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HL: Fachverband Halbleiterphysik

HL 40: II-VI semiconductors

HL 40.1: Vortrag

Donnerstag, 15. März 2018, 11:00–11:15, EW 201

High Resolution Second Harmonic Spectroscopy with Femtosecond Laser Pulses — •Johannes Mund, Dietmar Fröhlich, Dmitri R. Yakovlev, and Manfred Bayer — Experimentelle Physik 2, Technische Universität Dortmund, Germany

We present a new method of high resolution second-harmonic spectroscopy (SHS) by use of broad band femtosecond laser pulses. We show, that in a system with inversion symmetry (Cu₂O, point group O_h) wherein second-harmonic generation (SHG) is forbidden in electric-dipole approximation one can detect resonances of even as well as odd parity exciton states. SHG is allowed if one of the odd parity dipole operators is replaced by the even parity quadrupole operator. We also investigate exciton transitions in crystals without a center of inversion (CuCl, ZnSe, point group T_d), where parity is not a good quantum number and thus even and odd parity excitons can be excited by dipole transitions. Detailed polarization diagrams for linearly as well as circularly polarized light are derived and show good agreement with the experimental results. We discuss the implications of exciton-polariton effects, which result in a spectral shift of resonances in SHG spectra in respect to the ones measured by one-photon absorption.