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Frequency-agile terahertz-wave spectrometer for high-resolution gas sensing
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Image of FIG. 1.
FIG. 1.

High-resolution, tabletop, terahertz-wave spectrometer. The spectrometer system is packaged into three chambers with a total volume of about : the first chamber (I) consists of the gas cells for terahertz-wave spectroscopy, the second (II) contains the nonlinear crystals for terahertz-wave generation (the thick white line in the picture), and the third (III) has the optics for steering both the seeder beam (the thin white line in the picture) and the pump beam (the black line) to the nonlinear crystals.

Image of FIG. 2.
FIG. 2.

Accurate, rapid measurements of the absorption spectrum of the 12 purely rotational transitions of water vapor. The stick line shows the spectral data from the NASA database for comparison.

Image of FIG. 3.
FIG. 3.

[(a) and (b)] Pictures from video (1), showing real-time monitoring of the and rotational transitions under pressures from . The frequency interval between the and transitions is . It takes about to finish one scan using a frequency step.

Image of FIG. 4.
FIG. 4.

Set of absorption lines of the and rotational transitions of water vapor under pressures of 0.4, 1.5, 2.5, 3.5, 4.5, 6, and (circles). The nonlinear least-squares-fitted Voigt profiles of all the measured lines were added in solid line. The frequency interval between the and transitions is .

Image of FIG. 5.
FIG. 5.

Linewidth of the transition as a function of pressure. The straight line shows the linear least-squares fit to the HWHM data above a pressure of . The slope gives a pressure-broadening coefficient of .


Generic image for table
Table I.

Comparison of our experimental measurements with theoretical predictions and typical commercial Fourier-transform spectrophotometer (FTS) experimental results.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Frequency-agile terahertz-wave spectrometer for high-resolution gas sensing