Precision and Accuracy Testing of FMCW Ladar Based Length Metrology

TL;DR

This paper presents a method for calibrating FMCW ladar length measurement systems using molecular spectroscopy, achieving ppm-level accuracy validated through comparison with a laser interferometer.

Contribution

It introduces a novel calibration approach for FMCW ladar using molecular references, enabling high-precision length metrology with traceable uncertainties.

Findings

Achieved a few ppm uncertainty in FMCW ladar calibration.

Demonstrated ppm agreement between FMCW ladar and interferometer measurements.

Validated the calibration method with experimental comparisons.

Abstract

The calibration and traceability of high resolution frequency modulated continuous wave (FMCW) ladar sources is a requirement for their use in length and volume metrology. We report the calibration of a FMCW ladar length measurement system by use of spectroscopy of molecular frequency references HCN (C-band) or CO (L-band) to calibrate the chirp rate of the FMCW source. Propagating the stated uncertainties from the molecular calibrations provided by NIST and measurement errors provides an estimated uncertainty of a few ppm for the FMCW system. As a test of this calibration, a displacement measurement interferometer with a laser wavelength close to that of our FMCW system was built to make comparisons of the relative precision and accuracy. The comparisons performed show ppm agreement which is within the combined estimated uncertainties of the FMCW system and interferometer.