Dynamical mean-field theory for quantum chemistry

The dynamical mean-field concept of approximating an unsolvable many-body problem in terms of the solution of an auxiliary quantum impurity problem, introduced to study bulk materials with a continuous energy spectrum, is here extended to molecules, i.e., finite systems with a discrete energy spectrum. The application to small clusters of hydrogen atoms yields ground state energies which are competitive with leading quantum chemical approaches at intermediate and large interatomic distances as well as good approximations to the excitation spectrum.     

Acetylene adsorption on silicon (100)-(4 × 2) revisited

The aim of this work is to revisit the problem of acetylene adsorption on silicon (100). Extending previous theoretical work and including van der Waals forces explicitly in the simulations we remove existing ambiguities about the adsorption sites. The simulated adsorption energies and scanning tunneling microscopy contours are in good agreement with experimental data, they support the interpretation of a two-dimer feature at the surface as resulting from the adsorption of two individual molecules. It is also found that the simulated apparent heights agree with experimental values, if the actual bandgap of silicon is taken into account.     

Parameter determination from current–voltage characteristics of HgCdTe photodiodes in forward bias region

Current–voltage characteristics of HgCdTe photodiodes in the forward bias region have been modeled considering mechanisms including drift-diffusion current, recombination current, metal-semiconductor contact and constant series resistance. Moreover, a fitting method based on the genetic algorithm has been developed to obtain values of related physical parameters from the measured dynamic resistance–voltage curves. Fitting results of $n^+$ -on- $p$ planar devices with different cutoff wavelengths are presented to illustrate the model and method, which are available and promising in acquiring device parameter values and evaluating the electrode contact quality.     

Direct generation of a 10 GHz 816 fs pulse train from an erbium-fiber soliton laser with asynchronous phase modulation

By employing the technique of asynchronous mode locking, we have successfully demonstrated direct generation of stable 10 GHz 816 fs pulse trains with a supermode-suppression ratio >70 dB from a hybrid mode-locked Er-fiber laser. When the modulation frequency deviates from the cavity harmonic frequency by 15-40 kHz, stable femtosecond soliton pulses are formed. Our results demonstrate that asynchronous mode locking can act as an effective mechanism for achieving a shorter pulse width and for stabilizing high-repetition-rate pulse trains in soliton fiber lasers.     

Velocimetry microsensors driven by linearly polarized optical tweezers

We report on a new type of single-point velocimetry microsensor that can be positioned in microfluidic devices by use of optical tweezers. The flag-shaped microsensor is readily made by a low-cost two-photon polymerization technique. At rest the linearly polarized optical tweezer traps the microsensor at the focal point, and the flag-plate gets aligned in the polarization direction. Under a fluid flow, the plate rotates to an equilibrium angle that is used to measure the fluid velocity with a micrometer-size spatial resolution. Experimental results are in good agreement with theoretical calculations of optical and hydrodynamic torques on such a flag-shaped microsensor.     

Tunable light emission and decaying process of photoluminescence from a nanostructured Si-in-SiNx film

Strong photoluminescence (PL) covering the green-violet band was measured at room temperature in an as-deposited amorphous Si-in-SiN_x film, which was prepared by plasma-enhanced chemical vapor deposition on cold (below 60 °C) Si(1 0 0) wafer. With an increase in photon energy of excitation, the PL shifts its peak position from 510 to 416 nm at yet-comparable intensities, thus allowing an energy-selected excitation in practical application. Also, a time-resolved analysis was performed for the emissions at various wavelengths, which showed a decay time shorter than 1.0 ns. These results indicate that the nanostructured Si-in-SiN_x can be a promising candidate material for the fabrication of silicon-based optical interconnections and switches.     

Discrimination of basal cell carcinoma from normal dermal stroma by quantitative multiphoton imaging

We performed multiphoton fluorescence (MF) and second-harmonic generation (SHG) imaging on human basal cell carcinoma samples. In the dermis, basal cell carcinomas can be identified by masses of autofluorescent cells with relatively large nuclei and marked peripheral palisading. In the normal dermis, SHG from dermal collagen contributes largely to the multiphoton signal. However, within the cancer stroma, SHG signals diminish and are replaced by autofluorescent signals, indicating that normal collagen structures responsible for SHG have been altered. To better delineate the cancer cells and cancer stroma from the normal dermis, a quantitative MF to SHG index is developed. We demonstrate that this index can be used to differentiate cancer cells and adjacent cancer stroma from the normal dermis. Our work shows that MF and SHG imaging can be an alternative for Mohs' surgery in the real-time guidance of the secure removal of basal cell carcinoma.