if the beam-shaping filter is not perfectly manufactured.

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Section: Approachmentioning

confidence: 99%

Removal of central obscuration and spider arm effects with beam-shaping coronagraphy

Abe

Murakami

Nishikawa

et al. 2006

A&A

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“…This is a convenient location to insert coronagraphic pupil masks. Chakraborty et al (2005) placed a Gaussian-shaped pupil mask here to conduct lab-bench coronagraphic imaging tests. Because the UnISIS optics table is easy to access, a wide variety of coronographic configurations can be easily swapped in and out.…”

Section: Unisis Optical Designmentioning

confidence: 99%

UnISIS: Laser Guide Star and Natural Guide Star Adaptive Optics System

Thompson

Teare

Xiong

et al. 2009

PUBL ASTRON SOC PAC

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is a versatile adaptive optics system mounted on a large optics bench at the coudé focus of the Mount Wilson 2.5-m telescope. It was designed to have both laser guide star (LGS) and natural guide star (NGS) adaptive optics capabilities. The LGS side of the system relies on a pulsed UV laser with raw power of 30 W capable of creating an artificial laser star via Rayleigh scattering 18 km above the telescope. The LGS system can work at temporal response rates as high as 333 Hz-limited by the UV laser pulse rate-and the NGS system can work at rates up to 1.4 kHz. Each side of the system has its own highspeed wavefront sensor that runs separately, but in the LGS mode the NGS wavefront sensor is converted into a natural star tip-tilt sensor. The deformable mirror is conjugate to the telescope's primary mirror and has one of the most densely packed sets of actuators of any adaptive optics system currently in operation. This paper provides details of the UnISIS design and describes key updates we have made to the system. We show NGS AO-corrected images from the sky from the 900 nm z-band through the 2.12 μm K s band. The highest NGS Strehl achieved to date is 0.67 at K s band.

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“…(This picture is a great simplification, as Airy rings are generally both suppressed and shifted in position by a coronagraph, but it provides a useful framework for gross estimation of Airy amplitudes.) Coronagraph contrast of 10 -7 at 4.5λ/D has been reported 16 , roughly equivalent to R=7800.…”

mentioning

confidence: 92%

Suppression of speckles at high adaptive correction using speckle symmetry

Bloemhof

2006

SPIE Proceedings

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Focal-plane speckles set important sensitivity limits on ground-or space-based imagers and coronagraphs that may be used to search for faint companions, perhaps ultimately including exoplanets, around stars. As speckles vary with atmospheric fluctuations or with drifting beamtrain aberrations, they contribute speckle noise proportional to their full amplitude. Schemes to suppress speckles are thus of great interest. At high adaptive correction, speckles organize into species, represented by algebraic terms in the expansion of the phase exponential, that have distinct spatial symmetry, even or odd, under spatial inversion. Filtering speckle patterns by symmetry may eliminate a disproportionate fraction of the speckle noise while blocking (only) half of the image signal from the off-axis companion being sought. The fraction of speckle power and hence of speckle noise in each term will vary with degree of correction, and so also will the net symmetry in the speckle pattern. Systematic numerical investigations are presented of the net symmetry of noise variance as a function of adaptive correction, i.e., Strehl ratio S, and deformable mirror actuator density D/a, where a is the deformable mirror actuator spacing referred to the pupil of diameter D, which controls the characteristic transverse spatial frequency of the wavefront. The degree of speckle symmetry is found to be substantial even at current relatively modest ground-based corrections (S=0.6, D/a=16 in the near-infrared). With parameters representative of "extreme" adaptive optics of the near future (S=0.99, D/a=100), the antisymmetric noise variance fraction is 0.99967 averaged over two Airy rings in the inner halo, so simple image processing (symmetry filtering) can improve the net speckle-noiselimited companion-detection SNR by a factor of about 28. Analogous processing can enhance SNR in coronagraphic searches, where speckle patterns before processing are predominantly symmetric.

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10^-7 contrast ratio at 4.5 lambda/D: New results obtained in laboratory experiments using nano-fabricated coronagraph and multi-Gaussian shaped pupil masks

Cited by 12 publications

References 14 publications

Removal of central obscuration and spider arm effects with beam-shaping coronagraphy

Removal of central obscuration and spider arm effects with beam-shaping coronagraphy

UnISIS: Laser Guide Star and Natural Guide Star Adaptive Optics System

Suppression of speckles at high adaptive correction using speckle symmetry

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