Sum frequency generation from partially ordered media and interfaces: a polarization analysis

Abstract

Abstract. The theory of sum frequency generation (SFG) is treated within a molecular quantum electrodynamical framework and applied to an ensemble of partially oriented molecules, for lucid analysis of the SFG intensity dependence on beam polarization and molecular symmetry. By expanding the orientational distribution function in terms of an infinite set of Legendre polynomials, it is shown that the observed SFG intensity may be followed in terms of a finite set of distinct contributions. For a time-dependent distribution, each contribution has unique temporal characteristics which may be separated experimentally by manipulation of the laser beam and detection geometry. Specific configurations required for complete separation of the different terms are given. The theory is further developed for partially oriented molecules, within thin films or adsorbed onto surfaces. Consideration is also given to the effect of temperature variation, which should open new avenues for the elucidation of molecular orientation in such media.

Experimental Confirmation of the Importance of Orientation in the Anomalous Chiral Sensitivity of Second Harmonic Generation

“…From the more than 40 experimental and theoretical publications on the topic of chirality in SHG and SFG, three general models have emerged. In work led by Persoons and co-workers and by Schanne-Klein and co-workers, magnetic dipole contributions and/or interference between electric and magnetic dipole contributions have been suggested as potential candidates for generating large chiral effects in SHG and SFG. ,,− Alternatively, a number of groups have focused on explanations exclusively involving electric dipole-allowed contributions arising from chirality within the chromophore, ,,,,− often through the presence of at least one pair of coupled oscillators. ,,,,,, More recently, theoretical work from this laboratory for surfaces , and by Ostroverkhov et al for bulk media − suggests that macromolecular orientation can potentially generate significant chiral effects in uniaxial surface systems without the need for multiple coupled oscillators or even chiral chromophores at all.…”

Molecular QED of coherent and incoherent sum-frequency and second-harmonic generation in chiral liquids in the presence of a static electric field

“…SFG from a chiral molecule in solution depends on the first hyperpolarizability, a pseudoscalar quantity that changes sign when one enantiomer is replaced by its mirror image form. The integrated intensity also depends on the intensity of each impinging beam, and on the fourth power of the sumfrequency wavevector [6]. Application of a static electric field to a chiral solution undergoing SFG was also studied.…”

“…1 and ! 2 where Latin subscripts denote Cartesian tensor components, has been examined theoretically [5][6][7][8][9][10][11][12][13][14]. Generally, the quadratic polarization of the nonlinear medium, P ð2Þ i ð!…”

Quantum formulation for nanoscale optical and material chirality: symmetry issues, space and time parity, and observables

“…The only second harmonic signal from an isotropic fluid (in the absence of any static field) is the much weaker form known as hyper-Rayleigh scattering, involving the sixth rank average [123]; chiral behavior can only arise through the involvement of an M1 or E2 interaction. However, with sum-frequency generation, in which conversion of two dissimilar photons into another occurs,  symmetry can be broken at the E1 3 level, and it is possible to observe not only local molecular ordering [124] but also chiral discrimination [125]. This diagnostic capacity has for example recently been applied in the characterization of a helical structure in water molecules clustering around DNA [126].…”