Absolute pressure and gas species identification with an optically levitated rotor

TL;DR

This paper introduces a novel optically levitated microsphere-based vacuum gauge that measures pressure and gas composition by analyzing the microsphere's rotational damping, enabling localized absolute vacuum measurements and gas analysis without ionization.

Contribution

It presents a new spinning-rotor vacuum gauge using optically levitated silica microspheres, capable of measuring pressure, gas species, and molecular mass in a compact, contactless manner.

Findings

Damping time inversely proportional to residual gas pressure.

Calibration achieved through mass measurement and shape confirmation.

Effective in measuring gas composition and molecular mass up to 1 mbar.

Abstract

The authors describe a novel variety of spinning-rotor vacuum gauge in which the rotor is a ${\sim}4.7{\text -}\mu$m-diameter silica microsphere, optically levitated. A rotating electrostatic field is used to apply torque to the permanent electric dipole moment of the silica microsphere and control its rotational degrees of freedom. When released from a driving field, the microsphere's angular velocity decays exponentially with a damping time inversely proportional to the residual gas pressure, and dependent on gas composition. The gauge is calibrated by measuring the rotor mass with electrostatic co-levitation, and assuming a spherical shape, confirmed separately, and uniform density. The gauge is cross-checked against a capacitance manometer by observing the torsional drag due to a number of different gas species. The techniques presented can be used to perform absolute vacuum measurements localized in space, owing to the small dimensions of the microsphere and the ability to translate the optical trap in three dimensions, as well as measurements in magnetic field environments. In addition, the dynamics of the microsphere, paired with a calibrated vacuum gauge, can be used to measure the effective molecular mass of a gas mixture without the need for ionization and at pressures up to approximately 1 mbar.