Possible application of the optical tunnel effect to membrane biophysics.

The exploitation of the optical tunnel effect allows the detection of very small spatial variations. The theory of optical tunneling is extended to an absorbing medium and an experimental apparatus capable of detecting displacements down to 0.19 nm, with fluctuations equivalent to 0.10 nm, is described. Some possible applications to the measurement of electrically induced volume changes of biological membranes are discussed.