High-precision gas refractometer by comb-mode-resolved spectral interferometry

Abstract

High-accuracy knowledge of gas refractivity is typically crucial for optical interferometry, precise optical systems, and calculable pressure standard development. Here, we demonstrate an absolute gas refractometer by spectral interferometry and a high-resolution spectrometer. The spectral interferometry relies on a comb with fiber Fabry–Pérot filtering cavity, and a double-spaced vacuum cell. The spectrometer employs a virtually imaged phased array, diffraction grating and near-infrared camera to fully resolve the comb modes. Finally, by means of fast-Fourier-transform, the group refractivity can be derived from the spectrally resolved interferograms of the two beams propagating in the inside and outside of the vacuum cell. To confirm the feasibility and performance of the gas refractometer, the measurement of ambient air was conducted. The proposed scheme has a combined uncertainty of 1.3 × 10−9 for air and a single measurement only takes 10 ms, which is applicable for gas refractivity monitoring and compensating in real time.

Transient heating in fixed length optical cavities for use as temperature and pressure standards

“…These approaches have garnered global interest because traceability can be achieved through quantum chemical properties of the helium atom, thus a quantum traceability to the SI. Optical interferometric techniques for measuring gas density based on refractive index are advancing the field of pressure metrology [1][2][3][4][5][6][7][8]. The methodology has gained acceptance globally because of the demonstrated an expanded uncertainty (k = 2) less than 9 μPa Pa −1 at atmospheric pressure [4].…”