Electric field induced second harmonic generation in vacuum evaporated Disperse Red 1 films

Abstract We have observed the electric field induced second harmonic (EFISH) generation effect on vacuum deposited Disperse Red 1 (DR1) films using corona poling. There is no second harmonic generation (SHG) signal in the absence of the corona. Room temperature corona charging results in an SHG signal which appears and disappears almost instantaneously upon turning on and turning off the corona field respectively. Combined with earlier spectroscopic studies on molecular organization in vacuum deposited DR1 thin film which suggested vertical orientation of most of the molecules, these results clearly indicate that the DR1 molecules in the film are most likely aligned in antiparallel arrangement. The EFISH effect as well as its fast responses to the on–off operation of corona field and the reduction of the SHG signal at elevated film temperature are explained in terms of effective dc field induced polarization effect on the molecules due to third-order nonlinearity of DR1.