Dual-comb ranging yields reliable surface acoustic wave amplitude measurements

The ability to quantitatively evaluate the extremely small mechanical vibrations occurring on the surfaces of solids is important not only for fundamental physics but also for laboratory and field applications. Amplitudes of extremely small surface vibrations are typically found through optical interferometry. While precise, this method sometimes suffers from spurious reflections which can degrade the accuracy of the measurement.

Iwasaki et al. have developed a type of dual-comb ranging capable of determining the absolute displacement of a vibrating object with picometer axial precision.

Using a dual-comb vibrometer, the researchers were able to accurately measure surface acoustic wave vibration amplitudes which exist at sub-angstrom levels. Time-domain analysis improved the accuracy of the results, a delay between the two laser pulses reduced the effects of phase jitter, and the displacement was calculated from the observed phase difference and the exact optical frequencies of the laser pulse. The surface vibration was determined with an axial precision of 4 picometers.

“These methods ensure that the obtained amplitude value is very accurate and reliable,” said author Shinichi Watanabe. “The achieved precision is the highest among the displacement measurements using dual-comb ranging.”

The new approach opens an avenue for ultra-precise and accurate length metrology of extremely tiny displacements such as those found in mechanical-spin conversions.

“Because this technique to evaluate the surface acoustic wave vibration amplitude is reliable, many interesting physical phenomena associated with the vibration can be quantitatively investigated,” said Watanabe.

Source: “Temporal-offset dual-comb vibrometer with picometer axial precision,” by A. Iwasaki, D. Nishikawa, M. Okano, S. Tateno, K. Yamanoi, Y. Nozaki, and S. Watanabe, APL Photonics (2022). The article can be accessed at https://doi.org/10.1063/5.0099155 .