HiPERCAM is a five channel fast photometer to study high temporal variability of the universe, covering from 0.3 to 1.0 microns in five wavebands. HiPERCAM uses custom-made 2Kx1K split-frame transfer CCDs mounted in separate compact camera heads and cooled by thermoelectric coolers to 180K. The demands on the readout system are very unique to this instrument in that all five CCDs are operated in a pseudo drift window mode along with the normal windowing, binning and full-frame modes. The pseudo drift mode involves reading out small window regions from 2 quadrants of each CCD, with the possibility to exceed 1 kHz window rates per output channel. The CCDs are custom manufactured by Teledyne e2v to allow independent serial clock controls for each output. The devices are manufactured in standard and deep-depletion processes with appropriate anti-reflection coatings to achieve high quantum efficiencies in each of the five wavebands. An ESO NGC controller has been configured to control and readout all five CCDs. The data acquisition software has been modified to provide GPS timestamping of the data and access to the acquired data in real time for the data reduction software. The instrument has had its first light and first science observations on the 4.2m William Herschel Telescope, La Palma during a commissioning run in October 2017 and subsequently on the 10.4m Gran Telescopio Canarias in February 2018 and science observations in April 2018. This paper will present the details of the preamplifier electronics, configuration of the readout electronics and the data acquisition software to support the unique readout modes along with the overall performance of the instrument.
The construction of the next generation of 40 m-class astronomical telescopes poses an enormous challenge for the design of their instruments and the manufacture of their optics. Optical elements typically increase in both size and number, placing ever more demands on the system manufacturing and alignment tolerances. This challenge can be met by using the wider design space offered by freeform optics, by for instance allowing highly aspherical surfaces. Optical designs incorporating freeform optics can achieve a better performance with fewer components. This also leads to savings in volume and mass and, potentially, cost.
This paper describes the characterization of the FAME system (freeform active mirror experiment). The system consists of a thin hydroformed face sheet that is produced to be close to the required surface shape, a highly controllable active array that provides support and the ability to set local curvature of the optical surface and the actuator layout with control electronics that drives the active array.
A detailed characterisation of the fully-assembled freeform mirror was carried out with the physical and optical properties determined by coordinate measurements (CMM), laser scanning, spherometry and Fizeau interferometry. The numerical model of the mirror was refined to match the as-built features and to predict the performance more accurately.
Each of the 18 actuators was tested individually and the results allow the generation of look-up tables providing the force on the mirror for each actuator setting. The actuators were modelled with finite element analysis and compared to the detailed measurements to develop a closed-loop system simulation. After assembling the actuators in an array, the mirror surface was measured again using interferometry. The influence functions and Eigen-modes were also determined by interferometry and compared to the FEA results.
HiPERCAM is a quintuple-beam imager that saw first light on the 4.2 m William Herschel Telescope (WHT) in October 2017 and on the 10.4 m Gran Telescopio Canarias (GTC) in February 2018. The instrument uses re- imaging optics and 4 dichroic beamsplitters to record ugriz (300–1000 nm) images simultaneously on its five CCD cameras. The detectors in HiPERCAM are frame-transfer devices cooled thermo-electrically to 90°C, thereby allowing both long-exposure, deep imaging of faint targets, as well as high-speed (over 1000 windowed frames per second) imaging of rapidly varying targets. In this paper, we report on the as-built design of HiPERCAM, its first-light performance on the GTC, and some of the planned future enhancements.
ESA has been funding the industry in Europe to bring the technologies together to manufacture high performance infrared detectors from near infrared (NIR) to very long wavelength infrared (VLWIR) detectors. The UK Astronomy Technology Centre (UKATC) has undertaken the tasks of test and characterizing the new detectors being manufactured by Leonardo, UK (Selex ES Ltd). Initial test results from these programs were presented at previous SPIE meetings in 2012 and 2014. The work since has much progressed to test and characterize the Large Format NIR, SWIR and LW and VLWIR detectors. This paper will present the custom built test facilities for evaluation of large format (currently 1280x1024, 15μm pixel format) near infrared detectors for astronomy applications, the characterization of 1Kx1K shortwave infrared detectors (cut off at 2.5μm on a 2Kx2K ROIC) for satellite based earth observation programs, long wavelength (8 to 11.5μm) and very long wavelength (10 to 14.5μm) 288 x 384 pixel infrared arrays for cosmos applications. Also being evaluated in at the UKATC is a SAPHIRA APD array (mark 5) for photon sensing and high speed AO applications. Custom test facilities have been setup at the UKATC and are being routinely used to test and characterize these detectors under conditions representative of the applications. The paper will discuss the requirements placed on testing in each of these programs along with the associated challenges to evaluate the performance of these detectors. The paper will also include some of the latest test results from the characterization programs, where appropriate.
The UK ATC has developed a novel thermal actuator design as part of an OPTICON project focusing on the development of a Freeform Active Mirror Element (FAME). The actuator uses the well understood concept of thermal expansion to generate the required force and displacement. As heat is applied to the actuator material it expands linearly. A resistance temperature device (RTD) is embedded in the centre of the actuator and is used both as a heater and a sensor. The RTD temperature is controlled electronically by injecting a varying amount of current into the device whilst measuring the voltage across it. Temperature control of the RTD has been achieved to within 0.01°C.
A 3D printed version of the actuator is currently being used at the ATC to deform a mirror but it has several advantages that may make it suitable to other applications. The actuator is cheap to produce whilst obtaining a high accuracy and repeatability. The actuator design would be suitable for applications requiring large numbers of actuators with high precision.
FAME (Freeform Active Mirror Experiment - part of the FP7 OPTICON/FP7 development programme) intends to demonstrate the huge potential of active mirrors and freeform optical surfaces. Freeform active surfaces can help to address the new challenges of next generation astronomical instruments, which are bigger, more complex and have tighter specifications than their predecessors.
The FAME design consists of a pre-formed, deformable thin mirror sheet with an active support system. The thin face sheet provides a close to final surface shape with very high surface quality. The active array provides the support, and through actuation, the control to achieve final surface shape accuracy.
In this paper the development path, trade-offs and demonstrator design of the FAME active array is presented. The key step in the development process of the active array is the design of the mechanical structure and especially the optimization of the actuation node positions, where the actuator force is transmitted to the thin mirror sheet. This is crucial for the final performance of the mirror where the aim is to achieve an accurate surface shape, with low residual (high order) errors using the minimum number of actuators. These activities are based on the coupling of optical and mechanical engineering, using analytical and numerical methods, which results in an active array with optimized node positions and surface shape.
FAME is a four-year project and part of the OPTICON/FP7 program that is aimed at providing a breakthrough component for future compact, wide field, high resolution imagers or spectrographs, based on both Freeform technology, and the flexibility and versatility of active systems.
Due to the opening of a new parameter space in optical design, Freeform Optics are a revolution in imaging systems for a broad range of applications from high tech cameras to astronomy, via earth observation systems, drones and defense. Freeform mirrors are defined by a non-rotational symmetry of the surface shape, and the fact that the surface shape cannot be simply described by conicoids extensions, or off-axis conicoids. An extreme freeform surface is a significantly challenging optical surface, especially for UV/VIS/NIR diffraction limited instruments.
The aim of the FAME effort is to use an extreme freeform mirror with standard optics in order to propose an integrated system solution for use in future instruments. The work done so far concentrated on identification of compact, fast, widefield optical designs working in the visible, with diffraction limited performance; optimization of the number of required actuators and their layout; the design of an active array to manipulate the face sheet, as well as the actuator design.
In this paper we present the status of the demonstrator development, with focus on the different building blocks: an extreme freeform thin face sheet, the active array, a highly controllable thermal actuator array, and the metrology and control system.
This paper discusses the development of a demonstrator freeform active mirror for future
astronomical instruments both on Earth and in space. It consists of a system overview and progress
in various areas of technology in the building blocks of the mirror: an extreme freeform thin face
sheet, an active array, design tools and the metrology and control of the system. The demonstrator
aims to investigate the applicability of the technique in high end astronomical systems, also for space
The advent of extremely large telescopes will bring unprecedented light-collecting power and spatial resolution, but it will also lead to a significant increase in the size and complexity of focal-plane instruments. The use of freeform mirrors could drastically reduce the number of components in optical systems. Currently, manufacturing issues limit the common use of freeform mirrors at short wavelengths. This article outlines the use of freeform mirrors in astronomical instruments with a description of two efficient freeform optical systems. A new manufacturing method is presented which seeks to overcome the manufacturing issues through hydroforming of thin polished substrates. A specific design of an active array is detailed, which will compensate for residual manufacturing errors, thermoelastic deformation, and gravity-induced errors during observations. The combined hydroformed mirror and the active array comprise the Freeform Active Mirror Experiment, which will produce an accurate, compact, and stable freeform optics dedicated to visible and near-infrared observations.