A spectrometer for ultrashort gamma-ray pulses with photon energies greater than 10 MeV

We present a design for a pixelated scintillator based gamma-ray spectrometer for non-linear inverse Compton scattering experiments. By colliding a laser wakefield accelerated electron beam with a tightly focused, intense laser pulse, gamma-ray photons up to 100 MeV energies and with few femtosecond duration may be produced. To measure the energy spectrum and angular distribution, a 33 × 47 array of cesium-iodide crystals was oriented such that the 47 crystal length axis was parallel to the gamma-ray beam and the 33 crystal length axis was oriented in the vertical direction. Using an iterative deconvolution method similar to the YOGI code, modeling of the scintillator response using GEANT4 and fitting to a quantum Monte Carlo calculated photon spectrum, we are able to extract the gamma ray spectra generated by the inverse Compton interaction.

Controlling the Self-Injection Threshold in Laser Wakefield Accelerators

Controlling the parameters of a laser plasma accelerated electron beam is a topic of intense research with a particular focus placed on controlling the injection phase of electrons into the accelerating structure from the background plasma. An essential prerequisite for high-quality beams is dark-current free acceleration (i.e., no electrons accelerated beyond those deliberately injected). We show that small-scale density ripples in the background plasma are sufficient to cause the uncontrolled (self-)injection of electrons. Such ripples can be as short as ∼50  μm and can therefore not be resolved by standard interferometry. Background free injection with substantially improved beam characteristics (divergence and pointing) is demonstrated in a gas cell designed for a controlled gas flow. The results are supported by an analytical theory as well as 3D particle in cell simulations.

Noncollinear Polarization Gating of Attosecond Pulse Trains in the Relativistic Regime

High order harmonics generated at relativistic intensities have long been recognized as a route to the most powerful extreme ultraviolet pulses. Reliably generating isolated attosecond pulses requires gating to only a single dominant optical cycle, but techniques developed for lower power lasers have not been readily transferable. We present a novel method to temporally gate attosecond pulse trains by combining noncollinear and polarization gating. This scheme uses a split beam configuration which allows pulse gating to be implemented at the high beam fluence typical of multi-TW to PW class laser systems. Scalings for the gate width demonstrate that isolated attosecond pulses are possible even for modest pulse durations achievable for existing and planned future ultrashort high-power laser systems. Experimental results demonstrating the spectral effects of temporal gating on harmonic spectra generated by a relativistic laser plasma interaction are shown.

Sensitivity calibration of an imaging extreme ultraviolet spectrometer-detector system for determining the efficiency of broadband extreme ultraviolet sources

We report on the absolute sensitivity calibration of an extreme ultraviolet (XUV) spectrometer system that is frequently employed to study emission from short-pulse laser experiments. The XUV spectrometer, consisting of a toroidal mirror and a transmission grating, was characterized at a synchrotron source in respect of the ratio of the detected to the incident photon flux at photon energies ranging from 15.5 eV to 99 eV. The absolute calibration allows the determination of the XUV photon number emitted by laser-based XUV sources, e.g., high-harmonic generation from plasma surfaces or in gaseous media. We have demonstrated high-harmonic generation in gases and plasma surfaces providing 2.3 μW and μJ per harmonic using the respective generation mechanisms.

Simultaneous imaging electron- and ion-feature Thomson scattering measurements of radiatively heated Xe

Uniform density and temperature Xe plasmas have been produced over >4 mm scale-lengths using x-rays generated in a cylindrical Pb cavity. The cavity is 750 μm in depth and diameter, and is heated by a 300 J, 2 ns square, 1054 nm laser pulse focused to a spot size of 200 μm at the cavity entrance. The plasma is characterized by simultaneous imaging Thomson scattering measurements from both the electron and ion scattering features. The electron feature measurement determines the spatial electron density and temperature profile, and using these parameters as constraints in the ion feature analysis allows an accurate determination of the charge state of the Xe ions. The Thomson scattering probe beam is 40 J, 200 ps, and 527 nm, and is focused to a 100 μm spot size at the entrance of the Pb cavity. Each system has a spatial resolution of 25 μm, a temporal resolution of 200 ps (as determined by the probe duration), and a spectral resolution of 2 nm for the electron feature system and 0.025 nm for the ion feature system. The experiment is performed in a Xe filled target chamber at a neutral pressure of 3-10 Torr, and the x-rays produced in the Pb ionize and heat the Xe to a charge state of 20±4 at up to 200 eV electron temperatures.

Note: A large aperture four-mirror reflective wave-plate for high-intensity short-pulse laser experiments

We report on a four-mirror reflective wave-plate system based on a phase-shifting mirror (PSM) for a continuous variation of elliptical polarization without changing the beam position and direction. The system presented and characterized here can replace a conventional retardation plate providing all advantages of a PSM, such as high damage-threshold, large scalability, and low dispersion. This makes reflective wave-plates an ideal tool for ultra-high power laser applications.

[Levobupivacaine for parturients undergoing elective caesarean delivery. A dose-finding investigation]

BACKGROUND

The optimum intrathecal dose of hyperbaric levobupivacaine for spinal anaesthesia during elective caesarean section has not yet been investigated.

METHODS

A total of 30 parturients undergoing elective caesarean section were included in this prospective, randomised, double-blind study. Parturients received either 7.5, 10 or 12.5 mg hyperbaric 0.5% levobupivacaine intrathecally. Analgesic, sensory and motor block characteristics as well as maternal and fetal levobupivacaine plasma concentrations were determined.

RESULTS

Of the parturients receiving 7.5 mg levobupivacaine 40% required supplementary intravenous opioid analgesics intraoperatively and none achieved complete motor block. Compared to 7.5 mg levobupivacaine, 10 and 12.5 mg significantly prolonged duration of effective analgesia postoperatively (median: 45 vs. 81 and 96 min, respectively). Both maternal and fetal levobupivacaine plasma concentrations were low, with dose-dependent, statistically significant differences in maternal plasma concentrations.

CONCLUSIONS

Levobupivacaine 7.5 mg did not provide satisfactory intraoperative analgesia in all parturients. There were no statistically significant differences between 10 and 12.5 mg levobupivacaine with respect to analgesic, sensory and motor block characteristics. Therefore, based on these data, 10 mg levobupivacaine is recommended for parturients undergoing elective caesarean section with spinal anaesthesia.

Validation of in vitro potency assays for tetanus immunoglobulin

The European Pharmacopoeia (Ph. Eur.) monograph Human tetanus immunoglobulin (0398) gives a clear outline of the in vivo assay to be performed to determine the potency of human tetanus immunoglobulins during their development. Furthermore, it states that an in vitro method shall be validated for the potency estimation. Since no further guidance is given on the in vitro assay, every control laboratory concerned is free to design and validate an in-house method. At the moment there is no agreed method available. The aim of this study was to validate and compare 2 alternative in vitro assays, i.e. an enzyme-linked immunoassay (EIA) and a toxoid inhibition assay (TIA). The potency of 2 tetanus immunoglobulin preparations (Product 1, Product 2) was estimated against the WHO International Standard for tetanus immunoglobulin, using the tetanus EIA and TIA. The coefficient of variation (CV) to characterise the assay precision was 3.2% (EIA) and 3.6% (TIA), and the corresponding CV for intra-assay variation was 4.7% (EIA) and 5.5% (TIA). Using a spiking procedure, the 2nd part of the experiment investigated recovery of a known anti-tetanus potency. The recovery of samples spiked with defined amounts of reference preparation ranged from 104 112% (EIA) and 114 125% (TIA) respectively, resulting in a mean bias of 2.2 IU/ml (95% confidence interval (CI): -1.1-5.4 IU/ml, EIA) and 5.8 IU/ml (95% CI: 1.4 10.2 IU/ml, TIA). Good agreement was observed between the in vivo and in vitro assay results: the relative potency results of the EIA and TIA as compared to those of the in vivo assay performed by the manufacturers of the 2 tetanus immunoglobulins were for the EIA in the range of 104+/-10% for Product 1 and 100+/-6% for Product 2, and for the TIA in the range of 107+/-6% for Product 1 and 100+/-7% for Product 2. Tetanus EIA and TIA are suitable quality control methods for polyclonal tetanus immunoglobulin, which can be standardised in a quality control laboratory using a quality assurance system. In a collaborative study it will now be evaluated whether the validated methods can be proposed as common in vitro batch potency assays for replacement of the in vivo mouse assay.