EMCCDs: 10 MHz and beyond
ABSTRACT
EMCCDs are capable of MHz pixel rate whilst maintaining sub-electron readout noise. Tens of frames per second are common place for large and medium EMCCD formats (1k×1k, 512×512), while smaller formats can reach hundreds and even thousand of frames per second. For applications where speed is a key factor, overclocked EMCCD were used at or beyond the manufacturer’s specifications. Very few data were published on the impacts of high speed clocking of EMCCDs, either vertically or horizontally. This paper presents characterization results of EMCCDs clocked at high speed.
1. INTRODUCTION
Astronomical observations of rapidly pulsating stars such as white dwarfs, hot subdwarfs1 or roAp2 stars having the periods of oscillation as short as a few minutes require very fast and very precise time-domain photometric measurements. Faint space debris or asteroids passing on short time scales also demand fast and reliable data to determine their astrometric properties.3 Furthermore, correcting the distortion caused by atmospheric turbulence is essential for improving the image quality of the next generation of instruments for 8 to 40 m class telescopes employing sophisticated adaptive optics systems.
EMCCDs meet all requirements set by the previous applications with their speed, sensitivity, and low noise. To achieve even greater speeds for faster data acquisition, camera manufacturers and users have used the devices at or above the manufacturers’ specifications. Yet very few data were published regarding how high speed clocking alters EMCCD performances. In this paper, we explore the effect of high speed clocking over charge transfer efficiency (CTE), linearity and clock-induced charges (CIC) of an e2v Technologies grade-1 CCD201-20 1k×1k EMCCD chip. Measurements were performed using version 3 of the patented CCD Controller for Counting Photon (CCCP) designed by Nuv¨ u Cam ¨ ¯eras.
2. CCCP
The CCCP controller has been solely designed for optimal photon-counting imaging by reducing clock-induced charges, the dominant source of noise in such applications, while still allowing higher flux imaging with flawless image quality. Contrary to regular controllers, it generates arbitrary clock shapes to drive the EMCCD chip readout, among them sinusoidal clocks that have been shown to significantly decrease CIC.
Since 2008, Nuv¨ u Cam ¨ ¯eras has developed 3 generations of CCCP controllers, the latest (CCCPv3) being integrated in all the company’s camera lines. In only 4 years, several major improvements have been added to the controller. These significant modifications were made during the course of work under a contract with the Canadian Space Agency aimed at advancement of technology readiness level (TRL) of the detector control electronics and readout system. The controller design changes have resulted in substantial reduction of mass, power and volume budgets and current board designs are based on components having space qualified versions.
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