Fig. 1. Schematic diagram of a portable Raman probe extension kit.

Fig. 2. Experimental diagram of the portable Raman probe extension kit.

Fig. 3. Comparison of the Raman spectra for ethanol detected by SLHCF and direct detection.

Fig. 4. Comparison of the Raman spectra for ethanol detected by the Raman detection system with and without gold film.

Fig. 5. (a) Raman spectra for the ethanol solution whose concentration ranged from 5% to 100% with respect to water. (b) The linear fitting relationship between the Raman intensity at $881{\mathrm{cm}}^{-1}$ and the concentration for the ethanol solution.

Fig. 6. (a) The Raman intensity at $881{\mathrm{cm}}^{-1}$ for the ethanol solution in water with the concentration varied in time. (b) The Raman intensity at $818{\mathrm{cm}}^{-1}$ for the isopropanol solution in water with the concentration varied in time. (c) The concentration of the ethanol solution and isopropanol solution injected into the capillary varied with the time. (d) The schematic on the replacement and cleaning of the sample in experiments. (e) The Raman intensities at $881{\mathrm{cm}}^{-1}$ and $818{\mathrm{cm}}^{-1}$ are chosen to represent ethanol and isopropanol without mutual interference.