| 摘要 |
<p>An apparatus for detecting a predetermined gas in an absorption cell. The output of an infra-red laser source is transmitted to the absorption cell. The transmitted output is controlled to vary with time between at least two wavelengths one of which is more readily absorbed by the gas than the other. The amplitudes of the wavelengths after transmission are compared to detect the gas. The laser output may include the two frequencies and a filter may be used to alternate between them. Alternatively the laser output may be a single frequency which is scanned across a frequency at which the gas absorbs readily.</p> |
