A new determination of \alpha_s from hadronic \tau\ decays

We present a new framework for the extraction of the strong coupling from hadronic \tau decays through finite-energy sum rules. Our focus is on the small, but still significant non-perturbative effects that, in principle, affect both the central value and the systematic error. We employ a quantitative model in order to accommodate violations of quark-hadron duality, and enforce a consistent treatment of the higher-dimensional contributions of the Operator Product Expansion to our sum rules. Using 1998 OPAL data for the non-strange isovector vector and axial-vector spectral functions, we find the n_f=3 values \alpha_s(m_\tau^2)=0.307+-0.019 in fixed-order perturbation theory, and 0.322+-0.026 in contour-improved perturbation theory. For comparison, the original OPAL analysis of the same data led to the values 0.324+-0.014 (fixed-order) and 0.348+-0.021 (contour-improved).Comment: 31 pages, 7 figures, revtex, version accepted for publication, minor changes, reference adde

Solderability assessment of galvanic coatings in electronics

The problem of providing high-quality soldered joints during the assembly and installation of electronic products draws attention to the use of effective methods for controlling the solderabil-ity of electronic components and func-tional coatings of parts. The solderabil-ity of electroplated coatings used in electronics was studied by two meth-ods: evaluating the spreading of a dosed drop of solder and the wetting force by molten solder. The criteria for evaluating the solderability of coatings are systematized and refined

Modeling local induction heating of solder balls for flip-chip mounting in COMSOL Multiphysics

For Flip-chip mounting, it is necessary to form contact bumps for 2.5D and 3D electronic modules. Exposure to the energy of high-frequency (HF) electromagnetic oscillations allows for high-performance non-contact heating in various processes for soldering electronic components. This paper presents studies of temperature fields during induction heating of solder balls with several types of copper concentrators made in the COMSOL MULTIPHYSICS software. The dependences of frequency of inductor on heating time and geometric shapes of copper concentrators on quality of the soldered sample were revealed

Time-domain spectroscopy in the mid-infrared

When coupled to characteristic, fingerprint vibrational and rotational motions of molecules, an electromagnetic field with an appropriate frequency and waveform offers a highly sensitive, highly informative probe, enabling chemically specific studies on a broad class of systems in physics, chemistry, biology, geosciences, and medicine. The frequencies of these signature molecular modes, however, lie in a region where accurate spectroscopic measurements are extremely difficult because of the lack of efficient detectors and spectrometers. Here, we show that, with a combination of advanced ultrafast technologies and nonlinear-optical waveform characterization, time-domain techniques can be advantageously extended to the metrology of fundamental molecular motions in the mid-infrared. In our scheme, the spectral modulation of ultrashort mid-infrared pulses, induced by rovibrational motions of molecules, gives rise to interfering coherent dark waveforms in the time domain. These high-visibility interference patterns can be read out by cross-correlation frequency-resolved gating of the field in the visible generated through ultrabroadband four-wave mixing in a gas phase

The phase-controlled Raman effect

Unlike spontaneous Raman effect, nonlinear Raman scattering generates fields with a well-defined phase, allowing Raman signals from individual scatterers to add up into a highly directional, high-brightness coherent beam. Here, we show that the phase of coherent Raman scattering can be accurately controlled and finely tuned by using spectrally and temporally tailored optical driver fields. In our experiments, performed with spectrally optimized phase-tunable laser pulses, such a phase control is visualized through the interference of the coherent Raman signal with the field resulting from nonresonant four-wave mixing. This interference gives rise to Fano-type profiles in the overall nonlinear response measured as a function of the delay time between the laser pulses, featuring a well-resolved destructive-interference dip on the dark side of the Raman peak. This phase-control strategy is shown to radically enhance the coherent response from weak Raman modes, thus helping confront long-standing challenges in nonlinear Raman imaging and microspectroscopy

Air-guided photonic-crystal-fiber pulse-compression delivery of multimegawatt femtosecond laser output for nonlinear-optical imaging and neurosurgery

Cataloged from PDF version of article.Large-core hollow photonic- crystal fibers (PCFs) are shown to enable a fiber-format air-guided delivery of ultrashort infrared laser pulses for neurosurgery and nonlinear-optical imaging. With an appropriate dispersion precompensation, an anomalously dispersive 15-mu m-core hollow PCF compresses 510-fs, 1070-nm light pulses to a pulse width of about 110 fs, providing a peak power in excess of 5 MW. The compressed PCF output is employed to induce a local photodisruption of corpus callosum tissues in mouse brain and is used to generate the third harmonic in brain tissues, which is captured by the PCF and delivered to a detector through the PCF cladding. (C) 2012 American Institute of Physics