Kerr cell shutter

The Kerr Cell consists of a transparent container (A) filled with nitrobenzene[1] (B) with attached electrodes (C and D).

A high voltage is passed through the electrodes which causes an electric field perpendicular to the transmitted light beam to be applied.

The cell makes use of the Kerr effect, in which the nitrobenzene becomes birefringent under the influence of the electric field.

These have now largely been replaced by KTN (potassium tantalate niobate) and barium titanate (BaTiO3).

When the cell is activated the light beam is diverted and takes a different path to the receiver, this time difference is measured and the speed of light is calculated based on knowledge of the expected return time.