Dual-laser absorption spectroscopy of C2H2 at 1.4 μm

Spectroscopic parameters (line intensity factor, pressure self-broadening, and shifting coefficients) of C2H2 at 1.4 μm were accurately measured using a dual-laser approach, based upon the technique of optical phase locking. This generated an absolute frequency scale underneath the absorption spectra. A pair of extended-cavity diode laserswas used. One of them, the probe laser, is forced to maintain a precise frequency offset from a reference laser, which is an optical frequency standard based on noise-immune cavity-enhanced optical heterodyne molecular spectroscopy. Laser-gas interaction takes place inside an isothermal multipass cell that is stabilized at the temperature of the triple point of water. The fidelity in the observation of the shape associated to the Pe(14) line of the 2ν3 + ν5 band allowed us to measure the spectroscopic parameters, with a global uncertainty for the line strength of 0.22%.