Efficient conversion to radial polarization in the two-micron band using a continuously space-variant half-waveplate

We demonstrate efficient conversion of a linearly-polarized Gaussian beam to a radially-polarised doughnut beam in the two-micron band using a continuously space-variant half-waveplate created by femtosecond writing of subwavelength gratings. The low scattering loss (<0.07) of this device indicates that it would be suitable for use with high power lasers

High power radially-polarized Yb-doped fiber laser

A simple technique for directly generating a radially-polarized output beam from an ytterbium-doped fiber laser using an intracavity spatially-variant waveplate is reported. The laser yielded 32W of output with a corresponding slope efficiency of 65.8% in a radially-polarised beam with beam propagation factor ~2.1 and polarization purity >95%

Cladding-pumped Yb-doped fiber laser with vortex output beam

A simple technique for selectively generating a donut-shaped LP11 mode with vortex phase front in a cladding-pumped ytterbium-doped fiber laser is reported. The laser yielded 36W of output with a slope efficiency of 74%

A sharp stability criterion for the Vlasov-Maxwell system

We consider the linear stability problem for a 3D cylindrically symmetric equilibrium of the relativistic Vlasov-Maxwell system that describes a collisionless plasma. For an equilibrium whose distribution function decreases monotonically with the particle energy, we obtained a linear stability criterion in our previous paper. Here we prove that this criterion is sharp; that is, there would otherwise be an exponentially growing solution to the linearized system. Therefore for the class of symmetric Vlasov-Maxwell equilibria, we establish an energy principle for linear stability. We also treat the considerably simpler periodic 1.5D case. The new formulation introduced here is applicable as well to the nonrelativistic case, to other symmetries, and to general equilibria

Kinetics and mechanisms of key elementary processes of importance to high temperature combustion chemistry

We have investigated the kinetics and mechanisms numerous reactions involving many key reactive combustion species: CH[sub 2]O, CH[sub 3]O, CH, NO, NO[sub 2], CH[sub 3]OH, C[sub 2]H[sub 5]OH, i-C[sub 3]H[sub 7]OH, t-C[sub 4]H[sub 9]OH, C[sub 6]H[sub 5], C[sub 5]O and C[sub 6]H[sub 5]O and C[sub 6]H[sub 6], among others. A total of 24 reactive systems have been studied

Direct generation of radially-polarized output from an Yb-doped fiber laser

A simple technique for directly generating a radially-polarized output beam from an ytterbium-doped fiber laser using an intracavity S-waveplate is reported. The laser yielded 7W of output with a corresponding slope efficiency of 67%

Phosphoproteins and protein-kinase activity in isolated envelopes of pea (Pisum sativum L.) chloroplasts

A protein kinase was found in envelope membranes of purified pea (Pisum sativum L.) chloroplasts. Separation of the two envelope membranes showed that most of the enzyme activity was localized in the outer envelope. The kinase was activated by Mg2+ and inhibited by ADP and pyrophosphate. It showed no response to changes in pH in the physiological range (pH 7-8) or conventional protein substrates. Up to ten phosphorylated proteins could be detected in the envelope-membrane fraction. The molecular weights of these proteins, as determined by polyacrylamide-gel electrophoresis were: two proteins higher than 145 kDa, 97, 86, 62, 55, 46, 34 and 14 kDa. The 86-kDa band being the most pronounced. Experiments with separated inner and outer envelopes showed that most labeled proteins are also localized in the outer-envelope fraction. The results indicate a major function of the outer envelope in the communication between the chloroplast and the parent cell

Effect of dissipation and measurement on a tunneling system

We consider a parametrically driven Kerr medium in which the pumping may be sinusoidally varied. It has been previously found that this system exhibits coherent tunneling between two fixed points which can be either enhanced or suppressed by altering the driving frequency and strength. We numerically investigate the dynamics when damping is included. This is done both by solving a master equation and using the quantum-trajectory method. In the latter case it is also possible to model the result of a continuous heterodyne measurement of the cavity output. The dissipation destroys the coherences which give rise to the tunneling, causing the sinusoidal oscillation of the mean to give way to a stochastic jumping between the fixed points, manifested as a random telegraph signal. In the quantum-trajectory picture we show that the coherences responsible for tunneling are an exponentially decreasing function of the signal-to-noise ratio for heterodyne measurements. However, evidence of both the bare tunneling rate and the driving modified tunneling rate are still apparent in the random telegraph signal

Interpreting Helioseismic Structure Inversion Results of Solar Active Regions

Helioseismic techniques such as ring-diagram analysis have often been used to determine the subsurface structural differences between solar active and quiet regions. Results obtained by inverting the frequency differences between the regions are usually interpreted as the sound-speed differences between them. These in turn are used as a measure of temperature and magnetic-field strength differences between the two regions. In this paper we first show that the "sound-speed" difference obtained from inversions is actually a combination of sound-speed difference and a magnetic component. Hence, the inversion result is not directly related to the thermal structure. Next, using solar models that include magnetic fields, we develop a formulation to use the inversion results to infer the differences in the magnetic and thermal structures between active and quiet regions. We then apply our technique to existing structure inversion results for different pairs of active and quiet regions. We find that the effect of magnetic fields is strongest in a shallow region above 0.985R_sun and that the strengths of magnetic-field effects at the surface and in the deeper (r < 0.98R_sun) layers are inversely related, i.e., the stronger the surface magnetic field the smaller the magnetic effects in the deeper layers, and vice versa. We also find that the magnetic effects in the deeper layers are the strongest in the quiet regions, consistent with the fact that these are basically regions with weakest magnetic fields at the surface. Because the quiet regions were selected to precede or follow their companion active regions, the results could have implications about the evolution of magnetic fields under active regions.Comment: Accepted for publication in Solar Physic