5. Image sensors

In fluorescence, light levels are low, and sensor efficiency and noise play a significant role in the final image. Depending on the technology used, the image will be acquired point by point, line by line, or, more often, by direct filling of a CCD-type matrix sensor.

Sensors are characterized by their quantum efficiency and noise level. Efficiency is measured in % of electrons per photon. It depends on wavelength, and can approach 95%.

Thermal noise is the stochastic production of electrons in the absence of a light source. This noise is roughly doubled every 8°C. Sensors are cooled either to a temperature slightly above 0°C, or to a lower one, down to – 90 ^°C , taking into account the risk of icing and condensation (dry air blower, for example).

On cameras, read noise...