The next fundamental steps forward in understanding our place in the universe could be a result of advances in extreme contrast ratio (ECR) imaging and point spread function (PSF) suppression. For example, blinded by quasar light we have yet to fully understand the processes of galaxy and star formation and evolution, and there is an ongoing race to obtain a direct image of an exoearth lost in the glare of its host star. To fully explore the features of these systems we must perform observations in which contrast ratios of at least one billion can be regularly achieved with sub 0.′′ 1 inner working angles. Here we present the details of a latest generation 32-bit charge injection device (CID) that could conceivably achieve contrast ratios on the order of one billion. We also demonstrate some of its ECR imaging abilities for astronomical imaging. At a separation of two arc minutes, we report a direct contrast ratio of ∆m v = 18.3, log (CR) = 7.3, or 1 part in 20 million, from observations of the Sirius field. The atmospheric conditions present during the collection of this data prevented less modest results, and we expect to be able to achieve higher contrast ratios, with improved inner working angles, simply by operating a CID at a world-class observing site. However, CIDs do not directly provide any PSF suppression. Therefore, combining CID imaging with a simple PSF suppression technique like angular differential imaging, could provide a cheap and easy alternative to the complex ECR techniques currently being employed.
A scientific camera system having high dynamic range designed and manufactured by Thermo Electron for scientific and medical applications is presented.The newly developed CID820 image sensor with preamplifier-per-pixel technology is employed in this camera system. The 4 Mega-pixel imaging sensor has a raw dynamic range of 82dB. Each high-transparent pixel is based on a preamplifier-per-pixel architecture and contains two photogates for non-destructive readout of the photon-generated charge (NDRO). Readout is achieved via parallel row processing with on-chip correlated double sampling (CDS). The imager is capable of true random pixel access with a maximum operating speed of 4MHz.The camera controller consists of a custom camera signal processor (CSP) with an integrated 16-bit A/D converter and a PowerPC-based CPU running a Linux embedded operating system. The imager is cooled to -40C via three-stage cooler to minimize dark current. The camera housing is sealed and is designed to maintain the CID820 imager in the evacuated chamber for at least 5 years.Thermo Electron has also developed custom software and firmware to drive the SpectraCAM SPM camera. Included in this firmware package is the new Extreme DR TM algorithm that is designed to extend the effective dynamic range of the camera by several orders of magnitude up to 32-bit dynamic range. The RACID Exposure graphical user interface image analysis software runs on a standard PC that is connected to the camera via Gigabit Ethernet.
Charge Injection Devices (CIDs) have demonstrated direct contrast ratios in excess of 1:20 million from suboptimal ground-based astronomical observations. CIDs are therefore interesting prospects for obtaining direct images from a host of high contrast ratio celestial scenes. However, while CIDs are capable of much deeper contrast ratios, potentially exceeding 1:1 billion, they do not address the Inner Working Angle (IWA) problem. If the Point-Spread Function (PSF) of a bright target is not well understood and accounted for, then the IWA will be large and nearby faint objects, like exoplanets, will be challenging to observe regardless of the detector used. As Earth's atmosphere is a major contributor to the variability of a PSF, high contrast ratio imaging with small IWAs will be best achieved in space. Therefore, if CIDs are to be used on future space-telescopes, they must be flight qualified in the space environment and shown to be at the appropriate Technology Readiness Level (TRL). Here we report the results of an 8 months CID technology demonstration mission that used the Nano-Racks External Platform mounted to the Kibo Exposed Facility on-board the International Space Station. Over the course of the 236 days mission we find no significant on-orbit changes of CID performance in terms of dark current, linearity, read noise, and photon transfer efficiency. As a result, CIDs are now space-qualified to TRL-8 and can be considered for future space telescopes.
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