Rapid Shifted Excitation Raman Difference Spectroscopy with a Distributed Feedback Diode Laser Emitting at 785 nm

Ferdinand-Braun-Institut, Berlín, Berlin, Germany
Applied Physics B (Impact Factor: 1.86). 11/2006; 85(4):509-512. DOI: 10.1007/s00340-006-2459-8


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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    • "To realize a SERDS measurement head for near-infrared excitation, an in-house developed and tested Raman optical bench [9] was combined with a 783 nm distributed feedback (DFB) diode laser [10] [11]. By variation of the laser injection current from 110 mA to 260 mA, two operation points necessary to perform SERDS at λ 1 = 782.65 nm and λ 2 = 783.15 "
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    ABSTRACT: Shifted excitation Raman difference spectroscopy (SERDS) was applied for an effective fluorescence removal in the Raman spectra of meat, fat, connective tissue, and bone from pork and beef. As excitation light sources, microsystem diode lasers emitting at 783 nm, 671 nm, and 488 nm each incorporating two slightly shifted excitation wavelengths with a spectral difference of about 10 cm −1 necessary for SERDS operation were used. The moderate fluorescence interference for 783 nm excitation as well as the increased background level at 671 nm was efficiently rejected using SERDS resulting in a straight horizontal baseline. This allows for identification of all characteristic Raman signals including weak bands which are clearly visible and overlapping signals that are resolved in the SERDS spectra. At 488 nm excitation, the spectra contain an overwhelming fluorescence interference masking nearly all Raman signals of the probed tissue samples. However, the essentially background-free SERDS spectra enable determining the majority of characteristic Raman bands of the samples under investigation. Furthermore, 488 nm excitation reveals prominent carotenoid signals enhanced due to resonance Raman scattering which are present in the beef samples but absent in pork tissue enabling a rapid meat species differentiation.
    01/2012; 2012(8). DOI:10.5402/2012/256326
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    • "Also emission wavelengths below 900 nm which are vital for many applications in spectroscopy, pumping of solid state lasers, material science, laser cooling and life science are not easily achievable with (Ga)InAs QDs prepared by these techniques [7] [8] [9] [10] [11] [12]. Due to this lack of controllable short wavelength QDs most of these applications are currently implemented by QW lasers and thus can not benefit from the distinct advantages QD lasers can bring about; such as high material gain, low threshold current density and low temperature dependence of threshold current and wavelength [1] [2] [13]. "
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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).
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    ABSTRACT: We demonstrate the realization of narrow linewidth, high-power ridge waveguide DFB diode lasers emitting near 780 nm. The effects of the coupling coefficient, the laser chip length, and the fabrication process onto the spectral linewidth are discussed. By optimizing both the cavity length and the coupling coefficient, we achieve an intrinsic spectral linewidth as small as 35 kHz at an output power of 270 mW.
    Applied Physics B 09/2012; 108(4). DOI:10.1007/s00340-012-5131-5 · 1.86 Impact Factor
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