electro-optical shutters

Mechanical shutters are effective down to around 0.2 ms. Shorter exposures need to be controlled by devices without moving parts. The two most important of these are the Kerr and Pockels cells.

The Kerr cell is an optical cell filled with an optically active liquid such as nitrobenzene. When a strong electrical field is applied, a beam of linearly polarized light passing through it has its plane of polarization rotated by up to 90 degrees. If the cell is positioned between two crossed polarizing filters, this property can be used to operate the cell as a shutter. The Pockels cell operates in much the same way. It uses a crystal of a material such as potassium dihydrogen phosphate (KDP). A Pockels cell requires an electrical field of only a few kilovolts to achieve a 90-degree rotation, and can give nanosecond exposures.

Both types of shutter find uses in ultra-high-speed photography, and the Pockels cell is an important component of the pulse lasers used in industrial holography and holographic portraiture.

— Graham Saxby

Bibliography

• Wilson, J., and Hawkes, J. F. B., Lasers: Principles and Applications (2001)