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We present two new approaches in tunable diode laser absorption spectroscopy (TDLAS) for measuring the ratio of two components with high precision. These techniques, dual line fitting analysis and jump scanning, greatly extend the versatility and applicability of TDLAS. Three important applications for these approaches are discussed. In addition, we demonstrate the capability to quantify features that are different in amplitude by a factor of 22.4 with a precision of 0.3%. Such a precision is also achieved for features that are different in amplitude by a factor of 12.9 and separated by 0.2363 cm to the negative 1. Both jump scanning and dual line fitting analysis are being used on a routine basis in a laboratory kinetics study to measure simultaneously the concentrations of H2O and NO, whose features are separated by 0.4866 cm to the negative 1.

High-sensitivity detection of formaldehyde ([CH.sub.2]O) at 3.5315 [micro]m (2831.64 [cm.sup.-1]) is reported with a diode-laser-pumped, fiber-coupled, periodically poled LiNb[O.sub.3] 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]O. Spectra are recorded with 2f-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]) [CH.sub.2]O in air mixture, indicate replicate precisions as low as 0.24 ppbv. [C] 2000 Optical Society of America OCIS codes: 010.1120, 120.6200, 300.6340, 190.2620.