Discussion on Unique Characteristics of Second Order Harmonic in a Nonlinear Surface Acoustic Wave Investigated by Optical Diffraction Method

摘要

Unique capability of the second harmonic in a nonlinear surface acoustic wave (NLSAW) generated on 128° Y-X LiNbO3 substrate was investigated by optical diffraction technique. Amplitudes of the fundamental, the second harmonic, and the third harmonic in it were evaluated from an equation composed as a basis of the Beckmann-Spizzichino model. The experimental findings were as follows: the second harmonic velocity was faster than that of the fundamental; a full width at half maximum in envelope profile of the second harmonic was unchanged as if it experienced the gold thin film; total peak intensity in the envelope profile of the second harmonic during collision at gold thin film area was stronger than the sum of individual peak intensity of two second harmonics before the collision. From our experimental findings we conclude that the second harmonic has a soliton-like characteristic.