Absolute Frequency Readout of Cavity against Atomic Reference

Abstract

Future space-based geodesy missions such as the Mass Change Mission and the Next Generation Gravity Mission are expected to rely on laser ranging as their primary instrument. Short-term laser frequency stability has previously been achieved on the GRACE Follow On mission by stabilizing the lasers to an optical cavity. The development of a technique to provide long-term laser frequency stability is expected to be required. We have previously demonstrated a technique to track long-term frequency changes by using measurements of the optical cavity’s free spectral range. In this paper, we calibrate this technique to absolute frequency by using an atomic reference. We have also validated an approach for on-ground calibration to allow the absolute frequency to be determined whilst in orbit.

Scale Factor Determination for the GRACE Follow-On Laser Ranging Interferometer Including Thermal Coupling

“…The cavity resonance frequency and FSR are linearly related to each other through ν = n mode • FSR + offset, where the mode number n mode is an integer mode number. The offset must be calibrated on-ground [30]. The principle has been demonstrated in laboratory experiments with an accuracy of roughly 3 MHz ≈ 10 ppb.…”

“…The principle has been demonstrated in laboratory experiments with an accuracy of roughly 3 MHz ≈ 10 ppb. It is noteworthy that the scale factor tone and its sidebands have little influence on the conventional PDH readout [30,31]. The advantage of this technique is that only minor changes to existing flight hardware are needed, e.g., the use of GHz electro-optical modulators (EOMs) instead of MHz.…”

Scale Factor Determination for the GRACE-Follow On Laser Ranging Interferometer including Thermal Coupling

“…After determination of the USO frequency during precise orbit determination, this technique is able to provide an estimate for the FSR frequency with high accuracy. The principle has been demonstrated in laboratory experiments with an accuracy of roughly 3 MHz ≈ 1 ppb [30,31]. The advantage of this technique is that the changes in existing flight-hardware are only minor.…”

MaQuIs - Mars Quantum Gravity Mission

“…The longer timescales requirement could be met by minimally invasive measures to the experimental setup to further enhance the stability of these optical cavities. Applicable techniques are currently under investigation in the context of the next generation of Earth gravity field missions (Rees et al, 2021(Rees et al, , 2022.…”