Investigating breakdown thresholds of picosecond optical pulses and nano-second pulsed electric fields

Abstract

We investigate the effect of nanosecond pulsed electric fields on optical breakdown thresholds for picosecond optical pulses (6ps pulse duration at wavelength of 1064nm) in aqueous solutions. Optical breakdown thresholds are determined both with and without the application of the nanosecond pulsed electric fields in water, phosphate-buffered saline solution, and a typical buffer solution used for live cell imaging. As optical breakdown at this time-scale mostly on a combination of multi-photon ionization as well as free electrons in the focal volume to achieve an avalanche or cascade ionization phenomena, we hypothesize that the application of a strong external electric field will have a significant impact on the breakdown probability at the lower-end of pulse energy levels, effectively modifying the pulse-energy breakdown threshold of the materials. Single optical pulses were triggered at specific times with respect to the leadingedge of the applied electric field to determine if there were any time-dependent effects on breakdown thresholds. Results of the experiments are examined and the physical phenomena as well as the concept “electrostatic purification” are discussed.