Measurement of pressure-broadened, ultraweak transitions with noise-immune cavity-enhanced optical heterodyne molecular spectroscopy

Measurement of the sixth overtone band of nitric oxide, and its dipole moment function, using cavity-enhanced frequency modulation spectroscopy

“…15 with several improvements. Baseline variations due to etalon effects that cause RAM have been shown to be a significant problem for broad spectral scans, 12,13 and this problem was observed also in our spectrometer. Therefore, we made a number of modifications in order to reduce etalon effects and RAM, but also to obtain a more robust performance overall and a broader scanning range of the spectrometer.…”

“…The first continuous measurements of Doppler-broadened absorption features using NICE-OHMS were demonstrated by Gianfrani et al 12 They applied the method for measurements of Doppler-broadened absorption lines of molecular oxygen near 763 nm. The method has recently been further developed to be applicable also on pressure-broadened absorption features described by a Voigt profile 13 and it has been used to characterize weak rovibronic transitions in molecular oxygen. 14 In the present work, we apply NICE-OHMS to study the weak sixth overtone band of nitric oxide.…”

Cavity-based absorption spectroscopy techniques

“…The high-sensitivity capabilities of NICE-OHMS have been demonstrated by recording saturated-absorption spectra of weak vibrational overtone transitions in 12 C 2 H 2 , 12 CO 2 and 12 C 2 HD at λ ≈ 1.064 μ m. A 1-s MDAL of 5.2 × 10 − 13 and an NEA sensitivity of 1 × 10 − 14 cm − 1 Hz − 1/2 have been realised (Ye et al , 1998Ma et al , 1999;Ye and Hall, 2002); this result is only 1.5 times greater than the ultimate shot noise. Others (Gianfrani et al , 1999;van Leeuwen and Wilson, 2004;Bood et al , 2006;Schmidt et al , 2007) have developed NICE-OHMS variants for assorted applications, but with typical NEA sensitivities in the vicinity of 10 − 10 cm − 1 Hz − 1/2 , far short of the 10 − 14 cm − 1 Hz − 1/2 benchmark.…”

Absolute absorption cross sections for two selected lines of formaldehyde around 6625cm−1

“…4 are plotted the co-obtained absorption coefficients for both lines as a function of CH 2 O concentration: the upper graph shows the results from experiments at 14.5 mbar, the lower graph at 66 mbar. The error bars have been estimated from the signal-to-noise ratio of the cw-CRDS measurements and were more important during the 66 mbar measurements due to stronger etalon effects [43]. The slope of the linear regression leads directly to the absorption cross section at the center of the absorption line at the given pressure: the four values are gathered in Table 1.…”