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Presents a study which described an optimized version of a Q-switched, mode-locked and cavity-dumped ruby laser oscillator for plasma diagnostics. Principle of operation of the oscillator; Experimental setup; Discussion of modulator analysis; Results.

Preliminary experimental results on recording of phase and amplitude holograms using the radiation of electric-discharge HF lasers are presented, and prospects for applications of such lasers in diagnostics of various objects are discussed. It is shown that lasers with homogeneous working medium may generate coherent radiation with a coherence length of greater than 6 m in the absence of mode selection. Methods for control of spatial distribution of electron concentration in excimer and discharge chemical HF (DF) lasers and distributions of the main combustible components are considered. Deposition of holographic identification marks on artworks is studied. [ABSTRACT FROM AUTHOR]

Gaining information of species, temperature, and velocity distributions in turbulent combustion and high-speed reactive flows is challenging, particularly for conducting measurements without influencing the experimental object itself. The use of optical and spectroscopic techniques, and in particular laser-based diagnostics, has shown outstanding abilities for performing non-intrusive in situ diagnostics. The development of instrumentation, such as robust lasers with high pulse energy, ultra-short pulse duration, and high repetition rate along with digitized cameras exhibiting high sensitivity, large dynamic range, and frame rates on the order of MHz, has opened up for temporally and spatially resolved volumetric measurements of extreme dynamics and complexities. The aim of this article is to present selected important laser-based techniques for gas-phase diagnostics focusing on their applications in combustion and aerospace engineering. Applicable laser-based techniques for investigations of turbulent flows and combustion such as planar laser-induced fluorescence, Raman and Rayleigh scattering, coherent anti-Stokes Raman scattering, laser-induced grating scattering, particle image velocimetry, laser Doppler anemometry, and tomographic imaging are reviewed and described with some background physics. In addition, demands on instrumentation are further discussed to give insight in the possibilities that are offered by laser flow diagnostics. [ABSTRACT FROM AUTHOR]

Many parameters of non-equilibrium plasma generated by high intensity and fast lasers depend on the pulse intensity and the laser wavelength. In conditions favourable for the target normal sheath acceleration (TNSA) regime the ion acceleration from the rear side of the target can be enhanced by increasing the thin foil absorbance through the use of nanoparticles and nanostructures promoting the surface plasmon resonance effect. In conditions favourable for the backward plasma acceleration (BPA) regime, when thick targets are used, a special role is played by the laser focal position with respect to the target surface, a proper choice of which may result in induced self-focusing effects and non-linear acceleration enhancement. SiC detectors employed in the time-of-flight (TOF) configuration and a Thomson parabola spectrometer permit on-line diagnostics of the ion streams emitted at high kinetic energies. The target composition and geometry, apart from the laser parameters and to the irradiation conditions, allow further control of the plasma characteristics and can be varied by using advanced targets to reach the maximum ion acceleration. Measurements using advanced targets with enhanced the laser absorption effect in thin films are presented. Applications of accelerated ions in the field of ion source, hadrontherapy and nuclear physics are discussed. [ABSTRACT FROM AUTHOR]

We report the first measurements of x-ray single-pulse duration and two-pulse separation at the Linac Coherent Light Source using a cross-correlation technique involving x rays and electrons. An emittance-spoiling foil is adopted as a very simple and effective method to control the output x-ray pulse. A minimum pulse duration of about 3 fs full width at half maximum has been measured together with a controllable pulse separation (delay) between two pulses. This technique provides critical temporal diagnostics for x-ray experiments such as x-ray pump-probe studies. [ABSTRACT FROM AUTHOR]

Laser probe diagnostics: shadowgraphy, interferometry, and polarimetry were used for a comprehensive characterization of ionization wave dynamics inside a glass target induced by a laser-driven, reiativistic electron beam. Experiments were done using the 50-TW Leopard laser at the University of Nevada, Reno. We show that for a laser flux of ˜2 × 1018 W/cm² a hemispherical ionization wave propagates at c/3 for 10 ps and has a smooth electron-density distribution. The maximum free-electron density inside the glass target is ˜2 × 1019 cm-3, which corresponds to an ionization level of ˜0.1 %. Magnetic fields and electric fields do not exceed ˜ 15 kG and ˜1 MV/cm, respectively. The electron temperature has a hot, ringlike structure with a maximum of ˜0.7 eV. The topology of the interference phase shift shows the signature of the "fountain effect", a narrow electron beam that fans out from the propagation axis and heads back to the target surface. Two-dimensional particle-in-cell (PIC) computer simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields driven by laser. The very low ionization observed after the laser heating pulse suggests a fast recombination on the sub-ps time scale. [ABSTRACT FROM AUTHOR]

The plasma was produced by focusing Nd-YAG laser pulses of 1064-nm wavelength and 10-ns duration onto a copper target. A time-resolving plane Langmuir probe was used to record the electron and ion currents during the plasma expansion in vacuum. The Langmuir probe theory was used to determine the temporal variation of the plasma potential, electron temperature, and ion density. At the time of maximum ion current, the estimated plasma potential, electron temperature, and ion density were 2.42 V, 3.28 eV, and 2.30 \times 10^12\ \cm^-3, respectively. In addition, a time-of-flight signal was used to determine the ion density and velocity of the various ion components as a function of laser irradiance and probe angle w.r.t. target surface normal. For the range of laser irradiance, 4– 13 \times 10^8\ \W/cm^2, we found an ion density in the range of 6.88 \times 10^10– 2.64 \times 10^12\ \cm^-3 and an ion velocity in the range of 2.2–4.6 \times 10^6\ \cm s^-1 at the time of maximum ion current. In particular, the velocity of the fastest plume component was most affected by the irradiance. The estimated threshold irradiance for the onset of plasma was 3.95 \times 10^8\ \W/cm^2. The experimental scaling laws for the variation of ion velocity and ion charge with the laser irradiance and probe angle were proposed. [ABSTRACT FROM AUTHOR]

Phase-contrast or refraction-enhanced x-ray radiography can be useful for the diagnostic of low-Z high energy density plasmas, such as imploding inertial confinement fusion (ICF) pellets, due to its sensitivity to density gradients. To separate and quantify the absorption and refraction contributions to x-ray images, methods based on microperiodic optics, such as shearing interferometry, can be used. To enable applying such methods with the energetic x rays needed for ICF radiography, we investigate a new type of optics consisting of grazing incidence microperiodic mirrors. Using such mirrors, efficient phase-contrast imaging systems could be built for energies up to ∼100 keV. In addition, a simple lithographic method is proposed for the production of the microperiodic x-ray mirrors based on the difference in the total reflection between a low-Z substrate and a high-Z film. Prototype mirrors fabricated with this method show promising characteristics in laboratory tests. [ABSTRACT FROM AUTHOR]

The extreme physics of targets shocked by NIF's 192-beam laser is observed by a diverse suite of diagnostics. Many diagnostics are being developed by collaborators at other sites, but ad hoc controls could lead to unreliable and costly operations. A diagnostic control system (DCS) framework for both hardware and software facilitates development and eases integration. Each complex diagnostic typically uses an ensemble of electronic instruments attached to sensors, digitizers, cameras, and other devices. In the DCS architecture each instrument is interfaced to a low-cost WINDOWS XP processor and JAVA application. Each instrument is aggregated with others as needed in the supervisory system to form an integrated diagnostic. The JAVA framework provides data management, control services, and operator graphical user interface generation. DCS instruments are reusable by replication with reconfiguration for specific diagnostics in extensible markup language. Advantages include minimal application code, easy testing, and high reliability. Collaborators save costs by assembling diagnostics with existing DCS instruments. This talk discusses target diagnostic instrumentation used on NIF and presents the DCS architecture and framework. [ABSTRACT FROM AUTHOR]

A new Thomson scattering diagnostic has been designed and is currently being installed on the COMPASS tokamak in IPP Prague in the Czech Republic. The requirements for this system are very stringent with approximately 3 mm spatial resolution at the plasma edge. A critical part of this diagnostic is the laser source. To achieve the specified parameters, a multilaser solution is utilized. Two 30 Hz 1.5 J Nd:YAG laser systems, used at the fundamental wavelength of 1064 nm, are located outside the tokamak area at a distance of 20 m from the tokamak. The design of the laser beam transport path is presented. The approach leading to a final choice of optimal focusing optics is given. As well as the beam path to the tokamak, a test path of the same optical length was built. Performance tests of the laser system carried out using the test path are described. [ABSTRACT FROM AUTHOR]

Abstract: Broad-band near UV absorption spectroscopy was used to analyze atmospheric laser-induced plasmas formed on metallic and refractory targets. When the common emission spectroscopy only provides the density of the radiating atomic excited states, the technique reported in this paper is able to achieve high spatial resolution in the measurement of absolute number densities in expanding laser-induced plasmas. The reliability and the versatility of this technique, which is based on the comparison between results of the numerical integration of the radiative transfer equation and experimental spectra, were tested on different targets. The evolutions in time and space of the absolute population of the plasma species originating from metallic alloys (Al–Mg and Cu–Ni) and refractory materials (C/SiC) were achieved over large time scales. Owing to its accuracy, this absorption technique (that we call “LIPAS” for Laser Induced Plasma Absorption Spectroscopy) should bring a new and enhanced support to the validation of collisional-radiative models attempting to provide reliable evolutions of laser-induced plasmas. [Copyright &y& Elsevier]

Abstract: The paper describes past and present efforts in modeling of laser-induced plasma and overviews plasma diagnostics carried out by pump-probe techniques. Besides general information on existing plasma models, the emphasis is given to models relevant to spectrochemical analysis, i.e. models of radiating plasma. Special attention is paid to collisional-radiative (CR) and collisional-dominated (CD) plasma models where radiative processes play an important role. Also, calibration-free (CF) models are considered which may endow with the possibility for standardless spectroscopic analysis. In the diagnostic part, only methods based on the use of additional diagnostic tools (auxiliary lasers, optics, and probes) are described omitting those based on plasma own radiation. A short review is provided on image-based diagnostics (shadowgraphy, schlieren, and interferometry), absorption and fluorescence, Langmuir probe, and less frequently used cavity ringdown and Thomson scattering methods. [Copyright &y& Elsevier]

The spatiotemporal dynamics of the compression region of DT-gas filled micropellets was recorded using an optical streak camera in experiments on micropellet implosion in the Iskra-5 high-power laser facility. The experimental data agree with calculations and results of X-ray measurements. [ABSTRACT FROM AUTHOR]

Abstract: Long term tritium retention is one of the most critical issues for ITER and future fusion devices. While a global analysis of the T retention can be made by T accountancy in the activated phase of ITER, fuel retention and control must be already addressed in the non- activated phase, to identify the mechanism, location and amount of retention, its dependence on plasma and wall conditions and to qualify T retention mitigation and control techniques. For this purpose a new diagnostic, laser induced desorption spectroscopy of retained fuel has been developed and applied in TEXTOR. Hydrogen isotopes are desorbed from re-deposited layers on graphite plates by rapid heating with laser radiation. The released particles have been quantified in situ by spectroscopic measurements of hydrogen lines in a tokamak plasma. The results were validated by ex situ analysis of the hydrogen content of deposited a-C:H layers. [Copyright &y& Elsevier]

Abstract: The dynamics of transient plasmas generated by high-fluence nanosecond laser ablation has been investigated by means of optical methods (time- and space-resolved emission spectroscopy and fast ICCD imaging). Systematic measurements have been carried out on plasma produced in vacuum (10−8 Torr residual pressure) by Nd:YAG laser (10ns, 532nm) irradiation of Aluminum targets. Al neutral atoms and different charge state ions have been monitored through the evolution of corresponding spectral lines. The study evidenced the presence of two different groups of particles, tentatively related to two distinct ejection mechanisms. This behavior has been confirmed by the fast ICCD (20ns gate) recording of the total optical emission of the plume. The application of the relative line intensity method to the study of the excitation temperature axial profile is equally discussed. [Copyright &y& Elsevier]

X-ray pinhole detectors are a common and useful diagnostic for high temperature and fusion-grade plasmas. While the measurements from such diagnostics are line integrated, local emission can be recovered by inverting or modeling the data using varying assumptions including toroidal symmetry, flux surface isoemissivity, and one-dimensional (1D) chordal lines of sight. This last assumption is often valid when the structure sizes and gradient scale lengths of interest are much larger than the spatial resolution of the detector elements. However, x-ray measurements of, for example, the strong gradients in the H-mode pedestal may require a full three-dimensional (3D) treatment of the detector geometry when the emission of the plasma has a significant variation within the field of view, especially in a high-triangularity, low aspect ratio plasma. Modeling of a high spatial resolution tangential edge array for NSTX has shown that a proper 3D treatment can improve the effective spatial resolution of the detector by 10%–40% depending on the modeled signal-to-noise ratio and gradient scale length. Results from a general treatment of arbitrary detector geometry will provide a guideline for the amount of systematic error that can be expected by a 1D versus 3D field of view analysis. [ABSTRACT FROM AUTHOR]

Serum protein profiling by Surface-Enhanced Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (SELDI-TOF-MS) appears to be an important diagnostic tool for a whole range of diseases. Sensitivities and specificities obtained with this new technology often seem superior to those obtained with current biomarkers. However, reproducibility and standardization are still problematic. The present review explains the SELDI-TOF-MS technique and discusses some important aspects for proteomics studies, like pre- and post-analytical aspects and quality control procedures. Own data about biomarker discovery for the diagnosis of sarcoidosis are also presented in this review. [ABSTRACT FROM AUTHOR]

A method of online diagnostics of the surface state of materials exposed to high-power laser pulses is presented. The evolution of a graphite surface was observed on a laser monitor directly during the action of laser radiation on this surface. A method for reconstructing the surface relief from an image obtained using the laser monitor has been developed. It allows determination of the qualitative (based on the rms deviation of the image brightness) and quantitative (based on the correlation coefficient) characteristics of the surface. [ABSTRACT FROM AUTHOR]

A newly installed density diagnostic using CO[sub 2] laser interferometry and an H[sub α] diagnostic using interference filters and photomultiplier tubes for the recently constructed sustained spheromak physics experiment (SSPX) are described. First diagnostic results of the H[sub α] diagnostic were useful to understand the breakdown physics in the new SSPX experiments. Low-noise density data validates techniques to reduce vibration and electronic pickup. The data-processing electronics of the new interferometer can yield unambiguous density data that is equivalent to 16 fringe shifts. Density data is also critical to understand the particle source, and the J/n[sub e] parameter for SSPX. [ABSTRACT FROM AUTHOR]

The infrared CO[sub 2] laser polarimetry for electron density measurement based on the tangential Faraday rotation has been progressed in JT-60U tokamak. The reliability of polarimetry in a pellet-injected plasma was confirmed. The Faraday rotation was measured with good angle resolution of ∼0.01° under the sufficiently fast temporal resolution of 4 ms. Electron density evaluated from the tangential Faraday rotation measured by polarimetry shows good agreement with that measured by interferometry for an identical probing laser beam. The long-time continuous measurement was successful with good stability and accuracy. The basic feasibility of the infrared CO[sub 2] laser polarimetry for electron density measurement in long-time and steady-state operation in large fusion devices was demonstrated. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A CO[sub 2] laser polarimeter to measure the Faraday rotation in the large helical device (LHD) was developed and installed on a LHD. A CO[sub 2] laser whose wavelength is 10.6 μm was selected to avoid effects of the refraction. The Faraday rotation angle along toroidally tangential chords is of the order of one degree. The polarimeter utilizes the frequency-shift heterodyne technique with the use of acousto-optic modulators for high resolution. This polarimeter can be operated with a maximum of three channels. The accuracy of the Faraday rotation angle with a time resolution of 16 ms is about 0.01 deg by digital complex demodulation. We succeeded in performing preliminary measurements of the Faraday rotation angle from LHD plasmas and the values were 10%–30% larger than those estimated with the electron density profiles from interferometry. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A CO[sub 2] laser (λ=10.6 μm) imaging interferometer is designed for electron density profile and electron density fluctuation measurements on large helical device (LHD). The purposes of this diagnostic are reliable electron density monitor in high density operation (especially in pellet injection discharge), precise measurement of electron density profiles and observations of density fluctuations. By using a CO[sub 2] laser, refraction effect becomes negligible, and the interferometer promises to be free from fringe jumps at high density. We plan to get 5 mm spatial resolution, (56 ch for each of two 280 mm slab beams, 50 ch for one 250 mm and 16 ch for 80 mm crossed beam), 3×10[sup -3] rad phase resolution and 200 kHz frequency response for the above purpose. And fluctuation will be studied within the wave number range of 7×10[sup -3]<=k<=0.6 mm[sup -1]. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A collective Thomson scattering (CTS) diagnostic system using a carbon dioxide (CO[sub 2]) laser has been developed for the purpose of establishing measurement technique of ion temperature and fast alpha particle in a fusion reaction plasma. A pulsed CO[sub 2] laser (15 J, 1 μs at 10.6 μm) and a heterodyne receiver with a stray light notch filter has been successfully installed. The noise equivalent power of the heterodyne receiver is below 9×10[sup -19] W/Hz up to a frequency of 8 GHz. A six-channel filter bank analyzes the spectrum of the scattered light in the frequency range from 0.4 to 4.5 GHz to measure ion temperature and to detect fast ions generated by negative-ion source neutral beam injection of the JT-60U (Japan Atomic Energy Research Institute Tokamak 60-Upgrade) plasmas [S. Ishida, JT-60U Team, Nucl. Fusion 39, 1211 (1999)]. Test of the CTS system by injecting the CO[sub 2] laser into the vacuum vessel of JT-60U has started. Stray light signal around the JT-60U vacuum vessel was detected and optimization of the optical alignment has proceeded. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The two-dimensional (2D) structure of plasma density turbulence in a magnetically confined plasma can potentially be measured using a Thomson scattering system made from components of the Nova laser of Lawrence Livermore National Laboratory. For a plasma such as the National Spherical Torus Experiment at the Princeton Plasma Physics Laboratory, the laser would form an approx. 10-cm-wide plane sheet beam passing vertically through the chamber across the magnetic field. The scattered light would be imaged by a charge coupled device camera viewing along the direction of the magnetic field. The laser energy required to make 2D images of density turbulence is in the range 1–3 kJ, which can potentially be obtained from a set of frequency-doubled Nd:glass amplifiers with diameters in the range of 208–315 mm. A laser pulse width of <=100 ns would be short enough to capture the highest frequency components of the expected density fluctuations. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Characterization of hot electron production from an ultraintense laser–solid target plasma interaction by using a buried molybdenum K-shell fluor layer technique has been reported. Laser energy was typically 400 J and its intensity was from 2×10[sup 18] up to 3×10[sup 20] W cm[sup -2] at 20 TW to 1 PW laser power by changing pulse duration from 20 ps down to 0.5 ps. X-ray background noise level was significantly greater, i.e., gamma flash, in the shorter pulse experiments. Data analysis procedures for the experiments were developed. The conversion efficiency from the laser energy into the energy, carried by hot electrons, has been estimated to be ∼50% at 3×10[sup 20] W cm[sup -2] laser intensity, higher than ∼18% at 10[sup 19] W cm[sup -2] and ∼12% at 2×10[sup 18] W cm[sup -2] intensity. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In high flux (10[sup 13–15] W/cm[sup 2]) laser-plasma interaction, a large part of the incoming laser energy is radiated into soft x-rays. To determine both the shape of this spectrum and the conversion efficiency, we have designed and tested an absolutely calibrated broadband soft x-ray spectrometer with a high temporal resolution (100 ps). The detector in this spectrometer is a new coaxial x-ray diode coupled with a fast single shot oscilloscope (French IN7100 with 7 GHz frequency response cutoff). Both absolute calibrations (x-ray response of diodes) and relative calibrations (filters and mirrors) have used the French synchrotron beam lines at Laboratoire pour l’utilisation du Rayonnement Electromagne´tique (LURE) in Orsay. The initial version of this instrument was first successfully implemented on laser plasmas experiments at the Phe´bus facility in France and an improved version is now operating at the Omega laser facility in Rochester, New York. The emitted x-ray spectrum is absolutely measured in 18 broad bands from 50 eV up to 20 keV. The softer bands (<1.5 keV) combine mirror and filter responses coupled with the coaxial diode response to improve hard x-ray rejection. Intermediate energy channels (1.5 keV5 keV) we replace the x-ray diode (not sufficiently sensitive) with a photoconductive detector (neutron-damaged GaAs). An equivalent instrument will be designed for the future National Ignition Facility (NIF) in the United States and the Laser Me´gajoule (LMJ) in France. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this article, we review the phenomenon of dispersion, paying particular attention to its impact in the optics of ultrashort pulses, as well as its measurement and management. At present, lasers generating coherent bandwidths of several hundred nanometers have been demonstrated and correspondingly short pulses of 10 fs or so are quite usual. The limits to the breadth of optical spectra and brevity of pulse durations that may be achieved are often set by the dispersive properties of the linear optical elements of which the source is constructed. Progress in ultrafast optics to date has therefore relied extensively on the development of ways to characterize and manipulate dispersion. The means by which this can be accomplished are significantly different for laser oscillators and laser amplifiers, as well as for nonlinear interactions that are used to extend the range of frequencies at which short optical pulses are available, but in all cases it is this phenomenon that determines the output of current optical sources. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A compact, tabletop terawatt Ti:sapphire laser drive, ultrafast hard x-ray source for time-resolved x-ray diffraction studies is described. With a copper target the energy conversion efficiency from laser photons (800 nm) to copper K x-ray radiation (1.54 Å) is 0.008%. The optimal laser intensity for generating these x rays is 10[sup 18] W cm[sup -2], lower than the highest laser intensity available (5x10[sup 18] W cm[sup -2]) from the laser system. These results are consistent with a theoretical model proposed on the basis that the x rays are produced as a result of laser driven electron ionization of core level electrons of Cu atoms near room temperature. This source also provides features such as ultrashort pulse duration, extremely small source size, variable wavelengths, high peak spectral brightness, and the potential for multiple beam line experiments. X-ray diffraction patterns from GaAs single crystals and amorphous Ni films recorded with this source are presented. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A frequency modulated Coherent Laser Radar ranging diagnostic is being used on the National Spherical Torus Experiment (NSTX) for precision metrology. The distance (range) between the 1.5 μm laser source and the target is measured by the shift in frequency of the linearly modulated beam reflected off the target. The range can be measured to a precision of <100 μm at distances of up to 22 m. A description is given of the geometry and procedure for measuring NSTX interior and exterior surfaces during open vessel conditions, and the results of measurements are elaborated. [ABSTRACT FROM AUTHOR]

Indirect/direct-hybrid irradiation has been proposed for suppressing the initial imprint of laser-irradiation nonuniformities. Indirect soft x-ray preirradiation of the target generates a plasma expansion layer on the target surface. When the drive laser beam comes later, the target has a substantial stand-off distance between the ablation front and the beam absorption region, in which the thermal smoothing effect is expected to take place, and then, the initial imprint of the laser irradiation nonuniformities can be significantly reduced. Stand-off distance is of great importance in the imprint mitigation. We measured the preformed plasma profile by using the x-ray side-on backlighting method. The preformed plasma was backlit by x rays and imaged onto an x-ray streak camera. The scale length of the preformed plasma was found to increase with duration of the soft x-ray irradiation. The expansion velocity was found to be 6×10[sup 5] cm/s at an x-ray irradiation of 1×10[sup 11] W/cm[sup 2]. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies of compressed shell integrity of spherical targets on the 60-beam 30 kJ UV OMEGA laser system involve spatially and temporally resolved measurements of core emission at different x-ray energies. Hot-core emission backlights a titanium-doped shell that is imaged at x-ray energies above and below the titanium K edge. The difference between the two images is related to perturbations in the cold, or absorbing, part of the shell. The core emission has been imaged by a pinhole array on a framing camera and recorded on film. The resolution and noise of all parts of the imaging system have been characterized. Using this information, a Wiener filter that reduces noise, compensates for detector resolution, and facilitates measurement of shell nonuniformities has been formulated. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Z-Beamlet laser backlighter system at Sandia National Laboratories, which will be operational in 2001, will create a point or area source of high (or moderate) energy x rays behind a Z-accelerator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] -driven target. In the former case with >2 kJ in up to four pulses of <2 ns total duration in a 20 ns interval, and >80% of the 2ω energy in a ∼50-μm-diam focal spot, the resulting >4×10[sup 16] W/cm[sup 2] irradiances will generate >=8.950, 8.999 keV (zinc He-α, etc.) x rays. This high-energy source, as either a single point or four separate spots, will be used directly for four-frame point-projection x-ray imaging, and will attain spatial resolutions and signal-to-noise levels significantly better than presently possible on Z using existing methods. In combination with a ∼1 cm field of view, the technique will be well suited to the large, relatively opaque objects characteristic of Z experiments. This addition is anticipated to have a major impact upon the basic physics of z-pinch implosions, and therefore, possibly the ultimate x-ray powers and hohlraum (vacuum or dynamic) radiation temperatures that may be attainable. Furthermore, in combination with a slightly defocused point source and a medium-energy grazing-incidence microscope, Z-Beamlet may allow various inertial confinement fusion and high-energy-density physics experiments to be studied at even higher spatial resolution and signal-to-noise levels. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have performed experiments with planar targets on the OMEGA laser facility at the University of Rochester. These experiments investigated the scaling of x-ray yield and conversion efficiency with the laser energy and focusing properties for several different target materials. The experiments were also designed to investigate the feasibility of high-energy backlighters under typical irradiance geometries. The scaling of Fe emission near 6.7 keV was investigated by varying laser irradiance from 10[sup 14] to 10[sup 16] W/cm[sup 2]. In addition, the scaling of x-ray yield with emitted x-ray energy was studied at fixed laser irradiance near 10[sup 16] W/cm[sup 2] for Fe, Zn, and Ge. The time-integrated spectra as well as filtered x-ray film gave relative x-ray yields. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

With the operation of successively more intense and powerful lasers, such as the NOVA petawatt laser with I∼3×10[sup 20] W/cm[sup 2], several novel (to laser physics) nuclear diagnostics were used to determine the nature of the laser/matter interaction at the target surface. A broad beam of hot electrons, whose centroid varied from shot to shot, width was remarkably constant, and intensity was about 40% of the incident laser energy was observed. New nuclear phenomenon included photonuclear reactions [e.g., (γ,xn)], photofission of [sup 238]U and intense beams of ions. Photonuclear reactions were observed and quantified in Cu, Ni, and Au samples, and produced activation products as neutron deficient as [sup 191]Au [a (γ,6n) reaction!], requiring gamma rays exceeding 50 MeV in energy. The spectral features of the gamma-ray source have been investigated by comparing activation ratios in Ni and Au samples, and angular distributions of higher energy photons have been measured with activation of spatially distributed Au samples. Extraordinarily intense beams of charged particles (primarily protons) were observed normal to the rear surface of the target and quantified using the charged particle reaction [sup 48]Ti(p,n)[sup 48]V, radiochromic film and CR39 plastic track detectors. Approximately 3×10[sup 13] protons, with energies up to 55 MeV were observed in some experiments. Collimation of this beam increases with increasing proton energy. Correlations of activation with laser performance will be discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A single laser pulse is used to produce weakly nonideal plasma from a metallic aluminum target immersed in a dense neutral gas. The attendant increase in plasma density due to neutral gas confinement precipitates interfacial instability when the gas density exceeds a threshold value. This is accompanied by large fluctuations in the total attenuation of the laser beam by the laser-produced plasma plume. We have developed a new diagnostic method utilizing two mutually orthogonal side-view streak photographs of plasma continuum luminosity at a fixed distance from the target surface. The lack of axial symmetry is overcome by using a front-view luminosity image of the plasma at time zero as a two-dimensional weighting factor. The resulting profile at one time is used as the weighting factor for the next time segment. The time-resolved reconstructed plasma profiles clearly exhibit the near-threshold behavior of Rayleigh–Taylor type instability. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents an update on the progress of a diagnostic system proposed for ignition target experiments on the National Ignition Facility (NIF) glass laser system. NIF system design requirements; Startup and laser validation of the NIF experimental plan; Laser characterization diagnostics; Capsule performance diagnostics.

Describes x-ray streak camera measurements of wall motion and plasma filling in hohlraum targets heated by the AWE HELEN laser. Soft x-ray imaging; Design of the streak camera; One-dimensional numerical simulation and modeling.

Discusses measurements of neutron spectra from targets on the Nova laser. Direct-drive implosions; Indirect-drive implosions; Gas-filled hohlraums.

Recent laser upgrades on the Hot Helicon Experiment at West Virginia University have enabled multiplexed simultaneous measurements of the ion velocity distribution function at a single location, expanding our capabilities in laser-induced fluorescence diagnostics. The laser output is split into two beams, each modulated with an optical chopper and injected perpendicular and parallel to the magnetic field. Light from the crossing point of the beams is transported to a narrow-band photomultiplier tube filtered at the fluorescence wavelength and monitored by two lock-in amplifiers, each referenced to one of the two chopper frequencies. [ABSTRACT FROM AUTHOR]

In this article, extension of the He beam diagnostic, which is routinely applied in fusion devices for the characterization of the edge electronic parameters-ne and Te-and their profile, to the measurement of ion temperature and plasma rotation is proposed. The theoretical background for these new applications is reviewed and examples of their use in TJ-II are provided. Also, the shortcomings and their possible solutions are addressed. Finally, the field of application of the technique to other beam-based diagnostics is discussed. [ABSTRACT FROM AUTHOR]

A multipass intracavity laser probing system operating in a burst mode has been tested for the Torus Experiment for Technology Oriented Research Thomson scattering diagnostics. The parameters tested were the probing pulse energy and power as well as pulse repetition frequency. The system is to be applied for the dynamic study of fast plasma phenomena (e.g., transport barrier formation and filaments) requiring both high time and spatial resolutions of the electron temperature measurements. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Laser-produced plasmas driven by high-intensity, femtosecond-duration pulsed lasers have been recognized as sources of short-duration x-ray line emissions. Electron kinetics simulations of such transient and nonequilibrium plasmas predict non-Maxwellian electron distributions and even the presence of electron beams. X-ray line polarization spectroscopy is a diagnostic that can be used to study the directionality of the electron distribution function and thus test electron kinetics simulation results. To this end, we use a time-dependent, collisional-radiative atomic kinetics model of magnetic sublevels to understand the underlying processes and mechanisms leading to the formation of polarized x-ray line emission in Si plasmas driven by high-intensity, ultrashort duration pulsed lasers. We focus on the polarization properties of the He-like Si satellites of the Ly[sub α] line. In the cases under consideration, the relevant line emissions last less than 1 ps during which the plasma undergoes a rapid development. We identify suitable polarization markers, which are sensitive to the anisotropy of the electron distribution function and can be used for diagnostic applications. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]