No abstract

The methods of nonlinear optics are widely applied to the study of changes in structure of large biomolecules.1'2 The information obtained by these methods may be used for the investigation of relationship between structural changes of the biomolecules and their specific activity. Molecular left-right asymmetry is an origin of nonvanishing even order optical nonlinear susceptibilities of non-racemic solutions of chiral molecules. New nonlinear optical spectroscopic schemes based on three-and five-wave interactions in chiral homogeneous isotropic media (symmetry forbidden in centrosymmetric racemic solutions) are investigated with the aim to develop a novel technique to clearly distinguish between left and right mirror isomers of biological molecules and to measure their individualnonlinearopticalhyperpolarizabilities, and vibrational spectra.3Though second harmonic generation (SHG) due to quadratic dipolar nonlinearity is still symmetryforbidden in optically active liquids yet we have succeeded in experimental observation, for the first time, of noncollinear SHG due to five-mixing process according to a scheme 2 cv = 3cv -w, governed by a fourth order susceptibility tensor 4"• SHG signal is found to be well collimated and quasi phase-matched, it shows theoretically predicted polarization, spectral and temporal properties. 1.INTRODUCTION.An optically active isotropic liquid (for instance, non-racemic solution of mirror-asymmetric molecules) lacks the center of inversion and, hence, possesses non-vanishing even order dipolar nonlinear optical susceptibilities:(2)D (4)D 3-5 . .(2)D ... .x , x etc . Optical sum-frequency generation due to x in an optically active arabinose solutions was observed for the first time by Rentzepis et al.6 in a non-collinear, phase-mismatched geometry. However, second harmonic generation (SHG) due to dipolar quadratic nonlinearity is still forbidden in such liquids because of permutationsymmetryreason4.Some time ago, one of us (N.I.K.) has shown that higher order nonlinearity (namely, fourth-order one) does allow the SHG process to occur in phase-matched non-collinear scheme5. Is presented hereafter a Theory of interaction of strong laser field with mirror-asymmetric isotropic mediums, theory of five-wave interaction in chiral homogeneous isotropic media and new experimental results on observation of five-wave mixing 2w= 3w -cv 0-8194-1 155-8/93/$6.00 SPIE Vol. 1922 Laser Study of Macroscopic Biosystems (1992)129 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/16/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

We derive an improved prescription for the merging of matrix elements with parton showers, extending the CKKW approach. A flavour-dependent phase space separation criterion is proposed. We show that this new method preserves the logarithmic accuracy of the shower, and that the original proposal can be derived from it. One of the main requirements for the method is a truncated shower algorithm. We outline the corresponding Monte Carlo procedures and apply the new prescription to QCD jet production in e + e − collisions and Drell-Yan lepton pair production. Explicit colour information from matrix elements obtained through colour sampling is incorporated in the merging and the influence of different prescriptions to assign colours in the large N C limit is studied. We assess the systematic uncertainties of the new method.

Molecular left-right asymmetry is an origin of non-vanishing even order optical nonlinear susceptibilities of non-racemic solutions of chiral molecules. Though second harmonic generation (SHG) due to quadratic dipolar nonlinearity is still symmetry forbidden in optically active liquids yet we have succeeded in experimental observation, for the first time, of noncolli-near SHG due to five-mixing process according to a scheme 2ω=3ω−ω, governed by a fourth order susceptibility tensor χ(4)D(2ω;ω,ω,ω,−ω) SH signal is found to be well collimated and quasi phase-matched, it shows theoretically predicted polarization, spectral and temporal properties.