A femtosecond waveform transfer technique using type II second harmonic generation

We present a novel waveform frequency conversion technique by type II second harmonic generation (SHG). We have theoretically studied and experimentally demonstrated femtosecond waveform transfer from 800 to 400 nm wavelength by type II SHG in a lithium triborate (LBO) crystal. The output second harmonic (SH) waveform is a temporally magnified or compressed version of the input fundamental waveform, depending on the experimental configuration. Our experiments demonstrate that this technique can transfer not only the intensity profiles of the fundamental waveform, but also the phase profiles. This technique shows promise for programmable generation of shaped ultrafast optical waveforms down to the UV range, where direct pulse shaping is challenging.     

The Transient Phase of Amorphous Calcium Carbonate in Sea Urchin Larval Spicules: The Involvement of Proteins and Magnesium Ions in Its Formation and Stabilization

Amorphous calcium carbonate (ACC) is a precursor phase of calcite in the formation of the sea urchin larval spicule. The goal of this research is to study the formation and stabilization mode of this transient phase. We first characterized the mineralogy of the spicules from the sea urchin Strongylocentrotus purpuratus. We then examined the role of the macromolecules extracted from the spicules at different growth stages in the formation of transient ACC in vitro.The biogenic amorphous transient phase is shown to be both structurally and compositionally different from the known stable ACC phases. It does not contain bound water, and is thus the first dehydrated ACC phase to be detected. The macromolecules that were extracted at early stages of spicule growth, when the amorphous content of the biogenic mineral is high, induced the formation of transient ACC in vitro in the presence of magnesium ions. In contrast, the macromolecules extracted at a later stage, when the spicules are completely crystalline, induced the formation of single crystals of low magnesian calcite. We therefore deduce that the macromolecules from the sea urchin larval spicules together with magnesium ions, mediate the transient formation of ACC as a precursor to calcite. These observations may well provide novel ideas for improved materials synthesis.     

Coherent photonic processing of microwave signals using spatial light modulators: programmable amplitude filters

This paper presents a novel coherent optical signal processing approach for synthesis of programmable microwave amplitude filters over an ultrawideband. The authors' scheme relies on a programmable hyperfine optical filter implemented in a pulse-shaping geometry, which provides arbitrary, user-defined amplitude-filtering functions over a 50-GHz bandwidth with resolution better than 0.7 GHz. In contrast to previous work on discrete time optical processing of microwave signals, their approach allows direct synthesis of microwave filter functions in spectral domain without computing filter coefficients, which is needed for a discrete-time-domain approach.     

Optical arbitrary waveform generation and characterization using spectral line-by-line control

This paper demonstrates optical arbitrary waveform generation (O-AWG) and its characterization using spectral line-by-line control with high-resolution grating-based pulse shapers. Such integrated capabilities are the enabling techniques for high-fidelity O-AWG.     

Interferometry of pions and kaons in high energy collisions

A hydrodynamic model which reproduces the observed rapidity and transverse momentum spectra of mesons and baryons is applied to the study of Bose-Einstein correlations. The pion correlations are found to be strongly affected by resonance decays, except for pairs of large transverse momenta.For S+S at 200 A GeV, in the central rapidity region the effective longitudinal source radii for pions and kaons differ by a factor of 2, the transverse radii by a factor of 1.3. The lifetime of the source can be extracted from kaon interferometry.     

A Complete Spectral Polarimeter Design for Lightwave Communication Systems

The authors describe a fast spectral polarimeter operating in the lightwave communications band capable of measuring both state-of-polarization and degree-of-polarization of hundreds (up to thousands) of spectral components in parallel within milliseconds. In this paper, the design incorporates fast switching ferroelectric liquid crystals for polarization component selection on the 100-mus scale. Dispersion elements and an arrayed detector are used for wavelength-parallel sensing. Bandwidth of coverage can be scaled from a single wavelength-division multiplexed channel to more than 100 nm, and 256 spectral polarization measurements in under 1 ms are verified. Finally, a calibration algorithm is used to minimize measurement error. This instrument offers unprecedented sensing capability relevant to the monitoring and compensation of polarization-related impairments in high-speed lightwave communications     

Photoconductive impulse generation and radiation

The generation of extremely narrow, high peak power pulses using an optically activated impulse generator is described. Radiative measurements at 1 Hz PRF have been conducted at pulse bias levels up to 15 kV, using an optical pulse from a Nd:YAG laser to trigger the device. The measured pulse from a wideband antenna has a pulsewidth of 1.5 ns with a risetime of 900 ps. The frequency spectrum of this radiated waveform ranged from 50 MHz to 1 GHz     

Time-resolved hot luminescence and resonant Raman scattering: Cu2O revisited

Time-resolved resonant scattering of both one-phonon and two-phonon Raman modes at the 1s ortho-exciton state of the yellow series in Cu₂O is reported. From the time dependence of the one-phonon mode we determine the scattering rate among the triply degenerate ortho-exciton states to be 2.5 × 10⁸sec^-1. From the two-phonon modes we directly determine the exciton lifetime as a function of its kinetic energy. In both cases the resonant scattering is found to be dominated by hot luminescence.