Solvent effect in extra-cavity pulses by thermo-cavitation in natural dyes

Abstract

Optical cavitation is the formation of vapor cavities in a liquid when a pulsed laser is focused over highly absorbent liquid; however, when a continuous laser is used, the phenomenon is called thermo-cavitation. Recently, thermocavitation has been studied in different materials^1–3. In this work, we present the analysis of extra-cavity pulses generation by thermo-cavitation induced by a CW laser beam focused into solutions of Hibiscus Sabdariffa in ethanol and Hibiscus Sabdariffa in methanol. Due to the high absorption of the natural dye and the low boiling point of the solvents (< boiling point of the water), heating is produced which gives origin and implosion of bubbles. The process of explosion and implosion of the bubbles acts as an obturator allowing the pulses formation of the light passing through the sample. The characterization of the pulses was performed by moving the sample around the focus of the lens, we observe a modification in the thermo-cavitation time, an analysis of the changes in the frequency rate and the amplitude of pulses was performed. The frequency rate, the amplitude, and the full width half maximum (FWHM) of the pulses were measured. We found that the average frequency decreases, and the average amplitude increases when we move the sample at a distance from the focus. The temporary response of the pulses obtained in both solutions, change as a consequence of the difference between the boiling point of the methanol and ethanol.