The Low Order Wavefront Sensor (LOWFS) is a key component of the Active Optics System of the Daniel K Inouye Solar Telescope. It is designed to measure low order wavefront aberrations in the optical beam arising from gravitational and thermal flexure in the telescope as it moves through the sky during solar observations. These quasi-static aberrations are detrimental to the telescope image quality during seeing-limited observations. The LOWFS measures these quasistatic perturbations by averaging over the atmospheric turbulence. It sends its measurements to the Active Optics System, which computes a solution using the primary (M1) and secondary (M2) mirrors, and sends offsets to the M1 and M2 mirror control systems. The LOWFS is implemented using a 1k x 1k pixel Shack-Hartmann wavefront sensor coupled with a real-time cross correlating image processing engine running at 30 Hz. The real-time engine is implemented in C++ using the Armadillo linear algebra library, enabling equation-style programming with arrays and vectors, achieving essentially the same speed as hand coded loops over the same data structures. The cross correlation is implemented in the frequency domain leveraging the speed of the FFTW Fast Fourier Transform library. The entire realtime engine is embedded inside a DKIST Common Services Framework Controller, allowing for simple command and control of the wavefront sensor computations using the high-level Wavefront Correction Control System software. A Python-based script engine is used to implement various calibration tasks, allowing full access to the SciPy software stack for non-real-time scientific computations. This paper describes the design and implementation of the LOWFS and presents initial results from testing in the DKIST Wavefront Correction System Laboratory.
The Wavefront Correction (WFC) system for the Daniel K. Inouye Solar Telescope (DKIST) is in its final stages of laboratory integration. All optical, mechanical, and software components have been unit tested and installed and aligned in our laboratory testbed in Boulder, CO. We will verify all aspects of WFC system performance in the laboratory before disassembling and shipping it to Maui for final integration with the DKIST in early 2019. The DKIST Adaptive Optics (AO) system contains a 1600-actuator deformable mirror, a correlating Shack- Hartmann wavefront sensor, a fast tip-tilt mirror, and an FPGA-based control system. Running at a nominal rate of 1975 Hz, the AO system will deliver diffraction-limited images to five of the DKIST science instruments simultaneously. The DKIST AO system is designed to achieve the diffraction limit (on-axis Strehl > 0.3) at wavelengths up to 500 nm in median daytime seeing (r<sub>0</sub> = 7 cm). In addition to AO for diffraction-limited observing, the DKIST WFC system has a low-order wavefront sensor for sensing quasi-static wavefront errors, a context viewer for telescope pointing and image quality assessment, and an active optics engine. The active optics engine uses inputs from the low-order wavefront sensor and the AO system to actively correct for telescope misalignment. All routine alignment and calibration procedures are automated via motorized stages that can be controlled from Python scripts. We present the current state of the WFC system as we prepare for final integration with the DKIST, including verification test design, system performance metrics, and laboratory test data.
When the Daniel K. Inouye Solar Telescope (DKIST) achieves first light in 2019, it will deliver the highest spatial resolution images of the solar atmosphere ever recorded. Additionally, the DKIST will observe the Sun with unprecedented polarimetric sensitivity and spectral resolution, spurring a leap forward in our understanding of the physical processes occurring on the Sun. <p> </p>The DKIST wavefront correction system will provide active alignment control and jitter compensation for all six of the DKIST science instruments. Five of the instruments will also be fed by a conventional adaptive optics (AO) system, which corrects for high frequency jitter and atmospheric wavefront disturbances. The AO system is built around an extended-source correlating Shack-Hartmann wavefront sensor, a Physik Instrumente fast tip-tilt mirror (FTTM) and a Xinetics 1600-actuator deformable mirror (DM), which are controlled by an FPGA-based real-time system running at 1975 Hz. It is designed to achieve on-axis Strehl of 0.3 at 500 nm in median seeing (r<sub>0</sub> = 7 cm) and Strehl of 0.6 at 630 nm in excellent seeing (r<sub>0</sub> = 20 cm). <p> </p>The DKIST wavefront correction team has completed the design phase and is well into the fabrication phase. The FTTM and DM have both been delivered to the DKIST laboratory in Boulder, CO. The real-time controller has been completed and is able to read out the camera and deliver commands to the DM with a total latency of approximately 750 μs. All optics and optomechanics, including many high-precision custom optics, mounts, and stages, are completed or nearing the end of the fabrication process and will soon undergo rigorous acceptance testing. <p> </p>Before installing the wavefront correction system at the telescope, it will be assembled as a testbed in the laboratory. In the lab, performance tests beginning with component-level testing and continuing to full system testing will ensure that the wavefront correction system meets all performance requirements. Further work in the lab will focus on fine-tuning our alignment and calibration procedures so that installation and alignment on the summit will proceed as efficiently as possible.
The DKIST wavefront correction system will be an integral part of the telescope, providing active alignment control, wavefront correction, and jitter compensation to all DKIST instruments. The wavefront correction system will operate in four observing modes, diffraction-limited, seeing-limited on-disk, seeing-limited coronal, and limb occulting with image stabilization. Wavefront correction for DKIST includes two major components: active optics to correct low-order wavefront and alignment errors, and adaptive optics to correct wavefront errors and high-frequency jitter caused by atmospheric turbulence. The adaptive optics system is built around a fast tip-tilt mirror and a 1600 actuator deformable mirror, both of which are controlled by an FPGA-based real-time system running at 2 kHz. It is designed to achieve on-axis Strehl of 0.3 at 500 nm in median seeing (r<sub>0</sub> = 7 cm) and Strehl of 0.6 at 630 nm in excellent seeing (r<sub>0</sub> = 20 cm). We present the current status of the DKIST high-order adaptive optics, focusing on system design, hardware procurements, and error budget management.
In this paper we present Big Bear Solar Observatory’s (BBSO) newest adaptive optics system – AO-308. AO-308 is a result of collaboration between BBSO and National Solar Observatory (NSO). AO-308 uses a 357 actuators deformable mirror (DM) from Xinetics and its wave front sensor (WFS) has 308 sub-apertures. The WFS uses a Phantom V7.3 camera which runs at 2000 Hz with the region of interest of 416×400 pixels. AO-308 utilizes digital signal processors (DSPs) for image processing. AO-308 has been successfully used during the 2013 observing season. The system can correct up to 310 modes providing diffraction limited images at all wavelengths of interest.
The ATST Wavefront Correction Control System (WCCS) is the high-level control software for the Wavefront
Correction (WFC) system to be employed in the new Advanced Technology Solar Telescope. The WFC is comprised of
a set of subsystems: the high-order adaptive optics system for correction of wavefront aberrations, an active optics
system that calculates corrections for low-order distortions caused by optical misalignments, a context viewing camera to
provide quick-look quality analysis data, and a limb guider for positioning an occulting mask on the solar disk. The
operation and configuration of the WFC is determined by the operational modes set by the operator. The Telescope
Control System (TCS) sends these operational modes to the WCCS, which is the interface between the telescope and the
The WCCS adopts a modular approach to the organization of the software. At the top-level there is a high-level
management controller which is the interface to the TCS. This management controller is responsible for the validation
of commands received from the TCS and for the coordination and synchronization of the operation of the WFC
subsystems. Separate subsystem controllers manage the functional behavior of each WFC subsystem. In this way the
WCCS provides a consistent interface to the TCS for each subsystem while synchronizing and coordinating the
components of the Wavefront Correction system.
When completed, the Advanced Technology Solar Telescope (ATST) will be the largest and most technologically advanced solar telescope in the world. As such, it faces many challenges that have not previously been solved. One of these challenges is the high-order wavefront sensor (HOWFS) for the ATST adaptive optics system. The HOWFS requires a 960 x 960 detector array that must run at a 2 kHz frame rate in order for the adaptive optics to achieve its required bandwidth. This detector must be able to accurately image low-contrast solar granulation in order to provide usable wavefront information. We have identified the Vision Research DS-440 as an off-the-shelf solution for the HOWFS detector and demonstrate tests proving that the camera will be able to lock the adaptive optics loop on solar granulation in commonly-experienced daytime seeing conditions. Tests presented quantify the noise, linearity, gain, stability, and well depth of the camera. Laboratory tests with artificial targets demonstrate its ability to accurately track low-contrast objects and on-sky demonstrations showcase the camera's performance in realistic observing conditions.
The four meter Advanced Technology Solar Telescope (ATST) adaptive optics (AO) system will require at least twenty-four
times the real time processing power as the Dunn Solar Telescope AO system. An FPGA solution for ATST AO
real time processing is being pursued instead of the parallel DSP approach used for the Dunn AO76 system. An analysis
shows FPGAs will have lower latency and lower hardware cost than an equivalent DSP solution. Interfacing to the
proposed high speed camera and the deformable mirror will be simpler and have lower latency than with DSPs. This
paper will discuss the current design and progress toward implementing the FPGA solution.
The 4m Advance Technology Solar Telescope (ATST) will be the most powerful solar telescope and the world's leading
ground-based resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and
variability in the Sun's output. The project has successfully passed its final design review and the Environmental Impact
Study for construction of ATST on Haleakala, Maui, HI has been concluded in December of 2009. The project is now
entering its construction phase. As its highest priority science driver ATST shall provide high resolution and high
sensitivity observations of the dynamic solar magnetic fields throughout the solar atmosphere, including the corona at
infrared wavelengths. With its 4 m aperture, ATST will resolve features at 0."03 at visible wavelengths and obtain 0."1
resolution at the magnetically highly sensitive near infrared wavelengths. A high order adaptive optics system delivers a
corrected beam to the initial set of state-of-the-art, facility class instrumentation located in the coudé laboratory facility.
The initial set of first generation instruments consists of five facility class instruments, including imagers and spectropolarimeters.
The high polarimetric sensitivity and accuracy required for measurements of the illusive solar magnetic
fields place strong constraints on the polarization analysis and calibration. Development and construction of a fourmeter
solar telescope presents many technical challenges, including thermal control of the enclosure, telescope structure
and optics and wavefront control. A brief overview of the science goals and observational requirements of the ATST
will be given, followed by a summary of the design status of the telescope and its instrumentation, including design
status of major subsystems, such as the telescope mount assembly, enclosure, mirror assemblies, and wavefront
Solar observations are performed over an extended field of view and the isoplanatic patch over which conventional
adaptive optics (AO) provides diffraction limited resolution is a severe limitation. The development of multi-conjugate
adaptive optics (MCAO) for the next generation large aperture solar telescopes is thus a top priority. The Sun is an ideal
object for the development of MCAO since solar structure provides multiple "guide stars" in any desired configuration.
At the Dunn Solar Telescope (DST) we implemented a dedicated MCAO bench with the goal of developing wellcharacterized,
operational MCAO. The MCAO system uses two deformable mirrors conjugated to the telescope
entrance pupil and a layer in the upper atmosphere, respectively. The high altitude deformable mirror can be placed at
conjugates ranging from 2km to 10km altitude. We have successfully and stably locked the MCAO system on solar
granulation and demonstrated the MCAO system's ability to significantly extend the corrected field of view. We present
results derived from analysis of imagery taken simultaneously with conventional AO and MCAO. We also present first
results from solar Ground Layer AO (GLAO) experiments.
The high order adaptive optics (HOAO) system is the centerpiece of the ATST wavefront correction system. The ATST
wavefront correction system is required to achieve a Strehl of
S = 0.6 or better at visible wavelength. The system design
closely follows the successful HOAO implementation at the Dunn Solar Telescope and is based on the correlating
Shack-Hartmann wavefront sensor. In addition to HOAO the ATST will utilize wavefront sensors to implement active
optics (aO) and Quasi Static Alignment (QSA) of the telescope optics, which includes several off-axis elements.
Provisions for implementation of Multi-conjugate adaptive optics have been made with the design of the optical path that
feeds the instrumentation at the coudé station. We will give an overview of the design of individual subsystems of the
ATST wavefront correction system and describe some of the unique features of the ATST wavefront correction system,
such as the need for thermally controlled corrective elements.
The four-meter Advanced Technology Solar Telescope (ATST) will be the most powerful solar telescope and the
world's leading resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and
variability in the Sun's output. Development of a four-meter solar telescope presents many technical challenges (e.g.,
thermal control of the enclosure, telescope structure and optics). We give a status report of the ATST project (e.g.,
system design reviews, PDR, Haleakalä site environmental impact statement progress) and summarize the design of the
major subsystems, including the telescope mount assembly, enclosure, mirror assemblies, wavefront correction, and
Quantifying the results for a multi-conjugate adaptive optics (MCAO) system is more complex than a
traditional adaptive optics (AO) system. The complexity of analyzing a MCAO system stems from using
multiple deformable mirrors (DMs) and quantifying the influence functions at the wavefront sensor (WFS).
In this paper, analysis tools are developed to quantify MCAO performance. Influence functions from two
deformable mirrors are propagated to a WFS using CODEV to simulate an MCAO design comparable to
the Dunn Solar Telescope (DST). Using MATLAB, the propagated influence functions are mapped to the
appropriate field positions, and reconstructor matrices are built using the mapped influence functions. Next,
a correctability analysis was performed using theoretical random phase screens. The developed tools are
versatile and useful as a system design tool and in a laboratory setting.
The four-meter Advanced Technology Solar Telescope (ATST) will be the most powerful solar telescope and the world's leading resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and variability in the Sun's output. Development of a four-meter solar telescope presents many technical challenges (e.g., thermal control of the enclosure, telescope structure and optics). We give a status report of the ATST project (e.g., system design reviews, instrument PDR, Haleakala site environmental impact statement progress) and summarize the design of the major subsystems, including the telescope mount assembly, enclosure, mirror assemblies, wavefront correction, and instrumentation.
The four-meter Advanced Technology Solar Telescope (ATST) will be the most powerful solar telescope and the world's leading resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and variability in the Sun's output. Development of a four-meter solar telescope presents many technical challenges, which include: thermal control of optics and telescope structure; contamination control of the primary mirror to achieve low scattered light levels for coronal observations; control of instrumental polarization to allow accurate and precise polarimetric observations of solar magnetic fields; and high-order solar adaptive optics that uses solar granulation as the wavefront sensing target in order to achieve diffraction limited imaging and spectroscopy. We give a status report of the ATST project focusing on the substantial progress that has been made with the design of the ATST. We summarize the design of the major subsystems, including the enclosure, the primary and secondary mirror assemblies, the coude and Nasmyth focal stations, adaptive optics and instrumentation. The site selection has been successfully concluded and we discuss areas where the site selection impacts the design.
We report here the preliminary results obtained with the multi-conjugate adaptive optics (MCAO) system at the Dunn Solar Telescope (DST/NSO MCAO) and the optical setup and performances are presented in more details in Moretto et al. in this proceeding. This system relies on the tomography technique, in which three WFS are used, each of them coupled to extended images of the Sun’s granulation and/or sunspots, to retrieve a 3D measurement of the turbulent volume in order to command the two DMs. We used a 5x5 subaperture Shack-Hartmann with cross correlation applied on three selected guiding regions - 18" wide- within the 1.25' full FOV. We also report on the estimation of turbulence distribution and the future MCAO performances based on a separate tomographic wavefront sensing experiment using the Dunn Solar Telescope adaptive optics system. In addition, we obtained estimates of the turbulence distribution. The results from this article provides an important step forward for building a full solar multi-conjugate adaptive optics system for the Dunn Solar Telescope and in the long term for the future 4 meter ATST telescope.
The Sun is an ideal target for the development and application of Multi-Conjugate Adaptive Optics (MCAO). A solar MCAO system is being developed by the National Solar Observatory, Adaptive Optics Project, with the purpose of extending the corrected science field of view to 1.25Arcmin. A detailed optical set-up, design and optical performance for such a system is presented and discussed here. The preliminary results for this first MCAO/DST run, are presented in more details by Langlois et al  at this conference.
This paper describes a versatile camera designed to operate at high frame rates of > 2kHz. Such high frame rates are required to reduce the latency, i.e., achieve high bandwidth in a solar adaptive optics application. The camera was designed around a 1280x1024 pixel CMOS 10-bit sensor with a readout rate of 2 microseconds per row. The output is switchable between a standard Camera Link interface with four 10-bit ports (standard camera mode) and a non-standard Camera Link interface with twelve 8-bit ports (adaptive optics mode). The programmable camera interface maps blocks of pixels to output ports enabling multiple regions of interest. This mode is of particular interest for solar multi-conjugate adaptive optics (MCAO). The speed of the camera is determined by the number of rows of pixels needed in the application. For example, a 200x200 pixel sub-array that is needed for the 97-actuator solar adaptive optics system at the Dunn Solar Telescope can be read out at a rate of 2.5kHz. Camera design and performance will be discussed.
The National Solar Observatory and the New Jersey Institute of Technology have developed two 97 actuator solar adaptive optics (AO) systems based on a correlating Shack-Hartmann wavefront sensor approach. The first engineering run was successfully completed at the Dunn Solar Telescope (DST) at Sacramento Peak, New Mexico in December 2002. The first of two systems is now operational at Sacramento Peak. The second system will be deployed at the Big Bear Solar Observatory by the end of 2003. The correlating Shack-Hartmann wavefront sensor is able to measure wavefront aberrations for low-contrast, extended and time-varying objects, such as solar granulation. The 97-actuator solar AO system operates at a loop update rate of 2.5 kHz and achieves a closed loop bandwidth (0dB crossover error rejection) of about 130 Hz. The AO system is capable of correcting atmospheric seeing at visible wavelengths during median seeing conditions at both the NSO/Sacramento Peak site and the Big Bear Solar Observatory. We present an overview of the system design. The servo loop was successfully closed and first AO corrected images were recorded. We present first results from the new, high order AO system.
The National Solar Observatory in collaboration with the High-Altitude
Observatory is developing a new solar polarimeter, the Diffraction Limited Spectro-Polarimeter. In conjunction with a new high-order adaptive optics system at the NSO Dunn Solar Telescope, the DLSP design facilitates very high angular resolution observations of solar vector magnetic fields. This project is being carried out in two phases. As a follow-on to the successful completion of the first phase, the ongoing DLSP Phase II implements a high QE CCD camera system, a ferro-electric liquid crystal modulator, and a new opto-mechanical system for polarization calibration. This paper documents in detail the development of the modulator system and its performance, and presents preliminary results from an engineering run carried out in combination with the new NSO high-order AO system.
A diffraction limited spectro-polarimeter is under construction at the National Solar Observatory in collaboration with the High Altitude Observatory. The scientific objective of the project is to measure the magnetic fields on the Sun up to the diffraction limit of the Dunn Solar Telescope. The same instrument would also measure the magnetic field of large sunspots or sunspot groups with reasonable spatial resolution. This requires a flexible image scale which cannot be obtained with the current Advanced Stokes Polarimeter (ASP) without loosing 50% of the light. The new spectro-polarimeter is designed in such a way that the image scale can be changed without loosing much light. It can work either in high-spatial resolution mode (0.09 arcsec per pixel) with a small field of view (FOV: 65 arcsec) or in large FOV mode (163 arcsec) with low-spatial resolution (0.25 arcsec per pixel). The phase-I of this project is to design and build the spectrograph with flexible image scale. Using the existing modulation, calibration optics of the ASP and the ASP control and data acquisition system with ASP-CHILL camera, the spectrograph was tested for its performance. This paper will concentrate on the performance of the spectrograph and will discuss some preliminary results obtained with the test runs.
We present a high-order adaptive optical system for the 26-inch vacuum solar telescope of Big Bear Solar Observatory. A small elliptical tip/tilt mirror is installed at the end of the existing coude optical path on the fast two-axis tip/tilt platform with its resonant frequency around 3.3 kHz. A 77 mm diameter deformable mirror with 76 subapertures as well as wave-front sensors (correlation tracker and Shack-Hartman) and scientific channels for visible and IR polarimetry are installed on an optical table. The correlation tracker sensor can detect differences at 2 kHz between a 32×32 reference frame and real time frames. The WFS channel detects 2.5 kHz (in binned mode) high-order wave-front atmosphere aberrations to improve solar images for two imaging magnetographs based on Fabry-Perot etalons in telecentric configurations. The imaging magnetograph channels may work simultaneously in a visible and IR spectral windows with FOVs of about 180×180 arc sec, spatial resolution of about 0.2 arc sec/pixel and SNR of about 400 and 600 accordingly for 0.25 sec integration time.
We present a progress report of the solar adaptive optics (AO) development program at the National Solar Observatory (NSO) and the Big Bear Solar Observatory (BBSO). Examples of diffraction-limited observations obtained with the NSO low-order solar adaptive optics system at the Dunn Solar Telescope (DST) are presented. The design of the high order adaptive optics systems that will be deployed at the DST and the BBSO is discussed. The high order systems will provide diffraction-limited observations of the Sun in median seeing conditions at both sites.