Cavity length measurement: bias from misalignment and mismatching.

SR-POEM, the sounding rocket principle of equivalence measurement, uses a set of six tracking-frequency laser gauges operating in Fabry-Perot cavities to determine the relative acceleration of two test masses (TMs) that are chemically different. One end of each cavity is a flat mirror on a TM; the other end is a concave coupling mirror mounted to a common reference plate. The tracking-frequency laser gauges work by locking a variable frequency laser to the cavity by the method of Pound, Drever, and Hall.

Aligning a reflection cavity by Anderson's method.

The sounding rocket principle of equivalence measurement uses a set of four laser gauges operating in Fabry-Perot cavities to determine the relative acceleration of two test masses that are chemically different. One end of each cavity is a flat mirror on a test mass. Because the test masses are unconstrained and thus expected to rotate slightly during measurement, and because the distance measurements are made at the sub-picometer level, it is essential to have real-time alignment of the beam entering the cavity.

Subpicometer length measurement using semiconductor laser tracking frequency gauge.

We have demonstrated heretofore unattained distance precision of 0.14 pm (2 pm) incremental and 14 nm (2.9 μm) absolute in a resonant (nonresonant) interferometer at an averaging time of 1 s, using inexpensive telecommunications diode lasers.