| 摘要 |
A very long sample cell for spectrophotometric measurements can be used to extend sensitivity to very low levels of gaseous components, under about 50 parts per billion. The cell is an optical fiber positioned within the annular space of a housing, with a gas stream flowing along the annular space. The outer surface of the fiber is coated with a material, e.g., an adsorbent which concentrates at least one component of the gas stream at the interface of the fiber and annular space. An indispensable prerequisite is that the coating have a refractive index greater than that of the optical fiber core. Radiation is propagated along the core of the fiber, and the evanescent wave passes through the adsorbed component, ultimately changing the radiation detected at the output end of the fiber according to the nature and concentration of the component.
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