The low-power light source used for the experiments consisted of a laser diode (Thorlabs, L450P1600MM) emitting at 450 nm and operating at 1.6 W output power. The optical power was lowered to the milliwatt range by using a potentiometer that regulated the current through the diode, enabling the selection of the minimal current to achieve maximal signal enhancement to avoid signal distortion due to sample overheating. A photometer was used to monitor the desired power from the light beam coming out of a BFH optical fiber with 1000 μm diameter, purchased from Thorlabs (Germany). This current controller (Thorlabs, LDC 240C) could be switched on and off to regulate the duration and intensity of the light pulse either manually (continuous irradiation) or in a pulsed manner by a TTL signal directly from the spectrometer. A temperature controller (Thorlabs, TED 200C) was also used to ensure no variation in output light power of the current controller (LDC, 240C) for a certain current value [26 (link)].
The claddings of the optical fiber tip were stripped off, the main part of the fiber was masked, and the 21 mm at the tip of the fiber was sandblasted to roughen its surface, thus making it emit light over its whole range instead of just from its tip. Silicium carbide 180 was used as the abrasive material [23 (link)].
The claddings of the optical fiber tip were stripped off, the main part of the fiber was masked, and the 21 mm at the tip of the fiber was sandblasted to roughen its surface, thus making it emit light over its whole range instead of just from its tip. Silicium carbide 180 was used as the abrasive material [23 (link)].
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