2005 Volume 26 Issue 1 Pages 55-61
By providing a phase reversal at the focal region, another phase reversal due to diffraction is compensated and as a result, an enhancement of the second harmonic generation is expected. To attain this, the reflection of the focused beam at a water surface being set in the focal region is experimentally observed using a focusing source to receive the reflected second harmonic sound by itself, which employs a LiNbO3 plate with a ferroelectric inversion layer. The experimental result is compared with the theoretical calculation based on the Khokhlov-Zabolotskaya-Kuznetsov equation, where the condition of the phase reversal for both the fundamental and second harmonic components is assumed to be at the free surface. The experimental result agrees reasonably well with the predicted increase in the second harmonic amplitude by 2.0 times. Since this growth rate is sensitive to the velocity dispersion that occurs in different liquid media, such a measurement of second harmonic component may be potentially useful for estimating the dispersion.
