Alignment signal extraction of the optically degenerate RSE interferometer using the wave front sensing technique

The alignment sensing and control scheme of the resonant sideband extraction interferometer is still an unsettled issue for the next-generation gravitational wave antennas. The issue is that it is difficult to extract separate error signals for all 12 angular degrees of freedom, which is mainly arising from the complexity of the optical system and cavity “degeneracy”. We have suggested a new sensing scheme giving reasonably separated signals which is fully compatible with the length sensing scheme. The key of this idea is to resolve the “degeneracy” of the optical cavities. By choosing an appropriate Gouy phase for the degenerate cavities, alignment error signals with much less admixtures can be extracted.