Abstract

A new, compact, spatially scanning, open-path 2.7μm tunable diode laser absorption spectrometer with short absorption path lengths below 10cm was developed to analyze the spatiotemporal dynamics of one-dimensional (1D) spatial water vapor gradients. This spectrometer, which is based on a room- temperature distributed feedback diode laser, is capable of measuring absolute, calibration-free, line-of-sight averaged, but laterally resolved 1D H2O concentration profiles with a minimum fractional optical resolution of 2.1×103 optical density (OD) (2.5×104 OD after a background subtraction procedure), which permits a signal-to-noise-ratio of 407 (3400) at 10,000partsin106(ppm) H2O, or normalized sensitivities of 2.6ppmm (0.32ppmm) at 0.5Hz duty cycle. The spectrometer’s lateral spatial resolution (governed by the 500μm sampling beam diameter) was validated by analyzing a well-defined laminar jet of nitrogen gas in humidified air. This scanning setup was then used to (a) quantitatively investigate for what we believe to be the first time the H2O boundary layer from 0.7 to 11mm beneath the stomatous side of a single, undetached plant leaf, and (b) to study the temporal boundary layer dynamics and its dependence on stepwise light stimulation of the photosynthetic system. In addition the 2.7μm diode laser was carefully characterized in terms of spectral purity, beam profile, as well as quasi-static and dynamic wavelength tuning coefficients.

© 2009 Optical Society of America

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