High-sensitivity detection of formaldehyde (CH<sub>2</sub>O) at 3.5315 μm (2831.64 cm<sup>−1</sup>) is reported with a diode-laser-pumped, fiber-coupled, periodically poled LiNbO<sub>3</sub> spectroscopic source. This source replaced the Pb–salt diode laser Dewar assembly of an existing tunable diode-laser absorption spectrometer designed for ultrasensitive detection of CH<sub>2</sub>O. Spectra are recorded with <i>f</i>-modulation spectroscopy and zero-air rapid background subtraction. Initial measurements reported here, determined from multiple measurements of a flowing 7.7 parts per billion by volume (ppbv, parts in 10<sup>9</sup>) CH<sub>2</sub>O in air mixture, indicate replicate precisions as low as 0.24 ppbv.
© 2000 Optical Society of America
(010.1120) Atmospheric and oceanic optics : Air pollution monitoring
(120.6200) Instrumentation, measurement, and metrology : Spectrometers and spectroscopic instrumentation
(190.2620) Nonlinear optics : Harmonic generation and mixing
(300.6340) Spectroscopy : Spectroscopy, infrared
David G. Lancaster, Alan Fried, Bryan Wert, Bruce Henry, and Frank K. Tittel, "Difference-Frequency-Based Tunable Absorption Spectrometer for Detection of Atmospheric Formaldehyde," Appl. Opt. 39, 4436-4443 (2000)