Second harmonic Stark effect

The optical Stark-effect consits of a zlift of spectral lines due to the influence of an external electric field that oscillates with some optical frequency w . If one exposes an oriented molecule to two fields oscillating with frequencies w and 2w a part of the shift will become dependent on the relative phase of the two external oscillations. We call this phase dependent shift of spectral lines the second harmonic Stark-effect. It is liRely that the irreversible changes that occur in glass optical fibers during the preparation process of second harmonic generation are related to the second harmonic Stark- effect