Influence of spatial-intensity contrast in ultraintense laser-plasma interactions.

Increasing the intensity to which high power laser pulses are focused has opened up new research possibilities, including promising new approaches to particle acceleration and phenomena such as high field quantum electrodynamics. Whilst the intensity achievable with a laser pulse of a given power can be increased via tighter focusing, the focal spot profile also plays an important role in the interaction physics. Here we show that the spatial-intensity distribution, and specifically the ratio of the intensity in the peak of the laser focal spot to the halo surrounding it, is important in the interaction of ultraintense laser pulses with solid targets. By comparing proton acceleration measurements from foil targets irradiated with by a near-diffraction-limited wavelength scale focal spot and larger F-number focusing, we find that this spatial-intensity contrast parameter strongly influences laser energy coupling to fast electrons. We find that for multi-petawatt pulses, spatial-intensity contrast is potentially as important as temporal-intensity contrast.

Deconvolution of multi-Boltzmann x-ray distribution from linear absorption spectrometer via analytical parameter reduction.

Accurate characterization of incident radiation is a fundamental challenge for diagnostic design. Herein, we present an efficient spectral analysis routine that is able to characterize multiple components within the spectral emission by analytically reducing the number of parameters. The technique is presented alongside the design of a hard x-ray linear absorption spectrometer using the example of multiple Boltzmann-like spectral distributions; however, it is generally applicable to all absorption based spectrometer designs and can be adapted to any incident spectral shape. This routine is demonstrated to be tolerable to experimental noise and suitable for real-time data processing at multi-Hz repetition rates.

Novel scintillator-based x-ray spectrometer for use on high repetition laser plasma interaction experiments.

The characterisation of x-rays from laser-plasma interactions is of utmost importance as they can be useful for both monitoring electron dynamics and also applications in an industrial capacity. A novel versatile scintillator x-ray spectrometer diagnostic that is capable of single shot measurements of x-rays produced from laser-plasma interactions is presented here. Examples of the design and extraction of the temperature of the spectrum of x-rays produced in an intense laser-solid interaction (479 ± 39 keV) and the critical energy from a betatron source (30 ± 10 keV) are discussed. Finally, a simple optimisation process involving adjusting the scintillator thickness for a particular range of input spectra is demonstrated.

Age-dependent susceptibility of neonatal rats to group B streptococcal type III infection: correlation of severity of infection and response of myeloid pools.

A distinct age-dependent susceptibility to group B streptococcus type III (GBS) was demonstrated, utilizing a neonatal rat model. The most dramatic changes in susceptibility occurred within the first 7 days of postnatal life. To further investigate this susceptibility, experiments were performed utilizing two age groups of rats: (i) animals within the first 24 h of life (NB) and (ii) 7-day-old animals (7d). The infective dosage used was 10(4) GBS per g of body weight, a dose lethal to 100% of NB but only to 15% of 7d. The responses of the myeloid cells in the peripheral blood, spleen, and bone marrow were evaluated at intervals during the first 24 h post-GBS infection. The susceptibility of the NB to GBS appeared to be associated with a number of events, including smaller base-line levels of myeloid elements particularly in the bone marrow, a lag of at least 2 h in their initial response to infection, and an inability to maintain the myeloid pools. The band form of neutrophils appeared to be the predominant cell type in both total number and rapidity of response to infection. Moreover, an initial depletion of this band form was seen in both groups, which returned to base-line levels with recovery in 7d but persisted until death in NB animals. Similarly, shifts in numbers of peripheral nucleated erythrocytes appeared to reflect changes in the myeloid storage pools, with numbers of nucleated erythrocytes significantly decreasing in 7d animals with recovery in contrast to persistence in NB until death. Therefore, shifts in these cells in peripheral blood during infection appear to reflect the state of myeloid storage pools which parallel disease outcome.