Wavelength modulated off-axis integrated cavity output spectroscopy in the near infrared

• DOI: 10.1007/s00340-006-2451-3
• Publication Date: 2006-09-28T12:25:54Z
• Authors: W. Zhao; X. Gao; W. Chen; W. Zhang; T. Huang; T. Wu; H. Cha
• Keywords: Optical path; Cavity Ring-Down Spectroscopy; Modulation (music)

A novel instrument based on an improved off-axis alignment of integrated cavity output spectroscopy (OA-ICOS) in conjunction with a wavelength modulation (WM) technique, was developed using a DFB diode laser operating in the near infrared at 1.573 μm (6357.3 cm-1). The laser-based sensor employed a 44 cm optical cavity that provided an effective absorption path length of ∼68 m. A minimum detectable absorption of approximately 3.6 ppmv Hz-1/2 or 2.3×10-7 Hz-1/2 per optical pass was obtained using second harmonic detection. We demonstrated that by implementation of the WM technique to OA-ICOS in the near infrared, the detection sensitivity was improved by a factor of 14 compared to that obtained with OA-ICOS. Measurements of CO2 mixing ratios in ambient air have been performed by using both OA-ICOS and WM-OA-ICOS techniques for performance comparison.