Subaru telescope is currently in the process of upgrading its laser guide star (LGS) system. The newest upgrade will have a TOPTICA SodiumStar laser source (operates at ~22W and 589nm) which is then sent to a laser launch telescope (LLT) just behind the secondary mirror of the telescope. In order to send the laser light to the LLT, a system of 6 mirrors has been designed to relay the laser light. Since the distances between these mirrors are quite large (the largest is ~9m), it was necessary to model the system in order to determine the correct placement and proper alignment procedure of each of these mirrors. For simplicity, the complete mirror relay system (including parts of the LLT up to the beam expander lens) has been modeled as an 8 mirror system in order to complete a tolerance analysis. The results of this analysis suggest that alignment of the system should be possible to do with a simple pinhole alignment procedure.
Currently, two AO systems are operated at Subaru Telescope: AO188, which is a facility AO system, and SCExAO, which is a PI-type ExAO system operated behind AO188. In the next 5 year, large-scale upgrades are performed on AO188 for improving the AO performance and operation of AO188 and SCExAO and for the technical demonstration toward the future wide-field ULTIMATE-Subaru GLAO system at Subaru and an ExAO system at TMT, PSI. We are planning to upgrade the real-time control system, the LGS system, and bimorph DM. Also, a new NIR WFS, a LTAO WFS unit, and a beam-switching system will be installed into the Nasmyth IR platform. The installation of the LTAO WFS unit is a part of the ULTIMATE-START project, which implement a LTAO mode into AO188 and demonstrates technologies for the ULTIMATE-Subaru GLAO system. ULTIMATE-Subaru project aims at developing a next-generation, wide-field GLAO system and wide-field NIR instruments for Subaru Telescope, whose first light will be in FY2025.
ULTIMATE-Subaru Tomography Adaptive optics Research experimenT (ULTIMATE-START) is a laser tomography AO project on the Subaru telescope. The project is planned to achieve high Strehl Ratio AO correction in NIR bands, and moderate AO correction in visible bands above 600nm. An asterism of 4 laser guide stars (LGSs) will be launched from the laser launching telescope behind the secondary mirror. The tomography wavefront sensing unit with four 32$times$32 Shack-Hartmann wavefront sensors will be installed behind the current facility LGS AO system, AO188. The deformable mirror of AO188 will be upgraded to a 64$times$64 element DM. The corrected light will be fed to the optical integral field spectrograph, 3DII, and NIR camera and spectrograph, IRCS, through a beam switching optics for IR-side Nasmyth focus instruments under development. The first light of the laser launching system and wavefront sensing unit is planned in 2021.
We present a multiconjugate adaptive optics (MCAO) system simulator bench, Herzberg NFIRAOS Optical Simulator (HeNOS). HeNOS is developed to validate the performance of the MCAO system for the Thirty Meter Telescope, as well as to demonstrate techniques critical for future AO developments. We focus on describing the derivations of parameters that scale the 30-m telescope AO system down to a bench experiment and explain how these parameters are practically implemented on an optical bench. While referring to other papers for details of AO technique developments using HeNOS, we introduce the functionality of HeNOS, in particular, three different single-conjugate AO modes that HeNOS currently offers: a laser guide star AO with a Shack–Hartmann wavefront sensor, a natural guide star AO with a pyramid wavefront sensor, and a laser guide star AO with a sodium spot elongation on the Shack–Hartmann corrected by a truth wavefront sensing on a natural guide star. Laser tomography AO and ultimate MCAO are being prepared to be implemented in the near future.
The AO188 Single Conjugate facility AO system at Subaru Telescope delivers diffraction-limited images in near-IR in natural and laser guide star modes. We have recently started a major upgrade of AO188 to fulfill the high performance requirements of its downstream instruments, including the Subaru Coronagraphic Extreme-AO. The first phase of this upgrade started in 2017 with the integration of a new real time computer (RTC) and real time system (RTS) CACAO(https://github.com/CACAO-org/CACAO), an open-source real-time software for adaptive optics developed collaboratively and used extensively by the SCExAO instrument. This major upgrade will enable loop optimization, predictive control and include diagnosis tools, therefore improving the performance and stability of AO188 and its downstream instrument module. This paper introduces the architecture of the new RTS describing the different steps we followed to adapt CACAO to our AO interfaces and aging hardware, in preparation of our first engineering tests on-sky achieved successfully on July 23rd 2018.
We report the current status of the laser guide star upgrade at Subaru Telescope with a new, more powerful TOPTICA/MPBC laser. While we recycle many of our existing components, such as laser launch telescope, we need to design a new mirror-based laser relay system to replace the current fiber-based relay to accommodate the high power beam. The laser unit has been delivered to Subaru office in March 2018 and installed in a testing lab in June 2018. We describe the preliminary design and its requirements and report future plans. This upgrade will not only improve our current adaptive optics system but also be the first step toward the future laser tomography and ground layer adaptive optics system at Subaru Telescope.
KEYWORDS: Adaptive optics, Wavefront sensors, Prisms, Stars, Wavefronts, Near infrared, Monte Carlo methods, Modulation, Electron multiplying charge coupled devices, Sensors
There are long existing limitations of the sky coverage of astronomical Adaptive Optics (AO) systems that use natural guide stars (NGSs) as reference sources. In this work, we present numerical simulations and lab test results of an optical NGS pyramid wavefront sensor (PWFS) for the MMT AO system. The potential increase of sky coverage benefits from the gain in sensitivity of the PWFS in a closed-loop NIR AO system compared with the optical Shack-Hartmann wavefront sensor (SHWFS). The upgraded MMT AO WFS system will use IR avalanche photodiode (APD) array with extremely low readout noise (at sub-electron level), run at a high frame rate (over 1kHz), and cover the wavelength range from 0.85-1.8 μm. This upgraded system will access a larger portion of the sky by looking at fainter, redder reference stars. We use ”yao” simulation to show the expected limiting magnitude gain of NIR PWFS compared with the existing optical SHWFS. The sky coverage will increase by 11 times at the Galactic plane and by 6 times at the North Galactic Pole when compared to traditional optical WFSs. This novel WFS will also enable observations of the dust obscured plane of the Galaxy, where the optical light of most stars is more extincted. We demonstrate the basic lab test with a set of double roof prisms. We evaluate the overall performance of the PWFS on our lab AO bench, present captured micro-pupil images and do wavefront reconstruction. We will upgrade to SAPHIRA and pyramid prism for later lab test. We plan to implement this system at MMT and carry out on-sky tests in Spring 2019.
This paper presents the overview of on-going and future adaptive optics (AO) activities at the Subaru telescope on the top of Maunakea in Hawaii. Currently, two AO systems are running at the Subaru telescope: AO188, a facility single-conjugate AO system with a bimorph deformable mirror and a curvature wavefront sensor with 188 elements, and SCExAO, an additional extreme AO system operating behind AO188 and specialized for exoplanet sciences. We recently started AO188 upgrade project to improve its performance for the next 5-10 years, which will also help improving SCExAO performance. These upgrades are in line with a development for the ULTIMATE-Subaru ground layer AO system.
We report the optical design of an infrared (0.85-1.8 μm) pyramid wavefront sensor (IRPWFS) that is designed for the 6.5m MMT on telescope adaptive optics system using the latest developments in low-noise infrared avalanche photodiode arrays. The comparison between the pyramid and the double-roof prism based wavefront sensors and the evaluation of their micro pupils’ quality are presented. According to our analysis, the use of two double-roof prisms with achromatic materials produces the competitive performance when compared to the traditional pyramid prism, which is difficult to manufacture. The final micro pupils on the image plane have the residual errors of pupil position, chromatism, and distortion within 1/10 pixel over the 2×2 arcsecond field of view, which meet the original design goals.
The laboratory test bench HeNOS is a scaled down version of TMTs first light MCAO instrument NFIRAOS, it is designed to mimic the behavior within the limits of a lab. Its purpose is the verification of the performance predicted through simulations and the demonstration of calibration procedures. The MCAO correction includes LGS effects like spot elongation, tip/tilt uncertainty and sodium layer variations. Tests contain turbulent layer identification with SLODAR, tomographic NCPA correction, matched filter updates, a Pyramid Truth WFS and PSF reconstruction. We discuss the recent advances on the tests and the impact of the results on the control of NFIRAOS.
For today and future adaptive optics observations, sodium laser guide stars (LGSs) are crucial; however, the LGS elongation problem due to the sodium layer has to be compensated, in particular for extremely large telescopes. In this paper, we describe the concept of truth wavefront sensing as a solution and present its design using a pyramid wavefront sensor (PWFS) to improve NFIRAOS (Narrow Field InfraRed Adaptive Optics System), the first light adaptive optics system for Thirty Meter Telescope. We simulate and test the truth wavefront sensor function under a controlled environment using the HeNOS (Herzberg NFIRAOS Optical Simulator) bench, a scaled-down NFIRAOS bench at NRC-Herzberg. We also touch on alternative pyramid component options because despite recent high demands for PWFSs, we suffer from the lack of pyramid supplies due to engineering difficulties.
Maximizing the grating efficiency is a key goal for the first light instrument IRIS (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 6000l/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 IRIS as a potential
dispersing element in the spectrograph. Our team has procured near-infrared gratings from two separate vendors. We
have two gratings with the specifications needed for IRIS current design: 1.51-1.82μm (H-band) to produce a spectral
resolution of 4000 and 1.19-1.37μm (J-band) to produce a spectral resolution of 8000. The center wavelengths for each
grating are 1.629μm and 1.27μm, and the groove densities are 177l/mm and 440l/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 two
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 when 5° deviation from the Bragg angle.
We present the efficiency of near-infrared reflective ruled diffraction gratings designed for the InfraRed Imaging
Spectrograph (IRIS). IRIS is a first light, integral field spectrograph and imager for the Thirty Meter Telescope
(TMT) and narrow field infrared adaptive optics system (NFIRAOS). IRIS will operate across the near-infrared
encompassing the ZYJHK bands (~0.84 - 2.4μm) with multiple spectral resolutions. We present our experimental
setup and analysis of the efficiency of selected reflective diffraction gratings. These measurements are used as a
comparison sample against selected candidate Volume Phase Holographic (VPH) gratings (see Chen et al., this
conference). We investigate the efficiencies of five ruled gratings designed for IRIS from two separate vendors.
Three of the gratings accept a bandpass of 1.19-1.37μm (J band) with ideal spectral resolutions of R=4000 and
R=8000, groove densities of 249 and 516 lines/mm, and blaze angles of 9.86° and 20.54° respectively. The other
two gratings accept a bandpass of 1.51-1.82μm (H Band) with an ideal spectral resolution of R=4000, groove
density of 141 lines/mm, and blaze angle of 9.86°. The fraction of flux in each diffraction mode was compared to
both a pure reflection mirror as well as the sum of the flux measured in all observable modes. We measure the
efficiencies off blaze angle for all gratings and the efficiencies between the polarization transverse magnetic (TM)
and transverse electric (TE) states. The peak reflective efficiencies are 98.90 ± 3.36% (TM) and 84.99 ± 2.74%
(TM) for the H-band R=4000 and J-band R=4000 respectively. The peak reflective efficiency for the J-band R=8000
grating is 78.78 ± 2.54% (TE). We find that these ruled gratings do not exhibit a wide dependency on incident angle
within ±3°. Our best-manufactured gratings were found to exhibit a dependency on the polarization state of the
incident beam with a ~10-20% deviation, consistent with the theoretical efficiency predictions. This work will
significantly contribute to the selection of the final grating type and vendor for the IRIS optical system, and are also
pertinent to current and future near-infrared astronomical spectrographs.
We present the development of a portable SLODAR (SLOpe Detection and Ranging) instrument to measure the vertical atmosphere profile using several different telescopes (14”, 16”, and 20” aperture) and at varying worldwide sites. In particular, the portability and feasibility of this instrument motivated us to operate it at Ellesmere Island in the Canadian High Arctic. We discuss the SLODAR technique, the design of the instrument, and the results of the performance tests in the lab. The results of the Arctic site testing measurements in October and November 2012 are discussed by Maire et. al. (this conference).1
The Earth's polar regions offer unique advantages for ground-based astronomical observations with its cold and dry climate, long periods of darkness, and the potential for exquisite image quality. We present preliminary results from a site-testing campaign during nighttime from October to November 2012 at the Polar Environment Atmospheric Research Laboratory (PEARL), on a 610-m high ridge near the Eureka weatherstation on Ellesmere Island, Canada. A Shack-Hartmann wavefront sensor was employed, using the Slope Detection and Ranging (SloDAR) method. This instrument (Mieda et al, this conference) was designed to measure the altitude, strength and variability of atmospheric turbulence, in particular for operation under Arctic conditions. First SloDAR optical turbulence profiles above PEARL show roughly half of the optical turbulence confined to the boundary layer, below about 1 km, with the majority of the remainder in one or two thin layers between 2 km and 5 km, or above. The median seeing during this campaign was measured to be 0.65 arcsec.
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