Biomedical subjects

M A Belkin

Publications and source records attributed to M A Belkin.

6 recordsLinked to original sources

PubMed2004

Sum-frequency vibrational spectroscopy of a helically structured conjugated polymer.

Sum-frequency vibrational spectroscopy was used as a novel technique to probe the molecular chirality of thin polymer films. Chiral vibrational spectra of poly(bithienylene-phenylene) were obtained, and the two enantiomers were distinguished by an interference method. Vibration-electronic double resonance was responsible for the observation of unusually strong chiral spectra of the phenylene vibration modes.

Journal Article↗

PubMed2004

Optically active second-harmonic generation from a uniaxial fluid medium.

We have shown that optically active second-harmonic generation is allowed in a uniaxial fluid medium. A homeotropically aligned chiral smectic-A liquid crystal was used as an example. Phase matching was achievable by angle tuning. Chiral nonlinear susceptibility for the liquid crystal was deduced. The signal dropped precipitously as the sample underwent the transition from smectic-A to isotropic.

Journal Article↗

PubMed2004

Sum-frequency vibrational spectroscopy of chiral liquids off and close to electronic resonance and the antisymmetric Raman tensor.

The strength of the chiral vibrational peaks in infrared-visible sum-frequency (SF) vibrational spectra from isotropic chiral liquids is proportional to the square of the corresponding antisymmetric Raman element. Under the Born-Oppenheimer adiabatic approximation with nonadiabatic corrections, the antisymmetric Raman tensor is much weaker than the symmetric counterpart, but becomes significantly stronger as the input frequency (or the sum-frequency in SF generation) approaches electronic resonance. We verify the theory with experimental results obtained from infrared-visible doubly resonant sum-frequency generation from an isotropic solution of chiral molecules.

Journal Article↗

PubMed2003

Doubly resonant IR-UV sum-frequency vibrational spectroscopy on molecular chirality.

We show theoretically and experimentally that for sum-frequency vibrational spectroscopy near electronic transitions, resonant enhancement of the chiral response can be much stronger than that of the achiral response. The doubly resonant spectrum selectively enhances the vibrational modes through their different electron-vibration couplings. The unusually strong resonant enhancement significantly improves sensitivity of chiral spectroscopy and allows detection of the chiral vibrational spectrum of a molecular monolayer for the first time.

Mathematical Computing↗

PubMed2001

Sum-frequency generation in chiral liquids near electronic resonance.

We demonstrate experimentally that visible-visible sum-frequency generation in the bulk of a chiral liquid is observable near electronic resonant transitions. Although the process is electric dipole allowed, it is rather weak because the orientational average over molecules effectively reduces the bulk chiral nonlinearity.

Journal Article↗

PubMed2000

Sum-frequency vibrational spectroscopy on chiral liquids: a novel technique to probe molecular chirality.

Optical activity in sum-frequency vibrational spectra has been observed for the first time in chiral liquids. The electric-dipole allowed chiral element of the nonlinear susceptibility appears to be 3 orders of magnitude smaller than typical allowed achiral elements. This is partly because the observed chirality requires a breakdown of the Born-Oppenheimer approximation.

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