Theoretical and experimental investigations of resonance fluorescence lidar for measurements of N₂ in the auroral atmosphere

Abstract

"In this thesis, a series of experimental and theoretical studies of the resonance fluorescence lidar system at Poker Flat Research Range (located in Chatanika, Alaska) for use in obtaining measurements of aurorally produced molecular nitrogen ions (N₂) are presented. Obtaining measurements of N₂ is made challenging by both the operational performance of the resonance lidar system and the high degree of geophysical variability inherent in the aurora. Analyses are conducted of measurements obtained by the operational sodium and iron resonance lidar systems to verify the lidar system performance. To increase the strength and quality of the lidar measurements, the telescope in the lidar receiver system was upgraded from a 0.6 in Newtonian telescope to a Cassegrain telescope with a 1.02 m diameter primary mirror. Lidar measurements from the system operating with this telescope are presented and compared to previous measurements to confirm an improvement to the overall operation. A spectroscopic analysis of the laser dye used in the previous development of the molecular nitrogen resonance lidar system is conducted to determine the cause of decreased lidar system performance at the operational wavelength relevant for studies of N₂. A total of ten laser dyes are tested in the dye laser system. Based upon the performance of these dyes in the resonance lidar system, it is concluded that successful measurements of the strongest emission band in N⁺₂ are unlikely due the transmittance of the diffraction grating at the relevant wavelength and low system efficiency in the dye laser. Therefore, the resonance lidar system is being developed to obtain measurements of the second strongest band of emissions in N⁺₂ . To assess the capabilities of this system to obtain statistically significant measurements of aurorally produced N⁺₂, the expected resonance lidar signal is simulated by modifying an existing model. It is found that to obtain N⁺₂ resonance lidar measurements of reasonable strength with the current operational system, the data would be obtained at high resolution and post integrated over selected temporal and spatial ranges"--Leaf iii