RESUMO
The Laser Ranging Interferometer (LRI) instrument on the Gravity Recovery and Climate Experiment (GRACE) Follow-On mission has provided the first laser interferometric range measurements between remote spacecraft, separated by approximately 220 km. Autonomous controls that lock the laser frequency to a cavity reference and establish the 5 degrees of freedom two-way laser link between remote spacecraft succeeded on the first attempt. Active beam pointing based on differential wave front sensing compensates spacecraft attitude fluctuations. The LRI has operated continuously without breaks in phase tracking for more than 50 days, and has shown biased range measurements similar to the primary ranging instrument based on microwaves, but with much less noise at a level of 1 nm/sqrt[Hz] at Fourier frequencies above 100 mHz.
RESUMO
Accuracy in measuring displacement in optical interferometers is limited by cyclic errors introduced by various leakage paths within the system. Existing techniques to reduce this nonlinearity do not work when there is large optical loss in the target path, such as for long-range measurements. We describe a new approach to reducing nonlinearity that overcomes these limitations. Based on phase modulation of the laser light, and requiring minimal additional components, experiments have demonstrated rejection of the effects of leakage in the presence of large optical loss.
RESUMO
Cyclic errors that are due to optical leakage limit the precision of displacement measurements made with optical interferometers. A method for real-time estimation of leakage components is introduced and is used to implement a novel passive technique for suppression of cyclic nonlinearities that uses only adjustments of existing polarizers and quarter-wave plates. This approach is used to reduce the cyclic error from 3 nm to 300 pm for an interferometer operating at a wavelength of 1320 nm.
