Gan W.

We propose the new field of quantum nondestructive testing for nanotechnology. The applications are for nondestructive characterization of opaque nanometric multilayers of semiconductors on wafers. Picosecond ultrasonics has been applied to the nondestructive evaluation of opaque multilayer samples. Recently, it has been demonstrated the generation of THz-frequency acoustic waves in strained piezoelectric layers induced by femtosecond optical pulses. The optically generated nano-acoustic wave(NAW) is then applied to one-dimensional ultrasonic scan for thickness measurement. This nano-structured piezoelectric transducer(OPT) technology provides the key towards nano-ultrasonics. In this paper, we extend this OPT technique to 2D nano-ultrasonic imaging. We derive a microscopic theory using quantum mechanics to describe the mechanism of NAW generation in strained piezoelectric layers,induced by femtosecond optical pulses. The generation of coherent acoustic phonons is driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump laser and is treated theoretically by using the density matrix formalism. In addition, the many-body Coulomb interaction is treated in the screened time-dependent Hartree-Fock approximation. We find that under typical experimental condition, our microscopic theory can be simplified and mapped onto a driven uniform string model provided one uses the appropriate driving function which includes details of the superlattice band structure and photogeneration processes. Assuming that the acoustic phonon dispersion relation is linear, we find that the lattice displacement satisfies the loaded-string equation. The imaging modality used is diffraction tomography. The scattered wave amplitude which provides information on the object is given by the Lippmann-Schwinger integral which is expressed in terms of the driving function. Matrix formulation and discretization of the loaded-string equation and Kaczmarz algorithm is used in the reconstruction process to obtain the reconstructed image. Only the analytical results are given. Our next step will be the simulation procedure.