DH and the Effects of Optical Pressure on Fluid Surfaces

We introduce a noncontact purely optical approach to measuring the localized surface properties of an interface within a system using a single optical pressure pulse and a time-resolved digital holographic quantitative phase imaging technique to track the propagating nanometric capillary disturbance. We demonstrate the proposed method’s ability to measure the surface energy of deionized water, methanol, and chemical monolayers formed by surfactants with good agreement to published values. The development of this technique boasts immediate application to static and dynamic systems and near-future applications for living biological cell membranes.

A capillary wave response is induced by an optical pressure pulse and tracked by microsecond-resolved digital holographic phase imaging to determine fluid surface properties. The method will be applied to the biological cell membrane.

Dynamic response to an optical pressure pulse can be a useful indicator of the mechanical properties of a fluid surface or membrane. We have mapped the time-dependent response of the water surface using precise measurement and timing techniques.

Optical excitation of a fluid interface involves both momentum exchange and thermal effects. A time-resolved phase study has shown agreement with our combined model of the two effects which vary significantly in time scale.

Quantitative phase microscopy by digital holography gives direct access to the phase profile of a transparent subject with high precision. This is useful for observing phenomena that modulate phase, but are otherwise difficult or impossible to detect. In the current study, a carefully constructed digital holographic apparatus has been used to measure optically induced thermal lensing with an optical path difference precision of less than 1 nm. Furthermore, by taking advantage of the radial symmetry of a thermal lens, this data was processed to determine the absorption coefficient of transparent media with precisions as low as 1 x 10^-5cm^-1 using low power (30 mW) cw excitation.

It is evident that thermal effects should not be dismissed when pursuing optical radiation pressure experiments even for transparent media. We have developed a unified model and simulated and tested methods of decoupling the two effects.

Digital holographic microscopy produces quantitative phase analysis of a specimen with excellent optical precision. In this study, this imaging method has been used to observe and measure induced thermal lensing by optical excitation. Previous studies have derived these phase shifts from intensity profiles for the determination of photothermal properties of very transparent materials. We have measured physical observables and determined the absorption coefficients of methanol and ethanol with improved precision and accuracy over traditional thermal lens spectroscopy methods.

Digital Holographic Microscopy produces quantitative phase analysis of a specimen with excellent optical precision. In the current study, this imaging method has been used to measure induced thermal lensing by optical excitation in the time-resolved regime with excellent agreement to model predictions. We have found that the thermal effect should not be dismissed when pursuing optical radiation pressure experiments, even when the media involved are transparent. We have developed a unified model and simulated methods of decoupling the two effects. The results of this study and simulations suggest that our near term goal of nanometric measurement of an optical pressure induced deformation will prove successful. Precise measurement of this phenomenon can be useful in determining physical properties of interfacial surfaces, such as surface tension, and characterizing physical properties of cellular structures.