Tracking frequency laser distance gauge

Abstract

Advanced astronomical missions with greatly enhanced resolution and physics missions of unprecedented accuracy will require laser distance gauges of substantially improved performance. We describe a laser gauge, based on Pound–Drever–Hall locking, in which the optical frequency is adjusted to maintain an interferometer’s null condition. This technique has been demonstrated with pm performance. Automatic fringe hopping allows it to track arbitrary distance changes. The instrument is intrinsically free of the nm-scale cyclic bias present in traditional (heterodyne) high-precision laser gauges. The output is a radio frequency, readily measured to sufficient accuracy. The laser gauge has operated in a resonant cavity, which improves precision, can suppress the effects of misalignments, and makes possible precise automatic alignment. The measurement of absolute distance requires little or no additional hardware, and has also been demonstrated. The proof-of-concept version, based on a stabilized HeNe laser and operating on a 0.5 m path, has achieved 10 pm precision with 0.1 s integration time, and 0.1 mm absolute distance accuracy. This version has also followed substantial distance changes as fast as 16mm∕s. We show that, if the precision in optical frequency is a fixed fraction of the linewidth, both incremental and absolute distance precision are independent of the distance measured. We discuss systematic error sources, and present plans for a new version of the gauge based on semiconductor lasers and fiber-coupled components.

Experimental Tests of General Relativity

“…It will be able to detect a violation of the EP with a fractional acceleration accuracy of 5 parts in 10 14 in a short (few days) experiment and 3 to 10 fold better in a longer experiment. The experiment makes use of optical distance measurement (by TFG laser gauge [82]) and will be advantageously sensitive to short-range forces with a characteristic length scale of λ < 10 km. SR-POEM, a POEM-based proposed room-temperature test of the WEP during a sub-orbital flight on a sounding rocket (thus, SR-POEM), was recently also presented [3].…”

Space-Based Research in Fundamental Physics and Quantum Technologies

“…It will be able to detect a violation of the EP with a fractional acceleration accuracy of 5 parts in 10 14 in a short (few days) experiment and 3 to 10 fold better in a longer experiment. The experiment makes use of optical distance measurement (by TFG laser gauge [24]) and will be advantageously sensitive to short-range forces with a characteristic length scale of λ < 10 km. SR-POEM, a POEM-based proposed room-temperature test of the WEP during a sub-orbital flight on a sounding rocket, was recently also presented [25].…”

Toward a spaceworthy picometer laser gauge

“…In Ref. 5 it is shown that, assuming that all ofthe available frequency shift range is used for measuring absolute distance, this is equivalent to a<::'i. (5) Yp For the current TFG, this requires c<1.6x 106,a two order ofmagnitude improvement.…”

“…5 In Section 3, we discuss the current implementation ofthe TFG and the results from tests ofthat version. Finally, in Section 4, we introduce a series of techniques that we plan to use as part of a more robust, capable, and potentially spaceworthy laser gauge that we are developing, which we call the "new TFG.…”