Absolute frequency spectroscopy of CO2 lines at around 2.09 mu m by combined use of an Er:fiber comb and a Ho:YLF amplifier

The low-frequency tail of an octave-spanning supercontinuum (SC) generated by an Er:fiber comb is enhanced by a multipass Ho:YLF amplifier and used in a sum-frequency-generation scheme to obtain absolute referencing of a single-mode Tm-Ho:YAG laser tunable around 2.09 um. By tuning the comb repetition frequency, the probing laser is scanned across the absorption lines of a CO2 gas sample and highly accurate absorption profiles are measured. This approach can be readily scaled to any wavelength above 2¼m