Showing papers by "Brian J. Bauman published in 2010"

The Infrared Imaging Spectrograph (IRIS) for TMT: Instrument Overview

Abstract: IRIS is a near-infrared (0.84 to 2.4 micron) integral field spectrograph and wide-field imager being developed for first light with the Thirty Meter Telescope (TMT). It mounts to the advanced adaptive optics (AO) system NFIRAOS and has integrated on-instrument wavefront sensors (OIWFS) to achieve diffraction-limited spatial resolution at wavelengths longer than 1 μm. With moderate spectral resolution (R ~ 4000 – 8,000) and large bandpass over a continuous field of view, IRIS will open new opportunities in virtually every area of astrophysical science. It will be able to resolve surface features tens of kilometers across Titan, while also mapping the most distant galaxies at the scale of an individual star forming region. This paper summarizes the entire design and capabilities, and includes the results from the nearly completed preliminary design phase.

Gemini Planet Imager coronagraph testbed results

Abstract: The Gemini Planet Imager (GPI) is an extreme AO coronagraphic integral field unit YJHK spectrograph destined for first light on the 8m Gemini South telescope in 2011. GPI fields a 1500 channel AO system feeding an apodized pupil Lyot coronagraph, and a nIR non-common-path slow wavefront sensor. It targets detection and characterizion of relatively young (<2GYr), self luminous planets up to 10 million times as faint as their primary star. We present the coronagraph subsystem's in-lab performance, and describe the studies required to specify and fabricate the coronagraph. Coronagraphic pupil apodization is implemented with metallic half-tone screens on glass, and the focal plane occulters are deep reactive ion etched holes in optically polished silicon mirrors. Our JH testbed achieves H-band contrast below a million at separations above 5 resolution elements, without using an AO system. We present an overview of the coronagraphic masks and our testbed coronagraphic data. We also demonstrate the performance of an astrometric and photometric grid that enables coronagraphic astrometry relative to the primary star in every exposure, a proven technique that has yielded on-sky precision of the order of a milliarsecond.

The Infrared Imaging Spectrograph (IRIS) for TMT: the atmospheric dispersion corrector

Abstract: We present a conceptual design for the atmospheric dispersion corrector (ADC) for TMT's Infrared Imaging Spectrograph (IRIS). The severe requirements of this ADC are reviewed, as are limitations to observing caused by uncorrectable atmospheric effects. The requirement of residual dispersion less than 1 milliarcsecond can be met with certain glass combinations. The design decisions are discussed and the performance of the design ADC is described. Alternative options and their performance tradeoffs are also presented.

The infrared imaging spectrograph (IRIS) for TMT: spectrograph design

Abstract: The Infra-Red Imaging Spectrograph (IRIS) is one of the three first light instruments for the Thirty Meter Telescope (TMT) and is the only one to directly sample the diffraction limit. The instrument consists of a parallel imager and offaxis Integral Field Spectrograph (IFS) for optimum use of the near infrared (0.84um-2.4um) Adaptive Optics corrected focal surface. We present an overview of the IRIS spectrograph that is designed to probe a range of scientific targets from the dynamics and morphology of high-z galaxies to studying the atmospheres and surfaces of solar system objects, the latter requiring a narrow field and high Strehl performance. The IRIS spectrograph is a hybrid system consisting of two state of the art IFS technologies providing four plate scales (4mas, 9mas, 25mas, 50mas spaxel sizes). We present the design of the unique hybrid system that combines the power of a lenslet spectrograph and image slicer spectrograph in a configuration where major hardware is shared. The result is a powerful yet economical solution to what would otherwise require two separate 30m-class instruments.

The infrared imaging spectrograph (IRIS) for TMT: spectrograph design

Abstract: The Infra-Red Imaging Spectrograph (IRIS) is one of the three first light instruments for the Thirty Meter Telescope (TMT) and is the only one to directly sample the diffraction limit. The instrument consists of a parallel imager and off-axis Integral Field Spectrograph (IFS) for optimum use of the near infrared (0.84um-2.4um) Adaptive Optics corrected focal surface. We present an overview of the IRIS spectrograph that is designed to probe a range of scientific targets from the dynamics and morphology of high-z galaxies to studying the atmospheres and surfaces of solar system objects, the latter requiring a narrow field and high Strehl performance. The IRIS spectrograph is a hybrid system consisting of two state of the art IFS technologies providing four plate scales (4mas, 9mas, 25mas, 50mas spaxel sizes). We present the design of the unique hybrid system that combines the power of a lenslet spectrograph and image slicer spectrograph in a configuration where major hardware is shared. The result is a powerful yet economical solution to what would otherwise require two separate 30m-class instruments.

Gaussian quadrature for optical design with non-circular pupils and fields, and broad wavelength ranges

Abstract: Forbes introduced the usage of Gaussian quadratures in optical design for circular pupils and fields, and for a specific visible wavelength band. In this paper, Gaussian quadrature methods of selecting rays in ray-tracing are derived for noncircular pupil shapes, such as obscured and vignetted apertures. In addition, these methods are generalized for square fields, and for integrating performance over arbitrary wavelength bands. Integration over wavelength is aided by the use of a novel chromatic coordinate. These quadratures achieve low calculations with fewer rays (by orders of magnitude) than uniform sampling schemes.

The Infrared Imaging Spectrograph (IRIS) for TMT: the atmospheric dispersion corrector

Abstract: We present a conceptual design for the atmospheric dispersion corrector (ADC) for TMT's Infrared Imaging Spectrograph (IRIS). The severe requirements of this ADC are reviewed, as are limitations to observing caused by uncorrectable atmospheric effects. The requirement of residual dispersion less than 1 milliarcsecond can be met with certain glass combinations. The design decisions are discussed and the performance of the design ADC is described. Alternative options and their performance tradeoffs are also presented.

Integrated Laboratory Demonstrations of Multi-Object Adaptive Optics on a Simulated 10 Meter Telescope at Visible Wavelengths

Abstract: One important frontier for astronomical adaptive optics (AO) involves methods such as multi-object AO and multi-conjugate AO that have the potential to give a significantly larger field of view than conventional AO techniques. A second key emphasis over the next decade will be to push astronomical AO to visible wavelengths. We have conducted the first laboratory simulations of wide-field, laser guide star AO at visible wavelengths on a 10 m class telescope. These experiments, utilizing the UCO/Lick Observatory's multi-object/laser tomographic adaptive optics (MOAO/LTAO) test bed, demonstrate new techniques in wave front sensing and control that are crucial to future on-sky MOAO systems. We (1) test and confirm the feasibility of highly accurate atmospheric tomography with laser guide stars, (2) demonstrate key innovations allowing open-loop operation of Shack-Hartmann wave front sensors (with errors of ~30 nm) as will be needed for MOAO, and (3) build a complete error budget model describing system performance. The AO system maintains a performance of 32.4% Strehl ratio on-axis, with 24.5% and 22.6% at 10'' and 15'', respectively, at a science wavelength of 710 nm (R-band) over the equivalent of 0.8 s of simulation. The mean ensquared energy on-axis in a 50 mas spaxel is 46%. The off-axis Strehl ratios are obtained at radial separations 2-3 times the isoplanatic angle of the atmosphere at 710 nm. The MOAO-corrected field of view is ~25 times larger in area than that limited by anisoplanatism at R-band. The error budget we assemble is composed almost entirely of terms verified through independent, empirical experiments, with minimal parameterization of theoretical models. We find that error terms arising from calibration inaccuracies and optical drift are comparable in magnitude to traditional terms like fitting error and tomographic error. This makes a strong case for implementing additional calibration facilities in future AO systems, including accelerometers on powered optics, three-dimensional turbulators, telescopes, and laser guide star simulators, and external calibration ports for deformable mirrors. These laboratory demonstrations add strong credibility to the implementation of on-sky demonstrators of laser tomographic adaptive optics (LTAO) on 5-10 m telescopes in the coming years.

Update and image quality error budget for the LSST camera optical design

Abstract: The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, modified Paul-Baker design, with an 8.4-meter primary mirror, a 3.4-m secondary, and a 5.0-m tertiary feeding a refractive camera design with 3 lenses (0.69-1.55m) and a set of broadband filters/corrector lenses. Performance is excellent over a 9.6 square degree field and ultraviolet to near infrared wavelengths. We describe the image quality error budget analysis methodology which includes effects from optical and optomechanical considerations such as index inhomogeneity, fabrication and null-testing error, temperature gradients, gravity, pressure, stress, birefringence, and vibration.

Gaussian Quadrature Ray Selection on The Non-Circular Pupil

Abstract: Gaussian Quadrature methods of selecting rays in ray-tracing are derived for non-circular pupil shapes, such as obscured and vignetted apertures, and are generalized for use in arbitrary wavelength bands. These design conditions perform as efficiently as the circular pupil case.