This title appears in the Scientific Report : 2009 

Distributed feedback diode laser spectrometer at 2,7 µm for sensitive, spatially resolved H2O vapor detection
Wunderle, K.
Wagner, S. / Pasti, I. / Pieruschka, R. / Rascher, U. / Schurr, U. / Ebert, V.
Phytosphäre; ICG-3
Applied optics, 48 (2009) S. B172 - B182
Washington, DC Optical Soc. of America 2009
B172 - B182
Journal Article
Terrestrische Umwelt
Applied Optics 48
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A new, compact, spatially scanning, open-path 2.7 mu m 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 x 10(-3) optical density (OD) (2.5 x 10(-4) OD after a background subtraction procedure), which permits a signal-to-noise-ratio of 407 (3400) at 10, 000 parts in 10(6) (ppm) H2O, or normalized sensitivities of 2.6 ppm(.)m (0.32 ppm m) at 0.5 Hz duty cycle. The spectrometer's lateral spatial resolution (governed by the 500 mu m 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 11 mm 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 2.7 mu m diode laser was carefully characterized in terms of spectral purity, beam profile, as well as quasi-static and dynamic wavelength tuning coefficients. (C) 2009 Optical Society of America