Tilt-to-Length Coupling in the GRACE Follow-On Laser Ranging Interferometer

Wegener, Henry; Müller, Vitali; Heinzel, Gerhard; Misfeldt, Malte

doi:10.2514/1.a34790

Cited by 34 publications

(49 citation statements)

References 26 publications

(36 reference statements)

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“…Yet, due to many reasons we discuss below, the motion in any degree of freedom usually couples to a certain extent into the phase readout, an effect to which we refer to as tilt-to-length (TTL) coupling. The TTL coupling is a considerable noise source in high precision laser interferometry [1,2,3,4,5,6,7]. In LISA Pathfinder, TTL was visible as a 'bump' in the noise spectrum at frequencies between 20 mHz to 200 mHz [8,4,9,10] and was reduced by realignment and subtraction in data post-processing [11].…”

Section: Introductionmentioning

confidence: 99%

“…In LISA Pathfinder, TTL was visible as a 'bump' in the noise spectrum at frequencies between 20 mHz to 200 mHz [8,4,9,10] and was reduced by realignment and subtraction in data post-processing [11]. In the second generation Gravity Recovery And Climate Experiment (GRACE Follow-On) [12,13,5], TTL coupling was considered as one of the highest noise contributors after laser frequency noise in the Laser Ranging Interferometer (LRI). In flight, the TTL noise was then shown to lie within the requirements [5].…”

Section: Introductionmentioning

confidence: 99%

“…In the second generation Gravity Recovery And Climate Experiment (GRACE Follow-On) [12,13,5], TTL coupling was considered as one of the highest noise contributors after laser frequency noise in the Laser Ranging Interferometer (LRI). In flight, the TTL noise was then shown to lie within the requirements [5]. Furthermore, TTL coupling is of particular interest in the future space gravitational wave detector LISA [14,15,16,17,6,7] where it is one of the most significant noise sources, and a variety of measures are being taken to suppress it optimally.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Geometric tilt-to-length coupling in precision interferometry: mechanisms and analytical descriptions

Hartig,

Schuster,

Wanner

2022

Preprint

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Tilt-to-length coupling is a technical term for the cross-coupling of angular or lateral jitter into an interferometric phase signal. It is an important noise source in precision interferometers and originates either from changes in the optical path lengths or from wavefront and clipping effects. Within this paper, we focus on geometric TTL coupling and categorize it into a number of different mechanisms for which we give analytic expressions. We then show that this geometric description is not always sufficient to predict the TTL coupling noise within an interferometer. We, therefore, discuss how understanding the geometric effects allows TTL noise reduction already by smart design choices. Additionally, they can be used to counteract the total measured TTL noise in a system. The presented content applies to a large variety of precision interferometers, including space gravitational wave detectors like LISA.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Geometric tilt-to-length coupling in precision interferometry: mechanisms and analytical descriptions

Hartig,

Schuster,

Wanner

2022

Preprint

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“…The LRI was designed to have a minimal tilt-to-length coupling, which has been confirmed by in-flight measurements to be below 150 µm/rad [33]. The coupling is significantly lower than for the KBR [35], where the reference point for the range measurement is offset by approx.…”

Section: Introductionmentioning

confidence: 99%

Revisiting the light time correction in gravimetric missions like GRACE and GRACE follow-on

Yan

Müller

Heinzel

et al. 2021

J Geod

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The gravity field maps of the satellite gravimetry missions Gravity Recovery and Climate Experiment (GRACE ) and GRACE Follow-On are derived by means of precise orbit determination. The key observation is the biased inter-satellite range, which is measured primarily by a K-Band Ranging system (KBR) in GRACE and GRACE Follow-On. The GRACE Follow-On satellites are additionally equipped with a Laser Ranging Interferometer (LRI), which provides measurements with lower noise compared to the KBR. The biased range of KBR and LRI needs to be converted for gravity field recovery into an instantaneous range, i.e. the biased Euclidean distance between the satellites’ center-of-mass at the same time. One contributor to the difference between measured and instantaneous range arises due to the nonzero travel time of electro-magnetic waves between the spacecraft. We revisit the calculation of the light time correction (LTC) from first principles considering general relativistic effects and state-of-the-art models of Earth’s potential field. The novel analytical expressions for the LTC of KBR and LRI can circumvent numerical limitations of the classical approach. The dependency of the LTC on geopotential models and on the parameterization is studied, and afterwards the results are compared against the LTC provided in the official datasets of GRACE and GRACE Follow-On. It is shown that the new approach has a significantly lower noise, well below the instrument noise of current instruments, especially relevant for the LRI, and even if used with kinematic orbit products. This allows calculating the LTC accurate enough even for the next generation of gravimetric missions.

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“…This measurement is challenged by many noise sources at the local-instrument level, at the optical-link level, and of residual origin. Tilt-to-length coupling is one of the most significant contributions to the total noise budget in LISA (and also in LPF [10] and GRACE-FO [11,12]). Relative angular motion between the TM and the spacecraft, and between remote spacecraft, results in angular jitter of the interfering beams and a consequent error in the longitudinal displacement measurement.…”

Section: Introductionmentioning

confidence: 99%

Optical Suppression of Tilt-to-Length Coupling in the LISA Long-Arm Interferometer

et al. 2020

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The arm length and the isolation in space enable the Laser Interferometer Space Antenna (LISA) to probe for signals unattainable on the ground, opening a window to the subhertz gravitational-wave universe. The coupling of unavoidable angular spacecraft jitter into the longitudinal displacement measurement, an effect known as tilt-to-length (TTL) coupling, is critical for realizing the required sensitivity of picometer/ √ Hz. An ultrastable interferometer test bed has been developed in order to investigate this issue and validate mitigation strategies in a setup representative of LISA and in this paper it is operated in the long-arm interferometer configuration. The test bed is fitted with a flat-top beam generator to simulate the beam received by a LISA spacecraft. We demonstrate a reduction of TTL coupling between this flattop beam and a Gaussian reference beam via the introduction of two-and four-lens imaging systems. TTL coupling factors below ±25 μm/rad for beam tilts within ±300 μrad are obtained by careful optimization of the system. Moreover, we show that the additional TTL coupling due to lateral-alignment errors of elements of the imaging system can be compensated by introducing lateral shifts of the detector and vice versa. These findings help validate the suitability of this noise-reduction technique for the LISA long-arm interferometer.

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Tilt-to-Length Coupling in the GRACE Follow-On Laser Ranging Interferometer

Cited by 34 publications

References 26 publications

Geometric tilt-to-length coupling in precision interferometry: mechanisms and analytical descriptions

Geometric tilt-to-length coupling in precision interferometry: mechanisms and analytical descriptions

Revisiting the light time correction in gravimetric missions like GRACE and GRACE follow-on

Optical Suppression of Tilt-to-Length Coupling in the LISA Long-Arm Interferometer

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