Ultrafast response of water near hydrophobic and hydrophilic surfaces

Time-resolved ellipsometry is introduced on the study of water – surface interactions. A strong laser pulse gives a thermal and mechanical perturbation on the surface. Another laser is used to probe the ellipticity at the interface as shown in the figure.

Pump and probe pulses are from a dual Ti:sapphire laser with stable difference repetition rate. Every difference repetition rate, time delay is swept the whole pulse-to-pulse interval without an optical delay stage. The Pd surface is modified by thiol chemistry. Thiols with –OH and -CH3 end groups generate uniform hydrophilic and hydrophobic surfaces, and these mixtures modulate hydrophobicity two-dimensionally. Probe pulses with circular polarization impinge at the Brewster’s angle and are analyzed by a polarizer. The transient ellipticity shows a refractive index change of water by thermal conductance and novel insight into the peculiar qualities of interfacial water.

About me

My first Ph. D subject was developing an efficient and stable optical parametric oscillator using a low-power pump source. It took long time and there were many failures because I was not experienced and it’s really new. Finally, I got 100 nJ pulses using only 800 mW Ti:sapphire pumping laser. Using this laser I had studied energy transfer dynamics in DNA and J-aggregates, which was original interest. In this group, I developed high performance dual-cavity pump-probe system to solve water problems. I think I tried to chase lasers before and now lasers are following me.