An axial transmissive Raman spectrograph is described. The instrument employs volume-phase holograms as the laser line rejection filter and transmission grating. The on-axis configuration and the use of a high-spatial-frequency transmission grating allows nearly diffraction-limited imaging and pixel-limited resolution at f/1.8. The performance of the instrument is demonstrated for fiber-optic probe and microprobe Raman spectroscopy.

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A novel spectrograph configuration, ideally suited for process control applications, is discussed. The configuration, referred to as axial transmissive, consists of axially-symmetric refractive optics and a volume phase holographic transmission grating. The axial transmissive spectrograph is veiy compact and robust, featuring no moving optical elements. This configuration also results in very high spatial resolution, allowing a large number of different processes to be monitored simultaneously on a single two-dimensional array detector. Results are presented for experiments, performed using the axial transmissive spectrograph with a laser, fiber optic sampling, and a multi-channel CCD detector, that are representative ofprocess control applications.

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