*2.2. Portable Raman Spectrometer*

The BRAVO spectrometer uses a new patented technology called SSE™ (Sequentially Shifted Excitation, patent number US8570507B1) in order to mitigate fluorescence [6,7]. The laser is slightly wavelength-shifted during the acquisition three times, and three raw Raman spectra are recorded. A proper algorithm recognizes all the peaks that shift at different laser wavelengths as good Raman peaks, and other peaks, non-shifting, as fluorescence (or absorbance) peaks, removing them. Moreover, the BRAVO use two different lasers (DuoLaser™), ranging from 700 to 1100 nm, during the acquisition. The use of the second laser is not intended as in usual commercial handheld or portable Raman spectrometer as a tool to try to mitigate the fluorescence, but as a way to collect Raman spectra up to 3200 cm−<sup>1</sup> and hence to access the CH stretching region also. The first laser is dedicated to the acquisition of the Raman spectra in the first range (called fingerprint region), and the second one in the second range (called CH region). The BRAVO acquired spectrum is finally a Raman spectrum free from fluorescence on a whole spectral range from 3200 to 300 cm−<sup>1</sup> . The applied laser power is always less than 100 mW for both lasers. Obviously, using the two BRAVO lasers ranging from 700 to 1100 nm, the sensitivity to inorganic green and blue is very reduced compared to the use of a 532 nm laser. The spectral information from the enhanced spectral range are useful for identification, for example, of resins and waxes. The spectra were acquired with acquisition time ranging from 500 ms to 2 s and accumulation ranging from 5 to 100. For all the measurements, OPUS™ software (Version 7.7) has been used in order to select the appropriate acquisition parameters. We performed at least 4 acquisitions for each point.
