10-pm-order mechanical displacement measurements using heterodyne interferometry.

In this paper, we present 10-pm-order mechanical displacement measurements using heterodyne interferometry. The measuring system includes a single-path heterodyne interferometer and a phase meter based on a phase-locked loop (PLL). It is not easy to measure a mechanical displacement of 10 pm or less owing to electronics and environmental noises in the interferometer.

Securing noise-adaptive selection of interference signal by nonlinear detection.

In an interferometer, the interference fringe signal is typically linearly detected and modulated to a specific frequency region. A nonlinear detector yields the interference fringes of the fundamental and high-harmonic waves in different frequency regions. We analyze the formation of nonlinearly detected interference fringes.

Comparison of length measurements provided by a femtosecond optical frequency comb.

This paper presents a comparison of length measurements between the wavelength and the adjacent pulse repetition interval length (APRIL) provided by a femtosecond optical frequency comb. A theoretical estimation of the frequency stability for stabilizing the wavelength and APRIL, the frequency parameters that affect the stability of the APRIL in air, and the ambiguity in the length measurement by the APRIL are investigated. We find that the APRIL can be used as a low-cost measurement for the absolute length over a range of hundreds of meters in laboratory conditions.

Active suppression of air refractive index fluctuation using a Fabry-Perot cavity and a piezoelectric volume actuator.

Air refractive index fluctuation (Δn(air)) is one of the largest uncertainty sources in precision interferometry systems that require a resolution of nanometer order or less. We introduce a method for the active suppression of Δn(air) inside a normal air-environment chamber using a Fabry-Perot cavity and a piezoelectric volume actuator. The temporal air refractive index (n(air)) at a local point is maintained constant with an expanded uncertainty of ~4.