Towards the LISA backlink: experiment design for comparing optical phase reference distribution systems

Abstract

LISA is a proposed space-based laser interferometer detecting gravitational waves by measuring distances between free-floating test masses housed in three satellites in a triangular constellation with laser links in-between. Each satellite contains two optical benches that are articulated by moving optical subassemblies for compensating the breathing angle in the constellation. The phase reference distribution system, also known as backlink, forms an optical bi-directional path between the intra-satellite benches.In this work we discuss phase reference implementations with a target non-reciprocity of at most 2π µrad/ √ Hz, equivalent to 1 pm/ √ Hz for a wavelength of 1064 nm in the frequency band from 0.1 mHz to 1 Hz. One phase reference uses a steered free beam connection, the other one a fiber together with additional laser frequencies. The noise characteristics of these implementations will be compared in a single interferometric setup with a previously successfully tested direct fiber connection. We show the design of this interferometer created by optical simulations including ghost beam analysis, component alignment and noise estimation. First experimental results of a free beam laser link between two optical set-ups that are co-rotating by ±1 • are presented. This experiment demonstrates sufficient thermal stability during rotation of less than 10 −4 K/ √ Hz at 1 mHz and operation of the free beam steering mirror control over more than 1 week.

Single-Element Dual-Interferometer for Precision Inertial Sensing

“…For reaching displacement sensitivities on the order of or lower, it is essential to keep stray light noise in check, a lesson learned from experiments for LISA performed on ground (e.g., see [ 18 ]). Beams resulting from unwanted reflections or transmissions, known as “ghost beams”, inevitably occur due to imperfections in the optical surfaces of the interferometer, and will spoil the measurement when captured by the detectors.…”

Space-based Gravitational Wave Observatories

“…As shown in figure 1.2, the opening angle between the two MOSAs can be changed with a mechanism to independently track the far spacecraft. In LISA, the phase comparison needed to form the artificial beam splitter is realized using an optical fiber link between the two MOSAs [146]. The range of the MOSA actuation system of order one degree will allow to operate LISA for more than a decade.…”

Single-element dual-interferometer for precision inertial sensing

“…For reaching displacement sensitivities on the order of 1 pm/ √ Hz or lower, it is essential to keep stray light noise in check, a lesson learnt from experiments for LISA performed on ground (e.g., see [18]). Beams resulting from unwanted reflections or transmissions, known as "ghost beams", inevitably occur due to imperfections in the optical surfaces of the interferometer, and will spoil the measurement when captured by the detectors.…”