Pavel Alexeyevich Fomitchov

A theory for the ultrasonic modulation of incoherent light in turbid medium

A diffusion approximation to the radiative transfer in a medium with varying refractive index has been proposed as a theoretical model for the ultrasonic tagging of fluorescence or FluoroSound, in a scattering medium. It has been found that the diffuse modulation is a defocusing effect. Defocusing is related to scatter - more the scatter, more the defocusing and there exists a component of the defocusing effect of scatter at the ultrasonic frequency. This is in contrast to the modulation for ballistic photons that originates in the focusing effect of the acoustic lens created by the ultrasonic wave. Simulations with circular phantoms of 1.5 and 2.0cm radius have shown that defocusing is minimum when the acoustic lens is midway between the source and the detector. These results are consistent with physics and demonstrate the capability of the model to function as a predictive tool for FluoroSound instrument design. Both ballistic and diffuse FluoroSound signatures can help in the simultaneous localization of the anomaly and determination of its optical properties. As an adjunct, optimally designed ultrasound beams can be also used to enhance diffuse photon modulation signal through acoustic guidance. Optical properties provide a way to discriminate between normal and diseased tissue. FluoroSound could therefore potentially achieve a fusion of anatomical and functional information non-invasively in a single measurement. The additional information made available by this method will improve the speed and accuracy of optical imaging as a tool in the identification and validation of targets.

In situ evaluation of metallic coatings via laser plasma spectroscopy

We present a method and apparatus that provides in situ, near real-time evaluation of metallic coatings used as protective barriers for various industrial applications. Identification of the elemental constituents of the coating and substrate is accomplished using the technique of laser plasma spectroscopy, whereby optical emissions from the plasma formed by focusing a high energy pulsed laser onto a part coating or substrate surface uniquely identify the elements present in the vaporized material. We present several applications, including use of this technique to determine coating presence, coating composition, coating thickness, coating composition as a function of depth, and identification of deposits on metallic surfaces.We present a method and apparatus that provides in situ, near real-time evaluation of metallic coatings used as protective barriers for various industrial applications. Identification of the elemental constituents of the coating and substrate is accomplished using the technique of laser plasma spectroscopy, whereby optical emissions from the plasma formed by focusing a high energy pulsed laser onto a part coating or substrate surface uniquely identify the elements present in the vaporized material. We present several applications, including use of this technique to determine coating presence, coating composition, coating thickness, coating composition as a function of depth, and identification of deposits on metallic surfaces.