Standard design for National Ignition Facility x-ray streak and framing cameras

The x-ray streak camera and x-ray framing camera for the National Ignition Facility were redesigned to improve electromagnetic pulse hardening, protect high voltage circuits from pressure transients, and maximize the use of common parts and operational software. Both instruments use the same PC104 based controller, interface, power supply, charge coupled device camera, protective hermetically sealed housing, and mechanical interfaces. Communication is over fiber optics with identical facility hardware for both instruments. Each has three triggers that can be either fiber optic or coax. High voltage protection consists of a vacuum sensor to enable the high voltage and pulsed microchannel plate phosphor voltage. In the streak camera, the high voltage is removed after the sweep. Both rely on the hardened aluminum box and a custom power supply to reduce electromagnetic pulse/electromagnetic interference (EMP/EMI) getting into the electronics. In addition, the streak camera has an EMP/EMI shield enclosing the front of the streak tube.     

X-ray diffraction from shock-loaded polycrystals

X-ray diffraction was demonstrated from shock-compressed polycrystalline metals on nanosecond time scales. Laser ablation was used to induce shock waves in polycrystalline foils of Be, 25-125 microm thick. A second laser pulse was used to generate a plasma x-ray source by irradiation of a Ti foil. The x-ray source was collimated to produce a beam of controllable diameter, which was directed at the Be sample. X-rays were diffracted from the sample, and detected using films and x-ray streak cameras. The diffraction angle was observed to change with shock pressure. The diffraction angles were consistent with the uniaxial (elastic) and isotropic (plastic) compressions expected for the loading conditions used. Polycrystalline diffraction will be used to measure the response of the crystal lattice to high shock pressures and through phase changes.     

Development of a time-resolved soft x-ray spectrometer for laser produced plasma experiments

A 2400 lines/mm variable-spaced grating spectrometer has been used to measure soft x-ray emission (8-22 A?) from laser-produced plasma experiments at Lawrence Livermore National Laboratory's Compact Multipulse Terrawatt (COMET) Laser Facility. The spectrometer was coupled to a Kentech x-ray streak camera to study the temporal evolution of soft x rays emitted from the back of the Mylar and the copper foils irradiated at 10(15)?W/cm(2). The instrument demonstrated a resolving power of ～120 at 19 A? with a time resolution of 31 ps. The time-resolved copper emission spectrum was consistent with a photodiode monitoring the laser temporal pulse shape and indicated that the soft x-ray emission follows the laser heating of the target. The time and spectral resolutions of this diagnostic make it useful for studies of high temperature plasmas.     

聚变反应速率测量光学系统设计

基于塑料闪烁体和条纹相机设计了聚变反应速率测量系统,论述了测量光学系统的工作原理和设计方法。通过设置防辐射石英玻璃窗,防止了光学元件受强X射线辐射而变暗;采用晶体等紫外透过率高的光学材料,满足了光学系统对透过率的要求;光学系统像面与条纹相机的阴极面直接对接,解决了条纹相机孔径不匹配的问题;最后在一次像面设置场镜,大幅缩小了光学元件的口径。设计的光学系统总长为2 660mm,放大倍率为1/3,像方F/#数达到0.667,系统透过率达到67%,时间弥散小于7.3ps。这些结果能够适应不同中子产额的实验需求,在激光打靶实验中取得了较好的实验效果。     

Accurate and efficient characterization of streak camera using etalon and fitting method with constraints

Streak camera is widely used in continuous time diagnostics in fast physical process. To produce accurate result, it requires delicate calibration and a reliable analysis method. High quality sweep-rate data with uncertainty smaller than 0.5% are obtained over the full record area by a constrained fitting method of peak position measurement, with a short pulse laser and an etalon as the fiducial source. The temporal response is linearized by this full-screen sweep-rate data, which eliminates errors in measurement due to nonlinearity and space-distortion inherent in streak camera.     

Measurement of the Dead Time of an Optoelectronic Streak Camera with Different Linear Sweep Ranges

A method for measuring the dead time of an optoelectronic streak camera with different linear sweep ranges is described. The proposed method was used for the PN-1 streak camera. Photographs of the time-resolved emission of a DRSh350-2 mercury arc flash lamp for linear sweep ranges of 50 and 100 ns are presented. The dead times of the PN-1 streak camera for linear sweep ranges of 25, 50, and 100 ns were 5, 75, and 105 ns, respectively. The photographs of time-resolved second-harmonic spectra emitted by plasmas of copper and aluminum targets that were obtained in experiments on the interaction of nanosecond laser radiation with the matter using a streak camera are presented.     

High dynamic range streak camera for subpicosecond time-resolved x-ray spectroscopy

The full characterization of a time resolved x-ray spectrometer is presented. It is based on the coupling of a conical crystal with a subpicosecond x-ray streak camera. The detector is designed to operate in accumulation mode at high repetition rate (up to 1 kHz) allowing signal to noise ratio as high as 10(4):1. Optical switches have been used to limit the jitter induced in the subpicosecond range, demonstrating the very long term stability (a few hours) of the entire device. The data analysis have been developed to get the spectral and temporal resolution of an ultrashort laser-plasma-based x-ray source.     

Time resolved cathodoluminescence in the scanning electron microscope by use of the streak technique

Minority carrier lifetime is one of the basic material properties in optoelectronic devices and material. Both the micrometer range dimensions of the devices and lifetime variations around defects in materials require a lifetime measurement technique with both high spatial and high temporal resolution. In order to meet these requirements a highly efficient cathodoluminescence (CL) measurement system has been developed consisting of a commercial scanning electron microscope extended for integral and spectral CL-measurements and a streak camera with subnanosecond time resolution as time resolving detector. The lifetime is determined by evaluation of CL-decay time after excitation of the specimen by an electron beam pulse, which is blanked in less than 50 ps by an adjustable plate capacitor. The CL-light is collected by an adjustable, ellipsoidal mirror and can be dispersed in a vacuum monochromator. The monochromator exit slit is imaged on to the photocathode of the streak camera, which transforms the temporal distribution of the photon intensity into a lateral distribution on the camera phosphor screen after amplification by an integrated microchannel plate. By this technique it is possible to record the complete CL-decay simultaneously, thus avoiding all measurement falsifications by system instabilities. The resulting intensity distribution is read out by a SIT vidicon camera with subsequent multichannel analyser, providing an intensity plot versus streak time in less then 1 min for each beam spot location. The technique is therefore well suited for lifetime mapping experiments. The best time resolution of the complete system achieved today is about 100 ps. Its performance is here demonstrated by measurements of the temperature dependence of the CL-decay in a highly Se-doped GaAs specimen in the temperature range from 90 K to 300 K.     

A neutron camera system for MAST

A prototype neutron camera has been developed and installed at MAST as part of a feasibility study for a multichord neutron camera system with the aim to measure the spatial and time resolved 2.45 MeV neutron emissivity profile. Liquid scintillators coupled to a fast digitizer are used for neutron/gamma ray digital pulse shape discrimination. The preliminary results obtained clearly show the capability of this diagnostic to measure neutron emissivity profiles with sufficient time resolution to study the effect of fast ion loss and redistribution due to magnetohydrodynamic activity. A minimum time resolution of 2 ms has been achieved with a modest 1.5 MW of neutral beam injection heating with a measured neutron count rate of a few 100 kHz.     

Further improvements in Mössbauer spectroscopy with lead loaded plastic scintillators

It is shown that the use of lead loaded plastic scintillators allows a reduction of a factor 7 of the measuring time in single pulse transmission Mössbauer spectroscopy.     

X-ray imaging with grazing-incidence microscopes developed for the LIL program

This article describes x-ray imaging with grazing-incidence microscopes, developed for the experimental program carried out on the Ligne d'Integration Laser (LIL) facility [J. P. Le Breton et al., Inertial Fusion Sciences and Applications 2001 (Elsevier, Paris, 2002), pp. 856-862] (24 kJ, UV-0.35 nm). The design includes a large target-to-microscope (400-700 mm) distance required by the x-ray ablation issues anticipated on the Laser MégaJoule facility [P. A. Holstein et al., Laser Part. Beams 17, 403 (1999)] (1.8 MJ) which is under construction. Two eight-image Kirkpatrick-Baez microscopes [P. Kirkpatrick and A. V. Baez J. Opt. Soc. Am. 38, 766 (1948)] with different spectral wavelength ranges and with a 400 mm source-to-mirror distance image the target on a custom-built framing camera (time resolution of approximately 80 ps). The soft x-ray version microscope is sensitive below 1 keV and its spatial resolution is better than 30 microm over a 2-mm-diam region. The hard x-ray version microscope has a 10 microm resolution over an 800-microm-diam region and is sensitive in the 1-5 keV energy range. Two other x-ray microscopes based on an association of toroidal/spherical surfaces (T/S microscopes) produce an image on a streak camera with a spatial resolution better than 30 microm over a 3 mm field of view in the direction of the camera slit. Both microscopes have been designed to have, respectively, a maximum sensitivity in the 0.1-1 and 1-5 keV energy range. We present the original design of these four microscopes and their test on a dc x-ray tube in the laboratory. The diagnostics were successfully used on LIL first experiments early in 2005. Results of soft x-ray imaging of a radiative jet during conical shaped laser interaction are shown.     

Calibration Procedures for X-ray Streak Cameras and Elements of X-ray Measuring Circuits

Setups developed for the calibration of X-ray streak cameras and of elements of X-ray measuring circuits are described. Calibration procedures are described and calibration results related to the absolute spectral sensitivity, spatial resolution, distortion, sensitivity nonuniformity over the screen, sweep speed and nonlinearity of an X-ray streak camera, as well as the results of the calibration of filters and mirrors used in recording laser-plasma X-rays are presented. The absolute-calibration error for the streak camera is within ±10%, and the calibration error for the filter and mirrors is within ±2%. Methods for processing photochronograms are described that, using the calibration data, allow the correction of distortions introduced by the streak camera.     

A method for measuring the energy spectrum of neutrons with energies of 1–15 MeV

The characteristics of the detector prototype for 1–15 MeV neutrons are described. The prototype is a full absorption detector consisting of interlaced plastic scintillators and ⁶Li doped glasses. A neutron incident on the detector deposits all its energy in the plastic scintillator, is moderated to thermal energies, and detected in the lithium glass. The measured time of complete neutron moderation is ～60 μs. Recording two signals in this time interval from the first event of neutron scattering in the plastic scintillator and from the neutron absorption by a lithium atom in the glass, it is possible to effectively suppress background thermal neutrons and γ rays and, therefore, detect low-intensity neutron sources. Owing to the proposed detector design, the direction toward the neutron source can be determined.     

Electro-optical multichannel spectrometer for transient resonance Raman and absorption spectroscopy

An optical multichannel system is described, used for time-dependent absorption measurements in the gas phase and the liquid phase and for resonance Raman spectroscopy of short-lived transient species in the liquid phase in pulse radiolysis. It consists of either an image converter streak unit or an image intensifier coupled to a TV camera with computerized data handling. The system enables the recording of time-dependent absorption spectra or resonance Raman spectra of short-lived radicals and excited states with single electron and light pulses.     

A tabletop femtosecond time-resolved soft x-ray transient absorption spectrometer

A laser-based, tabletop instrument is constructed to perform femtosecond soft x-ray transient absorption spectroscopy. Ultrashort soft x-ray pulses produced via high-order harmonic generation of the amplified output of a femtosecond Ti:sapphire laser system are used to probe atomic core-level transient absorptions in atoms and molecules. The results provide chemically specific, time-resolved dynamics with sub-50-fs time resolution. In this setup, high-order harmonics generated in a Ne-filled capillary waveguide are refocused by a gold-coated toroidal mirror into the sample gas cell, where the soft x-ray light intersects with an optical pump pulse. The transmitted high-order harmonics are spectrally dispersed with a homebuilt soft x-ray spectrometer, which consists of a gold-coated toroidal mirror, a uniform-line spaced plane grating, and a soft x-ray charge coupled device camera. The optical layout of the instrument, design of the soft x-ray spectrometer, and spatial and temporal characterizations of the high-order harmonics are described. Examples of static and time-resolved photoabsorption spectra collected on this apparatus are presented.     

A gated liquid-scintillator-based neutron detector for fast-ignitor experiments and down-scattered neutron measurements

The detection of neutrons in fast-ignitor experiments or down-scattered neutrons in inertial fusion experiments is very challenging since it requires the neutron detection system to recover within 10-100 ns from a high background orders of magnitude stronger than the signal of interest. The background is either the hard x-ray emission from short-pulse laser target interactions for the fast-ignitor experiments or the primary neutron signal for the down-scattered neutrons. A liquid-scintillator detector has been developed using a gated photomultiplier that suppresses the background signal and eliminates the afterglow present in conventional plastic scintillators.     

时间分辨光谱测量中时间加宽效应的研究

本文推导和讨论了两高斯脉冲的卷积以及高斯脉冲与单一负e指数相卷积时脉宽间“勾股定理”关系的正确性,并结合实验中具体数据,借助计算机讨论了用条纹相机测量时间分辨荧光光谱中的解卷积问题.     

Note: Non-gain microchannel plate gated framing camera

An x-ray framing camera using a non-gain microchannel plate (MCP) is reported in this article. The advantage of the non-gain MCP is the less transit time spread. The non-gain MCP gated framing camera has four microstrip line cathodes with 6 mm in width. The time domain reflectometry curves of the four microstrip lines are measured, which show that the characteristic impedance of each microstrip line is about 17 Ω. While the photocathode is driven by the gating electrical pulse with width of 125 ps and amplitude of -1.48 kV with -400 V bias, the measured exposure time of this camera is about 72 ps.     

Nearly on-line picosecond streak camera diagnostics of the cw mode-locked YAG laser radiation

An image-converter streak camera incorporating a TV video-recording system interfaced to a computer HP 2100 was used to record and instantly display the processed shape of a picosecond laser pulse. The output versus input exposure response curve linearity of the whole system was verified over a dynamic range of at least 10. Performance testing of the system was done using a cw mode-locked YAG laser.     

Properties of severely deformed CsI-based scintillators

The scintillation characteristics of CsI-based inorganic scintillators subjected to a severe plastic deformation were studied. Nanosecond decay times were observed in some samples of severely deformed scintillators. The mechanisms of variations in the characteristics of severely deformed scintillators upon relaxation of their internal stresses were investigated.