The wavelength region over which high-sensitivity absorption measurements can be obtained via intracavity laser spectroscopy (ILS) is significantly expanded by utilizing a vibronic, solid-state laser, Tm3+:YAG laser, operating near 2.0 μm. Pumped by the 785-nm output of a Ti:sapphire laser, the bandwidth, intensity, and temporal properties of the Tm3+:YAG laser are quantitatively examined with respect to the spectroscopic requirements underlying ILS measurements of weak absorption features. Parasitic etalon fringes appearing on the output of the Tm3+:YAG laser are analyzed and eliminated by systematically changing the laser resonator length (i.e., piezo-electric modulation of the folding mirror position). Several CO2 absorption lines appearing near 2 μm were used to evaluate the ILS performance of Tm3+:YAG laser by measuring the wavelength-resolved intensity of the ILS laser output as a function of (i) the CO2 concentration at a fixed effective optical path length (i.e., fixed generation time or tg) and (ii) the tg value at a fixed CO2 concentration. The enhancement factor attributable to ILS is found to be 1.8×104 and the absolute value of the absorption coefficient for the 2.0129 μm CO2 feature is found to be 1.31×10-21 cm2, in excellent agreement with the previously reported value of 1.40×10-21 cm2. These Tm3+:YAG results can be generalized to other vibronic solid-state lasers operating in the 1-3 μm region and are of special interest for ILS measurements of absorption transitions in molecules of astrophysical and planetological interest.
Mehdizadeh, E., Lunine, J. I., & Atkinson, G. H. (2001). Intracavity laser spectroscopy with an ion-doped, solid-state Tm3+:YAG laser. Journal of Quantitative Spectroscopy and Radiative Transfer, 68(4), 453–465. https://doi.org/10.1016/S0022-4073(00)00037-6