Comb-Referenced Doppler-Free Spectrometry of the ^{200}Hg and ^{202}Hg Intercombination Line at 254 nm.

We report on precision spectroscopy of the 6s^{2} ^{1}S_{0}→6s6p ^{3}P_{1} intercombination line of mercury in the deep ultraviolet, by means of a frequency-comb referenced, wavelength-modulated, saturated absorption technique. This method allowed us to perform sub-Doppler investigations with an absolute frequency axis at 254 nm, while ensuring a relatively high signal-to-noise ratio. The absolute line center frequencies of the ^{200}Hg and ^{202}Hg bosonic isotopes were measured with a global uncertainty of 8 and 15 kHz (namely, 6.

On the CH near-infrared spectrum: absolute transition frequencies and an improved spectroscopic network at the kHz accuracy level.

Lamb dips of twenty lines in the P, Q, and R branches of the ν + ν + ν vibrational band of CH, in the spectral window of 7125-7230 cm, have been measured using an upgraded comb-calibrated frequency-stabilized cavity ring-down spectrometer, designed for extensive sub-Doppler measurements. Due to the large number of carefully executed Lamb-dip experiments, and to the extrapolation of absolute frequencies to zero pressure in each case, the combined average uncertainty of the measured line-center positions is 15 kHz (5 × 10 cm) with a 2-σ confidence level. Selection of the twenty lines was based on the theory of spectroscopic networks (SN), ensuring that a large number of transitions, measured previously by precision-spectroscopy investigations, could be connected to the and principal components of the SN of CH.

Absolute frequency stabilization of a QCL at 8.6 µm by modulation transfer spectroscopy.

Modulation transfer spectroscopy is used to demonstrate absolute frequency stabilization of an 8.6-µm-wavelength quantum cascade laser against a sub-Doppler absorption of the molecule. The obtained spectral emission properties are thoroughly characterized through a self-referenced optical frequency comb, stabilized against either a GPS-disciplined Rb clock or a 1.

Tunable UV spectrometer for Doppler broadening thermometry of mercury.

We realized a UV laser spectrometer at 253.7 nm for Doppler broadening thermometry on the - intercombination line in mercury vapors. Our setup is based on the two-stage duplication of a 1014.

The Boltzmann project.

The International Committee for Weights and Measures (CIPM), at its meeting in October 2017, followed the recommendation of the Consultative Committee for Units (CCU) on the redefinition of the kilogram, ampere, kelvin and mole. For the redefinition of the kelvin, the Boltzmann constant will be fixed with the numerical value 1.380 649 × 10 J K.