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Highly accurate determinations of line strengths using intensity-stabilized diode laser absorption spectrometry
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Image of FIG. 1.
FIG. 1.

Sketch of the intensity-stabilized diode laser spectrometer. ECDL stands for extended-cavity diode laser, OI for optical isolator, M for mirror, BS for beam splitter, AOM for acousto-optic modulator, FP for fiber port, Ph for photodetector, and PG for pressure gauge.

Image of FIG. 2.
FIG. 2.

Example of an experimental profile, corresponding to the line (a). The relative residuals are also shown, as a result of a nonlinear least-squares fit to a Voigt convolution (b) and to the Rautian and Sobel’man model (c).

Image of FIG. 3.
FIG. 3.

Plot of the molecular number density vs the integrated absorbance, for the line. The best-fit line exhibits an excellent agreement with the experimental points, also passing through zero without constraint. The slope of the line provides the quantity .

Image of FIG. 4.
FIG. 4.

Correction of the laser-power variations associated with a laser frequency scan around a absorption line. Trace (a) is the spectrum without the action of the AOM-based servo loop, showing a background with both the slope and curvature. Trace (b) represents the spectrum under the same experimental conditions, except that the servo loop is ON. The efficient flattening of the background is even more evident in trace (c), recorded with zero pressure inside the gas cell.

Image of FIG. 5.
FIG. 5.

Comparison with values reported in HITRAN04 and in Ref. 8. The two dashed lines show the range of HITRAN04 values resulting from the 5% uncertainty, as reported in the HITRAN database. The error bars for our values are smaller than the points’ size.

Image of FIG. 6.
FIG. 6.

Plot of the relative deviations between our values and the fit to the second-order Herman-Wallis expansion, with the two coefficients either considered as free parameters (solid circles) or kept fixed at the values reported in Ref. 8 (hollow circles).

Image of FIG. 7.
FIG. 7.

Example of a multiple-line fit. Also in this case, the fitted curve cannot be distinguished from the experimental one. In fact, relative residuals are of the same order as in Fig. 2(c).


Generic image for table
Table I.

Experimental transition strengths and comparison to previous works and to HITRAN04.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Highly accurate determinations of CO2 line strengths using intensity-stabilized diode laser absorption spectrometry