Circular-difference effects in second-harmonic generation from thin films

• Published in: Synthetic metals 2001-10, Vol.124 (1), p.191-193
• Main Authors: Sioncke, S., Van Elshocht, S., Verbiest, T., Kauranen, M., Phillips, K.E.S., Katz, T.J., Persoons, A.
• Format: Article
• Language: English
• Subjects: Anisotropy; CD–SHG; Chirality; Exact sciences and technology; Frequency conversion; harmonic generation, including high-order harmonic generation; Fundamental areas of phenomenology (including applications); Harmonic generation, frequency conversion; Helicenebisquinone; Nonlinear optics; Optics; Physics
• ISSN: 0379-6779; 1879-3290
• DOI: 10.1016/S0379-6779(01)00441-6

Chiral molecules have received much attention in nonlinear optics because they are inherently noncentrosymmetric. It has been shown that second-harmonic generation (SHG) from chiral, isotropic surfaces and thin films is sensitive to the handedness of circularly-polarized fundamental light. These circular-difference (CD)-effects in SHG are used to probe the chirality of a sample. However, an achiral, anisotropic surface can also give rise to CD-effects in SHG. This can be explained by the fact that for some orientations of the sample, the total geometry becomes chiral. We investigated a chiral, anisotropic Langmuir–Blodgett film. For such a sample both chirality and anisotropy give rise to CD-effects in SHG. Our goal was to extract the optical activity effects due to chirality. Our technique is based on the fact that CD-effects originating from anisotropy will critically depend on the azimuthal rotation angle of the sample in the set-up whereas the CD-effects coming from chirality will remain constant.