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We report on a new optical implementation of primary gas thermometry based on laser-absorption spectrometry in the near infrared. The method consists in retrieving the Doppler broadening from highly accurate observations of the line shape of the R(12) nu1+2nu2(0)+nu3 transition in CO2 gas at thermodynamic equilibrium. Doppler width measurements as a function of gas temperature, ranging between the triple point of water and the gallium melting point, allowed for a spectroscopic determination of the Boltzmann constant with a relative accuracy of approximately 1.6 x 10(-4).

The authors report on the first demonstration of mode locking in an active waveguide laser manufactured by femtosecond laser writing. The active waveguide is fabricated in an Er–Yb-doped phosphate glass, and the mode locker is a fiber-pigtailed saturable absorber device based on single-wall carbon nanotubes specially designed to efficiently operate at $1.5\mu \mathrm{m}$ . Transform-limited $1.6\mathrm{ps}$ pulses were observed in a ring laser cavity configuration.

We report on a new implementation of Doppler broadening thermometry based on precision absorption spectroscopy by means of a pair of offset-frequency locked extended-cavity diode lasers at $1.39\text{ }\text{ }$\mu${}\mathrm{m}$. The method consists in the highly accurate observation of the shape of the ${4}_{4,1}$\rightarrow${}{4}_{4,0}$ line of the ${\mathrm{H}}_{2}^{18}\mathrm{O}$ ${$\nu${}}_{1}+{$\nu${}}_{3}$ band, in a water vapor sample at thermodynamic equilibrium. A sophisticated and extremely refined spectral analysis procedure is adopted for the retrieval of the Doppler width as a function of the gas pressure, taking into account the Dicke narrowing effect, the speed dependence of relaxation rates, and the physical correlation between velocity-changing and dephasing collisions. A spectroscopic determination of the Boltzmann constant with a combined (type $A$ and type $B$) uncertainty of 24 parts over ${10}^{6}$ is reported. This is the best result obtained so far by means of an optical method. Our determination is in agreement with the recommended CODATA value.

We report on the generation of mid-infrared (mid-IR) pulses with a maximum average optical power of 4 mW and wide tunability in the 8–14 μm range via difference frequency generation (DFG) in GaSe from an Er:fiber laser oscillator. The DFG process is seeded with self-frequency shifted Raman solitons that are shown to be phase coherent within the whole tuning range, from 1.76 to 1.93 μm. Interference measurements between adjacent pulses at the idler wavelengths attest coherence transfer to the mid-IR.