Astronomical interferometry with near-IR e-APD at CHARA: characterization, optimization and on-sky operation

TL;DR

This paper characterizes and optimizes a near-IR e-APD camera for astronomical interferometry at CHARA, demonstrating improved performance and enabling enhanced observational capabilities.

Contribution

It introduces a new model for signal distribution in the e-APD camera, providing independent measurements of gain and ENF, and demonstrates on-sky performance improvements.

Findings

Gain is approximately half of the manufacturer's value.

ENF measured at 1.47 exceeds the expected 1.25.

Total noise can be below 1 e-/frame/pixel at high gain and frame rate.

Abstract

We characterize a near-infrared C-RED ONE camera from First Light Imaging (FLI). This camera uses a SAPHIRA electron avalanche photo-diode array (e-APD) from Leonardo (previously Selex). To do so, we developed a model of the signal distribution. This model allows a measurement of the gain and the Excess Noise Factor (ENF) independently of preexisting calibration such as the system gain. The results of this study show a gain which is 0.53 +/- 0.04 times the gain reported by the manufacturer. The measured ENF is 1.47 +/- 0.03 when we expected 1.25. For an avalanche gain of 60 and a frame rate larger than 100 Hz, the total noise can be lower than 1 e-/frame/pixel. The lowest dark current level is 90e-/s/pixel, in agreement with the expected H-band background passing through the camera window. These performance values provide a significant improvement compared to earlier-generation PICNIC camera and allowed us to improve the performance of the Michigan infrared combiner (MIRC) instrument at the Center for High Angular Resolution Astronomy (CHARA), as part of our MIRC-X instrumentation project.