Limitations on lasers for deep space communication

The energy associated with extremely-high-frequency photons of laser communication systems decreases their efficiency in transferring a given rate of information as compared to conventional radio systems. The increased efficiency made possible by narrower beamwidths at visible light frequencies more than compensates for this photon energy factor. However, if reliability in reception is to be maintained, extremely narrow beamwidths are forbidden unless elaborate and costly precision tracking gear is used and the receiver position is known to a high degree of accuracy. The 8- to 13-micron infrared range is optimum for space communications.