Abstract
We discuss the tilt-to-length (TTL) coupling noise caused by interference between a flat-top beam and a Gaussian beam. Several physical models are presented to research the effects of non-diffracted and diffracted beams on TTL noise. A special case that can remove TTL coupling noise is discovered and is verified via both theoretical analysis and numerical simulations. The proposed case could provide desirable suggestions for the construction of high-precision interferometers such as the Laser Interferometer Space Antenna (LISA), Taiji program, or other interferometry systems.
Highlights
In the detection processes of space-borne and long-baseline laser interferometers such as the LaserInterferometer Space Antenna (LISA) [1] and Taiji program [2,3], the coupling between the beam jitter and the path length readout represents a significant noise source, this coupling is called tilt-to-length (TTL) coupling [4]
The phase definition selected by Laser Interferometer Space Antenna (LISA) Pathfinder is LISA Pathfinder (LPF) signal, which first sums the complex amplitudes of each quadrant of QPD
We can conclude that in the case of the diffraction model shown in Figure 1, the TTL coupling noise can be eliminated if the detector used is a large single-element photo-diode (SEPD) and z0 = 0
Summary
Interferometer Space Antenna (LISA) [1] and Taiji program [2,3], the coupling between the beam jitter and the path length readout represents a significant noise source, this coupling is called tilt-to-length (TTL) coupling [4]. The wavefront will suffer diffraction and its propagation direction will jitter because of beam clipping and pointing accuracy limitations, and when the obvious beam type differences between the two interfering beams are considered, the above factors will produce more complex noise in the length readout. In this paper, both non-diffracted and diffracted models are constructed to research the interference between a flat-top beam and a Gaussian beam. A special case, in which the TTL noise can be made negligible by placing the beam waist in an appropriate position and using a suitably large detector without clipping, is found and is verified via both analytical solutions and numerical simulations
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