Proceedings Volume 5920

Ultrafast X-Ray Detectors, High-Speed Imaging, and Applications

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Proceedings Volume 5920

Ultrafast X-Ray Detectors, High-Speed Imaging, and Applications

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Volume Details

Date Published: 18 August 2005
Contents: 11 Sessions, 30 Papers, 0 Presentations
Conference: Optics and Photonics 2005 2005
Volume Number: 5920

Table of Contents

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Table of Contents

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  • Ultrafast Applications I
  • High-Harmonic Generation
  • Streak Camera I
  • Streak Camera II
  • Ultrafast Applications II
  • Streak Camera III
  • Laser Sources and Applications
  • X-ray Sources and Applications
  • High Speed Sensors and Systems
  • Fast Imaging Applications
  • Poster Session
Ultrafast Applications I
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Femtosecond electron and x-ray source based on laser wakefield accelerator
Dmitri A. Oulianov, Yuelin Li, Robert A. Crowell, et al.
A terawatt tabletop laser wakefield acceleration source of relativistic electrons has been developed in our Terawatt Ultrafast High Field Facility (TUHFF). The preliminary results for ultrafast radiolysis of liquid water using this femtosecond electron source are presented. A TUHFF based femtosecond x-ray source is proposed. Thomson scattering of the accelerated electrons off a counterpropagating terawatt laser beam will be used to generate keV x-ray photons. The expected parameters of this x-ray source have been estimated. The short pulse duration, high flux, and good collimation of the resulting x-ray beam would be conducive for ultrafast time-resolved x-ray absorption studies of short-lived transient species in gases, liquids, and solids. It is argued that the solvation dynamics of Br atoms generated in photoinduced electron detachment from aqueous bromide would make a convenient choice for the first pump-probe experiment using this x-ray source.
Experimental study of x-ray emission in laser-cluster interaction
T. Caillaud, F. Blasco, C. Bonte, et al.
Rare gas cluster jets are an intermediate medium between solid and gas targets. Laser-cluster jets interaction may generate a great number of energetic particles such as X-rays, UV, high harmonics, ions, electrons and neutrons. To understand all the mechanisms involved in this interaction we need to make a complete study of individual cluster response to an ultra-short laser pulse. We studied the laser interaction with our Argon cluster gas jet, which is well characterized in cluster size and density, to enlarge the knowledge of this interaction. We measured absorption, heating and X-ray emission spectra versus laser parameters and clusters size (~15-30 nm). We show that there is a strong refraction effect on laser propagation due to the residual gas density. This effect was confirmed by laser propagation simulation with a cylindrical 2D particle code WAKE. The role played by refraction was to limit maximum laser intensity on the focal spot and to increase interaction volume. By this way, X-ray emission was observed with laser intensity not so far from the ionization threshold (few 1014 W.cm-2). We also studied plasma expansion both at cluster scale and focal volume scale and deduced the deposited energy distribution as a function of time. Thanks to a simple hydrodynamic model, we used these results to study cluster expansion. X-ray emission is then simulated by TRANSPEC code in order to reproduce X-ray spectra and duration. Those results revealed an extremely brief X-ray emission consistent with a preliminary measure by streak camera (~ps).
Study of a soft x-ray (1-5 nm) laser plasma source for femtosecond time resolved XAS
S. Fourmaux, L. Lecherbourg, J. C. Kieffer, et al.
The dynamics of ultrafast phase transition and reaction mechanisms can be deduced from ultrafast x-ray diffraction or absorption measurements. Femtosecond lasers have been used recently to study matter dynamics with optical-pump and x-ray probe spectroscopy, using monochromatic K alpha x-ray radiation. We present here our most recent progress in the development of a femtosecond time- resolved x-ray absorption spectroscopy (XAS) system based on a broadband soft x-ray source in the 1-5 nm range. The femtosecond XAS system is designed to probe the electronic dynamics occurring during the vanadium dioxide (VO2) semiconductor to metal phase transition following excitation by a femtosecond laser pulse. In the present experiments, broadband spectra near the vanadium L edge (511 eV) and oxygen K edge (525 eV) of VO2 have been generated and measured with simultaneously high signal to noise ratio (100), high spectral resolution (ΔE/E=4x10-3) and a 1.2 ps temporal resolution.
High-Harmonic Generation
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Nonlinear multiphoton processes with soft x-ray photons and its application to autocorrelation measurement
Katsumi Midorikawa, Hirokazu Hasegawa, Yasuo Nabekawa
We have observed multi-photon ionization processes such as two-photon double ionization and above threshold ionization in He at 42 eV using intense soft X-ray pulses produced by high-order harmonics. Using the two-photon double ionization, the pulse width of the 27th (42 eV) harmonic was measured by an autocorrelation technique, and found it to be 8 ns. The high-intensity soft X-ray radiation achieved by phase-matched high-order harmonics enables the investigation of these nonlinear optical processes, which were beyond the reach of conventional light sources.
High-intensity high-order harmonic generation for attosecond autocorrelation measurements
T. Ozaki, H. C. Bandulet, S. Fourmaux, et al.
We demonstrate two methods of high-order harmonic generation, which has the potential of generating high-order harmonics with high intensities. The first method is solid surface harmonics. Using the second harmonic output of the 10 TW, 60 fs Ti:sapphire laser system at the INRS, we have observed multiple soft x-ray harmonics of the 397 nm pump laser. The highest order (23rd harmonic at 17.3 nm) observed in our experiments are limited by the 17 nm absorption edge of the thick 1.6 μm Al foil, which is used to eliminate the high intensity pump laser. The second method is harmonics from an ablation plume generated using a relatively low intensity prepulse. We demonstrate the generation of up to the 63rd harmonics (λ=12.6 nm) of a Ti:sapphire laser pulse (150 fs, 10 mJ), using pre-pulse (210 ps, 24 mJ) produced boron plasma as the nonlinear medium. The influence of various parameters on the harmonic conversion efficiency was analyzed. Typical conversion efficiencies were evaluated to be between 10-4 (for third harmonic) and 10-7 (within the plateau range).
Measuring attosecond pulses generated from polarization gating
Z. X. Zhao, Zenghu Chang, X. M. Tong, et al.
Angle-resolved photoelectron spectra of argon atoms by XUV attosecond pulses in the presence of a circularly polarized laser field are calculated to examine their dependence on the duration and the chirp of the attosecond pulses. From the calculated electron spectra, we show how to retrieve the duration and the chirp of the attosecond pulse using genetic algorithm. The method is expected to be used for characterizing the attosecond pulses which are produced by polarization gating of few-cycle left- and right-circularly polarized infrared laser pulses.
Streak Camera I
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A second-generation x-ray streak camera with true large format, high dynamic range, and high reliability
Ke-Xun Sun, William Nishimura, Theodore Perry, et al.
This paper will review the specifications, test and experiment performance features of Bechtel Nevada's Phase 2 X-ray Streak Camera (P2XSC). The P2XSC was developed to meet stringent inertial confinement fusion (ICF) and high energy density (HED) science requirements for experiments at Omega laser facility at Laboratory for Laser Energetics (LLE), and National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL). The paper reports recent progress in developing a large format, high dynamic range, and high-reliability Xray streak camera at Bechtel Nevada. We have designed, built, and tested an advanced X-ray camera. Bechtel Nevada's P2XSC substantially outperforms first generation streak cameras developed over a decade ago. Recent laboratory tests of P2XSC show that the channel dynamic range reaches 6000, the resolution reaches 50 micrometers at the photocathode (6~7 pixels at the image plane) at deep ultraviolet (UV) input wavelength, and 35 micrometers (4~5 pixels) at X-ray wavelength. The image resolution varies less than 30% across the photocathode. However, the 50 mm photocathode has a usable length of approximately 34 mm due to charge coupled device (CCD) camera limitations. The total number of resolution elements is approximately 900 in both spatial and temporal directions. The P2XSC is integrated into a compact airbox enclosure compatible with the ten-inch manipulator (TIM) specifications at LLE, Omega. The system is remotely controllable. The P2XSC system has been operated in the airbox for several thousands of shots for tests at Bechtel Nevada calibration facilities in Livermore and at the LLNL Janus laser facility. High-resolution data will be shown.
Streak Camera II
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An ultra-fast x-ray streak camera for the study of magnetization dynamics
J. Feng, W. Wan, J. Qiang, et al.
An ultrafast x-ray streak camera is under development at LBNL for application primarily to studies of ultrafast magnetization dynamics. In initial work, a temporal resolution of 900fs in accumulative mode at 5 KHz has been achieved. These results and methods currently being developed to improve the resolution and repetition rate are resented. One of the primary limits to temporal resolution is caused by the finite energy width of the electron distribution from the photocathode. The positive time of flight dispersion with energy in the accelerating region of the camera can be countered by introduction of downstream optics that give negative time of flight dispersion with energy, leading to an approximate overall cancellation of this temporal aberration. Initial results of an end-to-end simulation model using the full photoelectron distribution are presented.
Single-pulse measurement of synchrotron radiation using an ultrafast x-ray streak camera
We have demonstrated that a newly developed, ultrafast x-ray streak camera is sensitive to single x-ray pulses of highly monochromatic and unfocused synchrotron radiation at 8 keV. The high sensitivity was achieved by using CsI as the photocathode material. The individually measured x-ray pulses revealed that the bunch length was 120 ps long (full-width-at-half-maximum) and about 20-30 photon events were registered by streak camera in each pulse at the experimental conditions. The results demonstrated the feasibility of using this streak camera for single-shot experiments and using single x-ray pulses from the third-generation synchrotron sources with microfocused and/or polychromatic beams.
Ultrafast Applications II
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An x-ray autocorrelator and delay line for the VUV-FEL at TTF/DESY
Rolf Mitzner, Matthias Neeb, Tino Noll, et al.
In order to do jitter-free X-ray pump and probe experiments at the VUV-FEL at DESY / Hamburg (TTF2) as well as to characterize the temporal structure of its high power pulses an X-ray autocorrelator has been designed and is being engineered for photon energies up to 200 eV. The optomechanical design is based on geometrical beam splitting of the incomming FEL beam by a sharp mirror edge. Due to the limited reflection and the strong absorption of soft X-ray radiation an all-reflective geometry with grazing incidence angles at the mirrors has been chosen. The actual design represents a compromise between size and total delay range, on the one hand, and efficiency on the other hand. Thus the optomechanical device allows to handle high power X-ray pulses with high efficiency (50 %). The total delay is about 25 ps with a femtosecond resolution. A further advantage of the special autocorrelator design is the lack of any angle deviation of the outgoing beam direction. Thus the autocorrelator can be integrated permanently into one of the FEL beamlines and measurements can be done with or without the beam splitter by slighly moving the whole chamber without breaking the vacuum. First experiments are planned in 2006 utilizing two-photon photoemission from noble gases in order to measure the temporal width of the FEL pulses at 40 eV.
Visible/IR light and x-rays in femtosecond synchronism from an x-ray free-electron laser
A way is proposed to obtain pulses of visible/infrared light in femtosecond synchronism with x-rays from an x-ray free-electron laser (XFEL), using the recently proposed emittance-slicing technique. In an XFEL undulator, only the short section of an electron bunch whose emittance is left unchanged by the slicing will emit intense coherent x-rays in the XFEL undulator. At the same time, the bunch emits highly collimated transition undulator radiation (TUR) into a cone whose opening angle is the reciprocal relativisticity parameter gamma. Due to the variation of the transverse momentum induced by the emittance slicing, the effective number of charges contributing to the TUR varies along the bunch, and is higher in the sliced-out part that emits the coherent x-rays. As with coherent synchrotron radiation (CSR), the TUR is thus coherently enhanced (CTUR) at near-infrared wavelengths. Coming from the same part of the bunch the CTUR and the coherent x-rays are perfectly synchronized to each other. Because both types of radiation are generated in the long straight XFEL undulator, there are no dispersion effects that might induce a timing jitter. With typical XFEL parameters, the energy content of the single optical cycle of near-IR CTUR light is about 100 Nano-Joule, which is quite sufficient for most pump-probe experiments.
Tomographic imaging of electron orbital using high-harmonic generation
High harmonics produced in aligned molecules contain the structural information of the outermost electron orbital that preferentially ionizes in intense laser fields. We show a method to reconstruct a 3-dimensional (3D) structure of the molecular orbital. The method is based on the technologies to align molecules and to produce attosecond XUV pulses, both of which utilize intense ultrashort laser pulses. We measured a set of high harmonic spectra produced in differently aligned N2 molecules, and successfully reconstructed the image of the highest occupied molecular orbital (HOMO) with sub-angstrom resolution.
Streak Camera III
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The quantum efficiency and stability of UV and soft x-ray photocathodes
The sensitivity of many detection devices is established by the use photocathodes for the conversion of incoming photons into photoelectrons. The choice of photocathode material is determined by the spectral range where the sensitivity of the device is most important. Alkali halides are very efficient photocathodes in the ultraviolet and soft X-ray wavelength ranges and are widely used in many scientific applications. Although they are relatively stable under short exposure to atmosphere, which substantially simplifies production and handling of detection devices, it was found that their sensitivity can be substantially reduced by intense UV or X-ray irradiation (photocathode's ageing). A detailed study of alkali halide photocathodes efficiency and their ageing under intense UV and X-ray irradiation as well as some methods of increasing the stability are presented. The quantum efficiency of amorphous diamond films were shown to be slightly lower than the efficiency of some alkali halide films, but the chemical and mechanical stability and yet to be confirmed radiation hardness of diamond photocathodes make them very attractive for many UV and soft X-ray applications. Multialkalis and new materials such as GaN, AlGaN, GaAs could be used to extend the sensitivity to longer wavelengths, but require in situ processing in very high vacuum.
Laser Sources and Applications
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Motion picture of three-dimensional image of propagating femtosecond laser pulse
Yasuhiro Awatsuji, Kazunari Komai, Masatomo Yamagiwa, et al.
We propose a technique to record and observe a propagating ultrashort laser pulse as a form of motion picture of three-dimensional image. The technique is based on the light-in-flight recording by holography and it uses a weakly light-scattering three-dimensional medium to generate the three-dimensional image of the propagating laser pulse. In the reconstruction, we gaze the hologram illuminated with a continuous wave laser and move along the hologram, then the motion pictures can be seen. The motion pictures are continuous in terms of both time and space. The reconstruction speed of the motion pictures is determined by the speed of the moving. We constructed the light-scattering medium using gelatin jelly and conducted the experiment of the recording and reconstruction of the motion pictures of the ultrashort laser pulses propagating in three-dimensional space and conducted the experiment to record and to observe the motion picture. The motion pictures of the femtosecond laser pulse propagating in the gelatin jerry were observed as a form of three-dimensional images. We discuss the characteristics of the motion pictures acquired by the proposed technique.
High-speed shadowgraphy and interferometry using an acousto-optic laser deflector
Tetsuo Fukuchi, Koshichi Nemoto
An acousto-optic laser deflector was used to obtain shadowgraphs and laser interference fringe patterns at microsecond-order exposure times by blocking the undeflected light and exposing the imaging device to the deflected light. This method allows μ-order imaging using an ordinary CCD camera, and is less susceptible to damage resulting from incidence of high intensity light, which is a problem when using image intensifiers. Using this method, shadowgraphs and laser interference fringe patterns showing density changes accompanying spark discharges in air, pre-breakdown phenomena such as streamers and leaders, and laser-induced breakdown in air were obtained. In addition, by sequentially applying high frequency signals of different frequencies, the incident light was deflected to different regions of the CCD chip, which allowed time-resolved imaging of laser interference fringes.
Modular streak camera concept with independent design of electro-optical configuration and electronics
Patrick Summ, Bernd Reinke, Manuel Jung, et al.
Streak cameras are typically designed by a top-down concept. Top of the concept is the streak tube technology that is selected to obtain best measurement results for the application specific requirements. As streak tubes vary in physical dimensions and electrical characteristics, streak cameras are designed with different mechanical housings, tube polarisation electronics, sweep units and communication interfaces. This approach leads to a large number of individual and consequently expensive streak cameras. A new streak camera concept allows the integration of different streak tubes to offer more flexibility for specific application requirements but also general needs. The mechanical design provides interfaces for various sweep units, image intensifier units or electro-mechanical shutter devices. The concept supports a modular configuration using plug-in sweep units today only realised with standard streak cameras. Combined with standardised electrical interfaces, the streak camera can be configured for various applications without redesign. This additionally allows the adaptation to vacuum and other demanding environmental conditions.
X-ray Sources and Applications
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Preliminary study for producing higher harmonic hard x-rays from weakly ionized copper plasma
Eiichi Sato, Yasuomi Hayasi, Rudolf Germer, et al.
In the plasma flash x-ray generator, a 200 nF condenser is charged up to 50 kV by a power supply, and flash x-rays are produced by the discharging. The x-ray tube is a demountable triode with a trigger electrode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Target evaporation leads to the formation of weakly ionized linear plasma, consisting of copper ions and electrons, around the fine target, and intense Kα lines are left using a 10-μm-thick nickel filter. At a charging voltage of 50 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was about 16 kA. The K-series characteristic x-rays were clean and intense, and higher harmonic x-rays were observed. The x-ray pulse widths were approximately 300 ns, and the time-integrated x-ray intensity had a value of approximately 1.5 mGy per pulse at 1.0 m from the x-ray source with a charging voltage of 50 kV.
Energy-selective gadolinium angiography utilizing a stroboscopic x-ray generator
Eiichi Sato, Yasuomi Hayasi, Rudolf Germer, et al.
Energy-selective high-speed radiography utilizing a kilohertz-range stroboscopic x-ray generator and its application to high-speed angiography are described. This generator consists of the following major components: a main controller, a condenser unit with a Cockcroft-Walton circuit, and an x-ray tube unit in conjunction with a grid controller. The main condenser of about 500 nF in the unit is charged up to 120 kV by the circuit, and the electric charges in the condenser are discharged to the triode by the grid control circuit. Although the tube voltage decreased during the discharging for generating x-rays, the maximum value was equal to the initial charging voltage of the main condenser. The maximum tube current and the repetition rate were approximately 0.5 A and 50 kHz, respectively. The x-ray pulse width ranged from 0.01 to 1.0 ms, and the maximum shot number had a value of 32. At a charging voltage of 100 kV and a width of 1.0 ms, the x-ray intensity obtained using a 50-μm-thick tungsten filter was 9.88 μGy at 1.0 m, and the dimensions of the focal spot had values of approximately 1×1 mm. Angiography was performed using the filter at a charging voltage of 100 kV.
Superposition of x-ray spectra using a brass-target plasma triode
Haruo Obara, Eiichi Sato, Yasuomi Hayasi, et al.
In the plasma flash x-ray generator, a 200 nF condenser is charged up to 50 kV by a power supply, and flash x-rays are produced by the discharging. The x-ray tube is a demountable triode with a brass target containing 65% copper and 35% zinc by weight, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Target evaporation leads to the formation of weakly ionized linear plasma, consisting of metal ions and electrons, around the fine target, and intense characteristic x-rays are produced. At a charging voltage of 50 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was about 15 kA. When the charging voltage was increased, the linear plasma formed, and the K-series characteristic x-ray intensities of zinc Kα, copper Kα, and copper Kβ lines increased substantially. However hardly any zinc Kβ lines were detected. The x-ray pulse widths were approximately 700 ns, and the time-integrated x-ray intensity was approximately 1.2 mGy at 1.0 m from the x-ray source with a charging voltage of 50 kV.
High Speed Sensors and Systems
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High speed holographic cine-recorder
Donald Snyder, David Watts, Joseph Gordon, et al.
Air Force Research Laboratory and North Dancer Labs researchers have completed the initial development and transition to operational use of a high-speed holographic movie system. This paper documents the first fully operational use of a novel and unique experimental capability for high-speed holographic movies and high-speed cinema interferometry. In this paper we document the initial experiments that were performed with the High Speed Holographic Recorder (HSHR) at the Munitions Directorate, Air Force Research Laboratory Site at Eglin, AFB, Florida. These experiments were performed to assess the possibilities for high-speed cine-laser holography combined with high-speed videography to document the formation and propagation of plumes of materials created by impact of high-speed projectiles. This paper details the development of the experimental procedures and initial results of this new tool. After successful integration and testing the system was delivered to Arnold Engineering Development Center.
High-speed camera with internal real-time image processing
High-speed video cameras are powerful tools for investigating for instance the dynamics of fluids or the movements of mechanical parts in manufacturing processes. In the past years, the use of CMOS sensors instead of CCDs have made possible the development of high-speed video cameras offering digital outputs, readout flexibility and lower manufacturing costs. In this field, we designed a new fast CMOS camera with a 1280×1024 pixels resolution at 500 fps. In order to transmit from the camera only useful information from the fast images, we studied some specific algorithms like edge detection, wavelet analysis, image compression and object tracking. These image processing algorithms have been implemented into a FPGA embedded inside the camera. This FPGA technology allows us to process fast images in real time.
Temporally-resolved area-imaged velocimeter system for dynamic materials experiments
Thomas E. Tierney IV, Damian C. Swift, Billy N. Vigil, et al.
Shocks extending across crystals' grain boundaries can nucleate and grow velocity fluctuations on the order of 5-10% when the shock speeds differ in the adjacent grains. Dynamic materials experiments at the Los Alamos National Laboratory Trident Laser Laboratory aim to examine this phenomenon by temporally- and spatially-resolving free surface velocity over a large region of interest. While line-imaged velocimetry can serve as a quantitative method for examining the velocity fluctuations across a single boundary, it is more desirable to resolve the velocity field around an entire embedded grain. We present a novel diagnostic design that utilizes a four-frame gated-optical-imaging interferometric velocimeter in combination with a streaked line-imaging interferometric velocimeter. This diagnostic will provide high-spatial resolution velocigraphs of a shock as it hits a free surface in multigrain crystals.
Conception of a high-speed digital color imaging device
High-speed color digital imaging devices are desired for many applications, including civilian and military missions. To capture color images a color sensor has to divide the incidence light into three spectral bands: blue, green and red. Due to the limitation of the spectral bandwidth, the speed of a color digital sensor is significant slower than that of a black and white sensor covering the entire visible bandwidth or the entire bandwidth from visible to near infrared. This paper introduces the conception of a high-speed color imaging device which can significantly increase the imaging speed without losing image resolution and other image qualities. This device uses the concept of black and white imaging to increase the imaging speed while keeping the image resolution unchanged. It also uses the concept of color imaging to capture color information, but at a significantly lower resolution to allow more incidence light being received by each sensor detector (pixel) to increase the imaging speed. The final color image at the desired resolution is recovered by integrating the spatial information from the black and white image and the color information from the low-resolution color image. An automatic image fusion technique is used to integrate the spatial information and the color information. The quality of the image fusion technique plays a crucial role for quality of the recovered color image. The concept of this high-speed color imaging device has been tested with available low-resolution color images and high-resolution black and white images from the latest commercial satellites, Ikonos and QuickBird. The test results demonstrated that the concept of the high-speed digital color imaging device is promising for producing real high-speed color digital devices for practical applications.
Evaluation and comparison of three IR detectors and three amplifier designs for a new high-speed IR pyrometer
J. A. Young, S. Borror, A. W. Obst, et al.
At Los Alamos National Laboratory (LANL), a high-speed, four-wavelength, infrared (IR) pyrometer has been used for surface temperature measurements in shock-physics experiments for several years. The pyrometer uses solid-state detectors and a single fiber-optic cable for transmission of light from the target surface to the detectors. This instrument has recently been redesigned for an upcoming experiment at the Nevada Test Site (NTS). Three different IR detectors (two HgCdTe variants as well as the existing InSb chip) were compared for sensitivity, signal-to-noise ratio, and bandwidth. Of major concern was detector amplifier recovery time from overload saturation. In shock-physics experiments, a short but very bright precursor frequently accompanies shock breakout (often from trapped air). This precursor can saturate the amplifier and may "swamp-out" the signal of interest before the amplifier recovers. With this in mind, we evaluated two new amplifier designs by the Perry Amplifier Company for linearity, signal-to-noise characteristics, gain, and saturation recovery time. This paper describes experimental setup for detector comparison and results obtained. Furthermore, we discuss new amplifier design and suitability for high-speed infrared pyrometry in shock physics experiments.
Fast Imaging Applications
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Enhanced K-edge plasma angiography achieved with tungsten Kα rays utilizing gadolinium-based contrast media
Eiichi Sato, Yasuomi Hayasi, Rudolf Germer, et al.
The tungsten plasma flash x-ray generator is useful in order to perform high-speed enhanced K-edge angiography using cone beams because Kα rays from the tungsten target are absorbed effectively by gadolinium-based contrast media. In the flash x-ray generator, a 150 nF condenser is charged up to 80 kV by a power supply, and flash x-rays are produced by the discharging. The x-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Since the electric circuit of the high-voltage pulse generator employs a cable transmission line, the high-voltage pulse generator produces twice the potential of the condenser charging voltage. At a charging voltage of 80 kV, the estimated maximum tube voltage and current were approximately 160 kV and 40 kA, respectively. When the charging voltage was increased, the characteristic x-ray intensities of tungsten Kα lines increased. Using an ytterbium oxide filter, the Kα lines were clean, and hardly any Kβ lines and bremsstrahlung rays were detected. The x-ray pulse widths were approximately 60 ns, and the time-integrated x-ray intensity had a value of approximately 50 μGy at 1.0 m from the x-ray source with a charging voltage of 80 kV. Angiography was performed using a film-less computed radiography system and gadolinium-based contrast media. In angiography of non-living animals, we observed fine blood vessels of approximately 100 μm with high contrasts.
Fast optical recording of light-flash evoked neural activation in amphibian retina
Xin-Cheng Yao, John S. George
Imaging of fast intrinsic optical responses closely associated with neural activation promises important technical advantages over traditional single and multi-channel electrophysiological techniques for dynamic measurements of visual processing and early detection of eye diseases. We have developed a fast, no-moving-parts optical coherence tomography (OCT), system based on an electro-optic phase modulator, and used it to record dynamic near infrared (NIR) light scattering changes in frog retina activated by a visible light-flash. We also employed transmitted light for highly sensitive measurement and imaging of neural activation, and to optimize illumination and optical configuration. Using a photodiode detector, we routinely measured dynamic NIR transmitted optical responses in single passes. When the whole retina was illuminated by a visible light-flash, a positive peak was typically observed in transmitted light measurements. CCD image sequences disclosed larger fractional responses, in some cases exceeding 0.5% in individual pixels, and showed evidence of multiple response components with both negative- and positive-going signals with different timescales and complex but consistent spatial organization. The fast negative-going signals are highly correlated with the a-wave of the electrophysiological signals, and may reflect the activation of photoreceptors. The fast positive-going responses are related to the b-wave of the electrophysiological signals, and may result from the activation of ON bipolar cells. Slow optical responses may signal metabolic changes of retinal tissue. Our experimental results and theoretical analysis suggest that the optical responses may result from dynamic volume changes associated with neural activation, corresponding to ion and water flow across the cell membrane.
Experimental validation of advanced explosive/metal interactions
The extremely high power density stored in explosives drives their selection of use in military, mining, demolition, cladding, shock consolidation of powders, shock-induced chemical synthesis and magnetic flux compression processes. The use of distributed initiation locations has emerged as a primary method to customize the detonation front and create desirable output. Explosive/metal systems with multiple, distributed initiation locations create detonation states that do not follow the simple line of sight, or Huygens model and, hence, advanced detonation physics with associated theory are required. The theory of detonation shock dynamics (DSD) is one such description used to provide high fidelity modeling of complex wave structures. A collection of experiments using simultaneous ultra-high speed digital framing and streak film cameras is presented as a means of obtaining spatial and temporal characteristics of complex detonation fronts that validate the DSD descriptions. The method of test, operational conditions and results are given to demonstrate the use of high rate imaging of detonation events and how this validates our understanding of the physics and the capability of advanced detonation wave tracking models.
Calibration of the CCD photonic measuring system for railway inspection
D. V. Popov, R. B. Ryabichenko, E. A. Krivosheina
Increasing of traffic speed is the most important task in Moscow Metro. Requirements for traffic safety grow up simultaneously with the speed increasing. Currently for track inspection in Moscow Metro is used track measurement car has built in 1954. The main drawbacks of this system are absence of automated data processing and low accuracy. Non-contact photonic measurement system (KSIR) is developed for solving this problem. New track inspection car will be built in several months. This car will use two different track inspection systems and car locating subsystem based on track circuit counting. The KSIR consists of four subsystems: rail wear, height and track gauge measurement (BFSM); rail slump measurement (FIP); contact rail measurement (FKR); speed, level and car locating (USI). Currently new subsystem for wheel flange wear (IRK) is developed. The KSIR carry out measurements in real-time mode. The BFSM subsystem contains 4 matrix CCD cameras and 4 infrared stripe illuminators. The FIP subsystem contains 4 line CCD cameras and 4 spot illuminators. The FKR subsystem contains 2 matrix CCD cameras and 2 stripe illuminators. The IRK subsystem contains 2 CCD cameras and 2 stripe illuminators. Each system calibration was carried out for their adjustment. On the first step KSIR obtains data from photonic sensors which is valued in internal measurement units. Due to the calibration on the second step non-contact system converts the data to metric measurement system.
Poster Session
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Characterization laboratories for LIL and LMJ ultrafast detectors
T. Caillaud, S. Hubert, M. Mangeant, et al.
Streak cameras and framing cameras used for studying single shot laser created plasmas at LIL and soon at LMJ need to be regularly controlled to assure a good operating system. This poster presents the laboratories that have been set up at CEA-CESTA to overcome this task. To cover the entire spectral domain required, many sources have been designed. First, AZUR laboratory is supposed to deliver three measurements ways equipped with laser sources for static and dynamic visible detectors control. Second, CADENCE laboratory is ought to test temporal resolution in UV domain by delivering laser ps pulse train. X-ray cameras are then calibrated by replacing CsI photocathodes with Pd photocathodes sensitive in UV. Finally, STATIX laboratory aims at controlling X-ray streak and framing cameras in static regime with several continuous X-ray sources. Properties as linearity, homogeneity, sensitivity and temporal response are going to be measured to guaranty diagnostics performances on LIL plasma physics shots.
Ultrafast magnetization dynamics studies using an x-ray streak camera
A. F. Bartelt, A. Comin, J. Feng, et al.
The spin dynamics of ferromagnetic thin films following an excitation by ultrashort 100-fs near-infrared laser pulses has recently received much attention. Here, a new approach is described using x-ray magnetic circular dichroism to investigate demagnetization and magnetization switching processes. In contrast to magneto-optical measurements, x-ray dichroism has the advantage of determining separately the spin and orbital components of the magnetic moment. The relatively low time resolution of the synchrotron x-ray probe pulses (80 ps FWHM) is overcome by employing an ultrafast x-ray streak camera with a time resolution of < 1 ps. A description of the experimental setup including the x-ray/IR laser pulse synchronization and the streak camera is given.