Hamburg 2009 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 36: Laseranwendungen

Q 36.8: Talk

Wednesday, March 4, 2009, 18:15–18:30, Audi-A

On the interaction of highly focused beams with metallic edges or the knife-edge method in the nano-world — •Marchenko Pavel, Sergejus Orlovas, Susanne Quabis, Ulf Peschel, and Gerd Leuchs — MPI für die Physik des Lichts, Erlangen, Deutschland

The so-called "knifeedge" method is frequently used to determine the intensity distribution of laser beams. Metal edges of various orientations are moved across the spot and the transmitted power is measured with a photo diode. Finally the intensity distribution is reconstructed by analyzing the slope of the photocurrent. But if beams are focused down to the nanoscale the modification of the electric field by the metal edge cannot longer be ignored and simple evaluation schemes fail. Understanding the mechanisms of the interaction between the edges and the fields becomes essential to evaluate the measurement.

In our experiment we investigate this effect with nanometer resolution. Linearly and radially polarized beams at 633 and 780 nm are focused by a high numerical aperture objective onto a sample. The sample is a p-i-n photodiode covered with thin (<200nm) patterned films made of Au, Zn/Au, Cr and Ge. We move the spot over the edges of the respective structures and for each one record the photocurrent as a function of the position.

The measurements reveal material dependent shifts of the electric field distribution where the direction of the polarization vector and the conductivity of the respective structures play an important role.