Wolfgang Gurlit

Lightweight diode laser spectrometer CHILD (Compact High-altitude In-situ Laser Diode) for balloonborne measurements of water vapor and methane

A new lightweight near-infrared tunable diode laser spectrometer CHILD (Compact High-altitude In-situ Laser Diode spectrometer) was developed for flights to the stratosphere as an additional in situ sensor on existing balloonborne payloads. Free-air absorption measurements in the near infrared are made with an open-path Herriott cell with new design features. It offers two individual absorption path lengths optimized for CH4 with 74 m (136 pass) and H2O with 36 m (66 pass). New electronic features include a real-time gain control loop that provides an autocalibration function. In flight-ready configuration the instrument mass is approximately 20 kg, including batteries. It successfully measured stratospheric CH4 and H2O profiles on high-altitude balloons on four balloon campaigns (Environmental Satellite validation) between October 2001 and June 2003. On these first flights, in situ spectra were recorded from ground level to 32,000-m altitude with a sensitivity of 0.1 ppm [(parts per million), ground] to 0.4 ppm (32,000 m) for methane and 0.15-0.5 ppm for water.

Intracavity diode laser for atmospheric field measurements

Abstract In situ detection of the absorption of atmospheric trace gases in the near infrared is feasible by using a compact intracavity diode laser spectrometer. Provided that an effective absorber length of more than 1 km is achieved, the measurement of atmospheric peroxy radicals such as HO2 with a detection limit of 2.4 × 107 molecules per cm3 (1 ppt) is possible. During our prototype development, stable trace gases such as H2O and CO2 will be measured. This paper describes the design and development of our instrument, and first experimental results.

SPECTRALOGGER: an ultracompact tunable diode laser spectrometer for automated field use

A small size tunable diode laser (TDL) spectrometer with dimensions of only 280 x 190 x 130 mm (11 x 7.5 x 5 inch) was built for automated field use. The water-protected package also contains batteries and a data storage device for an independent operation of 15 hours. Mass of the complete instrument is 5 kg. Smallest absorptions recorded in fully auto-mated operation are in the 10-5 range. Data is stored as direct absorptions and as derivative as well. The instrument can be equipped with near infrared (NIR) laser diodes depending on target species (e.g. water vapor or methane). A high dyna-mic range is achieved by periodically tuning the laser over various molecular absorption lines of different line strength using temperature scan. The absorption path is set up using a retroreflector, the pathlength can be between 0.5 meters and 100 meters depending on requirements. The instrument is targeted at reliable and sensitive field measurements in fully automated and unattended mode, including e.g. aircraft and environmental measurements.

External resonator tunable diode laser (TDL) system for extracavity and intracavity absorption: experiments and modeling

A 1530nm multimode diode laser with an external resonator containing a grating achieved a single-mode tuning range of 100nm. Etalon effects and modehops during the frequency tuning of the laser were minimized by special design features. Absorptions of water vapor were recorded intracavity and extracavity. The intracavity experiments were impeded by modehops induced by the absorption itself. This effect could be reduced by increasing the selectivity of the resonator. Modeling of the optical properties of the resonator allows the quantitative specification of the optical parameters for a singlemode intracavity tunable diode laser (TDL) operation. This enables a resonator design to be realized which achieves an optimum stability and selectivity for a singlemode TDL for both extracavity applications.