Interferometric characterization and modeling of pathlength errors resulting from beamwalk across mirror surfaces in LISA

Abstract

An alternative payload concept with in-field pointing for the laser interferometer space antenna utilizes an actuated mirror in the telescope for beam tracking to the distant satellite. This actuation generates optical pathlength variations due to the resulting beamwalk over the surface of subsequent optical components, which could possibly have a detrimental influence on the accuracy of the measurement instrument. We have experimentally characterized such pathlength errors caused by a λ/10 mirror surface and used the results to validate a theoretical model. This model is then applied to predict the impact of this effect for the current optical design of the LISA off-axis wide-field telescope.

An experiment to test in-field pointing for Elisa

“…In addition to measuring the passive stability the dependence of the optical pathlength through both the mechanism and the telescope surfaces on the pointing angle can be investigated. Thus piston generated directly at the mechanism and due to systematic beam steering over the mirror topography within the telescope can be studied [3]. Moreover the coupling of pointing jitter to local topography gradients on mirror surfaces and the impact of misalignments, i.e.…”

Elisa technology consolidation study overview

“…The value used in the figure is the maximum change in pointing over the 6 year mission duration that was considered. The value is significant because the optical metrology system must actively be adjusted to accommodate this variation, either or by articulating the entire payload assembly or by utilising a small adjustable mirror within a wide-field telescope (in-field pointing) [6], this places limits on how large a variation can be easily accommodated, and is especially significant in the case of in-field pointing.…”

The analysis of the far-field phase and the tilt-to-length error contribution in space-based laser interferometry

“…Tilt-to-length (TTL) error is also one of the most significant noise sources in the spacebased interferometer, and it has been verified in the GRACE Follow-On [13][14][15]. TTL error is supposed to be reduced by redesigning the optical layout [16][17][18] or being subtracted in data post-processing [19]. The generation mechanism of the TTL error is very complex in the space-based interferometer and the studies provided the detailed analysis of the sources and precise values of TTL errors [20][21][22].…”