Comparative study of the dynamics of laser breakdown in water and hexane using interference microscopy

The changes in the optical properties of water and hexane under femtosecond irradiation (Ti : Al₂O₃ laser, wavelength 800 nm, intensity ~1013 W cm^-2) are investigated in the cavitation (bubble-formation) regime using interference microscopy in a time interval of ~1.5 ns since the impact onset. A comparison of the dynamics of radiation-induced processes (solvation of excess electrons, pair recombination, and development of precavitation processes) is performed. The excited-carrier concentration is estimated, and these estimates are found to be inconsistent with the amount of energy that must be transferred to the liquid during a pulse to implement its heating and subsequent cavitation. This inconsistency is especially pronounced for hexane, where ionisation processes can barely be detected by interferometry. The experimental results put new questions about the mechanisms of energy transfer in both polar and nonpolar liquids subjected to intense laser irradiation.