Speckle interferometry with nanoparticles

The sensitivity of one beam speckle interfeometry (also called speckle photography) is the size of speckles that can be generated. In the early days of this technique, speckle size is essentially controlled by the aperture size of the recording camera. When laser speckle is used, the wavelength of the laser beam, the f/number of the recording lens and magnification of the system determines how small the laser speckles can be generated. When white light speckle is used, the size is determined by the resolution of the recording lens. The theoretical limits of the these two approaches are actually the same in that no speckle smaller that 1/2 of the wavelength of the radiation can be recorded. However, speckles much smaller than lens resolution can be generated using either a chemical or a physical vapor deposition process. And they can be clearly recorded using a electron microscope. We have successfully created nanometer speckles and applied them to variety of solid mechanics problems of importance. Examples include characterization of mechanical properties of interphase in metal matrix composite, study of kinking failure mechanism of fibrous composite, measurement of thermal deformation of solder joint in electronic devices, etc. This nanospeckle technique has opened up a new field of investigation which heretofore was not accessible to experimentalist.