BTFI is developed for faint source observations. In order to achieve this goal, its detector has to work in a “rapid scanning” mode where the selected wavelength is continuously scanned. This means that a massive 3-dimensional data-cube is acquired and integrated to achieve the required signal-to-noise. By using a “rapid scanning” technique, problems from atmospheric turbulence and variable extinction over long exposures are eliminated by taking the average of all accumulated frames in the data-cube.

Normal CCDs are non-optimal under these circumstances, as the readout noise dominates the noise from the target’s signal. To avoid this problem, the BTFI instrument uses EMCCD detectors. The main advantage of the EMCCD is that its readout noise is very low when a high gain is applied. EMCCD detectors are basically a normal CCD with an extended register responsible for an electron multiplication caused by the impact ionization on silicon. This phenomenon increases the detection performance since it amplifies the input interest signal. Performance gets improved, with an equivalent noise of less than 1 electron at high pixel rates (~10MHz).

Details about BTFI Cameras