All optical measurement of tiny torques

Published: 10 June 2022

A collaboration with colleagues at the Medical University of Innsbruck has realised a technique to measure directly torques in the atto (10-18) Newton meter range. Such tiny torques are directly relevant for microscope-based measurements of cells and similarly sized bodies.

A collaboration with colleagues at the Medical University of Innsbruck has realised a technique to measure directly torques in the atto (10-18) Newton meter range.  Such tiny torques are directly relevant for microscope-based measurements of cells and similarly sized bodies. 

The principle behind the measurement, which was first proposed more than 20 years ago, relies on the global conservation of angular momentum.  If we can determine the angular momentum content of the light scattered by the microscopic object then we can calculate the angular momentum transferred to the scatterer and hence the torque.  The challenge is to measure, with sufficient precision, both the intensity and the phase of the entire scattered field.  This was achieved by means of a combination of optical traps and a specially designed imaging system.

The team’s paper, entitled ‘Generally applicable holographic torque measurement for optically trapped particles’ is published in Physical Review Letters.  The research was supported by funding from the Austrian Science Fund and the Royal Society.

tiny torques

 

 


First published: 10 June 2022

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