What filters are available for imaging in the 20 µm wavelength regime?
There are 4 filters currently installed in LWS for use in the 20 µm wavelength regime. The broadband 17.9 µm ( 2.0 µm wide) filter is recommended for imaging in the 20 µm region. This filter has good transmission properties and is the most sensitive in this region. Another choice is the narrow 18.7 µm ( 0.4 µm wide) filter. The 18.7 has poor transmission and is not very sensitive, however, it provides an alternate choice during marginal weather conditions. There are two other filters that do not have the proper diameter for use in LWS, the 20 and 22 µm ( 2.0 µm wide) . These filters are undersized and only transmit about 50% of the LWS beam, which effects the sensitivity and point spread function (PSF). They have been temporarily installed for testing and help extend the wavelength coverage for users that need measurements in this region. The 20 and 22 µm filters are NOT recommended for typical LWS programs.
