Abstract

Second order nonlinear optical effects have been thoroughly studied and used ever since the very first experiment in the early 1960’s It is also well known that only materials lacking the center of inversion symmetry possess the second order susceptibility χ⁽²⁾[1]. At the same time, externally applied fields can break the symmetry and cause the so-called field induced second order susceptibility. For example, this effect is believed to be behind the “seeded” second harmonic generation (SHG) in glass fibers where external field is produced by space charge [2]. In insulating materials it is not difficult to apply external fields high enough to produce appreciable χ⁽²⁾, One can then envision that this DC-induced SHG can be used to probe and map the distribution of the electric field. But what about the metals and semiconductors, where the electric fields are small while the currents can be quite strong? Here, using simple two-band model, we show that in the presence of a direct current a second order nonlinear susceptibility, proportional to the current exists.

© 1996 Optical Society of America