2014: Effect of circular dichroism in second harmonic generation from planar chiral nanostructures was discovered and studied in detail

Scientists of the Faculty of Physics (Chair of Quantum Electronics and General Physics), Lomonosov Moscow State University, together with colleagues from the Catholic University of Leuven, Belgium, discovered and studied the effect of circular dichroism of the optical second harmonic generation in planar chiral nanostructures. It is experimentally shown that the efficiency of second harmonic generation is different at the excitation with right- and left-circularly polarized pump wave.

Planar chiral materials are advanced objects for controlling over parameters of light interacting with them. A group of scientists from Physics Department of Lomonosov Moscow State University, Quantum Electronics and General Physics chairs, studied effect of circular dichroism in optical second harmonic generation (CD-SHG) in planar chiral “G”-shaped nanostructures. It was found in the experiments that the SHG efficiency is different for the left and right circularly polarized fundamental radiation.

The studied metamaterials consist of nanostructures with the lateral size of 1 micron arranged in a square lattice in such a way that it has a fourfold rotation axis. Second harmonic generation was studied for the two structures that are mirror images of each other (i.e. enantiomers). Both samples were made in the Katholieke Universiteit Leuven. It was found that the CD-SHG effect has a pronounced azimuthal dependence which brings about a modulation of its value up to 70%. The averaged CD-SHG effect that was obtained by averaging of its value over all the azimuthal positions of the sample reaches 10%. Importantly that the sign of the CD-SHG effect is opposite for the two enantiomers at every azimuthal position of the samples.

Experiments have shown that the CD-SHG averaged effect decreases with increasing angle of incidence of the fundamental radiation and changes its sign at a certain angle. The proposed phenomenological model based on the symmetry analysis of the second order susceptibility tensor of an isotropic chiral surface is consistent with the experimental results.

The results of this work were published in the paper: E. A. Mamonov, I. A. Kolmychek, S. Vandendriessche, M. Hojeij, Y. Ekinci, V. K. Valev, T. Verbiest, and T. V. Murzina, �Anisotropy versus circular dichroism in second harmonic generation from fourfold symmetric arrays of G-shaped nanostructures,� Phys. Rev. B 89, 121113(R) (2014).