Rapid shifted excitation Raman difference spectroscopy with a distributed feedback diode laser emitting at 785 nm
ABSTRACT A distributed feedback (DFB) laser diode emitting at 785nm 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 8cm-1 (0.5nm) 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 ±0.06cm-1 (0.004nm) 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 16dB (≈38 fold) improvement of the signal-to-background noise S̄/σB 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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ABSTRACT: In this paper, we propose an improved subtraction algorithm for rapid recovery of Raman spectra that can substantially reduce the computation time. This algorithm is based on an improved Savitzky–Golay (SG) iterative smoothing method, which involves two key novel approaches: (a) the use of the Gauss–Seidel method and (b) the introduction of a relaxation factor into the iterative procedure. By applying a novel successive relaxation (SG-SR) iterative method to the relaxation factor, additional improvement in the convergence speed over the standard Savitzky–Golay procedure is realized. The proposed improved algorithm (the RIA-SG-SR algorithm), which uses SG-SR-based iteration instead of Savitzky–Golay iteration, has been optimized and validated with a mathematically simulated Raman spectrum, as well as experimentally measured Raman spectra from non-biological and biological samples. The method results in a significant reduction in computing cost while yielding consistent rejection of fluorescence and noise for spectra with low signal-to-fluorescence ratios and varied baselines. In the simulation, RIA-SG-SR achieved 1 order of magnitude improvement in iteration number and 2 orders of magnitude improvement in computation time compared with the range-independent background-subtraction algorithm (RIA). Furthermore the computation time of the experimentally measured raw Raman spectrum processing from skin tissue decreased from 6.72 to 0.094 s. In general, the processing of the SG-SR method can be conducted within dozens of milliseconds, which can provide a real-time procedure in practical situations.Applied Optics 08/2014; 53(24). DOI:10.1364/AO.53.005559 · 1.69 Impact Factor
Energies 04/2015; 8(4):3165-3197. DOI:10.3390/en8043165 · 1.60 Impact Factor