Assessment of gas molar density by gas modulation refractometry: A review of its basic operating principles and extraordinary performance

A technique for high-precision and high-accuracy assessment of both gas molar (and number) density pressure, Gas Modulation Refractometry (GAMOR), is presented. The achieves its properties by assessing refractivity as a shift directly measurable beat frequency use Fabry-Perot cavity (FPC) based refractometry utilizing the Pound-Drever-Hall laser locking technique. Conventional FPC-based is, however, often limited fluctuations drifts FPC. GAMOR remedies this an additional utilization modulation methodology, built upon repeated filling evacuation measurement together with interpolation empty responses. procedure has demonstrated ability to reduce influence in non-temperature stabilized dual-FPC (DFPC)-based system, when more than three orders magnitude. When applied DFPC system active temperature stabilization, it demonstrated, pressure N2 at 4304 Pa room temperature, which corresponds 1.7 × 10−6 mol/cm3, sub-0.1 ppm precision (i.e. resolution 0.34 mPa). It claimed that assess least good so far been addressed, 1.2 10−13 mol/cm3). recently argued methodology should be capable providing accuracy low range. These levels are unprecedented among laser-based techniques detection atomic molecular species. Since polarizability He can calculated ab initio quantum mechanical calculations sub-ppm accuracy, also used primary or semi-primary standard pressure.