High Precision Measurement of the 3P0 - 3P1 Atomic Oxygen Fine Structure Splitting at 2.06 THz

Observation of the atomic oxygen fine structure line at 2.06 Terahertz from an orbiting limb sounder serves as a compelling platform for the characterization of neutral winds in the lower thermosphere and ionosphere (LTI, $\sim$110 - 250 km). The precision of wind measurements retrieved from this prospective instrument class are directly linked to the rest frequency of this targeted transition as determined from laboratory measurements. This effort details recent work at the Jet Propulsion Laboratory to deploy a custom designed transmitter and heterodyne receiver pair optimized for performance at 2.06 THz for use in obtaining high-precision rest frequencies for the oxygen atom $^3$P$_0$\,-\,$^3$P$_1$ atomic fine structure splitting. Oxygen atom ($^{16}$O) is generated by an inductively coupled plasma system with direct absorption measurements obtained by a combined frequency and plasma modulated experimental scheme. Results are discussed in the context of previous laboratory measurements and the impact on prospective neutral wind measurements in the LTI.