Photoacoustic (PA) spectra generated by current modulation of a distributed feedback diode laser (DFB-DL) were measured for the ammonia absorption line at and calculated using absorption spectra taken from a database. The algorithm is based on a combined amplitude- and wavelength-modulation (AM–WM) scheme. The spectral characteristics of the DFB-DL were determined by comparing simulated spectra with Fourier transform infrared measurements. PA spectra were measured and simulated from the first to fourth harmonic and a variation of the modulation depth with modulation frequency was observed. It was found that combined AM–WM modulation may produce larger PA signals than separate AM or WM detection for the first harmonic.
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