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A remote laboratory for optical levitation of charged droplets

Journal article
Authors D. Galan
Oscar Isaksson
Mats Rostedt
Jonas Enger
Dag Hanstorp
L. de la Torre
Published in European Journal of Physics
Volume 39
Issue 4
ISSN 0143-0807
Publication year 2018
Published at Department of Physics (GU)
Language en
Keywords remote laboratories, optical levitation, lasers, particles in electrical fields, size measurement by diffraction, online experimentation, mobile devices, education, labs, web, Education & Educational Research, Physics
Subject categories Physical Sciences


We present a remotely controlled experiment in which liquid droplets are levitated by a vertically aligned focused laser beam. The droplets levitate at the point where the photon pressure of the focused laser beam balances the gravitational force. The size of a trapped droplet can be measured by detecting the diffraction pattern created by the trapping laser light. The charge on the trapped droplet can thereafter be determined by observing its motion when a vertically directed electrical field is applied. This experiment allows a student to study many fundamental physics processes, such as photon pressure, diffraction of light, or the motion of charged particles in electrical fields. The complexity of the experiments and the concept studied make this suitable for advanced studies in physics. The laser power required in the experiment is about 1 W, which is a thousand times greater than the value of 1 mW at which lasers begin to be capable of causing harm to eyes; high voltages are also used. Further, the cost of the equipment is relatively high, which limits its availability to most undergraduate teaching laboratories. It thus constitutes an ideal experiment for remote control.

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