High-Efficiency Charge-Coupled Devices Enable On-Sky Observations
This blog post originated in the 2016 Science Mission Directorate Technology Highlights Report (20 MB PDF).
In 2016, NASA delivered three types of detectors developed for Ultraviolet (UV), Near UV (NUV), and Near Infrared (NIR) applications to several different projects involving on-sky observations. Development of these charge-coupled devices (CCDs) required several new processes formulated by NASA. Successful observations using the new CCDs validated detector performance, and next the Agency plans to refine these detectors for use in suborbital flight. The high efficiency and stable response of these CCDs make them ideal for astronomy applications, and each is tailored for a different type of observation.
Delta doped and custom coated Electron-multiplying Charge-coupled Devices (EMCCDs), with their high signal-tonoise ratio, are particularly suitable for faint signal detection of phenomena such as intergalactic medium, circumgalactic halos, and star formation outflows. In collaboration with e2v, Inc., the NASA team developed an EMCCD that is back-illuminated and that has an electronic band structure that is modified using two-dimensional (2-D) doping (i.e., delta doping and super-lattice doping). This process produces 100% internal quantum efficiency. Further enhancement included the addition of antireflection (AR) coating. NASA delivered the coated, delta-doped EMCCD for observations at the Palomar observatory and subsequently for flight in the Faint Intergalactic Redshifted Emission Balloon (FIREBALL).
P-channel Charge-coupled Devices (CCDs) offer high radiation tolerance and are therefore very suitable for spacebased applications, including nextgeneration observatories that will conduct wide-field imaging surveys to study the formation and survival of stellar and planet-forming environments. Working with collaborators from Lawrence Berkeley National Laboratory, NASA enhanced a broadband p-channel CCD with 2-D doping and custom AR coating for use in the 320-1000-nm range. The new p-channel CCD was provided to Arizona State University for use at the Mount Bigelow observatory and to the Orion program for use in future missions. NASA also delivered a similar CCD enhanced for far UV to the Colorado High-resolution Echelle Stellar Spectrograph (CHESS) sounding rocket.
N-channel CCDs that are fabricated in thick, ultra-high purity silicon can be used in applications where broadband response is required. An example of such application is a star formation observatory concept named High Orbit Ultraviolet-Visible Satellite (HORUS). NASA delivered a broadband n-channel, fully depletable, thick CCD optimized for observations in the NUV to NIR spectrum TECHNOLOGY INFUSION 24 | 2016 SMD Technology Highlights to the Palomar Observatory for use with the WAfer-Scale camera for Prime (WaSP) camera.
Future NASA missions will require highperformance detector arrays. All three of these silicon arrays take advantage of processes developed at NASA to produce high-efficiency arrays with extended response in the ultraviolet and near infrared.
Status and Future Plans
The on-sky observations have revealed good performance and the team is continuing to develop and mature this technology. NASA is planning suborbital flights for the p-channel (a sounding rocket experiment) and n-channel EMCCD arrays (a balloon-borne experiment).
The Astrophysics Division supported development of these technologies through the SAT program. Shouleh Nikzad, April Jewell, Timothy Goodsall, Todd Jones, and Michael Hoenk from NASA JPL led these development efforts.
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