Trace-gas sensor based on mid-IR difference-frequency generation in PPLN with saturated output power |
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| Affiliation: | 1. Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, 64287 Darmstadt, Germany;2. Department of Materials and Geoscience, Technische Universität Darmstadt, Alarich-Weiss-Str. 2, 64287 Darmstadt, Germany;1. Functional Morphology and Biomechanics, Zoological Institute, Kiel University, Am Botanischen Garten 1–9, 24098 Kiel, Germany;2. Technische Universität Darmstadt, Fachbereich Chemie, Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Alarich-Weiss-Str. 12, 64287 Darmstadt, Germany;1. MTA-PTE High-Field Terahertz Research Group, Ifjúság ú. 6, 7624 Pécs, Hungary;2. Institute of Physics, University of Pécs, Ifjúság ú. 6, 7624 Pécs, Hungary;3. Szentágothai Research Centre, University of Pécs, Ifjúság ú. 20, 7624 Pécs, Hungary;4. ELI-ALPS, ELI-Hu Nkft., Dugonics tér 13, 6720 Szeged, Hungary;1. Institute of Botany of the Czech Academy of Sciences, Section of Plant Ecology, Dukelská 135, CZ-379 82 Třeboň, Czech Republic;2. Plant Biomechanics Group, Botanic Garden, Faculty of Biology, University of Freiburg, Schänzlestr 1, D-79104 Freiburg im Breisgau, Germany |
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| Abstract: | The development and characterization of a compact pulsed mid-IR laser source for sensitive on-line trace-gas analyses in the 3–4 μm wavelength range is reported. The source is based on an advantageous difference-frequency mixing configuration in periodically poled LiNbO3 (PPLN) with a cw external-cavity diode laser (ECDL; 810–830 nm) for broad and accurate tunability and a diode-pumped passively Q-switched Nd:YAG laser (1064 nm) for high mid-IR peak power. With 5 mW cw pump and 4.7 kW signal peak power incident on a 19 mm long PPLN crystal, a maximum of 360 μW mid-IR peak power was generated. The narrowband (∼150 MHz) radiation was saturated by a factor of 15 compared with the nonsaturated case due to depletion of the pump laser radiation. This results in a very high amplitude stability of the generated mid-IR power and thus in a high detection sensitivity. A minimum detectable absorption coefficient of 2.8×10−8 cm−1 was achieved in combination with a 36.2 m multipass cell in an averaging time of 20 s, as demonstrated by on-line analyses of formaldehyde traces near 3.53 μm. |
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