Monolithic DFB laser diodes emitting at 785 nm for in situ SER Spectroscopy

M. Maiwald^a, G. Erbert^a, A. Klehr^a, B. Sumpf^a, H. Wenzel^a, H. Schmidt^b, H.-D. Kronfeldt^b

^a Ferdinand-Braun-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, D-12489 Berlin, Germany
^b Technische Universität Berlin, Optisches Institut, Straße des 17 Juni 135, 10623 Berlin, Germany

Published in:
Conference Optics East 2005 Optoelectronic devices; Physics, Fabrication, and Application II Proc. SPIE Vol. 6013 S.Proc. of SPIE Vol. 5993 599305-1 - 599305-10.
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Abstract:
A distributed feedback (DFB) laser diode emitting at 785 nm was used as light source for Raman spectroscopy. An in situ surface enhanced Raman spectroscopic (SERS) sensor was developed to detect polycyclic aromatic hydrocarbons (PAHs) in marine environment at concentration levels down to nmol/l. The DFB diode used in our SERS experiments had an output power of 150 mW at 785 nm and a spectral linewidth of 3 MHz. The wavelength stability of this laser was ± 0.004 nm over 12 hours. A side mode suppression ratio up to 45 dB was determined. For trace detection of chemicals in marine environment, SERS active substrates were employed based on silver colloids encapsulated in a sol-gel derived matrix. The resulting spectra and a limit of detection (LOD) of phenathrene (34 nmol/l) as an example for PAHs in seawater are presented. A concentration of 1 nmol/l of pyrene was detected.

Keywords:
DFB laser, Raman, SERS, PAH, in situ monitoring, seawater, marine environment

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