Calibration and characterization of optical and x-ray streak cameras using a Ti:Sapphire laser system.

Optical and x-ray streak cameras are used to study transient phenomena, particularly in the high-energy density physics regime. The Orion laser facility employs many different types of streak cameras, which are used to collect data on laser-plasma interactions as well as to verify the temporal profile and timing between the multiple Orion beamlines. Streak cameras are complex devices with very precise timing associated with them, which can often malfunction, resulting in the loss of shot data. Since Orion is a kJ-class Nd:glass laser system, it is not optimal to try and fault-find using Orion shots since this is both time consuming and prohibitively expensive. To enable the facile set-up, fault-finding, timing-in, and in-house calibration of Orion optical and x-ray diagnostics, a single laboratory system has been commissioned to provide an adjustable stimulus to streak cameras and other Orion short pulse diagnostics (such as pulse dilation photomultiplier tubes). The system comprises a Ti:Sapphire laser system capable of generating 400 nm or 266 nm laser pulses of duration less than 0.1 ps; an optical system to deliver single pulses, pulse pairs, or a train of pulses; and timing electronics to synchronize the streak cameras with the laser and to record output data. The system can operate at Hertz repetition rates rather than the sub-mHz rate of the Orion laser. We present the commissioned system and results from initial testing of both optical and x-ray streak cameras used on Orion laser-plasma experiments.

Development of a full aperture backscatter system for the Orion laser.

A full aperture backscatter system (FABS) is currently in development on the Orion laser at AWE to measure scattered light from the stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) processes. The light is to be collected through the full aperture of the final optic assembly and traverse back down the beam path, with fractions of this light being directed to an optics table. By measuring the energy of this backscattered light, it is possible to gain insight into some of the laser-plasma instabilities that are present on the laser system and should give an indication of some of the scattered light losses due to the SBS and SRS processes. The uncontrolled scattered light can lead to hotter electrons, which then preheat the target causing a degradation in compression and can inhibit ignition in inertial confinement fusion experiments, as well as secondary instabilities whereby the scattered light may in itself cause further LPIs, such as two-ion decay or the Langmuir decay instability. The FABS diagnostic on Orion is planned to enhance the plasma diagnostics suite available and provide quantitative guidance on increasing the energy coupling. Current progress includes the characterization of filters and, hence, a broadband xenon lamp to be used in measuring the transmission efficiency of the optics chain, desktop alignment of the backscatter optics, and characterization of the streak cameras.

ORION laser target diagnostics.

The ORION laser facility is one of the UK's premier laser facilities which became operational at AWE in 2010. Its primary mission is one of stockpile stewardship, ORION will extend the UK's experimental plasma physics capability to the high temperature, high density regime relevant to Atomic Weapons Establishment's (AWE) program. The ORION laser combines ten laser beams operating in the ns regime with two sub ps short pulse chirped pulse amplification beams. This gives the UK a unique combined long pulse/short pulse laser capability which is not only available to AWE personnel but also gives access to our international partners and visiting UK academia. The ORION laser facility is equipped with a comprehensive suite of some 45 diagnostics covering optical, particle, and x-ray diagnostics all able to image the laser target interaction point. This paper focuses on a small selection of these diagnostics.

Evidence for high-efficiency laser-heated hohlraum performance at 527 nm.

A series of experiments conducted on the HELEN laser system [M. J. Norman, Appl. Opt.4120023497], into thermal x-ray generation from hohlraum targets using 527 nm (2omega) wavelength laser light, has shown that it is possible to exceed radiation temperatures previously thought limited by high levels of superthermal or hot electron production or stimulated backscatter. This Letter questions whether the assumptions traditionally applied to hohlraum design with respect to hot plasma filling and the use of 2omega light are too conservative.

alpha4beta3delta GABA(A) receptors characterized by fluorescence resonance energy transfer-derived measurements of membrane potential.

Selective modulators of gamma-aminobutyric acid, type A (GABA(A)) receptors containing alpha(4) subunits may provide new treatments for epilepsy and premenstrual syndrome. Using mouse L(-tk) cells, we stably expressed the native GABA(A) receptor subunit combinations alpha(3)beta(3)gamma(2,) alpha(4)beta(3)gamma(2), and, for the first time, alpha(4)beta(3)delta and characterized their properties using a novel fluorescence resonance energy transfer assay of GABA-evoked depolarizations. GABA evoked concentration-dependent decreases in fluorescence resonance energy transfer that were blocked by GABA(A) receptor antagonists and, for alpha(3)beta(3)gamma(2) and alpha(4)beta(3)gamma(2) receptors, modulated by benzodiazepines with the expected subtype specificity. When combined with alpha(4) and beta(3), delta subunits, compared with gamma(2), conferred greater sensitivity to the agonists GABA, 4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridin-3-ol (THIP), and muscimol and greater maximal efficacy to THIP. alpha(4)beta(3)delta responses were markedly modulated by steroids and anesthetics. Alphaxalone, pentobarbital, and pregnanolone were all 3-7-fold more efficacious at alpha(4)beta(3)delta compared with alpha(4)beta(3)gamma(2.) The fluorescence technique used in this study has proven valuable for extensive characterization of a novel GABA(A) receptor. For GABA(A) receptors containing alpha(4) subunits, our experiments reveal that inclusion of delta instead of gamma(2) subunits can increase the affinity and in some cases the efficacy of agonists and can increase the efficacy of allosteric modulators. Pregnanolone was a particularly efficacious modulator of alpha(4)beta(3)delta receptors, consistent with a central role for this subunit combination in premenstrual syndrome.

Cell-based assays and instrumentation for screening ion-channel targets.

Ion channels are an important class of drug targets. They comprise the molecular basis for essential physiological functions including fluid secretion, electrolyte balance, bioenergetics and membrane excitability. High-throughput screening for ion-channel function requires sensitive, simple assays and instrumentation that will report ion channel activity in living cells. This article will review relevant assay technologies for ion channels and describe voltage-sensitive probes and instruments based on fluorescence resonance energy transfer (FRET) that enable ion-channel drug discovery.

The skeletal muscle transverse tubular Mg-ATPase: identity with Mg-ATPases of smooth muscle and brain.

Purified chicken skeletal muscle transverse tubule (T-tubule, TT) membrane preparations contain a very active Ca- or Mg-ATPase (EC 3.6.1.3) previously thought to be a T-system-specific marker enzyme. The function of the Mg-ATPase has not yet been determined although its prominent activity and concentration in junctional complexes supports a possible role in the excitation-contraction cycle. An essential component of the Mg-ATPase has been identified as a M(r) 85,000 glycoprotein (85k-GP). Polyclonal antibodies raised against the TT 85k-GP were specific and exhibited no cross-reactivity with other skeletal muscle proteins on immunoblots. Using this anti-85k-glycoprotein IgG, we have explored other chicken tissues to determine the tissue distribution of the 85k-GP. Antibody reactive polypeptides of M(r) 85,000 were found in gizzard smooth muscle, brain, heart, spleen, and lung tissue. The brain and smooth muscle membrane proteins were further purified and characterized for 85k-GP-associated Mg-ATPase activity. The brain and smooth muscle enzymes exhibited properties indistinguishable from the skeletal muscle TT-specific Mg-ATPase with regard to a series of activators and inhibitors, amino terminal amino acid sequences, and the effects of deglycosylation. The enzyme in all three tissues was inhibited by the diacylglycerol kinase inhibitor R 59022. Identification of the TT Mg-ATPase in gizzard smooth muscle has allowed the investigation of the Mg-ATPase membrane topology using isolated whole smooth muscle cells. The data support an ecto-orientation for the smooth muscle cell enzyme. Although the orientations of the brain and skeletal muscle enzymes have not been conclusively determined, the nearly identical properties of all three enzymes argues for an ecto-orientation of the active sites of these enzymes as well. The responsiveness of the three enzymes to regulatory lipids suggests that the ecto-Mg-ATPase may serve as a master switch controlling extracellular ATP concentrations and ligand accessibility to P1- and P2-purinoceptors. It is also proposed that the ecto-MgATPase may regulate ATP accessibility to ectoprotein kinases in a variety of tissues, and, in brain, the ecto-MgATPase may modulate the neurotransmitter role of ATP.