We report on electrically modulating and switching the wavy properties of acoustic phonons in nanoscale piezoelectric heterostructures which are strained both from the pseudomorphic growth at the interfaces as well as through external electric fields. In symmetry planes of such structures, the generation and detection of the transverse acoustic modes are forbidden, and only longitudinal acoustic phonons are generated by ultrafast displacive screening of strains. We show that the combined application of lateral and vertical electric fields can not only turn on and off various modes but they can also modulate the amplitudes and frequencies of the modes [1-3]. The role of the electrical controllability of phonons was further demonstrated as changes to the propagation velocities; the electrically polarized TA waves; and the geometrically varying optical sensitivities of phonons. The capability to manipulate the phononic functionalities with electric fields is analogous to that for manipulating photons and electrons in major technological devices and can be a practical route for integrated phononic circuitry.
 C. S. Kim et al., Appl. Phys. Lett. 100, 101105 (2012).
 H. Jeong et al., Phys. Rev. Lett. 114, 043603 (2015).
 H. Jeong et al., Phys. Rev. B (to appear).
An optical integrating system composed of optical coherence tomography (OCT) and fluorescence spectroscopy (FS) has
been designed and utilized to distinguish pearls by determining their mother oysters used in pearl culturing as well as
discriminate and evaluate the pearls, nondestructively. By adopting a wavelength division multiplexing (WDM) and a
double clad fiber (DCF) coupler, a FS system could be successfully combined with a fiber-based swept source OCT (SSOCT)
system. Applying a common-path configuration, furthermore, the integrating system could be implemented in a
simple and effective way with highly minimized group velocity dispersion (GVD) and polarization mismatch problems.
The internal structure measurement and the fluorescence spectrum measurement, which were previously performed by
two independent apparatus, were concurrently made with the proposed system. From the OCT measurement, we could
measure the thickness of the nacre layer, observe the fine sub-structure of the nacre, and inspect the nucleus through the
nacre of a pearl. With the fluorescence spectrum measurement, we could categorize the pearls by determining their
Currently it is very popular to use off-axis illumination technique for higher resolution with wider depth of focus. However there are several problems in the technique, one of which is deterioration of image quality induced by the non- uniform effective source distribution. If the intensity distribution on the illumination aperture lacks of spatial symmetry, each diffraction order beam impinging on the wafer surface has angularly asymmetric distribution. This makes the optical system have pattern size dependent telecentricity error. For a simple line or grouped lines it gives rise to only the pattern displacement with defocus which can hardly be detected unless there are any reference. But the periodic island type patterns which have discrete features and multiple pitch components in one direction can be bent and deformed asymmetrically with defocus. Asymmetric imaging for island type patterns gives rise to also the pattern CD asymmetry with defocus. We present schematic explanation of the effects of non-uniform effective source and the simulation result. We also investigated the phenomena in a high density DRAM cell active layer of 460 nm minimum pitch and characterized it by various approach.