Use of Optical Frequencies for Space Communication

The spectrum from the infrared through the visible to gamma rays has been surveyed for signalling from Earth or an Earth satellite to a spaceship at planetary distances. The best region for signalling from a satellite vehicle appears to be from 2000 to 400 angstroms. One information bit per second could be sent for a distance many times the diameter of the solar system. If the source is to be on the Earth´s surface, the best wavelength region would be 4000 to 3000 angstroms. One could probably then reach the neighborhood of Mars at one bit per second when that planet is closest to the Earth. Greater distances would be possible at slower information rates.