Characterization results of EMCCDs for extreme low light imaging

ABSTRACT

EMCCDs are capable of extreme low light imaging thanks to sub-electron read-out noise, enabling single-photon counting. The characterization of e2v’s CCD60 (128 x 128), CCD97 (512 x 512) and CCD201-20 (1024 x 1024) using a controller optimized for the driving of EMCCDs at a high (≥ 10 MHz) pixel rate per output with < 0.002 e¯ total background signal. Using the CCD Controller for Counting Photons (CCCP), the horizontal and vertical CIC, dark current and EM gain stability are characterized.

1. INTRODUCTION

The CCD Controller for Counting Photons1 (CCCP), an electronic controller built with the aim of driving Electron Multiplying Charge Coupled Devices (EMCCDs) at a high (≥ 10 MHz) speed, with low ( 1 e¯) effective read-out noise, and the lowest possible Clock Induced Charges (CIC), was used to drive e2v’s∗ CCD60 (128 × 128 FT), CCD97 (512 × 512 FT) CCD201-20 (1024 × 1024 FT) and CCD207-40 (1600 × 1600 FF). Cameras built with the CCCP and the CCD60, CCD97 or the CCD201-20, respectively named EMN2 128, EMN2 512 and EMN2 1024, are now commercially available from Nuv¨ u Cam ¨ ¯eras† . In this paper, the characterization results of theses cameras is presented. For data regarding the CCD207-40, the reader is referred to [2].

First results were presented in [3] regarding the performance of an EMN2 512 camera. It was demonstrated that it was possible to drive the EMCCD in Inverted Mode Operation (IMO) and, at -85◦C, to get an effective read-out noise of 0.02e¯ (G/σ ratio of 50) while generating 0.0025e¯/pixel/image of CIC (measured with a 5σ threshold) and generate less than 0.001e¯/pixel/s of dark current. This extreme low noise enabled the use of this EMCCD in Photon Counting (PC) and, for low light applications (< 10 photons/pixel/s), reducing by 33% the time required to reach a given SNR when compared to the analog Mode (AM, sometimes called Linear Mode), despite a frame-rate 10× larger.

In this paper, the horizontal charge transfer efficiency measurements are presented in section 2. Measurements of the CIC generated by the vertical and horizontal transfers are presented in section 3. The dark current, as a function of temperature, was measured and the data are presented in section 4. The stability of the EM gain is presented in section 5.

2. CHARGE TRANSFER EFFICIENCY

The horizontal charge transfer efficiency of the EMCCDs was measured on the CCD60 by using a relative technique, the extended pixel edge response4 (EPER). Flat-fields were taken with moderate (>10 ke¯ / pixel) illumination and the deferred charges were measured in an overscan region. In order to increase the SNR, lines were averaged on half of the EMCCD and 10 images were taken with the same integration time under a stabilized light source. The CTE was measured by using three columns, taking the last one as the zero reference (Zm), the second one as the deferred measurement (Dm) and the first one as the signal level (Sm).

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