Remote detection of CARS employing fiber optic guides

Coherent anti-Stokes Raman spectroscopy (CARS) is being increasingly used in the diagnosis of a wide variety of physical phenomena. In many real-world applications, the physical environment surrounding the test phenomenon is often hostile. The paper demonstrates the use of fiber optic guides as a means to pipe CARS signals efficiently from the test area to more benign environments, such as nearby control centers. Furthermore, efficient coupling through the spectrometer can be realized by proper selection of the fiber parameters. In the demonstration outlined, CARS is generated from N2 over a premixed methane-air flame at 2100 K using the apparatus reported by Eckbreth et al. (1979). The CARS signal is focused into a 62-micron-diam fiber using a 50-mm focal length lens. The output end of the fiber is inserted directly into a 0.6-m spectrometer fitted with an optical multichannel analyzer. Efficient remote detection of CARS signatures using fiber optic guides is demonstrated, the approach being expected to be very useful in instrumentally hostile environments.