J. Phys. IV France
Volume 125, June 2005
Page(s) 579 - 581

J. Phys. IV France 125 (2005) 579-581

DOI: 10.1051/jp4:2005125133

Application of a wavelength-amplitude double-modulation method in photoacoustic detection using a pulsed optical parametric oscillator

A. Miklós1, J. Ng2, P. Hess1 and A.H. Kung2

1  Physical Chemistry Institute, University of Heidelberg, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany
2  Institute of Atomic & Molecular Sciences, Academia Sinica, Taipei 106, Taiwan R.O.C., PO Box 23-166, Taipei, Taiwan

A wavelength-amplitude (WM-AM) double-modulation technique that uses the acoustic wave generated via light absorption by a gaseous medium as the carrier wave is demonstrated. By modulating the excitation wavelength of the light pulses from a multi-kHz optical parametric oscillator at a lower frequency than the acoustic frequency, differential infrared spectra with a vanishing baseline are obtained when employing photoacoustic detection. This modulation technique is used to enhance the sensitivity in trace gas analysis to an estimated detection sensitivity of 136 pptv for methane using the all-solid-state optical parametric oscillator.

© EDP Sciences 2005