Rapid shifted excitation Raman difference spectroscopy with a distributed feedback diode laser emitting at 785 nm

M. Maiwald¹, G. Erbert¹, A. Klehr¹, H.-D. Kronfeldt², H. Schmidt², B. Sumpf¹, G. Tränkle¹
¹ Ferdinand-Braun-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, D-12489 Berlin, Germany
² Technische Universität Berlin, Optisches Institut, Hardenbergstr. 36, 10623 Berlin, Germany

Published in:
Appl. Phys. B 85, 509-512 (2006).
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Abstract:
A distributed feedback (DFB) laser diode emitting at 785 nm was tested and applied as a light source for shifted excitation Raman difference spectroscopy (SERDS). Due to the physical properties of the laser diode, it was possible to shift the emission wavelength by 8 cm^-1 (0.5 nm) required for our SERDS measurements by simply changing the injection current. The internal grating ensured single mode operation at both wavelength with the frequency stability of ±0.06 cm^-1 (0.004 nm) required for high resolution Raman spectroscopic applications. The shifted spectra were used for calculating enhanced Raman spectra being obscured by a strong scattering background. A 16 dB (≈38 fold) improvement of the signal-to-background noise /σ_B was demonstrated using blackboard chalk as a sample. The tunable DFB laser is a versatile excitation source for SERDS, which could be used in any dispersive Raman system to subtract fluorescence contributions and scattering background.

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