Temporal-offset dual-comb vibrometer with picometer axial precision

TL;DR

This paper introduces a dual-comb vibrometer with a novel Sagnac-based delay cancellation method, achieving picometer axial precision for measuring tiny surface vibrations with high accuracy.

Contribution

The work presents a new dual-comb vibrometer design that uses a Sagnac geometry to cancel delays and reduce phase jitter, enabling picometer-level displacement measurements.

Findings

Achieved 4 pm axial precision in surface vibration measurement

Reduced phase jitter through Sagnac geometry

Eliminated spurious signals with time gating

Abstract

We demonstrate a dual-comb vibrometer where the pulses of one frequency-comb are split into pulse pairs. We introduce a delay between the two pulses of each pulse pair in front of the sample, and after the corresponding two consecutive reflections at the vibrating sample surface, the initially introduced delay is cancelled by a modified Sagnac geometry. The remaining phase difference between the two pulses corresponds to the change in the axial position of the surface during the two consecutive reflections. The Sagnac geometry reduces the effect of phase jitter since both pulses propagate through nearly the same optical path (in opposite directions), and spurious signals are eliminated by time gating. We determine the amplitude of a surface vibration on a surface-acoustic-wave device with an axial precision of 4 pm. This technique enables highly accurate determination of extremely small displacements.