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

Phillips, Andrew C.; Bauman, Brian; Larkin, James E.; Moore, Anna; Niehaus, Cynthia N.; Crampton, D.; Simard, Luc

doi:10.1117/12.856475

Cited by 14 publications

(14 citation statements)

References 9 publications

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“…There is one ADC located in each probe arm of the OIWFS, plus two more in IRIS. Drew Phillips has investigated many glass combinations for ADCs in IRIS [3]. One of the best combinations for the IRIS imager is Ohara's S-NPH2 and Spinel, therefore a study was initiated to see if it was a viable material to be used for all ADC's in IRIS.…”

Section: Spinel Adc Glass Studymentioning

confidence: 99%

On-instrument wavefront sensor design for the TMT infrared imaging spectrograph (IRIS) update

et al. 2014

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The first light instrument on the Thirty Meter Telescope (TMT) project will be the InfraRed Imaging Spectrograph (lRIS). lRlS will be mounted on a bottom port of the faci lity AO instrument NFIRAOS. IRIS will report guiding information to the NFlRAOS through the On-lnstrument Wavefront Sensor (OlWFS) that is part of IR1 S. This will be in a self-contained compartment of JRJS and will provide three deployable wavefront sensor probe arms. This entire unit wi ll be rotated to provide field de-rotation. Currently in our preliminary design stage our efforts have included: prototyping of the probe arm to determine the accuracy of this critical component, handling cart design and reviewing different types of glass for the atmospheric dispersion.

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Section: Spinel Adc Glass Studymentioning

confidence: 99%

On-instrument wavefront sensor design for the TMT infrared imaging spectrograph (IRIS) update

et al. 2014

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“…(ADCs) are necessary. 5,6 However, even with an ADC there remain residual errors because 1. even the perfectly built ADC has a wavelength-dependent residual and 2. our knowledge of the atmospheric profiles is incomplete and has uncertainties. Our simulations have shown that the residual dispersion can be on the order of ±15 µas for large zenith angles.…”

Section: Atmosphere [µAs]mentioning

confidence: 99%

Thirty Meter Telescope astrometry error budget

Schoeck

Ellerbroek

et al. 2014

SPIE Proceedings

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The Thirty Meter Telescope (TMT) with its first-light multi-conjugate adaptive optics system, NFIRAOS, and high-resolution imager, IRIS, is expected to take differential astrometric measurements with an accuracy on the order of tens of micro arcsec. This requires the control, correction, characterization and calibration of a large number of error sources and uncertainties, many of which have magnitudes much in excess of this level of accuracy. In addition to designing the observatory such that very high precision and accuracy astrometric observations are enabled, satisfying the TMT requirements can only be achieved by a careful calibration, observation and data reduction strategy. In this paper, we present descriptions of the individual errors sources, how and when they apply to different astrometry science cases and the mitigation methods required for each of them, as well as example results for individual error terms and the overall error budgets for a variety of different science cases.

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“…The peak efficiency for a given order is defined as the measured flux of a monochromatic light source diffracted into that order relative to the total incidence flux. The typical efficiency measurement procedure is as follows: (1) Set up the VPH grating perpendicular to the incidence light beam; (2) rotate the VPH grating to the specific incidence angle; (3) adjust the camera position and angle to measure the diffracted order; (4) change the gain of the attenuator to get a reasonable incidence intensity; (5) take 100 frames of the flux with the best exposure time; (6) block the laser, and take the background of the setup with the same exposure time; (7) repeat the above steps for each order; (8) remove the VPH grating, and measure the pure incidence flux of the laser; and (9) using the flux of the specific diffracted order to divide the total incidence flux of the laser, the efficiency will be calculated. It is important to note that we observed reflected light off the incoming light surface of the VPH grating, which would decrease the total efficiency.…”

Section: Adjustment Process For Measurementmentioning

confidence: 99%

The infrared imaging spectrograph (IRIS) for TMT: volume phase holographic grating performance testing and discussion

et al. 2014

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Maximizing the grating efficiency is a key goal for the first light instrument IR.IS (Infrared Imaging Spectrograph) currently being designed to sample the diffraction limit of the TMT (Thirty Meter Telescope). Volume Phase Holographic (VPH) gratings have been shown to offer extremely high efficiencies that approach 100% for high line frequencies (i.e., 600 to 60001/mm), which has been applicable for astronomical optical spectrographs. However, VPH gratings have been less exploited in the near-infrared, particularly for gratings that have lower line frequencies. Given their potential to offer high throughputs and low scattered light, VPH gratings are being explored for IR.IS as a potential dispersing element in the spectrograph. Our team has procured near-infrared gratings from t\¥0 separate vendors. We have t\¥0 gratings with the specifications needed for IR.IS current design: l.5 l-l.82µm (H-band) to produce a spectral resolution of 4000 and 1.19-1.3 7µm (J-band) to produce a spectral resolution of 8000. ' The center wavelengths for each grating are l.629µm and l.27µm, and the groove densities are 1771/mm and 4401/mm for H-band R=4000 and J-band R=8000, respectively. We directly measure the efficiencies in the lab and find that the peak efficiencies of these t\¥0 types of gratings are quite good with a peak efficiency of ~88% at the Bragg angle in both TM and TE modes at H-band, and 90.23% in TM mode, 79.91 % in TE mode at J-band for the best vendor. We determine the drop in efficiency off the Bragg angle, with a 20-23% decrease in efficiency at H-band when 2.5° deviation from the Bragg angle, and 25%-28% decrease at J-band \Vhen 5° dev iation from the Bragg angle.

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

Cited by 14 publications

References 9 publications

On-instrument wavefront sensor design for the TMT infrared imaging spectrograph (IRIS) update

On-instrument wavefront sensor design for the TMT infrared imaging spectrograph (IRIS) update

Thirty Meter Telescope astrometry error budget

The infrared imaging spectrograph (IRIS) for TMT: volume phase holographic grating performance testing and discussion

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