Fig. 1. Overview of acetonitrile differential Raman spectroscopy processing steps. (a) Raw spectra at two different excitation wavelengths; (b) differential spectrum; (c) Raman spectrum restored using integral method; (d) ideally, Raman spectrum restored using integral method

Fig. 2. Raman spectra reduced by curve fitting method

Fig. 3. Acetonitrile differential Raman spectra. (a) Raman spectra of acetonitrile excited by 784.5 nm and 785.5 nm wavelengths; (b) deconvolution and restore of Raman spectra

Fig. 4. Workflow of NNLS based spectral reconstruction^[15]

Fig. 5. Optical path structure of SERDS instrument. (a) Structure diagram of SERDS with dual-wavelength lasers at 532 nm and 526 nm^[37]; (b) structure diagram of SERDS based on external cavity tunable semiconductor laser^[38]; (c) optical path of SERDS based on dual-wavelength laser and area array CCD^[44]; (d) internal structure diagram of portable SERDS^[41]

Fig. 6. Instrument structure diagram of multi-wavelength defluorescence Raman spectrometer^[46]

Fig. 7. Raw spectra, difference spectra, and reconstructed spectra of tree pollen and non-tree pollen under excitation at 784‒786 nm wavelength^[52]

Fig. 8. Raman spectra of nasopharyngeal tissue in vitro excited at the wavelength of 784.5 nm and 785.2 nm with different detection distances^[54]. (a) 5 mm; (b) 10 mm; (c) 15 mm; (d) normalized shifted excitation Raman difference spectroscopy with different detection distances