We discuss the use of the thin film compression (TFC) technique for generating an ultrafast X-ray beam having a few femtoseconds in duration which could be appropriate for pump and probe experiment. Our results demonstrate the potential of the technique for the generation of a few fs hard X-ray beam through the LWFA-based betatron process, enabling an extraordinary short X-ray probe for doing time resolved X-ray absorption spectroscopy of ultra-relativistic plasmas.
We present the recent progress done at the Advanced Laser Light Source (ALLS) on the development of a Laser Wakefield Acceleration (LWFA) based X-ray machine. We will describe the pathway we follow to progress towards an industrial solution guided by the concept of Solution Readiness Level (SRL) metric. Two different approaches have been recently studied and assessed to optimize the X-ray beam in the 20keV - 50keV range. This paves the way to the development of a laser-based X-ray machine addressing, with different working points, various strategic challenges. We discuss in the present work the usefulness of the various operational approaches for some aspects of Global Food Security and for the realization of mammography with dose well below the actual clinical standard.
We review the results obtained with the INRS laser system on the scaling of X-ray sources based on laser wake-field acceleration (LWFA) of electrons. We have successfully generated stable propagation in gas jets of a relativistic pulse through self-guiding on length well larger than the classical LWFA dephasing and depletion lengths, generating very intense beams of hard X-rays with 200TW on target. Our experimental scaling law obtained for the photon yield is presented and the level of X-ray emission in a 30keV-40keV band at the 1PW laser peak power level, now available at several laser facilities, is estimated.
Compact optical sources of radiation with high average power are needed for many applications from sensing to imaging and spectroscopy. The control of non-linear effects during the propagation of intense ultra-short laser pulses in various gas allows the generation of novel very intense radiation beams which can be used for sensing and imaging. We discussed non-linear effects during ultrafast laser beam propagation in two very different interaction regimes, long distance propagation in ambient air and short distance propagation at very high intensity and in high density gas, obtained with high peak and high average power laser systems.
We describe our system for generating intense beams of hard X-rays optimized for high throughput phase contrast plant imaging and rapid identification of phenotype in a plant production setting. High peak and average power X-ray beams are generated in a novel regime of ultra-relativistic self-guiding. X-ray beams at 40keV with 4μJ per pulse (30keV – 40keV band) and an average power of 10μW (30keV – 40keV band) are currently produced and used to demonstrate the potential of the LWFA based X-ray sources.
We present the development of a high throughput phase contrast screening system based on LWFA Xray
sources for plant imaging. We upgraded the INRS laser-betatron beam line and we illustrate its
imaging potential through the innovative development of new tools for addressing issues relevant to
global food security. This initiative, led by the Global Institute of Food Security (GIFS) at the U of
Saskatchewan, aims to elucidate that part of the function that maps environmental inputs onto specific
plant phenotypes. The prospect of correlating phenotypic expression with adaptation to environmental
stresses will provide researchers with a new tool to assess breeding programs for crops meant to thrive
under the climate extremes.
We are developing ultrahigh spatial resolution (FWHM < 2 μm) high-brilliance x-ray source for rapid in vivo tomographic microvasculature imaging micro-CT angiography (μCTA) in small animal models using optimized contrast agent. It exploits Laser Wakefield Accelerator (LWFA) betatron x-ray emission phenomenon. Ultrashort high-intensity laser pulse interacting with a supersonic gas jet produces an ion cavity (“bubble”) in the plasma in the wake of the laser pulse. Electrons that are injected into this bubble gain energy, perform wiggler-like oscillations and generate burst of incoherent x-rays with characteristic duration time comparable to the laser pulse duration, continuous synchrotron-like spectral distribution that might extend to hundreds keV, very high brilliance, very small focal spot and highly directional emission in the cone-beam geometry. Such LWFA betatron x-ray source created in our lab produced 1021 –1023 photons⋅ shot-1⋅mrad-2⋅mm-2/0.1%bw with mean critical energy in the12–30 keV range. X-ray source size for a single laser shot was FWHM=1.7 μm; x-ray beam divergence 20–30 mrad, and effective focal spot size for multiple shots FWHM= ~2 μm. Projection images of simple phantoms and complex biological objects including insects and mice were obtained in single laser shots. We conclude that ultrahigh spatial resolution μCTA (FWHM ~2 μm) requiring thousands of projection images could be accomplished using LWFA betatron x-ray radiation in approximately 40 s with our existing 220 TW laser and sub seconds with next generation of ultrafast lasers and x-ray detectors, as opposed to several hours required using conventional microfocal x-ray tubes. Thus, sub second ultrahigh resolution in vivo microtomographic microvasculature imaging (in both absorption and phase contrast mode) in small animal models of cancer and vascular diseases will be feasible with LWFA betatron x-ray source.
This paper reviews recent progresses in ultrafast laser-based X-ray sources and their potential applications to high throughput X-ray imaging. Prospects for the utilization of X-rays sources related to the Laser Wakefield electron Acceleration (LWFA) are more specifically discussed with emphasis on application in diagnostic radiology.
The 200TW ALLS laser system (30 fs, 5J) is used to accelerate electrons through laser wakefield and generate betatron emission in the 10keV range. Single shot phase contrast images of a series of nylon fibers with diameter ranging from 10μm to 400μm have been obtained in different geometries and are interpreted with a comprehensive model of x-ray propagation integrating the properties and geometries of the imaging beam line. A simple figure of merit, which can give indication on the interface sharpness of a phase object, is used to assess the quality of the imaging beam line.
This paper discusses some aspect of the experimental effort in high field science (up to 1022 W/cm2) done with the high peak power (>200TW) laser system at the Advanced Laser Light Source facility (ALLS). A maximum intensity of 1022 W/cm2 has been achieved on target. The present experiments explore the acceleration of electrons directly by the laser field (DLFA) in the transition between the relativistic and ultra-relatisitic regimes. Electrons are accelerated to multi-MeV energies using radially (TM01) and azimuthally (TE01) polarized modes and the contribution of various acceleration processes is briefly discussed.
High intensity femtosecond laser pulses can be used to generate X-ray radiation. In the laser wakefield process, when a
high intensity laser pulse (<1018 W/cm2) is focused onto a gas jet target, it interacts with the instantaneously created under-dense plasma and excites a wakefield wave. In the wakefield electrons are trapped and accelerated to high energies in short distances. The electrons trapped in the wakefield can perform Betatron oscillations across the
propagation axis and emit X-ray photons. The Betatron X-ray beam is broadband as the radiation emission has a
synchrotron distribution. The X-ray beam is collimated and its pulse duration is femtosecond. For high resolution and
phase contrast X-ray imaging applications, the important feature of the X-ray Betatron beam is the μm source size.
Using ALLS 100 TW class laser system we demonstrate that the Betatron X-ray beam is both energetic and bright
enough to produce single laser shot phase contrast imaging of complex objects located in air.
The 200TW laser system, (Ti:Sapphire CPA system) delivering 5J in 25fs pulse with a 10Hz repetition rate and a contrast ratio of 1:10^-11 at the fundamental 800nm frequency, is used at the Advanced Laser Light Source (ALLS) facility to develop new generation of x-ray and pulsed particle beam sources (electrons, protons, neutrons). Experimental results on the betatron emission and electron emission from high intensity (<10^19 W/cm2) interactions with gas jet targets (1cm long supersonic nozzle) and on proton generation during high intensity (10^20 W/cm2) laser interaction with thin foil (10nm) and thick (several µm) targets will be presented and discussed. With gas jet targets, very high-resolution single shot phase contrast imaging with 10-20 keV X-rays has been demonstrated, and electrons are currently generated in the GeV range. X-ray source characterization will be presented. With foil targets, the target expansion has been measured on both sides of the target as well as proton generation (15 MeV range) at these relativistic intensities with various diagnostics (folding wave interferometer, time of flight, Thomson parabola...) We will describe the progresses we are doing to move from the laboratory experiments system to the application levels with integrated systems and compact light sources, with a special emphasis on medical applications. We are exploring the use of these high power lasers as a basic tool to image in real time with X-rays (betatron emission) tumors during their irradiation by protons (accelerated by the same laser).
+ funded by NSERC, CIPI, CFI, FQRNT, MDEIE, INRS, CRC program.
Energetic electrons generation by longitudinal field acceleration from a laser pulse was demonstrated. The longitudinal field was generated by focusing a radially polarised TM01 ultrashort laser pulse (1,8 microns, 550 uJ, 15 fs) with a high numerical aperture parabola. The created longitudinal field was intense enough to ionised and accelerated electrons with a few tens of keV from a low density oxygen gaz. The energy, spectrum, number of charges per shot and divergence of the generated electron bunches have been measured and will be presented. Electron bunch pulse duration, space charge effects and energy tunability will also be discussed.
S. Fourmaux, S. Buffechoux, S. Gnedyuk, B. Albertazzi, D. Capelli, L. Lecherbourg, A. Lévy, P. Audebert, D. Houde, R. Marjoribanks, F. Martin, H. Pépin, J. Fuchs, J. C. Kieffer
Focusing a high intensity laser pulse, onto a thin foil target generates a plasma and energetic proton and ion beams from
the target rear and front sides, propagating along the target normal. Such laser produced collimated and energetic protons
beams are of high interest because of the wide range of applications: ion based fast ignitor schemes, probing of
electromagnetic fields in plasma, isotopes production or hadron therapy. The 100 TW class laser system at the Advanced
Laser Light Source facility, is used with an intensity close to 1019 W/cm2, to study protons acceleration with
femtosecond laser pulses, ultra thin foil target and high contrast laser pulse ratio. To characterize the plasma expansion,
we monitor it with an imaging technique using a femtosecond laser probe. In this configuration we were able to reach a
proton critical energy of 12 MeV and to work with target foil thickness as small as 15 nm.
We are exploring the use of the ultra-high contrast 200 TW ALLS facility (5 J, 28 fs, 10 Hz repetition rate) as a
basic tool to image in real time with X-rays (generated by the laser) tumors during their irradiation by protons
(accelerated by the same laser). The feasibility of phase contrast imaging in in-line geometry and proton acceleration
with 100 TW (3 J, 30 fs) on targets is studied and presented in the present paper. We demonstrate here that phase
contrast x-ray imaging, of tests and complex objects located in air at 1m from the X-ray source, can be achieved in one
shot using our betatron x-ray source generated in a supersonic gas jet. Using solid targets (thin and thick foils) our
experiments indicate that protons are accelerated at a maximum energy of 12 MeV.
Beams of X-rays of few keV energy have been produced from laser-supersonic gas jet interaction. Betatron X-ray
radiation is generated when energetic electrons are accelerated and experience betatron oscillations in the ion channel
produced in the wake of a high intensity femtosecond laser pulse. Experiments took place at the 200 TW laser system (5
J, 25 fs, 10 Hz) of the Advanced Laser Light source facility (ALLS). Thanks to the laser system performance these
preliminary results are the first steps to an expected improvement of the X-rays beams characteristics (collimation,
brightness and energy above the keV range).
S. Fourmaux, S. Buffechoux, B. Albertazzi, S. Gnedyuk, L. Lecherbourg, S. Payeur, P. Audebert, D. Houde, R. Marjoribanks, F. Martin, H. Pépin, J. Fuchs, J. C. Kieffer
Collimated beams of energetic protons are produced by the interaction of short duration high intensity laser pulses with
solid foils. This field has been the subject of many studies in the last decade. This interest is motivated by the wide range
of application of such beams: ion based fast ignitor schemes, probing of electromagnetic fields in plasma, isotope
production or hadron therapy. The recently commissioned 200 TW laser system (5 J, 25 fs, 1010 laser pulse contrast, 10
Hz repetition rate at 800 nm) at the Advanced Laser Light Source (ALLS) facility has been used to study proton
acceleration with femtosecond laser pulses. The proton spectrum was characterized using a time of flight detector. Due
to the high contrast of the laser pulse, foil targets as thin as 30 nm could be studied.
K-alpha x-ray sources from laser produced plasmas provide completely new possibilities for x-ray phase-contrast imaging applications. By tightly focusing intense femtosecond laser pulses onto a solid target, K-alpha x-ray pulses are generated through the interaction of energetic electrons created in the plasma with the bulk target. In this paper, we present a continuous and efficient Mo K-alpha x-ray source produced by a femtosecond laser system operating at 100 Hz
repetition rate with maximum pulse energy of 110 mJ before compression. The source has x-ray conversion efficiency greater than 10-5 into K-alpha line emission. In preparation for phase contrast imaging applications, the size of the resultant K-alpha x-ray emission spot has been also characterized. The source exhibits sufficient spatial coherence to observe phase contrast. We observe a relatively small broadening of the K-alpha source size compared to the size of the laser beam itself. Detailed characterization of the source including the x-ray spectrum and the x-ray average yield along
with phase contrast images of test objects will be presented.
We report observation of laser beam distortion due to the thermal load associated with high energy (110 mJ) and high average power (11 Watts) femtosecond laser system with vacuum compressor. To improve laser-based light source brightness, it is crucial to develop laser systems with higher energy and higher average power. Managing the high thermal loading on vacuum optical components and demonstration of brightness stability are key issues in the implementation of this approach. We characterize such thermally induced distortions using beam wavefront measurements and propose compensation methods to attain long term stability.
We are developing and exploring the imaging performance of, an in vivo, in-line holography, x-ray phase-contrast, micro-CT system with an ultrafast laser-based x-ray (ULX) source. By testing and refining our system, and by performing computer simulations, we plan to improve system performance in terms of contrast resolution and
multi-energy imaging to a level beyond what can be obtained using a conventional microfocal x-ray tube. Initial CT projection sets at single energy (Mo Kα and Kβ lines) were acquired in the Fresnel regime and reconstructed for phantoms and a euthanized mouse. We also performed computer simulations of phase-contrast micro-CT scans for low-contrast, soft-tissue, tumor imaging. We determined that, in order to perform a phase-contrast, complete micro-CT scan using ULX, the following conditions must be met: (i) the x-ray source needs to be stable during the scan; (ii) the laser focal spot size needs to be less than 10 μm for source-to-object distance greater than 30 cm; (iii) the laser light intensity on the target needs to be in the range of 5 × 1017 to 5 × 1019 W/cm2; (iv) the ablation protection system needs to allow uninterrupted scans; (v) the laser light focusing on the target needs to remain accurate during the entire scan; (vi) a fresh surface of the target must be exposed to consecutive laser shots during the entire scan; (vii) the effective detector element size must be less than 12 μm. Based on the results obtained in this research project, we anticipate that the new 10 Hz, 200 TW laser with 50W average power that is being commissioned at ALLS will allow us practical implementation of in vivo x-ray phase-contrast micro-CT.
To assess the feasibility of small soft tissue avascular tumor
micro-CT imaging with x-ray phase-contrast in-line
holography, we have studied micro-CT imaging with in-line geometry of small spheroidal avascular tumor models
with quiescent cell core (< 250 μm) and various distributions of the proliferating cell density (PCD) forming the outer
shell. We have simulated imaging with an ultrafast laser-based x-ray source with a Mo target. We observe
phase-contrast enhancement of the tumor boundaries in the reconstructed transaxial images, resulting in improved
detection of small soft tissue tumors, providing that the PCD density gradient is sufficiently large.
We present here a laser based time resolved ultrafast XANES beam line operating with the 100 Hz ALLS facility
laser system (100 mJ and 35 fs at 800 nm wavelength). This system is based on a broadband soft x-ray plasma
source, produced with a tantalum solid target, and a grazing flat field incidence grating designed to work in the 1-5 nm range. This femtosecond x-ray absorption spectroscopy experimental set up is used to study ultrafast phase
transition in vanadium dioxide (VO2). In this model system we are probing the electronic dynamics occurring
during semiconductor to metal phase transition following excitation by a femtosecond laser pulse.
The Advanced Laser Light Source (ALLS) infrastructure is a new state-of-the-art multi-beams femtosecond laser
facility currently in operation at INRS near Montreal, Canada. The use of a wide range of energy radiation from hard
x-ray up to infrared light on the ultrafast time scale requires the development of ultrafast detector diagnostics tools to
study the emission spectrum of these sources. To fulfill these requirements, new streak cameras have been developed
for ALLS facility. We present the new FXR streak camera which has been specifically developed for ALLS and
which is dedicated to x-ray spectroscopy with sub-picosecond time resolution combined with a very high spatial
resolution.
The Advanced Laser light Source (ALLS) infrastructure is a new state-of-the-art multi-beams femtosecond laser facility
currently in operation at INRS near Montreal, Canada. Multi-beams experiments and pump-probe geometry lead to the
need of synchronization instrumentation tools. The use of a wide range of energy radiation from hard x-ray up to infrared
light on the ultrafast time scale requires the development of ultrafast detector diagnostics tools to study the emission
spectrum of these sources. To fulfill these requirements, new streak cameras have been developed for ALLS facility. The
SV streak camera is a simple and compact multi-purpose instrument that will be used for beams synchronization with
picosecond time resolution and good spatial resolution. The FXR streak camera is dedicated to x-ray spectroscopy with
sub-picosecond time resolution combined with a very high spatial resolution.
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.
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).
We investigated performance of ultrafast laser-based x-ray source for phase contrast imaging in 2D projection imaging and in enhanced micro-CT imaging. Good quality images were obtained, including images of small animals, in the single energy and multiple energy, in line phase-contrast enhancing geometry using x-ray line energy matching object thickness and density. Phase information has been inferred from images obtained at the same x-ray energy but at different object-to-detector distances and also from images obtained at the same object-to-detector distance but with different K-alpha line energies. Ultrafast laser-based, compact, x-ray source is a promising technique for micro-CT systems. Its utilization might result in faster scans with lower radiation dose, better spatial and contrast resolution and also femtosecond temporal resolution. In addition, it might allow practical implementation of dual-energy and phase-contrast imaging micro-CT that is not possible with conventional micro-CT.
Hard x-ray (8-100 keV) spectrum emission from plasma produced by femtosecond laser solid target interactions and Kα x-ray conversion efficiency have been studied as a function of laser intensity (1017 W/cm2 ~ 1019 W/cm2), pulse duration (70 fs ~ 400 fs), laser pulse fluence and laser wavelength (800 nm and 400 nm). The Ag Kα x-ray conversion efficiency produced by a laser pulse at 800 nm with an intensity I = 4x1018 W/cm2 can reach 2x10-5. We discuss the behavior of Kα conversion efficiency scaling laws as a function of the laser parameters. We found that the Kα x-ray conversion efficiency is more dependent on laser fluence than on pulse duration or laser pulse intensity. The conversion efficiency exhibits a similar value at I ~ 1x1018 W/cm2 when we work with a high contrast laser pulse at 400 nm or with a low contrast laser pulse at 800 nm, but in the first case it presents a higher scaling law. Consequently, the use of 400 nm laser pulses could be an effective method to optimize the Kα x-ray emission via vacuum heating mechanisms.
In this paper we discuss some result achieved at Laboratoire d'Optique Appliquee that may improve the capabilities of the laser-produced plasma x-ray source for applications in the study of ultrafast transient structures.
We have characterized the ultrafast solid-liquid transition of InSb and CdTe semiconductors by time resolved x-ray diffraction in the femtosecond timescale. Visible spectroscopic data were obtained together with x-ray measurements to characterize the dense electron-ho9le plasma at the origin of the phase transition following the IR excitation.
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