Since most metal lidars at present are operated at night, daytime measurements are badly needed, without which many important geophysical phenomena can not be properly studied. Daytime operation of a Na lidar has been implemented by different research groups with varied success. The first daytime temperature measurements using sodium atoms as tracer were carried out by Chen et al. using a Faraday filter. Although sodium atoms are preferred tracers due to its abundance, potassium atoms have also been used for mesopause temperature measurements as the result of a recently developed all solid-state, narrowband Alexandrite laser which has a longer pulse width. In order to allow daytime measurements, a narrowband filter is obviously needed. That a circular birefringent, dichroic medium between crossed polarizers could be used to reject considerable skylight background was demonstrated by Ohman before the laser was invented. We have constructed a potassium Faraday filter with a 1 inch long potassium vapor cell that may be used in observatories with a narrowband K lidar for daytime temperature and wind measurements. By choosing an axial magnetic field in an appropriate range and adjusting the oven temperature, we have "engineered" the Faraday filter to have a very narrow passband and a respectable peak transmission for the K D, transition at 770 nm. In this paper, we will discuss the development, measurement, and performance evaluation of a potassium Faraday filter in skybackground rejection, as compared to a comparable sodium Faraday filter and a 10 GHz wide Pabry-Perot interferometer, as well as the proposed integration of a K Faraday filter into a narrowbad potassium lidar receiver for daytime temperature, line-of-sight wind, and potassium density measurements in the mesopause region (80-110 km in altitude).
A potassium Faraday filter based narrowband lidar for day and night observation of the mesopause region
01.01.1999
166761 byte
Aufsatz (Konferenz)
Elektronische Ressource
Englisch
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