Development and transmission measurement of an ultra-narrow optical band pass filter for sodium lidar daytime observations

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Summary of this research based on the fund is as followed.Developing a new sodium cell for a Faraday filter with the stable material against high temperature sodium vapor:A commercial type Pyrex-glass sodium cell does not work well when the cell is heated and sodium vapor is activated. We developed a Sapphire sodium cell using the special technique, optical contact method Sapphire is extremely stable against strong acid or base as well as sodium vaporEstablishing the procedure to measure transmissions of ultra-narrow optical band-pass filter with ring dye laser:The transmission width of a Faraday filter is about 10 pico meter that an ordinary spectrometer cannot resolve. The transmission measurement was done with a ring dye laser as an ultra-narrow light source at Tokyo Metropolitan University to precisely scan the transmission profile. The measured profile was reasonable but the results suggest the effective temperature is 10 degree lower than the monitored value.Doppler free spectrum measurements for absolute frequency measurements:Doppler free technique is the absolute frequency monitoring system around sodium D2 line using a sodium cell. By warming the laser with a special optical configuration, the spectrum was measured and the absolute frequencies were determined. This is necessary to determine the absolute frequency when the Faraday filter transmission is measured.Lidar receiving system with optical fibers:Optical fiber system is designed for the Mar receiving system bemuse strong magnetic field of Faraday filter affects the photoelectric detection using a photomultiplier tube. Designing an optical alignment with lenses was done and the efficiency was measured without Faraday filter The efficiency is 1/3 of the common system. Faraday filter may decrease the signal to 1/4. The results show the signal intensity decreases to roughly 1/10 in daytime.