Robo-AO is the first robotic autonomous laser-guided adaptive optics (AO) system operating in the sky. It is a very economical AO system especially suitable for observations with 1- to 3-m class telescopes. A second Robo-AO system, which works both in the visible and near-infrared wavelengths, has been developed to improve the image quality of the 2-m diameter telescope at Inter-university Centre for Astronomy and Astrophysics Girawali Observatory in India. We present the optomechanical design and development of the Laser Guide Star Facility (LGSF) and the Cassegrain AO facility with various test results. Effects of different projection geometries of the LGSF have been discussed with modeling results. Comprehensive study of an atmospheric dispersion corrector with dispersion model and development of a generic software are elaborated with experimental results. Toward the end, AO loop test results in the presence of artificial turbulence generated in the laboratory are presented.
The next generation of adaptive optics (AO) systems on large telescopes will require immense computation performance and memory bandwidth, both of which are challenging with the technology available today. The objective of this work is to create a future-proof AO platform on a field programmable gate array (FPGA) architecture, which scales with the number of subapertures, pixels per subaperture, and external memory. We have created a scalable AO platform with an off-the-shelf FPGA development board, which provides an AO reconstruction time only limited by the external memory bandwidth. SPARC uses the same logic resources irrespective of the number of subapertures in the AO system. This paper is aimed at embedded developers who are interested in the FPGA design and the accompanying hardware interfaces. The central theme of this paper is to show how scalability is incorporated at different levels of the FPGA implementation. This work is a continuation of part 1 of the paper, which explains the concept, objectives, control scheme, and method of validation used for testing the platform.
We demonstrate an architecture for adaptive optics (AO) control based on field programmable gate arrays (FPGAs), making active use of their configurable parallel processing capability. The unique capabilities of scalable platform for adaptive optics real-time control (SPARC) are demonstrated through an implementation on an off-the-shelf inexpensive Xilinx VC-709 development board. The architecture makes SPARC a generic and powerful real-time control kernel for a broad spectrum of AO scenarios. SPARC is scalable across different numbers of subapertures and pixels per subaperture. The overall concept, objectives, architecture, validation, and results from simulation as well as hardware tests are presented here. For Shack–Hartmann wavefront sensors, the total AO reconstruction time ranges from a median of 39.4 μs (11 × 11 subapertures) to 1.283 ms (50 × 50 subapertures) on the development board. For large wavefront sensors, the latency is dominated by access time (∼1 ms) of the standard dual data rate memory available on the board. This paper is divided into two parts. Part 1 is targeted at astronomers interested in the capability of the current hardware. Part 2 explains the FPGA implementation of the wavefront processing unit, the reconstruction algorithm, and the hardware interfaces of the platform. Part 2 mainly targets the embedded developers interested in the hardware implementation of SPARC.
Atmospheric turbulence is gentle in the infrared regime than visible. Hence adaptive optics (AO) efficiently works in the infrared. The large overheads and low efficiency still limit the applicability of AO on large telescopes for which operational costs per unit time are high. On the other hand, small and medium-sized telescopes are many more in number, and their operational costs are substantially lower. A reasonably powerful AO system, which works with minimal overheads and provides good sky coverage, will greatly enhance the scientific capabilities of small and medium-sized telescopes. Robotic Adaptive Optics (Robo-AO) is an AO system for medium-sized telescopes which is built by Caltech, USA, and IUCAA, India collaboratively. It works with minimal overheads and provides good sky coverage in both visible and infrared regime. The first version of Robo-AO does not have a high-quality IR camera. An IR camera is being developed to accommodate AO-corrected 1.5 0 field of view in near-infrared bands. It can be used as a science camera as well as a tip-tilt camera. It is being built at IUCAA with a HAWAII detector. Here we describe the salient features of the IR camera like optics, optomechanical design, etc.
The IUCAA digital sampling array controller (IDSAC) is a flexible and generic yet powerful CCD controller that can handle a wide range of scientific detectors. Based on an easily scalable modular backplane architecture consisting of single board controllers (SBC), IDSAC can control large detector arrays and mosaics. Each of the SBCs offers the full functionality required to control a CCD independently. The SBCs can be cold swapped without the need to reconfigure them. IDSAC is also available in a backplane-less architecture. Each SBC can handle data from up to four video channels with or without dummy outputs at speeds up to 500-kilo pixels per second (kPPS) per channel with a resolution of 16 bits. Communication with a Linux-based host computer is through a USB3.0 interface, with the option of using copper or optical fibers. A field programmable gate array (FPGA) is used as the master controller in each SBC, which allows great flexibility in optimizing performance by adjusting gain, timing signals, bias levels, etc., using user-editable configuration files without altering the circuit topology. Elimination of thermal kTC noise is achieved via digital correlated double sampling (DCDS). The number of digital samples per pixel (for both reset and signal levels) is user configurable. We present the results of noise performance characterization of IDSAC through simulation, theoretical modeling, and actual measurements. The contribution of different types of noise sources is modeled using a tool to predict noise of a generic DCDS signal chain analytically. The analytical model predicts the net input referenced noise of the signal chain to be 5 electrons for 200-k pixels/s per channel readout rate with three samples per pixel. Using a cryogenic test setup in the lab, the noise is measured to be 5.4 e (24.3 μV), for the same readout configuration. With a better-optimized configuration of 500-kPPS readout rate, the measured noise is down to 3.8 electrons RMS (17 μV), with three samples per interval.
MIRADAS (Mid-resolution InfRAreD Astronomical Spectrograph) is the facility near-infrared multi-object echelle spectrograph for the Gran Telescopio Canarias (GTC) 10.4-meter telescope. MIRADAS operates at spectral resolution R=20,000 over the 1-2.5µm bandpass), and provides multiplexing (up to N=12 targets) and spectro-polarimetry. The MIRADAS consortium includes the University of Florida, Universidad de Barcelona, Universidad Complutense de Madrid, Instituto de Astrofísica de Canarias, Institut d'Estudis Espacials de Catalunya and Universidad Nacional Autonoma de Mexico, as well as partners at A-V-S (Spain), New England Optical Systems (USA), and IUCAA (India). MIRADAS completed its Final Design Review in 2015, and in this paper, we review the current status and overall system design for the instrument, with scheduled delivery in 2018. We particularly emphasize key developments in cryogenic robotic probe arms for multiplexing, a macro-slicer mini-IFU, an advanced cryogenic spectrograph optical system, and a SIDECAR-based array control system for the 1x2 HAWAII-2RG detector mosaic.
The South African Astronomical Observatory (SAAO) is currently developing WiNCam, the Wide-field Nasmyth Camera, to be mounted on Lesedi, the observatory’s new 1-metre telescope. This paper discusses the design and results for the remotely-operated camera system. The camera consists of an E2V-231-C6 Back Illuminated Scientific Charge Coupled Device (CCD) sensor with 6144x6160 pixels, four outputs operating in non-inverted mode. This is to date the largest single chip CCD-system developed at SAAO. The CCD is controlled with a modified Inter-University Centre for Astronomy and Astrophysics (IUCAA) Digital Sampler Array Controller (IDSAC) utilizing digital correlated double sampling. The camera system will have full-frame and frame-transfer read out modes available with sub-windowing and pre-binning abilities. Vacuum through-wall PCB technology is used to route signals through the vacuum interface between the controller and the CCD. A thin, compact, 125x125mm aperture, sliding-curtain-mechanism shutter was designed and manufactured together with a saddle-type filter-magazine-gripper system. The CCD is cryogenically cooled using a Stirling Cooler with active vibration cancellation; CCD temperature control is done with a Lake Shore Temperature Controller. A Varian Ion Pump and Activated Charcoal are used to maintain good vacuum and to prolong intervals between vacuum pump down. The various hardware components of the system are connected using distributed software architecture, and a web-based GUI allows remote and scripted operation of the instrument.
At the University of Wisconsin-Madison, we are building and testing the near-infrared (NIR) spectrograph for the Southern African Large Telescope—RSS-NIR. RSS-NIR will be an enclosed cooled integral field spectrograph. The RSS-NIR detector system uses a HAWAII-2RG (H2RG) HgCdTe detector from Teledyne controlled by the SIDECAR ASIC and an Inter-University Centre for Astronomy and Astrophysics (IUCCA) ISDEC card. We have successfully characterized and optimized the detector system and report on the optimization steps and performance of the system. We have reduced the CDS read noise to ∼20 e− for 200 kHz operation by optimizing ASIC settings. We show an additional factor of 3 reduction of read noise using Fowler sampling techniques and a factor of 2 reduction using up-the-ramp group sampling techniques. We also provide calculations to quantify the conditions for sky-limited observations using these sampling techniques.
CIRCE is a near-infrared (1-2.5 micron) imager (including low-resolution spectroscopy and polarimetery) in operation as a visitor instrument on the Gran Telescopio Canarias 10.-4m tele scope. It was built largely by graduate students and postdocs, with help from the UF Astronomy engineering group, and is funded by the University of Florida and the U.S. National Science Foundation. CIRCE is helping to fill the gap in time between GTC first light and the arrival of EMIR, and will also provide the following scientific capabilities to compliment EMIR after its arrival: high-resolution imaging, narrowband imaging, high-time-resolution photometry, polarimetry, and low-resolution spectroscopy. There are already scientific results from CIRCE, some of which we will review. Additionally, we will go over the observing modes of CIRCE, including the two additional modes that were added during a service and upgrading run in March 2016.
The Mid-resolution InfRAreD Astronomical Spectrograph (MIRADAS, a near-infrared multi-object echelle spectrograph operating at spectral resolution R=20,000 over the 1-2.5μm bandpass) was selected by the Gran Telescopio Canarias (GTC) partnership as the next-generation near-infrared spectrograph for the world's largest optical/infrared telescope, and is being developed by an international consortium. The MIRADAS consortium includes the University of Florida, Universidad de Barcelona, Universidad Complutense de Madrid, Instituto de Astrofísica de Canarias, and Institut d'Estudis Espacials de Catalunya, as well as probe arm industrial partner A-V-S (Spain), with more than 45 Science Working Group members in 10 institutions primarily in Spain, Mexico, and the USA. In this paper, we review the overall system design and project status for MIRADAS during its early fabrication phase in 2016.
KEYWORDS: Sensors, Wavefront sensors, Control systems, Analog electronics, Multiplexers, Stars, Field programmable gate arrays, Power supplies, Electrons, Interfaces
As a part of a design study for the On-Instrument Low Order Wave-front Sensor (OIWFS) for the TMT Infra-Red Imaging Spectrograph (IRIS), we recently evaluated the noise performance of a detector control system consisting of IUCAA SIDECAR DRIVE ELECRONICS CONTROLLER (ISDEC), SIDECAR ASIC and HAWAII-2RG (H2RG) MUX. To understand and improve the performance of this system to serve as a near infrared wavefront sensor, we implemented new read out modes like multiple regions of interest with differential multi-accumulate readout schemes for the HAWAII-2RG (H2RG) detector. In this system, the firmware running in SIDECAR ASIC programs the detector for ROI readout, reads the detector, processes the detector output and writes the digitized data into its internal memory. ISDEC reads the digitized data from ASIC, performs the differential multi-accumulate operations and then sends the processed data to a PC over a USB interface. A special loopback board was designed and used to measure and reduce the noise from SIDECAR ASIC DC biases2. We were able to reduce the mean r.m.s read noise of this system down to 1-2 e. for any arbitrary window frame of 4x4 size at frame rates below about 200 Hz.
KEYWORDS: Charge-coupled devices, Video processing, Cadmium sulfide, Video, Analog electronics, Interference (communication), Clocks, Sensors, Power supplies, Signal to noise ratio
In order to run the large format detector arrays and mosaics that are required by most astronomical instruments, readout electronic controllers are required which can process multiple CCD outputs simultaneously at high speeds and low noise levels. These CCD controllers need to be modular and configurable, should be able to run multiple detector types to cater to a wide variety of requirements. IUCAA Digital Sampler Array Controller (IDSAC), is a generic CCD Controller based on a fully scalable architecture which is adequately flexible and powerful enough to control a wide variety of detectors used in ground based astronomy. The controller has a modular backplane architecture that consists of Single Board Controller Cards (SBCs) and can control up to 5 CCDs (mosaic or independent). Each Single Board Controller (SBC) has all the resources to a run Single large format CCD having up to four outputs. All SBCs are identical and are easily interchangeable without needing any reconfiguration. A four channel video processor on each SBC can process up to four output CCDs with or without dummy outputs at 0.5 Megapixels/Sec/Channel with 16 bit resolution. Each SBC has a USB 2.0 interface which can be connected to a host computer via optional USB to Fibre converters. The SBC uses a reconfigurable hardware (FPGA) as a Master Controller. IDSAC offers Digital Correlated Double Sampling (DCDS) to eliminate thermal kTC noise. CDS performed in Digital domain (DCDS) has several advantages over its analog counterpart, such as - less electronics, faster readout and easier post processing. It is also flexible with sampling rate and pixel throughput while maintaining the core circuit topology intact. Noise characterization of the IDSAC CDS signal chain has been performed by analytical modelling and practical measurements. Various types of noise such as white, pink, power supply, bias etc. has been considered while creating an analytical noise model tool to predict noise of a controller system like IDSAC. Several tests are performed to measure the actual noise of IDSAC. The theoretical calculation matches very well with practical measurements within 10% accuracy.
ISDEC-2 - IUCAA1 SIDECAR Drive Electronics Controller is an alternative for Teledyne make JADE2 based controller for HAWAII detectors. It is a ready to use complete package and has been developed keeping in mind general astronomical requirements and widely used observatory set-ups like preferred OS-Linux , multi-extension fits output with fully populated headers (with detector as well as telescope and observation specific information), etc. Actual exposure time is measured for each frame to a few tens of microsecond accuracy and put in the fits header. It also caters to several application specific requirements like fast resets, strip mode, multiple region readout with on board co-adding, etc. ISDEC-2 is designed to work at -40 deg. and is already in use at observatories worldwide. ISDEC-3 is an Artix-7 FPGA based SIDECAR Drive Electronics Controller currently being developed at IUCAA. It will retain all the functionality supported by ISDEC-2 and will also support the operation of H2RG in continuos, fast (32 output, 5 MSPS, 12 bit) mode. It will have a 5 Gbps USB 3.0 PC interface and 1 Gbps Ethernet interface for image data transfer from SIDECAR to host PC. Additionally, the board will have DDR-3 memory for on-board storage and processing. ISDEC-3 will be capable of handling two SIDECARs simultaneously (in sync) for H2RG slow modes.
The main objective of the present project is to explore the viability of an adaptive optics control system based exclusively on Field Programmable Gate Arrays (FPGAs), making strong use of their parallel processing capability. In an Adaptive Optics (AO) system, the generation of the Deformable Mirror (DM) control voltages from the Wavefront Sensor (WFS) measurements is usually through the multiplication of the wavefront slopes with a predetermined reconstructor matrix. The ability to access several hundred hard multipliers and memories concurrently in an FPGA allows performance far beyond that of a modern CPU or GPU for tasks with a well-defined structure such as Adaptive Optics control. The target of the current project is to generate a signal for a real time wavefront correction, from the signals coming from a Wavefront Sensor, wherein the system would be flexible to accommodate all the current Wavefront Sensing techniques and also the different methods which are used for wavefront compensation. The system should also accommodate for different data transmission protocols (like Ethernet, USB, IEEE 1394 etc.) for transmitting data to and from the FPGA device, thus providing a more flexible platform for Adaptive Optics control. Preliminary simulation results for the formulation of the platform, and a design of a fully scalable slope computer is presented.
The Robert Stobie Spectrograph Near Infrared Instrument (RSS-NIR), a prime focus facility instrument for the 11-meter
Southern African Large Telescope (SALT), is well into its laboratory integration and testing phase. RSS-NIR will
initially provide imaging and single or multi-object medium resolution spectroscopy in an 8 arcmin field of view at
wavelengths of 0.9 - 1.7 μm. Future modes, including tunable Fabry-Perot spectral imaging and polarimetry, have been
designed in and can be easily added later. RSS-NIR will mate to the existing visible wavelength RSS-VIS via a dichroic
beamsplitter, allowing simultaneous operation of the two instruments in all modes. Multi-object spectroscopy covering a
wavelength range of 0.32 - 1.7 μm on 10-meter class telescopes is a rare capability and once all the existing VIS modes
are incorporated into the NIR, the combined RSS will provide observational modes that are completely unique.
The VIS and NIR instruments share a common telescope focal plane, and slit mask for spectroscopic modes, and
collimator optics that operate at ambient observatory temperature. Beyond the dichroic beamsplitter, RSS-NIR is
enclosed in a pre-dewar box operating at -40 °C, and within that is a cryogenic dewar operating at 120 K housing the
detector and final camera optics and filters. This semi-warm configuration with compartments at multiple operating
temperatures poses a number of design and implementation challenges. In this paper we present overviews of the RSSNIR
instrument design and solutions to design challenges, measured performance of optical components, detector
system optimization results, and an update on the overall project status.
Robo-AO is the first astronomical laser guide star adaptive optics (AO) system designed to operate completely independent of human supervision. A single computer commands the AO system, the laser guide star, visible and near-infrared science cameras (which double as tip-tip sensors), the telescope, and other instrument functions. Autonomous startup and shutdown sequences as well as concatenated visible observations were demonstrated in late 2011. The fully robotic software is currently operating during a month long demonstration of Robo- AO at the Palomar Observatory 60-inch telescope.
We have created a new autonomous laser-guide-star adaptive-optics (AO) instrument on the 60-inch (1.5-m) telescope at Palomar Observatory called Robo-AO. The instrument enables diffraction-limited resolution observing in the visible and near-infrared with the ability to observe well over one-hundred targets per night due to its fully robotic operation. Robo-AO is being used for AO surveys of targets numbering in the thousands, rapid AO imaging of transient events and long-term AO monitoring not feasible on large diameter telescope systems. We have taken advantage of cost-effective advances in deformable mirror and laser technology while engineering Robo-AO with the intention of cloning the system for other few-meter class telescopes around the world.
SIDECAR is an Application Specific Integrated Circuit (ASIC), which can be used for control and data acquisition from
near-IR HAWAII detectors offered by Teledyne Imaging Sensors (TIS), USA. The standard interfaces provided by
Teledyne are COM API and socket servers running under MS Windows platform. These interfaces communicate to the
ASIC (and the detector) through an intermediate card called JWST ASIC Drive Electronics (JADE2). As part of an
ongoing programme of several years, for developing astronomical focal plane array (CCDs, CMOS and Hybrid)
controllers and data acquisition systems (CDAQs), IUCAA is currently developing the next generation controllers
employing Virtex-5 family FPGA devices. We present here the capabilities which are built into these new CDAQs for
handling HAWAII detectors. In our system, the computer which hosts the application programme, user interface and
device drivers runs on a Linux platform. It communicates through a hot-pluggable USB interface (with an optional
optical fibre extender) to the FPGA-based card which replaces the JADE2. The FPGA board in turn, controls the
SIDECAR ASIC and through it a HAWAII-2RG detector, both of which are located in a cryogenic test Dewar set up
which is liquid nitrogen cooled. The system can acquire data over 1, 4, or 32 readout channels, with or without binning,
at different speeds, can define sub-regions for readout, offers various readout schemes like Fowler sampling, up-theramp
etc. In this paper, we present the performance results obtained from a prototype system.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.