A method and apparatus are described for determining the absorption spectra, and other properties, of aerosol particles. A heating beam source provides a beam of electromagnetic energy which is scanned through the region of the spectrum which is of interest. Particles exposed to the heating beam which have absorption bands within the band width of the heating beam absorb energy from the beam. The particles are also illuminated by light of a wave length such that the light is scattered by the particles. The absorption spectra of the particles can thus be determined from an analysis of the scattered light since the absorption of energy by the particles will affect the way the light is scattered. Preferably the heating beam is modulated to simplify the analysis of the scattered light. In one embodiment the heating beam is intensity modulated so that the scattered light will also be intensity modulated when the particles absorb energy. In another embodiment the heating beam passes through an interferometer and the scattered light reflects the Fourier Transform of the absorption spectra.

This disclosure relates generally to nondestructive testing for identifying structural characteristics of an object by scanned holographic techniques using a known source of radiation, such as electromagnetic or acoustical radiation. It is an object of this invention to provide an apparatus and method for synthetic aperture expansion in holographic imaging applications to construct fringe patterns capable of holographic reproduction where aperture restrictions in nondestructive testing applications would conventionally make such imaging techniques impossible. The apparatus and method result in the production of a sharply defined frontal image of structural characteristics which could not otherwise be imaged because they occur either near the surface of the object or are confined by geometry restricting aperture dimensions available for scanning purposes. The depth of the structural characteristic below the surface of the object can also be determined by the reconstruction parameters which produce the sharpest focus. Lateral resolution is established by simulated reduction in the radiation wavelength and may easily be an order of magnitude less than the electromagnetic wavelength in the material or 2 times the standard depth of penetration. Since the phase multiplication technique is performed on the detected data, the penetration depth available due to the longer wavelength signals applied …

Disclosed is a locking mechanism for an indexing spindle. A conventional spur gear having outwardly extending teeth is affixed to the spindle. Also included is a rotatably mounted camshaft whose axis is arranged in skewed relationship with the axis of the spindle. A disk-like wedge having opposing camming surfaces is eccentrically mounted on the camshaft. As the camshaft is rotated, the camming surfaces of the disk are interposed between adjacent gear teeth with a wiping action that wedges the disk between the gear teeth. A zero backlash engagement between disk and gear results, with the engagement having a high mechanical advantage so as to effectively lock the spindle against bi-directional rotation.