Frequency stepwise fiber laser for practical gas spectroscopy

We introduce the concept of frequency stepwise fiber laser and its potential application in gas spectroscopy with simple time-domain retrieval. Three different setups of the in-loop frequency shifter are demonstrated with different options of frequency step sizes. Spectroscopy in O₂ and CO₂ is carried out in gas cell to verify the spectral retrieval capability. The retrieved curves are in good agreement with the calculated results from HITRAN database. The output wavelength band of such a frequency stepwise fiber laser can be further extended with different in-loop gain fiber and/or nonlinear frequency conversion, providing promising solutions to practical spectroscopy of many important gases.