title: Wavelength- and amplitude-modulated photoacoustics: comparison of simulated and measured spectra of higher harmonics.
abstract: Photoacoustic (PA) spectra generated by current modulation of a distributed feedback diode laser (DFB-DL) were measured for the ammonia absorption line at 1.53 microm 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.
authors.affiliation: Institute of Physical Chemistry, University of Heidelberg, Heidelberg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Angelmahr
authors.forename: A
authors.initials: A
authors.lastname: Miklós
authors.forename: P
authors.initials: P
authors.lastname: Hess