Terahertz Time Domain Gas-phase Spectroscopy of Carbon Monoxide

Free induction decay signals emitted from Carbon Monoxide (CO) excited by sub-picosecond pulses of Terahertz (THz) radiation are directly measured in the time domain and compared to model calculations using a linear dispersion model to good agreement. Best fitting techniques of the data using the model allow the self-pressure broadening of CO to be measured across a range of absolute pressures, and the rotational constant to be determined. We find B (V) = 5.770 +/- 0.003 x 10(10) Hz in agreement with previous measurements. A partial pressure limit of detection for CO of 7900 ppm is estimated at atmosphere through extrapolating the calculated commensurate echo peaks down to low pressures with respect to the RMS noise floor of our THz time domain spectroscopy (THz-TDS) apparatus, which implies a limit of detection in the range of 40 ppm for commercial THz-TDS systems.