Second-harmonic generation circular-dichroism spectroscopy from chiral monolayers

The second-harmonic-generation (SHG) efficiency from a monolayer of oriented chiral molecules (R- or S-2,2'-dihydroxyl-1,1'binaphthyl) has a strong dependence upon the handedness of the circularly polarized excitation beam. The SHG circular-dichroism (CD) effect is much larger than in ordinary CD spectroscopy because SHG-CD is electric dipole allowed. The technique allows the study of chiral surfaces. The preference for left or right circularly polarized light is dependent on both the chirality (R or S) and the absolute orientation of the molecules (pointed up or down).