Wavelength Control for a Potassium Resonance Lidar

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Utah State University Student Showcase for Undergraduate Research

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A., Everett E.; Wickwar, Vincent B
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Rayleigh-scatter lidar; mesosphere; Atmospheric Lidar Observatory; Physics
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An important ground-based way to measure temperatures and winds in the transition region between the upper mesosphere and lower thermosphere (80 to 105 km) is with a resonance-scatter lidar. An alexandrite laser, with a wavelength in the near infrared at 770 nm, is being added to the Atmospheric Lidar Observatory to make this type of observation of potassium. These observations will complement those that have been made for many years with the green Rayleigh-scatter lidar. For these resonance-scatter observations it is necessary to accurately and precisely control the laser wavelength. The intent is to carefully step across the 4 pm (2 GHz) wide potassium spectrum (Figure 1). The width of the spectrum has to be determined within 6.0 fm (3.0 MHz ) to obtain a temperature precision of ±5 K. The Doppler shift of the spectrum has to be determined within 5.1 fm (2.6 MHz) to obtain a wind-speed precision of ±2 m/s. This project is a step in that direction. It involves developing a method, based around a scanning Fabry-Perot interferometer (FPI), to control a CW seed laser that, in turn, controls the alexandrite laser.