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: We present a compact wavelength stabilized diode laser system at 671 nm on a micro-optical bench as a light source for shifted excitation Raman difference spectroscopy (SERDS). The laser system consists of two broad-area gain media in separate laser cavities using two reflection Bragg gratings with slightly different center wavelengths. A spectral width below 100 pm and a constant wavelength shift of 0.57 +/- 0.06 nm is obtained up to output powers of 250 mW. The suitability of this light source for SERDS is demonstrated using Raman spectra of ethanol with increasing concentrations of Cresyl Violet as the fluorescent contaminant.Applied Optics 06/2009; 48(15):2789-92. · 1.69 Impact Factor
Article: Portable Raman explosives detection[Show abstract] [Hide abstract]
ABSTRACT: Recent advances in portable Raman instruments have dramatically increased their application to emergency response and forensics, as well as homeland defense. This paper reviews the relevant attributes and disadvantages of portable Raman spectroscopy, both essentially and instrumentally, to the task of explosives detection in the field.Analytical and Bioanalytical Chemistry 02/2009; 393(6):1571-1578. · 3.66 Impact Factor
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ABSTRACT: By adjusting the Al and In concentration of AlGaInAs quantum dots (QDs), their morphologic and spectral properties (i.e., size, height, density, and emission wavelength) can be engineered partly independently. In this paper, we report that this tunability can be used to improve QD laser properties and to realize QD lasers at wavelengths not achievable with the commonly used (Ga) InAs QDs. We show that using tailored AlGaInAs QDs grown on GaAs substrate, the device properties of QD lasers can be improved with respect to material gain, accessible wavelength range, and temperature stability of the wavelength. In particular, we report that the material gain in QD lasers can be notably increased (by a factor of 2.1). Furthermore, we demonstrate QD lasers with application key wavelengths in the range between 760 and 920 nm. The presented short-wavelength ( ~ 760 nm) QD lasers exhibit characteristics comparable to state-of-the-art quantum well (QW) lasers (light output > 20 mW, sidemode suppression ratios ~ 40 dB, I<sub>tr</sub> = 43 mA). We also demonstrate that AlGaInAs QDs can be used to fabricate QD lasers with extremely high temperature stabilities of the wavelength (0.072 nm/K).IEEE Journal of Selected Topics in Quantum Electronics 07/2009; · 4.08 Impact Factor