A Study of Power Saturation in Spectroscopic Gas Analysis in the Terahertz Spectral Range

Quantitative spectroscopic gas analysis requires high confidence in the relationship between measured and theoretical absorption coefficient for a molecule under study. In the presence of oscillating electric field, two quantum states are linked into a time dependent superposition. The probability of finding a particle in either state oscillates at a rate dependent on the amplitude of the electric field, called Rabi Frequency. If a radiation source produces intense electric field, oscillations between states can occur faster than the rate of collisional thermalization, effectively reducing the absorption strength. This effect is known as power saturation. The 230.538 GHz J=1->2 rotational transition of carbon monoxide was measured at several powers and collisional rates to assess the impact of power on absorption strength. A model of population difference dependent on power and collisional rate was created to account for power saturation of an absorption line and compared to experimentally measured carbon monoxide absorption lines.