Yuen Ron Shen

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A phase-sensitive sum-frequency vibrational spectroscopic technique is developed to study interfacial water structure of water/quartz interfaces. Measurements allow deduction of both real and imaginary parts of the surface nonlinear spectral response, revealing an unprecedentedly detailed picture of the net polar orientations of the water species at the(More)
Phase-sensitive sum-frequency spectroscopy provides correct characterization of vibrational resonances of water-vapor interfaces and allows better identification of interfacial water species contributing to different parts of the spectra. Iodine ions emerging at an interface create a surface field that tends to reorient the more loosely bonded water(More)
We studied the insulator-metal transition (IMT) in single-domain, single crystalline vanadium dioxide (VO(2)) microbeams with infrared microspectroscopy. The unique nature of such samples allowed us to probe the intrinsic behavior of both insulating and metallic phases in the close vicinity of IMT, and investigate the IMT driven by either strain or(More)
Infrared-visible sum-frequency spectroscopy was used to probe surface vibrations of alpha-quartz(0001) under ambient conditions. Two modes at 880 and 980 cm(-1) were observed and identified as arising from Si-O-Si and Si-OH structures of the surface. Heat treatment and hydroxylation could convert Si-OH to Si-O-Si and vice versa. The technique is generally(More)
  • Yuen Ron Shen
  • Proceedings of the National Academy of Sciences…
  • 1996
As a second-order nonlinear optical process, sum-frequency generation is highly surface-specific and accordingly has been developed into a very powerful and versatile surface spectroscopic tool. It has found many unique applications in different disciplines and thus provided many exciting new research opportunities in surface and surface-related science.(More)
We report the first observation of stimulated emission of terahertz radiation from internal transitions of excitons. The far-infrared electromagnetic response of Cu2O is monitored via broadband terahertz pulses after ultrafast resonant excitation of three-dimensional 3p excitons. Stimulated emission from the 3p to the energetically lower 2s bound level(More)
The wave-front curvature of an incident laser beam can modify the spatial phase modulation of the beam, and hence the diffraction of the beam, traversing a liquid-crystal film. It is shown both theoretically and experimentally that this explains the anomalous fine structure in the diffraction ring pattern observed with laser intensities above the(More)