  Optical tracking was used to characterize acoustic radiation force (ARF)
induced displacements in a tissue-mimicking phantom. Amplitude modulated (AM)
3.3 MHz ultrasound was used to induce ARF in the phantom which was embedded
with 10 {\mu}m microspheres that were tracked using a microscope objective and
high speed camera. For sine and square AM the harmonic components of the
fundamental and second and third harmonic frequencies were measured. The
displacement amplitudes were found to increase linearly with ARF up to 10
{\mu}m with sine modulation having 19.5% lower peak-to-peak amplitude values
than square modulation. Square modulation produced almost no second harmonic
but energy was present in the third harmonic. For the sine modulation energy
was present in the second harmonic and low energy in the third harmonic. A
finite element model was used to simulate the deformation and was both
qualitatively and quantitatively in agreement with the measurements.
