Insitu Raman Setup for Deep Ocean Investigations Applying Two 1000 m Optical Fiber Cables and a 785 nm High Power Diode Laser
H. Ahmad1, B. Sumpf2, K. Sowoidnich1, A. Klehr2, H.-D. Kronfeldt1
Published in:
Marine Science, vol. 2, no. 6, pp. 132-138 (2012).
Abstract:
A laboratory Raman-set-up is used to demonstrate the feasibility of deep ocean measurements using 1000 m long low OH optical fibres for the excitation of the substances under study and the collection of the Raman photons. As excitation laser a 785 nm broad area distributed feedback (DFB-BA) high-power diode laser with an optical power of 1.25 W and a spectral emission width below 0.6 nm suitable for Raman spectroscopy was used.After passing beam shaping and focusing optics, a 1000 m long fiber, and a pressure-resistant optode275 mW of optical power were available at the sample. The optode also collects the Raman photons and focuses the light into the second 1000 m long fibre, which transfers the light into a spectrometer. To determine the reachable signal-to-noise ratio, Raman spectra were taken from natural minerals (sulfates, carbonates, sulfur). Even for weak Raman-signal and short integration times of 0.5 s per spectrum, the signal-to-noise ratio of 60 would be suitable for the in-situ Raman spectroscopy in deep ocean applications. Even longer optical fibres would increase to integration time up to 60 s. The shown set-up offers the opportunity to used different laser sources and spectrometers on board of a ship, only the fibres and the optode had to be suitable for deep sea conditions.
1 Technische Universität Berlin, Institut für Optik und Atomare Physik, Sekr. EW 0-1, Hardenbergstraße, 36, 10623 Berlin, Germany
2 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, D-12489 Berlin, Germany
Keywords:
In-Situ Raman Spectroscopy, High Power Broad Area DFB Diode Laser, Long Low OH Optical Fiber, Deep Ocean, Natural Minerals.
© 2012 Scientific & Academic Publishing Co. All rights reserved. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the Scientific & Academic Publishing Co.
Full version in pdf-format.