Difference-frequency-based tunable absorption spectrometer for detection of atmospheric formaldehyde

High-sensitivity detection of formaldehyde (CH2O) at 3.5315 mu m (2831.64 c m(-1)) is reported with a diode-laser-pumped, fiber-coupled, periodically p oled LiNbO3 spectroscopic source. This source replaced the Pb-salt diode la ser Dewar assembly of an existing tunable diode-laser absorption spectromet er designed for ultrasensitive detection of CH2O. Spectra are recorded with 2f-modulation spectroscopy and zero-air rapid background subtraction. Init ial measurements reported here, determined from multiple measurements of a flowing 7.7 parts per billion by volume (ppbv, parts in 10(9)) CH2O in air mixture, indicate replicate precisions as low as 0.24 ppbv. (C) 2000 Optica l Society of America OCIS codes: 010.1120, 120.6200, 300.6340, 190.2620.