| 摘要 |
<p>An optical detection system including a transform means to modulate the received radiation to sensitise the system to selected features dependent on the coherence function profile within the received optical field includes a spectral processor. The spectral processor has a band limiting filter (BLF) and a modifying filter (MF) having a pass band at least partly overlapping the passband of the BLF (103). The BLF and the MF are selected to concentrate key information on the target radiation in a small region of the coherence function profile. Preferably the BLF filter has a rectangular transmission profile and the MF filter has a Gaussian profile, matching that of the absorption line of a gas to be detected. The centre of the MF absorption profile is offset with respect to the centre of the BLF profile. In alternative arrangements the MF filter may be such as to provide two or more absorption profiles (122, 123) within the BLF profile. The transmission function of one of the filters may be time dependent so as to enhance detection of the transformed optical field. This is achieved by periodic movement of the filter: by varying the tilt angle of an interference filter to modulate the centre frequency of the transmission profile of the filter or arranging that the area of the periodically moved filter inserted in the optical path of the system varies to periodically modulate the depth of absorption of the filter.</p> |
