Long fiber-optic remote Raman probe for detection and identification of weak scatterers.

A long-length fiber-optic remote Raman probe that can detect materials (e.g., Fe(2)O(3)) that are weak Raman scatterers is described. The 100-m-long probe consists of one excitation and one collection fiber and accessory optics and is <3 mm in diameter. We used special filters to solve the problems of Raman scattering and luminescence generated in the silica excitation and collection fibers and a liquid-nitrogencooled charge-coupled detector to analyze weak Raman signals.