Block diagram of the experimental setup.
Empty resonator loss per pass as a function of frequency. Single scan, taking about and containing ringdowns is shown. For the mirror separation, is equivalent to 1% loss per pass.
Triggering scheme. The sum of the ramp voltage and the SVC voltage is applied to the BWO, resulting in a rapid frequency jump of the source frequency.
Typical amplitude and mode voltage separation variations of the resonator modes. Higher order FP modes are clearly visible, especially at the high frequency end of the scan.
Absorption of of water vapor. The five lines used for the frequency calibration are marked.
Subtraction of two consecutive scans (grey) and two groups of 50 scans, averaged (black), of the empty resonator.
Baseline structure of the empty resonator loss. Fifty scans averaged, Fourier transform processed. The structure on the zoomed part of the graph is due to the detector reflections.
Absorption of of pure nitrogen as a function of frequency. Single scan, no averaging (grey), 66 point averages (black markers), and the fit (solid black line).
Fifty scan-averaged absorption of of pure nitrogen as a function of frequency. Systematic effect in the form of the standing waves of varying periods can be seen after the averaging.
Typical small scale structure of the frequency-voltage characteristic of a BWO. Mode separation as a function of the resonance mode number for two empty resonator scans.
Single scan, 66 points averaged, absorptions of of oxygen (+), nitrogen (∎), and dry air (▵) as a function of frequency. Solid and dashed lines are frequency squared fits of the nitrogen and dry air absorptions, respectively.
Fifteen points average of the room temperature moist air absorption with water partial pressure of (about 5% relative humidity). Solid line is a fit to the Van Vleck-Weisskopf line shape with addition of a frequency squared continuum absorption term. Dry air absorption is shown to demonstrate the relative size of the effects. Residual of the fit is presented above.
FT processed loss of the resonator filled with of Ar, after subtracting the empty resonator loss. No averaging (grey) and 250 points average (▴).
Absorption of of nitrogen. Vacuum used for baseline subtraction (grey). Ar used for baseline subtraction (black). In both cases FT processed 50 scan averages are shown.
Moist continuum absorption dependence on the product of water and dry air pressures at . Two days of data are shown with the same temperature and close starting water pressures (at of the total moist air pressure).
Moist air absorption with partial water pressure. The solid line is a fit to the Van Vleck-Weisskopf profile and a quadratic in frequency continuum absorption term. Only frequencies with absorption below one half of the peak absorption (∎) are used in the fit. The rest of the points (◻) are presented on the same graph, showing no signs of the line profile distortion related to insufficient detecting bandwidth.
The magnitude of the room temperature nitrogen absorption fit coefficient as a function of nitrogen pressure squared. Solid line is a linear fit of the data.
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