Photoacoustic Imaging.

This is the final report on the work done in the area of high resolution photoacoustic and photothermal imaging. It contains recent advances in photoacoustic and photothermal theory and the experimental demonstration of new techiques. Photoacoustic and photothermal theories have been extended to include the effects of the highly focused optical power sources necessary for high resolution imaging and three high frequency techniques 1 GHz have been demonstrated and used to characterize the material properties of solids. The formalism behind photothermal characterization of solids is established under general focusing conditions. The three dimensional thermoacoustic field equation is derived and discussed. Two high resolution photoacoustic techniques have been demonstrated. These techniques involve the use of an acoustic lens for collection for the acoustic power generated by a highly focused optical beam modulated at 1 GHz frequency. Images of gold and laser recrystallized silicon films are presented demonstrating the high resolution and sensitivity of these techniques. A high resolution photothermal probe has been demonstrated. This optical technique provides a means of photothermal characterization with sub-micrometer resolution and high sensitivity. The theory behind the probe is presented along with the experimental verification. Images of boron implanted silicon are included which demonstrate the resolution and sensitivity of this technique.