NEW ASPECTS OF 2ND-HARMONIC OPTICAL-ACTIVITY FROM CHIRAL SURFACES ANDINTERFACES

New expressions are developed within the electric dipole approximation for the four Stokes parameters characterizing the polarization proper ties of coherent second-harmonic radiation generated from chiral isotr opic surfaces in reflection. These are employed to derive, in addition to the three well-known incident circular polarization second-harmoni c optical activity (SHOA) observables, thirteen new basic observables for the detection of surface SHOA which involve second-harmonic intens ity difference measurements using right and left circular, and +45 deg rees and -45 degrees linear, polarization modulation in the incident a nd second-harmonic radiation and in both simultaneously. Because of th eir dependence on a fully electric dipole allowed tensor these circula r and linear intensity differences and the corresponding intensity sum s have the same order of magnitude, so that all the dimensionless surf ace SHOA effects they generate are of the order of unity. The circular intensity differences (CIDs) depend on the imaginary part of products of second-order surface susceptibility tensor components and can ther efore be observed only under preresonance or resonance scattering cond itions; whereas the linear intensity differences (LIDs) depend on the real part of the same tensor component products and can therefore also be detected at transparent frequencies. Employing elliptically polari zed incident radiation, appropriate combinations of CIDs and LIDs also measure, respectively, real and imaginary parts of the relevant surfa ce susceptibility tensor products so that a suitable CID combination m ay also be detected under non-resonance scattering conditions. The bes t experimental strategies are identified for SHOA detection and extrac tion of complete SHOA information and relationships are discussed betw een the SHOA observables and the second-harmonic polarization azimuth, ellipticity and degree of polarization. Because only pure electric di pole scattering processes are considered, the basic formalism applies also to magnetically induced SHOA phenomena.