Low-coherence reflectometry based on DFWM in a thin liquid layer

We describe a coherence filtering technique based on degenerate four wave mixing (DFWM) in a thin nonlinear optical material. In contrast to previous works which used ultra-short laser pulses, we performed low-coherence filtering techniques through scattering media with broad- spectrum nanosecond pulses. In our first 'proof of principle' experiments we used a 100 micrometer thick layer of dye solution as a nonlinear optical material and investigated a one dimensional case for depth-resolved measurements through a scattering media consisting of a highly scattering suspension of dielectric microspheres in water. We also describe a technique to obtain instantaneous cross-sectional images (which can be depth scanned to obtain the third dimension) performed with a low-coherence nanosecond laser source on a liquid crystal doped with an infrared dye. Experimental results were obtained with room temperature LiF:F2- and LiF:F2+ color center lasers, and a Q-switched alexandrite laser. This technique can be used to provide instantaneous, single-shot, two-dimensional images of the internal structure of materials versus depth.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.