Soft X-ray Streak Camera Research Articles

Theoretical calculation of response sensitivity of CsI photocathode of soft X-ray streak camera

The response sensitivity of CsI photocathode is an important parameter for the quantitative diagnosis of X-ray spectroscopy by soft X-ray streak camera, and its theoretical calculation has important guiding significance. The current theoretical analytical models are based on the one-dimensional random walking model of secondary electrons generated by thin film photocathodes, including the Henke model under the condition of normal incidence of X-rays and energy greater than 1 keV, and the Fraser model under variable angle incidence and photocathode thickness greater than 100 nm, which have certain limitations. In this paper, the basic expression of the probability of secondary electron transmission is introduced, and the general expression of the response sensitivity of CsI photocathode is deduced, which varies with X-ray energy <i>E</i>, photocathode thickness <i>t</i>, and angle <i>θ</i> between X-ray and cathode surface in a larger parameter range (X-ray energy 0.1–10 keV, photocathode thickness 10–200 nm). Finally, the theoretical calculation results of this paper are discussed by comparing it with those from the Henke model, Fraser model, literature data and experimental data on Beijing synchrotron radiation facility, which verifies the accuracy and universality of the computational model, and a theoretical reference is provided for optimally designing the CsI photocathode in high-time-resolution spectrometric quantitative measurement.

A scintillator-based soft X-ray streak camera system for Z-pinch experiments on the Primary Test Stand.

A soft x-ray streak camera system based on the conversion of fast scintillator has been developed to diagnose 10-MA Z-pinch implosions on the Primary Test Stand facility. The streak camera system is used to measure the continuous time history of the 0.2-10 keV x-ray emission from pinch plasmas and proved to be free from the intense electromagnetic environment effectively during the discharge of the Primary Test Stand. The spatial resolution of the streak camera system is estimated to be less than 120 μm, and its temporal resolution has been calibrated to be about 1 ns. X-ray streak images of aluminum wire-array plasmas have been obtained successfully in experiments, and the nonuniformity of the x-ray emission along the axial direction has been observed.

Large dynamic soft X-ray streak camera for ICF applications

Large dynamic soft X-ray streak camera for ICF applications

A new method to calibrate the absolute sensitivity of a soft X-ray streak camera.

In this paper, we introduce a new method to calibrate the absolute sensitivity of a soft X-ray streak camera (SXRSC). The calibrations are done in the static mode by using a small laser-produced X-ray source. A calibrated X-ray CCD is used as a secondary standard detector to monitor the X-ray source intensity. In addition, two sets of holographic flat-field grating spectrometers are chosen as the spectral discrimination systems of the SXRSC and the X-ray CCD. The absolute sensitivity of the SXRSC is obtained by comparing the signal counts of the SXRSC to the output counts of the X-ray CCD. Results show that the calibrated spectrum covers the range from 200 eV to 1040 eV. The change of the absolute sensitivity in the vicinity of the K-edge of the carbon can also be clearly seen. The experimental values agree with the calculated values to within 29% error. Compared with previous calibration methods, the proposed method has several advantages: a wide spectral range, high accuracy, and simple data processing. Our calibration results can be used to make quantitative X-ray flux measurements in laser fusion research.

Time-Resolved Soft X-Ray Imaging of Femtosecond Laser Ablation Processes on Metals

Femtosecond laser ablation processes on platinum, gold, and tungsten were observed by the single shot pump and probe reflective imaging using a soft x-ray laser probe. To avoid the timing error due to the jitter, we adopted a posteriori correction technique by simultaneous measurement of timing between the pump and probe pulses for every single shot, using a soft x-ray streak camera. A clear difference was found in the temporal behavior of the dynamical response of the soft x-ray reflectivity depending on the irradiated laser fluence in these three materials. On the other hand, the narrow dark rings were found in Pt and W, while an additional bright ring was found outside the dark disk in Au. Our result gives the experimental data comparable with various numerical simulations.

软X射线条纹相机光阴极能谱响应灵敏度

软X射线条纹相机光阴极能谱响应灵敏度

Studies of intense-laser plasma instabilities

The PALS high power iodine laser system in Prague (λ=1.315μm) was used to study non-linear processes in a laser-produced plasma at intense laser beam interactions with planar targets. The focus setting allows to alter the non-linear interaction of the main laser pulse with the ablated plasma produced by the front edge of a nanosecond laser pulse (300ps FWHM). The arisen non-linear effects significantly influence the behavior of electrons, which accelerate fully striped or highly charged fast ions. Variations in time of the expanding plasma, recorded at the target surface by the use of Kentech low-magnification soft X-ray streak camera on ∼2ns time scale, are presented and discussed. Narrowing, arching and even splitting of expansion paths in the target-normal space-time diagram are shown. These phenomena are ascribed to the magnetic field, self-generated at high laser intensities, which may become strong enough to cause pinching of the expanding plasma.

Spectral response calibration of Au and CsI transmission photocathodes of X-ray streak camera in a 605500 eV photon energy region

A method is described of measuring absolute spectral response for Au and CsI transmission photocathodes in soft X-ray streak camera, which is of great importance for the inertial confinement fusion (ICF) diagnostics. Transmission photocathode is conventionally employed as photo-to-electron conversion accessories. To derive quantity information of X-ray spectra, the absolute response of photocathode must be calibrated in a range of interest. Here Au and CsI transmission photocathodes with slits are calibrated respectively on Beijing Synchrotron Radiation Facility (BSRF), in a photon energy range of 60 eV5500 eV. This method has an uncertainty less than 10% and good feasibility. Calibration results are in good agreement with the calculation results obtained from the Henke's photon emission model, with CH substrate effect revised.

Intensity correlation measurement system by picosecond single shot soft x-ray laser

We developed a new soft x-ray speckle intensity correlation spectroscopy system by use of a single shot high brilliant plasma soft x-ray laser. The plasma soft x-ray laser is characterized by several picoseconds in pulse width, more than 90% special coherence, and 10(11) soft x-ray photons within a single pulse. We developed a Michelson type delay pulse generator using a soft x-ray beam splitter to measure the intensity correlation of x-ray speckles from materials and succeeded in generating double coherent x-ray pulses with picosecond delay times. Moreover, we employed a high-speed soft x-ray streak camera for the picosecond time-resolved measurement of x-ray speckles caused by double coherent x-ray pulse illumination. We performed the x-ray speckle intensity correlation measurements for probing the relaxation phenomena of polarizations in polarization clusters in the paraelectric phase of the ferroelectric material BaTiO(3) near its Curie temperature and verified its performance.

Grazing-incidence mirror streak camera diagnostic for emission measurements of imploding z pinches on the Sandia Z-machine

A soft x-ray (0.1–1 keV) streak camera using a grazing-incidence mirror has been developed for the Sandia Z facility, a 20 MA, 100 ns rise-time accelerator that can generate >200 TW,2 MJ, x-ray pulses. The streak camera is used to measure with one dimension of spatial resolution the continuous time history of sub-kilo-electron-volts emission from z-pinch and radiation flow experiments. Radiation >1 keV is eliminated by the use of a grazing-incidence mirror and transmission filters. The diagnostic has a magnification of 1.22, a 20 mm field-of-view and a spatial resolution of ∼350 μm. The recording length of the instrument is variable in duration up to a maximum of 33 ns, making it well suited for the typical 100 ns Z pinch implosion times. The spatial resolution can readily be changed to be along either the axial or the radial direction.

Absolutely calibrated, time-resolved measurements of soft x rays using transmission grating spectrometers at the Nike Laser Facility

Accurate simulation of pellet implosions for direct drive inertial confinement fusion requires benchmarking the codes with experimental data. The Naval Research Laboratory (NRL) has begun to measure the absolute intensity of radiation from laser irradiated targets to provide critical information for the radiatively preheated pellet designs developed by the Nike laser group. Two main diagnostics for this effort are two spectrometers incorporating three detection systems. While both spectrometers use 2500 lines/mm transmission gratings, one instrument is coupled to a soft x-ray streak camera and the other is coupled to both an absolutely calibrated Si photodiode array and a charge coupled device (CCD) camera. Absolute calibration of spectrometer components has been undertaken at the National Synchrotron Light Source at Brookhaven National Laboratories. Currently, the system has been used to measure the spatially integrated soft x-ray flux as a function of target material, laser power, and laser spot size. A comparison between measured and calculated flux for Au and CH targets shows reasonable agreement to one-dimensional modeling for two laser power densities.

Effects of self-generated magnetic fields and nonlocal electron transport in laser produced plasmas

Experiments using planar gold targets were performed at the Phebus facility [G. Thiell, Laser Part. Beams 16, 253 (1998)] in order to characterize the deposition of laser energy. These experiments have been simulated with a two-dimensional radiation-hydrodynamic code. Using flux limited Spitzer–Härm transport [L. Spitzer and R. Härm, Phys. Rev. 89, 977 (1953)], no agreement was obtained between simulations and experiments. Soft x-ray streak camera and two-dimensional time-resolved radiography data cannot be reproduced. For the first time, self-generated magnetic fields and nonlocal heat fluxes have been taken into account in a two-dimensional code. Both effects are simultaneously computed. The artificially limited Spitzer–Härm fluxes are not needed anymore with this treatment of the heat conduction. The simulations obtained with the latter are in good agreement with all the experimental results. Based on the numerical results, effects of the magnetic fields and nonlocal fluxes on electron temperature and x-ray conversion of the plasma are also presented.

A transmission grating spectrograph and its application in both laser plasma and plasma focus

A new transmission grating spectrograph for soft x-ray measurement in pulsed plasmas was designed and studied. The spectrograph has an adjustment system with three degrees of freedom, together with an electronic-controlled camera. This design makes it easy to align and use for laser-produced plasmas or the plasma focus. The spectrograph provides spatially resolved spectrum in two dimensions and has a wavelength range of 0.3–30 nm. A transmission grating was used to obtain spatially resolved spectra from plasmas produced by laser-irradiated solid target and gas filled plasma focus. Such a spectrograph is suitable for coupling with a soft x-ray streak camera or a soft x-ray charge coupled device detector for time-resolved studies.

Calibrated Time-Resolved Transmission Grating Spectrometer for the Study of Ultrafast X-Ray Sources

A transmission grating spectrometer has been coupled to a high-temporal-resolution soft x-ray streak camera for the study of picosecond laser-plasma x-ray sources. A procedure to deconvolve the overlapping contributions of diffraction orders and to calibrate the instrument has been established in order to obtain absolute time-resolved x-ray emission spectra in the 0.1–1.2 keV spectral region. The deconvolution and calibration techniques are presented along with measurements establishing the temporal resolution of this diagnostic at ∼2 ps. Examples of calibrated spectra of laser-plasma x-ray sources created by 400 fs laser pulses at intensities of 1018W/cm2are also shown.

Calibrated Time-Resolved Transmission Grating Spectrometer for the Study of Ultrafast X-Ray Sources

A transmission grating spectrometer has been coupled to a high-temporal-resolution soft x-ray streak camera for the study of picosecond laser-plasma x-ray sources. A procedure to deconvolve the overlapping contributions of diffraction orders and to calibrate the instrument has been established in order to obtain absolute time-resolved x-ray emission spectra in the 0.1-1.2 keV spectral region. The deconvolution and calibration techniques are presented along with measurements establishing the temporal resolution of this diagnostic at ~2 ps. Examples of calibrated spectra of laser-plasma x-ray sources created by 400 fs laser pulses at intensities of 1018 W/cm2 are also shown.

EXPERIMENTAL INVESTIGATION OF RADIATION TEMPERATURE IN HOHLRAUMS

Radiation temperature in hohlraums is diagnosed using two soft X-ray spectrometers and multi-pinhole soft X-ray streak camera. We have improved the accuracy taking plasma closure effects of the diagnostic hole into consideration. We have obtained 2D-images and processes of the hole closure and radiation temperature in the hohlraums νs time. A preliminary model of the closure effect of diagnostic hole is proposed based on the experimental data.

Time and space resolved studies of recombination x-ray lasers

A novel experimental technique of time- and space-resolved X-ray diagnostics has been developed by coupling a stigmatic flatfield grating spectrometer to a soft X-ray streak camera to study the dynamics of recombination X-ray lasers. Time and space characteristics of Li-like Si X-ray lasers have been investigated and some interesting results have been obtained. Preliminary results with CaF 2 target are given.

Angular distribution of plasma ablation in laser-irradiated cylindrical cavities

Cylindrical cavities of 300 μm diameter were transversely irradiated by 80 ps/1.05 μm laser pulses directed through a longitudinal slit. Off-center irradiation was used to reduce reflection losses. Time-resolved spatial information was obtained by pinhole imaging onto a soft X-ray streak camera. Plasma ablation is shown to coincide with the locations of (multiple) reflections of laser light inside the cavity obtained from ray tracing calculations.

RADIATION TEMPERATURE OF LASER-PLASMAS EXPERI-MENTAL INVESTIGATION

A method bas been developed for measuring radiation temperatures using a set of absorption-foils coupled to a soft X-ray streak camera in laser plasme experiments. A result has been given for a planar gold target irrdiatcd by laser (λ = 1.053μm) pulses of about 360ps in duration with average intensities of about 1014W/cm2 from the LF-11# Nd: glass laser facility. In addition, applications to measuring time-resolved spectra and space-resolved temperature are discussed.

EXPANSION PROCESSES OF LASER-HEATED PLASMAS ON CARBON AND GOLD PLANAR TARGET

Space-time resolved X-ray photograms of carbon (4671? thick with substrate) and gold (15μm in thickness) planar targets were obtained using a pinhole coupled to a soft X-ray streak camera. The planar targets were irradiated with laser (λ = 1.06 μm) pulses of about 100 ps duration from a LF-12 Nd: glass laser. The spectral response of the soft X-ray camera is defined to be 0.1-10 keV. Average plasma expansion velocities on the C and Au traget surface measured at a laser power density of about 1014 w/cm2 for were 5.l×107cm/s and 6.1×107 cm/s respectively.