Lamb-dip cavity ring-down spectroscopy of acetylene at 1.4 μm

Doppler-free saturated-absorption Lamb dips are observed for weak vibration-rotation transitions of C2H2 between 7167 and 7217 cm−1, using a frequency-comb assisted cavity ring-down spectrometer based on the use of a pair of phase-locked diode lasers.We measured the absolute center frequency of sixteen lines belonging to the 2ν3 + ν1 5 band, targeting ortho and para states of the molecule. Line pairs of the P and Q branches were selected so as to form a ‘V’-scheme, sharing the lower energy level. Such a choice made it possible to determine the rotational energy separations of the excited vibrational state for J-values from 11 to 20. Line-center frequencies are determined with an overall uncertainty between 3 and 13 kHz. This is over three orders of magnitude more accurate than previous experimental studies in the spectral region around the wavelength of 1.4 μm. The retrieved energy separations provide a stringent test of the so-called MARVEL method recently applied to acetylene

The Boltzmann constant from the shape of a molecular spectral line

We report on our recent determination of the Boltzmann constant, k(B), by means of Doppler broadening thermometry. This relatively new method of primary gas thermometry was implemented by using a pair of offset-frequency locked extended-cavity diode lasers at 1.39 mu m, to probe a particular vibration-rotation transition of the (H2O)-O-18 molecule. Adopting a rather sophisticated and extremely refined line shape model in the spectral analysis procedure, we were able to determine the Doppler width from high-quality absorption spectra with unprecedented accuracy. Our spectroscopic determination of kB exhibits a combined (type A plus type B) uncertainty of 24 parts over 10(6). The complete uncertainty budget is presented and discussed

Water vapor concentration measurements in high purity gases by means of comb assisted cavity ring down spectroscopy

In manufacturing processes of semiconductor industry accurate detection and monitoring of water vapor concentration in trace amount is of great importance. The ability to perform reliable measurements in ultrapure gases, with a wide dynamic range and low uncertainty, can have a substantial impact on product quality and process performances. Here, we report on the development of a second-generation comb-assisted cavity ring-down spectrometer and present H2O mole fraction measurements in high-purity N2 gas. Based on the use of a pair of phase-locked lasers and referenced to an optical frequency comb synthesizer, the spectrometer allowed to record high-quality absorption spectra in coincidence with the 32,2 → 22,1 H2O transition at 1.3946 μm. Retrieval of water mole fractions, at levels as low as 380 part per billion, was accomplished through a careful spectra analysis procedure based on the use of refined line shape models which include speed-dependent effects. Measurements were performed with a statistical reproducibility of 5 parts per billion, for an integration time of about 0.2 s. The noise equivalent and minimum detectable absorption coefficients were found to be 3.1 × 10−11 cm−1/ √ and 6.5 × 10−12 cm−1 , respectively. This latter allowed for a minimum detectable water mole fraction (limit of detection) of 160 parts per trillion. Finally, the main sources of systematic uncertainty have been discussed and quantified.This work was done within the project PROMETH2O (EMPIR 20IND06), which received funding from the EMPIR programme cofinanced by the Participating States and from the European Union's Horizon 2020 research and innovation programme

Absolute frequency measurements of CHF3 Doppler-free ro-vibrational transitions at 8.6 μm

We report on absolute measurements of saturated-absorption line-center frequencies of room-temperature trifluoromethane using a quantum cascade laser at 8.6 μm and the frequency modulation spectroscopy method. Absolute calibration of the laser frequency is obtained by direct comparison with a mid-infrared optical frequency comb synthesizer referenced to a radio-frequency Rb standard. Several sub-Doppler transitions falling in the v5 vibrational band are investigated at around 1158.9 cm-1 with a fractional frequency precision of 8.6·10-12 at 1-s integration time, limited by the Rb-clock stability. The demonstrated frequency uncertainty of 6.6·10-11 is mainly limited by the reproducibility of the frequency measurements

Doppler-limited precision spectroscopy of HD at 1.4 μm: An improved determination of the R(1) center frequency

We report on the improved determination of the center frequency of a hydrogen deuteride vibration-rotation transition. As a result of a refined analysis of cavity ring-down absorption spectra, it was possible to quantify the influence of the hyperfine structure on the line center frequency of the weak 2-0 R(1) line, as retrieved in the Doppler-limited regime. It turns out that ignoring the hyperfine structure leads to an underestimation of the center frequency of about 350 kHz. The updated determination gives an absolute frequency of the R(1) centroid of 217 105 181.936 MHz with a global uncertainty of 76 kHz

Dual-laser frequency-stabilized cavity ring-down spectroscopy for water vapor density measurements

Absolute measurements of water vapor densities have been carried out using a new concept of frequency-stabilized cavity ring-down spectroscopy. Our scheme is based on the use of a pair of phase-locked extended cavity diode lasers, emitting at 1.39 $\mu$m, one of them being locked to a self-referenced optical frequency comb synthesizer. An intrinsically stable high-finesse optical cavity that tracks the laser frequency scans has been used. High quality, comb-calibrated, absorption spectra have been recorded in a certified H$_2$O/N$_2$ gas mixture at different gas pressures, in coincidence with the 2$_{1,2}→$1$1,1$transitionoftheH$2^{18}$O $\nu_1$+$\nu_3$ band. Water vapor mole fractions have been determined with a statistical uncertainty of 0.6 \%. Systematic deviations have been identified and carefully quantified, thus leading to an overall uncertainty of 0.8 \%

Absolute frequency stabilization of an extended-cavity diode laser against Doppler-free H217O absorption lines at 1.384 micron

We report the frequency stabilization of a cw extended-cavity diode laser against saturated absorption lines of the H217O isotopologue of water vapor at around 1.384 μm. The saturation of rotovibrational transitions is achieved by filling a high-finesse optical resonator with H2 O at low pressure and by locking the laser frequency to the resonator by using the Pound-Drever-Hall technique. Absolute frequency stabilization is obtained, locking the cavity resonance to the center of the sub-Doppler line by means of the wavelength modulation method. A relative frequency stability of σy (τ)= 10-18(0. 1τ-2 + 0.9)1/2 is demonstrated for integration times in the range 4 ms< τ<30 S. © 2009 Optical Society of America

Offset-frequency locking of extended-cavity diode lasers for precision spectroscopy of water at 1.38um

Offset-frequency locking of extended-cavity diode lasers for precision spectroscopy of water at 1.38u

Optical Determination of Thermodynamic Temperatures from a C2H2 Line-Doublet in the Near Infrared

This paper reports the implementation of Doppler-broadening gas thermometry by use of line-shape analysis of a line-doublet. The two spectral components are vibration-rotation transitions belonging to a pair of acetylene combination bands at a wavelength of 1.39 μm. Characterized by an extraordinary spectral fidelity in combination with high resolution, the spectrometer is based on two phase-locked extended-cavity diode lasers, one of them being referenced to an optical-frequency-comb synthesizer. The global analysis of 1180 spectra, which are recorded as a function of the C2H2 pressure at the constant temperature of the triple point of water, yields an optical determination of the thermodynamic temperature with a combined relative uncertainty (type A plus type B) of 23 parts per million. Similar results are obtained at the melting point of gallium (approximately 303 K). Furthermore, we apply line-absorbance analysis to the acquired spectra, demonstrating a reduction by a factor of approximately 6 of the statistical uncertainty for the retrieved gas temperature

Precision spectroscopy of HD at 1.38 μ m

The technique of frequency-stabilized comb-calibrated cavity ring-down spectroscopy was used to observe the weak R(1) transition of the deuturated molecular hydrogen (HD) first overtone band in the near infrared. Like molecular hydrogen, HD is a benchmark system to test quantum electrodynamics, looking for new physics beyond the standard model. The spectral line shape was measured with an extremely high fidelity at relatively low gas pressures. The use of a very refined line-shape model allowed us to retrieve the unperturbed line-center frequency of the R(1) line with a global uncertainty of about 100 kHz (δν/ν=5×10-10). Our value may solve the ambiguity that recently emerged for this line from a pair of sub-Doppler experiments. We also determined other parameters of interest, such as the line strength, the transition dipole moment, and the pressure-broadening coefficient