ABSTRACT
The surface polarization caused by traveling SAWs at 1.585 GHz has been imaged using a dynamic homodyne electrostatic force microscope technique. Instead of measuring topographic changes caused by the SAW, the reported technique measures polarization in the piezoelectric substrate arising from mechanical stress caused by the SAW. The polarization associated with this stress field modulates the scanning probe cantilever deflection amplitude, which is extracted using a lock-in-based technique. High-resolution imaging is presented with images of the interference arising from a metal reflector on a SAW device. A mathematical model combining SAW generation and force interactions between the probe and the substrate was used to verify the experimental data. In addition to overcoming the challenge associated with detecting and imaging polarization effects at gigahertz frequencies, this imaging technique will greatly assist the development of SAW-based devices that exploit the reflection and interference of SAWs in areas as diverse as microfluidic mixing, cell sorting, and quantum entanglement.
ABSTRACT
Photoelectron counting distributions are obtained for sources which obey compound Poisson statistics. Various cases are considered in which the sources (semiconductor lasers) emit coherent light and their intensity fluctuates in accordance with a Gaussian distribution of operating temperatures. The lasers are otherwise assumed to be ideal, and the quantum efficiency of the detector is assumed to be unity. This paper represents an ideal situation where the source is the only concern in the calculation of the photoelectron counting distributions. It is found that for large temperature fluctuations (a > 10 K), a substantial downward shift of the peak of the photon probability density function is observed. The function becomes more asymmetric and the mean value decreases as the standard deviation of the temperature increases.
