Robust phase-stepping interferometry for traceable length measurements in a Hilger–Watts gauge-block interferometer

Abstract

We demonstrate a simple adaptation of the venerable Hilger-Watts gauge-block interferometer capable of performing automated, traceable calibrations of gauge block length by phase-stepping interferometry (PSI). We discuss the selection of robust PSI filtering algorithms to counteract in software the flaws of the hardware implementation, including markedly non-sinusoidal fringes and inhomogeneous phase step size. We find that the length measurement errors attributable to the phase measurement can be reduced to 0.6 nm, even with a simple retrofit to an instrument not originally designed for PSI.

Choosing wavelengths and assessing blunder risk for the method of exact fractions

“…When operators must visually assess the fringe displacements, η i might be on the order of 0.05 [3,6]. With automated reading using phase-stepping interferometry one can reach η i = 0.002 even in simple instruments [25], and lower values have been reported for measurements in vacuum with careful control of phase-step sizes and correction for camera nonlinearities [5,26]. As discussed in section 2, η i also becomes sensitive to wavelength uncertainties as L 0 increases, with η i u(p i )L 0 .…”