Gated sCMOS Imaging detectors for fast Transient Plasmas diagnostics

Challenge Background

Research grade iCCDs are used to sample in time and accurately reconstruct the chemical properties and distributions of transient plasma dynamics. Plasmas such as laser-induced, RF or inductively-coupled, Dielectric Barrier Discharge plasmas are studied in order to derive fundamental properties, such as, electron temperature and density. Importantly iCCDs can achieve temporal resolution that can effectively ‘freeze’ transient phenomenon at the nanosecond level via gating of an image-intensifier. Moreover, iCCDs can move this gate very precisely (<2 ns) in time to obtain consecutive, high accuracy snapshots of plasma behaviour and phases. In order to accurately image a rapidly transient phenomenon such as plasma there are several key experimental challenges that an imaging platform must overcome:

Figure 2: Plasma streamer dynamics of an underwater discharge observed using an Andor iStar sCMOS camera by Jessica Stobbs, Bucur Novac, Peter Senior at the Plasma and Pulsed Power Group, Loughborough University, UK

• Large dataset acquisitions – The reconstruction of transient plasmas requires the acquisition of hundreds or thousands of imaging cycles. This can result in long dataset acquisition times.
• Ultra-fast phenomena – The short nanosecond lifetimes of plasmas require an ultrafast shutter to sequentially image formation dynamics. Failure to meet this need can result in streaking of images or an inability to capture each phase of a plasma formation cycle.
• Low light intensities – The quantity of light emitted by some plasma structures is exceptionally low, hence single photon sensitivity is required to properly visualise finer details.
• Fine structures – In order to fully capture all the complex features of plasma formation a high-resolution sensor is required.
• Oversaturation – Plasmas, such as dielectric barrier discharge plasmas, can have significant variations in optical intensity across the surface of the plasma, this can lead to the over saturation of camera sensors. To avoid this a camera must have a high dynamic range to capture weak and bright signals within one image.

Current time gated technologies such as CCDs, Interline CCDs and EMCCD based cameras are limited by their poor frame rates and limited dynamic range. Slow frame rates can result in long experimental timescales. Furthermore, the limited dynamic range of these devices mean compromises must be made to simultaneously capture weak or bright optical signatures during an experiment.

Technology Solution

Gated intensified sCMOS cameras offer the ideal solution for plasma imaging. The coupling of an intensifier to a sCMOS camera combines the ultra-fast nanosecond time resolution of an intensifier tube with the high frame rate and dynamic range of sCMOS technology. Offering an ideal versatile solution for plasma imaging and diagnostics whilst affording high speed and dynamic range to minimise experimental time and avoid over saturation.

Andor Camera Solutions for Transient Plasma Imaging

Andor strongly recommends its cutting edge, rapid high dynamic range iStar sCMOS camera system for transient plasma imaging applications. The iStar sCMOS offers top of the market <2 ns gating speeds with a rapid 50 fps full frame with a high resolution 5.5-megapixel camera. The low noise readout (2.5 e^-) coupled with a deep electron well depth allows enables 16-bit dynamic range. Additionally, frame rates of up to 4000 Hz can also be achieved in spectroscopy & crop modes making it also ideal for plasma spectroscopy applications such as Thomson Scattering, OES and LIBS. Andor also offers a range of intensified CCDs ideal for spectroscopy applications and slower imaging requirements.

A review of the key imaging requirements for plasmas and the iStar sCMOS:

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