Ultra-stable microwave generation with a diode-pumped solid-state laser in the 1.5-μm range

We demonstrate the first ultra-stable microwave generation based on a 1.5-μm diode-pumped solid-state laser (DPSSL) frequency comb. Our system relies on optical-to-microwave frequency division from a planar-waveguide external cavity laser referenced to an ultra-stable Fabry–Perot cavity. The evaluation of the microwave signal at ~10 GHz uses the transportable ultra-low-instability signal source ULISS^®, which employs a cryo-cooled sapphire oscillator. With the DPSSL comb, we measured ?125 dBc/Hz phase noise at 1 kHz offset frequency, likely limited by the photo-detection shot-noise or by the noise floor of the reference cryo-cooled sapphire oscillator. For comparison, we also generated low-noise microwave using a commercial Er:fiber comb stabilized in similar conditions and observed >20 dB lower phase noise in the microwave generated from the DPSSL comb. Our results confirm the high potential of the DPSSL technology for low-noise comb applications.     

Nonlinear wave interactions in patterned Silica and AlGaAs waveguides

We study nonlinear interactions between discrete optical solitons that propagate in different regimes of diffraction, and the nonlinear scattering of dispersive waves by local optical potentials. It is well known in optics that when linear coherent waves meet, they interfere without interactions. Linear waves also scatter through local optical structures not exchanging any power with the guided modes of these structures. As a focusing Kerr nonlinearity is present, such linearly-inhibited phenomena can exist. Our studies are performed in silica and AlGaAs nonlinear waveguides, excited by ultra-short pulses in the near infrared. Presented at 9-th International Workshop on Nonlinear Optics Applications, NOA 2007, May 17–20, 2007, Świnoujście, Poland     

Inclusive photon and π0 production inK + p interactions at 70 GeV/c

Inclusive and semi-inclusive cross sections and distributions of γ's and π⁰'s inK ⁺ p interactions at 70 GeV/c are presented. The results are compared to other experiments and to the Lund model for low-p _T hadron collisions.     

Properties of a vector soliton laser passively mode-locked by a fiber-based semiconductor saturable absorber operating in transmission

We experimentally demonstrate a passively mode-locked fiber laser employing a fiber-based semiconductor saturable absorber (SSA) operating in transmission. Polarization rotation locked vector solitons are observed in the laser. Due to the intrinsic dynamic feature of the laser, period-doubling of these vector solitons has also been observed. Furthermore, extra spectral sidebands are formed on the optical spectrum, caused by the energy exchange between the two orthogonal polarization components of the vector solitons. By careful reduction of the pump power together with fine adjustment to the cavity birefringence, period-one state can further be obtained. Additionally, the phase noise properties of the vector soliton fiber laser have also been characterized experimentally and analytically.     

Anomalous optical constants of thin films

The explanation of anomalous optical constants in thin chemically distinct layers on substrates offered by Plumb is re-examined and extended. The model invokes the concept of the space charged boundary layer and treats the charge carrier population as a free-electron gas to derive the optical behaviour of thin surface films. The implication of the space charge means that the optical constants of a dielectric film on a metal will vary over a distance directly proportional to the dielectric constant of the film and inversly proportional to the concentration of the electrons at the metal/film interface. Similarly as the temperature increases this space charge region should extend to larger distances from the interface.     

CVM modeling of the square Ising lattice with one next-nearest-neighbor interaction

As an analysis of the development of first-order behavior in two-dimensional Ising lattices, the square lattice with antiferromagnetic nearest-neighbor interactions and a ferromagnetic next-nearest-neighbor interaction in the (11) direction has been modeled. The phase diagram was calculated for a range of interaction parameters and imposed fields; the calculations were performed using the cluster variation method (CVM). Analysis of the calculations suggests that no first-order behavior is developed in this system, so that higher dimensionality or connectivities are required before such behavior is developed.     

Experiments on the active control of transformer noise

This paper describes an experiment which demonstrates how a useful degree of active noise control can be achieved with ordinary sound amplification and reproduction equipment. A loudspeaker positioned next to a large pair of noisy electricity transformers was made to mimic their noise but in antiphase. The aim of the study was to investigate the degree to which the “antisound” would cancel a disturbing noise heard in a nearby office. Some 20 decibels of control was achieved very easily for the 100 Hz component of the noise but the higher frequency sound could only be controlled in localized patches. The experiment suggests that sounds of discrete frequencies of less than 100 Hz are relatively easily controlled with unsophisticated audio equipment, but that useful control of higher frequency elements is much more difficult.     

Molecular-orbital X-rays from 1 GeV 208Pb + 208Pb and 209Bi + 209Bi collisions

We have measured the spectra of continuum X-rays above the characteristic K lines for 4.5 to 4.8 MeV/N ²⁰⁸₈₂Pb → ²⁰⁸₈₂Pb, Pb → Bi, Bi → Pb and Bi → Bi collisions. Above ≈400 keV X-ray energy the spectral shape and intensity agree roughly with calculations of Kirsch et al. for the 1sσ molecular-orbital (MO) X-ray spectrum from Pb-Pb. Deviations from the theory below ≈400 keV suggest transitions to other MO's.