Tailored diode lasers: enabling Raman spectroscopy in the presence of disturbing fluorescence and background light

Raman spectroscopy is a well-established tool for material analysis, investigation of biological targets, food control, and medical applications. Analyzing real-world samples, fluorescence and intense background light can superimpose the weak Raman signals. Due to a different spectral behavior of these interferences compared to the Raman effect, experimental methods have been demonstrated to overcome this drawback. The so-called shifted excitation Raman difference spectroscopy (SERDS) utilizes shifts of the Raman lines with respect to shifts in the excitation wavelengths by a distance comparable to the width of the Raman lines under study. Disturbing background light remains spectrally constant and subsequent signal subtraction separates the Raman signal from the background. This technique relies on dual-wavelength light sources as key elements. In this contribution, tailored diode laser based light sources suitable for SERDS will be presented. First, we present hybrid and monolithic devices in the spectral range between 457 nm and 830 nm with output powers up to the watt range. This includes dual-wavelength lasers as well as DBR lasers with an adjustable emission wavelength, e.g. at 785 nm, enabling SERDS and related methods separating Raman signals from background interferences. Second, we present a compact UV light source at 222.5 nm with 160 μW output power suitable for UV Raman spectroscopy. This light source enables detecting Raman signals in a fluorescence-free spectral region.