Optical SHG for ZnO films with different morphology stimulated by UV-laser thermotreatment

We have discovered a strong influence of the ZnO grain sizes on the output second harmonic generation stimulated by nanosecond pulses of 371 nm nitrogen laser during simultaneous superposition of the electrostatic electric field with electric strength about 2 kV/cm. To explore an influence of film morphology on the second order optical susceptibility we have explored the films prepared by electron sputtering with averaged grain sizes about 1000 nm and films synthesized by rf-magnetron sputtering on the two different substrates - glass and amorphous quartz with average grain sizes about 137 nin and 29 nm, respectively. Comparing the UV-induced optical second harmonic generation for the ZnO films with different grain sizes we have concluded that the samples with nanorods are characterized by considerably larger second order susceptibility (up to 5.7 pm/V at 1064 nin fundamental wavelength) compared to those for the films with smaller grain sizes (1.5 pm/V). This may be caused by a fact that UV-illumination deals only effectively with simultaneous electric field treatment enhancing the second order optical susceptibility. A correlation between the temperature of local laser thermo-heating and the output optical second harmonic generation may indicate on principal role of the local thermal expansion in the observed output second harmonic generation.