Optical Sciences

Biomolecules and nanostructures

The Optical Sciences group studies the interaction of light and matter at the nanoscale. We do this by exploring ways to shape light and its environment. It's what we call active and passive control. Our current focus is on the interaction of light with biomolecules and nanostructures. We are part of Twente University's Department of Science and Technology and member of the MESA+ institute.
We participate in the EU-COST actions MP1102: Coherent Raman microscopy (MicroCor) and CM1202: Supramolecular photocatalytic water splitting (PERSPECT-H2O)


A theoretical investigation of super-resolution CARS imaging via coherent and incoherent saturation of transitions

(full pdf)

Willem P. Beeker, Chris J. Lee, Klaus J. Boller, Petra Groß, Carsten Cleff, Carsten Fallnich, Herman L. Offerhaus and Jennifer L. Herek
Journal of Raman Spectroscopy
vol 42, p1854–1858 may 3, 2011

We review two approaches to achieving sub-diffraction-limited resolution coherent anti-Stokes Raman scattering (CARS)microscopy (Beeker et al., Opt. Express, 2009, 17, 22632 and Beeker et al., J.Herek,Phys. Rev. A, 2010, 81, 012507).We performed a numerical investigation, based on the densitymatrixmodel, of the CARS emission process and identified two modified CARS experiments that lead to sub-diffraction-limited resolution images. At the heart of both processes is the spatialmanipulation of the coherence between the ground state and the vibrational state being probed by the CARS process via a control state and a control laser that is resonant with the ground state to control state transition.We find two possible regimes of operation: in the first regime, the control and vibrational states are coupled via incoherent processes so that the populations of the two states reach equilibrium very quickly compared to the relevant coherence times. Under these conditions, pre-populating the control state provides a saturable suppression of the coherence between the ground state and the vibrational state, suppressing CARS emission. By using a donut mode to pre-populate the control state, CARS is suppressed everywhere but the central node, allowing sub-diffraction-limited resolution imaging. In the second regime, the control state has a rather long coherence lifetime, and the resonant laser drives Rabi oscillations that periodically deplete the ground state. As a result, the CARS emission process is amplitude-modulated, which appear as sidebands on the CARS spectrum. By a process of spectral resolution and trilateration, sub-diffraction-limited resolution images can be obtained. © 2011 JohnWiley & Sons, Ltd.
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