Femtosecond-Laser-Induced Nanocavitation in Water: Implications for Optical Breakdown Threshold and Cell Surgery

Abstract

We determined the bubble radius ${R}_{\mathrm{max}}$ for femtosecond optical breakdown in water at 347, 520, and 1040 nm with an unprecedented accuracy ($\ifmmode\pm\else\textpm\fi{}10\text{ }\text{ }\mathrm{nm}$). At threshold, ${R}_{\mathrm{max}}$ was smaller than the diffraction-limited focus radius and ranged from 190 nm to 320 nm. The increase of ${R}_{\mathrm{max}}$ with laser energy ${E}_{L}$ is slowest at 347 nm, providing optimum control of cell surgery. Experimental results agree with a model of bubble formation in heated and thermoelastically stretched liquids. Theory predicts a threshold temperature ${T}_{\mathrm{th}}\ensuremath{\approx}168\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. For $T>300\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, a phase explosion sets in, and ${R}_{\mathrm{max}}$ increases rapidly with ${E}_{L}$.