  Laser interferometry serves a fundamental role in science and technology,
assisting precision metrology and dimensional length measurement. During the
past decade, laser frequency combs - a coherent optical-microwave frequency
ruler over a broad spectral range with traceability to time-frequency standards
- have contributed pivotal roles in laser dimensional metrology with
ever-growing demands in measurement precision. Here we report
spectrally-resolved laser dimensional metrology via a soliton frequency
microcomb, with nanometric-scale precision. Spectral interferometry provides
information on the optical time-of-flight signature, and the large
free-spectral range and high-coherence of the microcomb enables tooth-resolved
and high-visibility interferograms that can be directly readout with optical
spectrum instrumentation. We employ a hybrid timing signal from comb-line
homodyne interferometry and microcomb spectrally-resolved interferometry - all
from the same spectral interferogram. Our combined soliton and homodyne
architecture demonstrates a 3-nm repeatability achieved via homodyne
interferometry, and over 1,000-seconds stability in the long-term precision
metrology at the white noise limits.

Instrumentation and Detectors;Applied Physics;Optics