Fig. 2: Rotational ladder with signal and noise floor measurements.
a Plot of rotational transitions at room temperature, normalized to the strongest absorption, as a function of terahertz radiation frequency28. The numbers above the transitions are the lower rotational state quantum number, J. The transition utilized in this experiment is highlighted in red. b Error and transmission signals corresponding to typical experimental conditions. The error signal is the black trace, and its corresponding axis is on the left. The transmission signal is the red trace axis is on the right, normalized to the power detected without gas present, showing a peak absorption strength of 30%. c Time trace of the signal detected without gas. The long-term fluctuations are a direct measurement of the residual amplitude modulation (RAM). d Power spectral density (PSD) of the RAM signal time trace. These data are indicative of the spectrometer noise floor.
