Peter van Oostrum

Co-founder (CTO) at Holloid

I develop Digital Holographic Microscopy at the BOKU to study self-assembly in colloidal systems, measure forces between colloidal particles, study the interactions between bacteria and substrates and identify cells and bacteria.

PhD student of physics at the University of Utrecht. I am responsible for the maintenance and further development of the optical tweezers setup and the confocals in our lab. Together with people at the New York University I developed a holographic technique to track and characterize individual particles in three dimensions at unprecedented accuracy using in-line holography and Mie-scattering. By numerically solving the inverse problem posed by the interference pattern below a coherently illuminated Mie-particle, we can determine the position in three dimensions with nm accuracy while also measuring the individual particle’s radius and refractive index. Using a fast CCD camera we can track particles with an resolution in time and space. Using optical tweezers I can place multiple particles in interesting configurations to measure the interaction forces. These interaction forces can be the result the charge on the particles and screening, but can also be caused by electric dipoles that we induce by applying high frequency electric fields or by the presence of other, refractive index matched particles that induce a depletion attraction. I gained experience with a wide variety of particles, solvents and techniques. Moreover, I have performed calculations on the trapping forces of optical tweezers in a wide parameter space to explore the possibilities.

Applied Physics (University Twente, Enschede) Group: PoF (Physics of Fluids) Graduation assignment: a study of the Path-, Wake- and Shape-Oscillations of a Rising bubble. In many applications rising bubbles play a crucial role. Rising bubbles greatly increase the exchange of gasses. For instance, CO2 is being removed from the atmosphere by algae after being dissolved from a bubble. My work on the topic entails the further development of an experimental setup used to stereoscopically film rising bubbles. I wrote a program in Matlab to analyze the results of these experiments. I have been able to calculate the three dimensional shape of the bubbles from the information gathered from the two mutually perpendicular views. Moreover the setup also uses Schlieren optics to visualize the wake of the bubble.