Electron multiplication CCDs for astronomical applications Ives, Derek
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2009, Letnik:
604, Številka:
1
Journal Article
Recenzirano
Electron multiplication CCDs have been commercially available for a few years but have yet to make a wider impact in the astronomical community. They have specifically been designed to use an ...avalanche gain process during the serial charge transfer process to give large signal gain. In all other respects they are identical to the very latest generation of low-noise CCDs. They have been used with great success in “lucky” imaging, for adaptive optics systems and also in high-speed faint object spectroscopy science programs. Their sub-electron read noise makes them an obvious choice for any observation, which is normally detector read noise limited. I present a detailed summary of the typical performance and characteristics of these devices and compare and contrast them against standard low-noise astronomical CCDs. I also present modeled and real data for these detectors with particular regard to some of their lesser known issues such as clock-induced charge. Finally, I present results from real-world astronomical testing, which shows the superior performance of these devices.
MOONS is a multi‐object spectrograph that will be installed at the Nasmyth focus of the VLT ESO Telescopes in Chile. The instrument has the capacity to deploy approximately 1000 fibers over a field ...of view of 500 square arcminutes, with a total wavelength coverage of from 0.6 to 1.8 μ$$ \mu $$m, offering both low‐ and medium‐resolution modes. The high demand for fast and large optics in all spectral channels prompted the use of similar f/0.95$$ f/0.95 $$ Schmidt cameras. As a result, the Detector Unit (DU) must be located within the optical beam and its footprint must be minimized to reduce vignetting. The instrument consists of four H4RG‐15um pixel detectors and two fully depleted LBNL CCDs. This article provides a comprehensive description of the detector systems, focusing particularly on the H4RG‐15, including a brief overview of the newly developed cryogenic pre‐amplifier for 64‐output operation, and a detailed discussion of the woven cable technology used for signal routing. Some results of the characterization of three H4RG detectors are presented, with a focus on crosstalk and buffer output performance. The use of the buffer output for the H4RG results in a glow‐per‐read observed at the bottom of the detectors. This article also describes the trade‐offs and alternatives used to optimize detector performance in this situation.
Near‐infrared adaptive optics as well as fringe tracking for coherent beam combination in optical interferometry require the development of high‐speed sensors. Because of the high speed, a large ...analog bandwidth is required. The short exposure times result in small signal levels which require noiseless detection. Both requirements cannot be met by state‐of‐the‐art conventional CMOS technology of near‐infrared arrays as has been attempted previously. A total of five near‐infrared SAPHIRA 320 × 256 pixel HgCdTe e−APD arrays have been deployed in the wavefront sensors and in the fringe tracker of the VLTI instrument GRAVITY. The current limiting magnitude for coherent exposures with GRAVITY is mk = 19, which is made possible with ADP technology. New avalanche photo‐diode array (APD) developments since GRAVITY include the extension of the spectral sensitivity to the wavelength range from 0.8 to 2.5 μm. After GRAVITY a larger format array with 512 × 512 pixels has been developed for both AO applications at the ELT and for long integration times. Since dark currents of <10−3 e−/s have been demonstrated with 1Kx1K e−APD arrays and 2Kx2K e−APD arrays have already been developed, the possibilities and adaptations of e−APD technology to provide noiseless large‐format science‐grade arrays for long integration times are also discussed.
New mid‐infrared HgCdTe (MCT) detector arrays developed in collaboration with Teledyne Imaging Sensors (TIS) have paved the way for improved 10‐μ$$ \mu $$m sensors for space‐ and ground‐based ...observatories. Building on the successful development of longwave HAWAII‐2RGs for space missions such as NEO Surveyor, we characterize the first 13‐μ$$ \mu $$m GeoSnap detector manufactured to overcome the challenges of high‐background rates inherent in ground‐based mid‐IR astronomy. This test device merges the longwave HgCdTe photosensitive material with Teledyne's 2048×2048$$ 2048\times 2048 $$ GeoSnap‐18 (18‐μ$$ \mu $$m pixel) focal plane module, which is equipped with a capacitive transimpedance amplifier (CTIA) readout circuit paired with an onboard 14‐bit analog‐to‐digital converter (ADC). The final assembly yields a mid‐IR detector with high QE, fast readout (>85 Hz), large well depth (>1.2 million electrons), and linear readout. Longwave GeoSnap arrays would ideally be deployed on existing ground‐based telescopes as well as the next generation of extremely large telescopes. While employing advanced adaptive optics (AO) along with state‐of‐the‐art diffraction suppression techniques, instruments utilizing these detectors could attain background‐ and diffraction‐limited imaging at inner working angles <10 λ$$ \lambda $$/D, providing improved contrast‐limited performance compared with JWST MIRI while operating at comparable wavelengths. We describe the performance characteristics of the 13‐μ$$ \mu $$m GeoSnap array operating between 38 and$$ and $$ 45 K, including quantum efficiency, well depth, linearity, gain, dark current, and frequency‐dependent (1/f$$ 1/f $$) noise profile.
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