Using the evanescent-wave-ellipsometry technique, we have studied the orientational wetting behavior of the homologous series of alkyl cyanobiphenyl liquid crystals (nCB, n=5 to 9) on a glass coated with silane surfactant molecules. The results show complete wetting for 6CB to 9CB and partial wetting for 5CB. They compare well with existing theories.

W. Chen;L. J. Martinez-Miranda;H. Hsiung;元壤 沈

Physical Review Letters

1989

The general conclusions of the recent article by Andrews and Blake [Phys. Rev. A 38, 3113 (1988)] on the forbidden nature of higher-order multipolar contributions to optical second-harmonic generation are misleading and not generally valid.

X. D. Zhu;元壤 沈

Physical Review A

1990

We have studied experimentally self-focusing of light in the liquid crystalline medium p-ethoxybenzyldine-p-butylaniline (EBBA). By variation of temperature, the response time of the field-induced refractive index was adjusted from larger than to smaller than the Q-switched laser pulsewidth. Accordingly, self-focusing varied from transient to quasi-steady-state. The results agree well with existing theoretical predictions and can be qualitatively understood from a simple physical description. The induced stimulated Brillouin scattering was also measured and was shown to be responsible for the limiting diameter of the self-focused beam in the present case.

E. G. Hanson;元壤 沈;G. K.L. Wong

Applied Physics

1977-9

We report the performance of a type-I barium borate optical parametric amplifier pumped by 15 ps, 355 nm laser pulses. We show that it is possible to obtain narrowband (approximately-equal-to3 Å), high-energy (≥200 μJ), widely tunable (0.4-2 μm) picosecond pulses with a maximum pump-to-signal energy conversion better than 30%.

J. Y. Huang;J. Y. Zhang;元壤 沈;C. Chen;B. Wu

Applied Physics Letters

1990

Picosecond laser pulses were used to study the highly forbidden resonant second-harmonic generation (SHG) in potassium vapor. The input intensity dependence, vapor density dependence, buffer-gas pressure dependence, and spatial profile of the SHG were measured. A pump-probe experiment was conducted to probe the time dependence of the SHG signal. The experimental results can be understood from an ionization-initiated dc-field-induced SHG model. A theory of a dc-field-induced SHG model is developed that takes into account the time development of the dc electric field in detail. This temporal buildup of the dc field along with transient coherent excitation between two-photon-allowed transitions can explain the experimental results quantitatively, including the previous vapor SHG results with nanosecond laser pulses.

Doseok Kim;Christopher S. Mullin;元壤 沈

Journal of the Optical Society of America B: Optical Physics

1997-10

Wavelength-modulation spectroscopy is used to obtain the temperature dependence of the reflectivity spectrum for GaAs. Results are given in the regions of the E1 doublet and the major E2 peak at 5, 80, 150, 225, and 300°K. The theoretical temperature dependence in these regions is obtained through use of Debye-Waller factors and thermal expansion coefficients in an empirical pseudopotential calculation of the 3-1 and 2-1 energy splittings.

John P. Walter;Ricardo R.L. Zucca;Marvin L. Cohen;元壤 沈

Physical Review Letters

1970

Dramatic changes were observed in the optical second-harmonic generation from the Rh(111) crystal surface as the surface was covered with alkali atoms. For low alkali coverage, these changes are explained qualitatively in terms of optical transitions between alkali atomic-derived electronic states and, for high coverage, in terms of the plasmon resonance of the alkali layer. The results establish the surface specificity of second-harmonic generation to the topmost 1 or 2 atomic layers of alkali metals.

H. W.K. Tom;C. M. Mate;X. D. Zhu;J. E. Crowell;元壤 沈;G. A. Somorjai

Surface Science

1986-7-1

Second-harmonic generation at a silver-air interface was enhanced by a factor of 104 by surface roughness. The local-field enhancement is believed to be responsible for the effect. An unusually broad luminescence background extending far beyond the anti-Stokes side of the second harmonic was also observed.

C. K. Chen;A. R.B. De Castro;元壤 沈

Physical Review Letters

1981

Anisotropic surface diffusion of CO on Ni(110) has been studied using the newly developed technique of optical second-harmonic diffraction from a laser-induced CO monolayer grating. Two distinct orthogonal diffusion channels, along [11»0] and [001], were found. The measured diffusion coefficients yield the diffusion activation energies Ed(11»0)=1.1±0.2 kcal/mol and Ed(001)=3.1±0.4 kcal/mol and the preexponential factors D0(11»0)=(3.8±2.0)×10-9 cm2/sec and D0(001)=(4.8±4.4) ×10-6 cm2/sec. The anisotropy in the surface diffusion appears to cross over at T 1/4 60 K.

旭东 肖;X. D. Zhu;W. Daum;元壤 沈

Physical Review Letters

1991

In the past decade the interest in the dynamics of the interaction between molecules and clean and well-characterized solid-state surfaces has steadily increased. Most information has been obtained from angular and velocity distribution measurements in surface scattering experiments, giving insight into the dynamics only where atoms are involved. For molecules, it is necessary to have additional information on the internal state distribution. It was demonstrated that the population distribution of the rotational and/or vibrational states of the scattered molecules can be investigated by laser-induced fluorescence and laser-induced resonance ionization. Resonance ionization in connection with time-of-flight measurements gives information on the velocity distributions of the scattered particles. As these measurements are angle and state-selective, they yield a full description of the average energy and momentum exchange between the molecules and the surface. Such investigations were performed in our laboratory for the NO/Pt system as well as for the weak inelastic NO/graphite system and are discussed.

J. Haeger;元壤 沈;H. Walther

1984