A discussion is provided of the ability of Raman spectroscopic probes to work in hostile environments. A coaxial fiber-optic Raman problem includes integrated filtering of extraneous radiation. The probe is outfitted with standard ANSI flanges or compression fittings and has to be designed to withstand chemical baths and pressures. Among the advantages of Raman spectroscopy for monitoring of chemical changes is the light-scattering technique, which eliminates sample thickness challenges related to FT-IR. For the chemist, Raman spectra have fundamental vibrational modes instead of overtones and combinations seen in near-IR spectroscopy. That characteristic of Raman spectroscopy makes spectral data easer to correlate to molecular structure. The main drawback of Raman spectroscopy is lack of sensitivity. The primary advantage of the two-fiber coaxial probe is high attenuation of the described Rayleigh line. Each probe is designed for one excitation wavelength and includes three types of optical filters: bandpass, dichroic, and longpass. In combination, the filters eliminate silica background and false radiation from the excitation beam before sample excitation and filter the Rayleigh line from the collected scattered light. Hard-coated metal oxide filters provide resistance to temperature and humidity. Another approach to making immersible Raman fiber-optic probes is to ensure that the probe head is outside of the chemical process by collimating the optical beam through a tube where the final focusing optic is installed.