Enhancing the Range and Information Grasp by Improving Coherenceof the Lidar Reference Oscillator

摘要

One issue which can offer a significant gain in the information content of echo-returns from remote objects is improving the phase stability of the Optical Frequency Reference Oscillator used for the coherence base for the system. If we neglect echo phase noise added due to atmospheric effects (turbulence, scattering ...), one can make some estimates to usefully guide our thinking about the feasible range and phase noise of a Coherent Lidar system, for example as could be used in space. Long delay times are particularly challenging as the return power is reduced by diffractive losses and the large time-differential samples the optical source phase noise after a larger number of cycles have been emitted - both effects deteriorate the readout quality. For example, free-running lasers rarely are phase-coherent for 1 ms, corresponding to 150 km range. The practical case is normally made drastically worse by vibrations inadvertently applied to the source and antenna. With the methods described, we have shown optical phase stability for times >1s.