Jenny Atwood

Progress toward developing the TMT adaptive optical systems and their components

Atmospheric turbulence compensation via adaptive optics (AO) will be essential for achieving most objectives of the TMT science case. The performance requirements for the initial implementation of the observatorys facility AO system include diffraction-limited performance in the near IR with 50 per cent sky coverage at the galactic pole. This capability will be achieved via an order 60x60 multi-conjugate AO system (NFIRAOS) with two deformable mirrors optically conjugate to ranges of 0 and 12 km, six high-order wavefront sensors observing laser guide stars in the mesospheric sodium layer, and up to three low-order, IR, natural guide star wavefront sensors located within each client instrument. The associated laser guide star facility (LGSF) will consist of 3 50W class, solid state, sum frequency lasers, conventional beam transport optics, and a launch telescope located behind the TMT secondary mirror. In this paper, we report on the progress made in designing, modeling, and validating these systems and their components over the last two years. This includes work on the overall layout and detailed opto-mechanical designs of NFIRAOS and the LGSF; reliable wavefront sensing methods for use with elongated and time-varying sodium laser guide stars; developing and validating a robust tip/tilt control architecture and its components; computationally efficient algorithms for very high order wavefront control; detailed AO system modeling and performance optimization incorporating all of these effects; and a range of supporting lab/field tests and component prototyping activities at TMT partners. Further details may be found in the additional papers on each of the above topics.

The Gemini planet imager: first light and commissioning

The Gemini Planet Imager (GPI) is a facility extreme-AO high-contrast instrument – optimized solely for study of faint companions – on the Gemini telescope. It combines a high-order MEMS AO system (1493 active actuators), an apodized pupil Lyot coronagraph, a high-accuracy IR post-coronagraph wavefront sensor, and a near-infrared integral field spectrograph. GPI incorporates several other novel features such as ultra-high quality optics, a spatially-filtered wavefront sensor, and new calibration techniques. GPI had first light in November 2013. This paper presnets results of first-light and performance verification and optimization and shows early science results including extrasolar planet spectra and polarimetric detection of the HR4696A disk. GPI is now achieving contrasts approaching 10-6 at 0.5” in 30 minute exposures.

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

The first light instrument on the Thirty Meter Telescope (TMT) project will be the InfraRed Imaging Spectrograph (IRIS). IRIS will be mounted on a bottom port of the facility AO instrument NFIRAOS. IRIS will report guiding information to the NFIRAOS through the On-Instrument Wavefront Sensor (OIWFS) that is part of IRIS. This will be in a self-contained compartment of IRIS and will provide three deployable wavefront sensor probe arms. This entire unit will 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.

NFIRAOS: The optical design of an adaptive optics system for the Thirty Meter Telescope

NFIRAOS (Narrow Field InfraRed Adaptive Optics System, pronounced nefarious) is the first light adaptive optics system for the Thirty Meter Telescope (TMT). It is a near-IR, diffraction limited, multi-conjugate adaptive optics (MCAO) system that uses two deformable mirrors to correct aberrations due to atmospheric turbulence. The two arcminute field of view f/15 beam delivered by the telescope is relayed to one of three client instrument ports. Wavefront sensing is accomplished with six high order sodium laser guide star (LGS) wavefront sensors (WFSs) and three visible natural guide star (NGS) wavefront sensors. In this paper, we describe the general layout and design drivers of each optical system in NFIRAOS. The primary subsystems are the science path optics, the LGS wavefront sensors, the visible NGS truth WFSs, the IR acquisition camera and the calibration unit. Particular attention is given to the design of the LGS system, which uses all spherical components and a zoom system to compensate for aberrations and changes in distance to the sodium layer.

Present optical and mechanical design status of NFIRAOS for TMT

This paper describes the current optical and mechanical designs of NFIRAOS (Narrow Field InfraRed Adaptive Optics System, pronounced nefarious). The main subsystems are the science path optics, the laser guide star (LGS) wavefront sensors (WFSs), the visible natural guide star (NGS) truth WFSs, the IR acquisition camera, and a source and calibration unit. The science optics deliver a diffraction limited f/15 beam with a two arcminute field of view (FOV) to one of three instruments mounted to NFIRAOS. The LGS system relies on an asterism of five laser guide stars oriented in a 35 arcsecond radius pentagon with a sixth guide star at the center. The LGS optics are comprised of six separate optical trains that feed individual WFSs. Each optical train includes three zoom mechanisms catering to sodium layer height variations of 85-235 km. The visible WFS system includes an atmospheric dispersion corrector (ADC); the NGS WFS, used only for NGS mode; the moderate order radial (MOR) truth WFS, used for fast tracking of radially symmetric aberrations while in LGS mode; and the high-order low-bandwidth (HOL) truth WFS, used for sensing high-order LGS WFS offsets. The majority of NFIRAOS is cooled to -30 C to reduce background emissivity. Within the thermal enclosure are standard optical benches which are semi-kinematically mounted to a sub-structure, which is in turn connected via bipod flexures to the external NFIFAOS structure. This protects the optics benches from thermal distortion while maintaining alignment to instruments and TMT.

Design of a laser guide star wavefront sensor system for NFIRAOS

The application of phase diversity is first invested in simulation to characterize ideal parameters to GPI with faithfully simulated calibration source data. The best working simulation parameters are applied to real GPI data and shown to recover an injected astigmatism. The estimated GPI NCPA are then corrected and the Strehl ratio is improve by ⇠ 5%, although the application is rudimentary and a more thorough correction will be applied in the near future.

NFIRAOS adaptive optics for the Thirty Meter Telescope

NFIRAOS (Narrow-Field InfraRed Adaptive Optics System) will be the first-light multi-conjugate adaptive optics system for the Thirty Meter Telescope (TMT). NFIRAOS houses all of its opto-mechanical sub-systems within an optics enclosure cooled to precisely -30°C in order to improve sensitivity in the near-infrared. It supports up to three client science instruments, including the first-light InfraRed Imaging Spectrograph (IRIS). Powering NFIRAOS is a Real Time Controller that will process the signals from six laser wavefront sensors, one natural guide star pyramid WFS, up to three low-order on-instrument WFS and up to four guide windows on the client instrument’s science detector in order to correct for atmospheric turbulence, windshake, optical errors and plate-scale distortion. NFIRAOS is currently preparing for its final design review in late June 2018 at NRC Herzberg in Victoria, British Columbia in partnership with Canadian industry and TMT.

Acquisition and Dithering with the TMT IRIS On-Instrument Wavefront Sensor System

IRIS is a first-light facility instrument for the TMT that operates as a client of the NFIRAOS MCAO system. IRIS is a collaboration between TMT, Caltech, the University of California, NAOJ and NRC Herzberg. IRIS contains three OnInstrument WaveFront Sensors (OIWFS) probes which together with On-Detector Guide Windows (ODGW) on the IRIS imager, pick off light from natural guide stars over a two arcminute diameter field of regard. Here, we present typical use cases for the OIWFS and ODGW including acquisition, dithering, and tracking non-sidereal targets while highlighting design choices that allow these operations to be performed in the minimal amount of time while achieving the required performance. We conclude with some potential changes that will be explored early in the final design phase.

Design and analysis of the NFIRAOS thermal optics enclosure

The Narrow Field InfraRed Adaptive Optics System (NFIRAOS) will be the first-light facility adaptive optics system for the Thirty Meter Telescope (TMT). In order to meet the optical performance and stability specifications essential to leveraging the extraordinary capabilities of the TMT, all of the optical components within NFIRAOS will be protected within a large thermally-controlled optics enclosure (ENCL). Among the many functions performed by the ENCL, the most critical functions include providing a highly stable, light-tight, cold, dry environment maintained at 243±0.5 K for the NFIRAOS opto-mechanical sub-systems and supporting TABL structure. Although the performance of the ENCL during the science operation of NFIRAOS is critical, the maximum thermal loading will be defined by the cooldown/ warm-up cycle which must be accomplished within a time-frame that will minimize the on-sky operational impact due to daytime maintenance work. This study describes the thermal/mechanical design development and supporting analyses (analytical and finite element analyses (FEA)) completed during the preliminary design phase and through the current progression of the ENCL final design phase. The walls of the ENCL consist of interlocking, multilayered, thermally insulated panels, which are supported by an externally located structural framework which attaches to the NFIRAOS Instrument Support Structure. The regulation of the interior ENCL wall surface temperature to within ±0.5 K requires that the heat flux into the interior of NFIRAOS be eliminated by cooling a thermal conduction plate embedded between multiple layers of insulation. The thermal design of the enclosure was evaluated for both steady-state (SS) performance and transient performance (cool-down and warm-up cycles). The transient analysis utilizes a hybrid of a one-dimensional thermal network approach combined with three-dimensional conjugate heat transfer analyses of explicit opto-mechanical components within the ENCL. Many design-parameter combinations were evaluated to determine the performance impact of cooling power and transient temperature profiles. The results derived from the analyses of these design iterations indicate the multi-layer enclosure wall design will meet all thermal requirements. During SS operation, the interior temperature variation is within ±0.5 K of the target operational temperature, while the heat influx from the exterior TMT environment is 1528 W (extracted by the embedded cold plate). The transient cool-down cycle will take approximately 15 hours to complete and requires the in-situ air handling units to deliver 14KW of cooling power (derated for the TMT site conditions) throughout the interior space of the NFIRAOS ENCL.

NFIRAOS —TMT Early Light Adaptive Optics System

NFIRAOS is the early-light facility Adaptive Optics System for the Thirty Meter Telescope. We present the specifications, novel architecture and design of NFIRAOS