Increasing Optical Detectability

9301-012

The are two basic methods to increase the detectability of optical signals:

Method 1

Transmit powerful CW signals and expect the recipients to employ (coherent) heterodyne detection. The internal receiver noise will be overcome by the local-oscillator laser, and background radiation by the narrow optical bandwidth.

Method 2

Transmit very powerful pulse signals and expect the recipients to employ (incoherent) photon-counting. Discrimination of the signal count from the background is possible even for relatively large optical bandwidths.

Method 1 was chosen for Professional Optical SETI since it is a direct analog of conventional microwave systems. Method 2 was chosen for Amateur Optical SETI.

This is not meant to suggest that Professional Optical SETI Observatories would not use incoherent photon-counting. However, it probably implies that Amateur Optical SETI Observatories would not use coherent heterodyne detection, if only because of the very high receiver complexity and cost.