An infrared diode laser is frequency stabilized to a tunable internally coupled Fabry-Perot interferometer (icFPI). Diode laser spectra are digitally recorded utilizing a step-by-step tuning and stabilization sequence of the icFPI. Fringes from a frequency stabilized reference He–Ne laser are used to control digital sampling steps. While improving significantly the spectral SNR, this method is combined with a confocal Fabry-Perot etalon, thus providing a frequency scale accuracy of ∼3.5 × 10−5 cm−1 over a 1-cm−1 scan. The method is shown to be consistent with high resolution Fourier transform and heterodyne spectroscopy results.
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