Jose Marino

Solar Adaptive Optics

Adaptive optics (AO) has become an indispensable tool at ground-based solar telescopes. AO enables the ground-based observer to overcome the adverse effects of atmospheric seeing and obtain diffraction limited observations. Over the last decade adaptive optics systems have been deployed at major ground-based solar telescopes and revitalized ground-based solar astronomy. The relatively small aperture of solar telescopes and the bright source make solar AO possible for visible wavelengths where the majority of solar observations are still performed. Solar AO systems enable diffraction limited observations of the Sun for a significant fraction of the available observing time at ground-based solar telescopes, which often have a larger aperture than equivalent space based observatories, such as HINODE. New ground breaking scientific results have been achieved with solar adaptive optics and this trend continues. New large aperture telescopes are currently being deployed or are under construction. With the aid of solar AO these telescopes will obtain observations of the highly structured and dynamic solar atmosphere with unprecedented resolution. This paper reviews solar adaptive optics techniques and summarizes the recent progress in the field of solar adaptive optics. An outlook to future solar AO developments, including a discussion of Multi-Conjugate AO (MCAO) and Ground-Layer AO (GLAO) will be given.

Profiles of the daytime atmospheric turbulence above Big Bear solar observatory

Context. Space weather has become acutely critical for today’s global communication networks. To understand its driving forces we need to observe the Sun with high angular-resolution, and within large fields-of-view, i.e. with multi-conjugate adaptive optics correction. Aims. The design of a multi-conjugate adaptive optical system requires the knowledge of the altitude distribution of atmospheric turbulence. We have therefore measured daytime turbulence profiles above the New Solar Telescope (NST), on Big Bear Lake. Methods. To this purpose, a wide-field wavefront sensor was installed behind the NST. The variation of the wavefront distortions with angular direction allows the reconstruction of the distribution of turbulence. Results. The turbulence is found to have three origins: 1. a ground layer (<500 m) that contains 55–65% of the turbulence, 2. a boundary layer between 1–7 km comprises 30–40% of the turbulent energy, 3. and the remaining ∼5% are generated in the tropopause, which is above 12 km in summer and between 8 and 12 km in winter. Conclusions. A multi-conjugate adaptive optical system should thus aim at correcting the ground turbulence, the center of the boundary layer at roughly 3 km altitude and, eventually, the upper boundary layer around 6 km altitude.

Feasibility study of a layer-oriented wavefront sensor for solar telescopes

Solar multiconjugate adaptive optics systems rely on several wavefront sensors, which measure the incoming turbulent phase along several field directions to produce a tomographic reconstruction of the turbulent phase. In this paper, we explore an alternative wavefront sensing approach that attempts to directly measure the turbulent phase present at a particular height in the atmosphere: a layer-oriented cross-correlating Shack-Hartmann wavefront sensor (SHWFS). In an experiment at the Dunn Solar Telescope, we built a prototype layer-oriented cross-correlating SHWFS system conjugated to two separate atmospheric heights. We present the data obtained in the observations and complement these with ray-tracing computations to achieve a better understanding of the instruments performance and limitations. The results obtained in this study strongly indicate that a layer-oriented cross-correlating SHWFS is not a practical design to measure the wavefront at a high layer in the atmosphere.

AO-308: the high-order adaptive optics system at Big Bear Solar Observatory

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.

Clear widens the field for observations of the Sun with multi-conjugate adaptive optics

The multi-conjugate adaptive optics (MCAO) pathfinder Clear on the New Solar Telescope in Big Bear Lake has provided the first-ever MCAO-corrected observations of the Sun that show a clearly and visibly widened corrected field of view compared to quasi-simultaneous observations with classical adaptive optics (CAO) correction. Clear simultaneously uses three deformable mirrors, each conjugated to a different altitude, to compensate for atmospheric turbulence. While the MCAO correction was most effective over an angle that is approximately three times wider than the angle that was corrected by CAO, the full 53′′ field of view did benefit from MCAO correction. We further demonstrate that ground-layer-only correction is attractive for solar observations as a complementary flavor of adaptive optics for observational programs that require homogenous seeing improvement over a wide field rather than diffraction-limited resolution. We show illustrative images of solar granulation and of a sunspot obtained on different days in July 2016, and present a brief quantitative analysis of the generalized Fried parameters of the images.

The multi-conjugate adaptive optics system of the New Solar Telescope at Big Bear Solar Observatory

We report on the multi-conjugate adaptive optics (MCAO) system of the New Solar Telescope (NST) at Big Bear Solar Observatory which has been integrated in October 2013 and is now available for MCAO experiments. The NST MCAO system features three deformable mirrors (DM), and it is purposely flexible in order to offer a valuable facility for development of solar MCAO. Two of the deformable mirrors are dedicated to compensation of field dependent aberrations due to high-altitude turbulence, whereas the other deformable mirror compensates field independent aberrations in a pupil image. The opto-mechanical design allows for changing the conjugate plane of the two high-altitude DMs independently between two and nine kilometers. The pupil plane DM can be placed either in a pupil image upstream of the high-altitude DMs or downstream. This capability allows for performing experimental studies on the impact of the geometrical order of the deformable mirrors and the conjugate position. The control system is flexible, too, which allows for real-world analysis of various control approaches. This paper gives an overview of the NST MCAO system and reveals the first MCAO corrected image taken at Big Bear Solar Observatory.

Expected performance of solar adaptive optics in large-aperture solar telescopes

Abstract. High resolution ground based solar observations require adaptive optics correction. The next generation of solar telescopes will have large aperture sizes, in the range of 4 m, and will require larger and more complex adaptive optics systems. We study the effects that extended field wavefront sensors have on the correction performance for large aperture size telescopes. These effects are more pronounced for observations at low elevation angles, which are common during high resolution solar observations. Additionally, atmospheric dispersion is strongest at low elevation angle observations and can cause further reductions of the adaptive optics performance. We present a study of the expected correction performance of solar adaptive optics systems in large-aperture solar telescopes using an end-to-end adaptive optics simulation package.

Progress in multi-conjugate adaptive optics at Big Bear Solar Observatory

The multi-conjugate adaptive optics (MCAO) system for solar observations at the 1.6-meter clear aperture New Solar Telescope (NST) of the Big Bear Solar Observatory (BBSO) in Big Bear Lake, California, enables us to study fundamental design questions in solar MCAO experimentally. It is the pathfinder for MCAO of the upcoming Daniel K. Inoyue Solar Telescope (DKIST). This system is very flexible and offers various optical configurations such as different sequencings of deformable mirrors (DMs) and wavefront sensors (WFS), which are hard to simulate conclusively. We show preliminary results and summarize the design, and 2016 updates to the MCAO system. The system utilizes three DMs. One of which is conjugate to the telescope pupil, and the other two to distinct higher altitudes. The pupil DM can be either placed into a pupil image up- or downstream of the high-altitude DMs. The high-altitude DMs can be separately and quickly conjugated to various altitudes between 2 and 8 km. Three Shack-Hartmann WFS units are available, one for low-order, multi-directional sensing and two high-order on-axis sensing.

Solar adaptive optics with the DKIST: status report

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 (r0 = 7 cm) and Strehl of 0.6 at 630 nm in excellent seeing (r0 = 20 cm). We present the current status of the DKIST high-order adaptive optics, focusing on system design, hardware procurements, and error budget management.

Status of the DKIST system for solar adaptive optics

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. 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 (r0 = 7 cm) and Strehl of 0.6 at 630 nm in excellent seeing (r0 = 20 cm). 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. 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.