Ultrafast laser induced condensation of molecules

Abstract

We have found that ultrafast laser microbeam inducing bubble(s) can lead to condensation of molecules in solution. The laser microbeam was generated by coupling a near infrared mode-locked femtosecond (fs) laser beam onto an inverted fluorescence microscope and focusing it with a 100X objective. Fluorescence imaging revealed that collapse of cavitation micro-bubbles created high-concentration regions of dye molecules in the aqueous solution. Further, twophoton excitation of the molecules under the ultrafast laser microbeam showed significant increase in fluorescence intensity as a function of laser exposure time without micro-bubble formation. This may be attributed to nano-bubble formation and or conformational change in the molecules under intense laser intensity at the focused spot to significantly enhance the molar absorptivity (extinction coefficient) or fluorescence excitation cross-section. High-concentration regions of the dye molecules are found to be retained for a longer period of time and therefore provide an opportunity for collection of these condensed molecules using microcapilary and/or for further analysis.