LITTLE JOE CCD67 CAMERA

Optimized for High speed and Best SNR

Little Joe cameras are specialized to run scientific CCDs at their maximum speed with the highest possible Signal to Noise Ratio (SNR). At the lowest light levels, CCDs are limited by read noise and at the highest light levels, CCDs are limited by photon noise. Our back-thinned CCDs are selected to have the highest possible Quantum Efficiency (QE) for the wavelengths of interest. This yields the maximum photon-noise-limited SNR by maximizing the number of electrons produced by photons. Our CCDs are also selected to have the lowest possible readnoise to maximize SNR when read noise limited.

CCDs – better than EMCCDs and CMOS

EMCCDs offer low noise at low photon fluxes by using extremely high gain in their serial outputs, which leads to several problems.In high gain mode, EMCCDs suffer degradation in photon noise SNR due to the statistical processes used in the amplification process. This reduces the SNR by the square root of 2. These statistical processes also result in rogue multiplication events (spurious charge), leading to pixel spikes which when digitally eliminated in the camera can result in the elimination of real pixel spikes. The extremely high gain in the output depends on very high clock voltages in the camera. This leads to long-term damage to the sensor and the potential for gain instability.

CMOS sensors can offer low readnoise but have low QE since there is a light-mask over the electronic circuit contained in each pixel. Since the photons are not absorbed uniformly across the sensor, they are unsuitable for wavefront sensing. They also suffer from random noise spikes that are digitally eliminated in the camera and can result in real noise spikes being eliminated. Pixel lenslets can improve QE but make uniformity even worse.