Methods

μ-Raman spectroscopy

Confocal LabRAM Aramis Vis (400-1100 nm) instrument of Horiba Jobin Yvon was applicable for the Raman measurements. The Olympus BXFM microscope (with 10x, 50x, 50x LWD, and 100x objectives) was coupled to 460 mm spectrometer. The instrument was equipped with three lasers: 532 nm (Nd:YAG, 50 mW), 632.8 nm (HeNe, 17 mW), and 785 nm (Diode, 80 mW). A CCD camera (1024 x 256 pixels, Peltier cooled at -70°C), three edge filters for rejection of lasers excitation lines, and four gratings (300, 600, 1200, and 1800) were implemented in the instrument. Different optical density filters were used for the regulation of the laser power at the sample surface.

For measurements, small sample amounts were placed and flattened on microscope glass slides. To minimize or avoid the heating of the samples during the measurements — if necessary — pigments were measured on aluminum foil. Depending on the pigment samples, lasers and measuring conditions were set for analyses.

Confocal LabRAM Aramis Vis Raman spectrometer (Horiba Jobin Yvon)