Software-switching between direct absorption and wavelength modulation spectroscopy for the investigation of ADC resolution requirements
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We present a tunable diode laser spectrometer that can be software-switched between a wavelength modulation spectroscopy (WMS) operation mode and the direct absorption spectroscopy (DAS) technique on a per-scan basis. The new setup allows a direct comparison between the two techniques under equal hardware and system environment conditions. In this work, we compare the impact of analog-to-digital converter resolution for operation in WMS and DAS mode. Example concentration evaluations show that in the DAS approach, relative absorptions smaller than the least significant bit can be measured with scan averaging and FIR-filtering applied. With full resolution, both techniques show similar performance in our setup, with a slight advantage for the WMS implementation.
KeywordsTunable Diode Laser Absorption Spectroscopy Wavelength Modulation Spectroscopy Direct Absorption Spectroscopy Resolution Reduction Residual Amplitude Modulation
The authors gratefully acknowledge funding of the Erlangen Graduate School in Advanced Optical Technologies (SAOT) by the German Research Foundation (DFG) in the framework of the German excellence initiative.
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