David Neely was an internationally recognised scientist who formed collaborations and friendships... more David Neely was an internationally recognised scientist who formed collaborations and friendships across the world. His passion for his work always shone through. He always made time for early-career scientists and became a mentor and supervisor to many. He was an active Editorial Board Member of the international journal High Power Laser Science and Engineering. Sadly, David was taken from us much too early. In this Editorial we pay tribute to his work through his publications in the journal.
Relativistic electrons generated by the interaction of petawatt-class short laser pulses with sol... more Relativistic electrons generated by the interaction of petawatt-class short laser pulses with solid targets can be used to generate bright x-rays via bremsstrahlung. The efficiency of laser energy transfer into these electrons depends on multiple parameters including the focused intensity and pre-plasma level. This paper reports experimental results from the interaction of a high intensity petawatt-class glass laser pulses with solid targets at a maximum intensity of 1019 W cm−2. In-situ measurements of specularly reflected light are used to provide an upper bound of laser absorption and to characterize focused laser intensity, the pre-plasma level and the generation mechanism of second harmonic light. The measured spectrum of electrons and bremsstrahlung radiation provide information about the efficiency of laser energy transfer.
After a population of laser-driven hot electrons traverses a limited thickness solid target, thes... more After a population of laser-driven hot electrons traverses a limited thickness solid target, these electrons will encounter the rear surface, creating TV/m fields that heavily influence the subsequent hot-electron propagation. Electrons that fail to overcome the electrostatic potential reflux back into the target. Those electrons that do overcome the field will escape the target. Here, using the particle-in-cell (PIC) code EPOCH and particle tracking of a large population of macro-particles, we investigate the refluxing and escaping electron populations, as well as the magnitude, spatial and temporal evolution of the rear surface electrostatic fields. The temperature of both the escaping and refluxing electrons is reduced by 30%–50% when compared to the initial hot-electron temperature as a function of intensity between $10^{19}$ and $10^{21}~~\text{W}/\text{cm}^{2}$ . Using particle tracking we conclude that the highest energy internal hot electrons are guaranteed to escape up to a...
Journal of Physics B: Atomic, Molecular and Optical Physics, 2000
Elastic scattering of electrons by highly charged ions, in particular the measurements of differe... more Elastic scattering of electrons by highly charged ions, in particular the measurements of differential cross sections, is the focus of the present research. By using a 150° crossed beam method, we have successfully measured the angular distributions of electrons elastically scattered from Ar7+ and Ar8+ ions over a wide angular range, employing a novel toroidal electron energy analyser, which is capable of simultaneous determination of the angle and the energy of the scattered electrons over a wide range. Relative differential cross sections for the e + Ar7+ system have been derived by employing results of e + Ar8+, which can be treated as pure Rutherford scattering, as a calibration for the detection efficiency over the angular range. In the angular range studied, between 34°-85°, experimental data of the e + Ar7+ system agree with the Rutherford classical cross sections fairly well, indicating that the Coulombic interaction dominates over this angular range, at a collision energy of 100 eV. Some small deviations from the Rutherford cross sections are considered to be due to the influences of the ionic structure to the scattering cross sections.
Laser-produced plasmas are bright, short sources of x-rays commonly used for time-resolved imagin... more Laser-produced plasmas are bright, short sources of x-rays commonly used for time-resolved imaging and spectroscopy. Their usage implies accurate knowledge of laser-to-x-ray conversion efficiency (CE), spectrum, photon yield and angular distribution. Here, we report on soft x-ray emission in the direction close to the target normal from a thin Si foil irradiated by a sub-PW picosecond laser pulse. These absolute measurements cover a continuous and broad spectral range that extends from 4.75 to 7.3 Å (1.7–2.6 keV). The x-ray spectrum consists of spectral line transitions from highly charged ions and broadband emission with contributions from recombination and free-free processes that occur when electrons decelerate in plasma electromagnetic fields. Angular distribution of the emission was investigated via particle-in-cell simulations, which allowed to estimate the yield into the full solid angle. We find that experimental and simulation estimations of laser to free-free emission CE a...
A novel scheme of staged laser-plasma accelerators produces extremely brilliant γ-rays with photo... more A novel scheme of staged laser-plasma accelerators produces extremely brilliant γ-rays with photon energies up to GeV level.
ABSTRACT Hot electron generation plays an important role in the fast ignition approach to inertia... more ABSTRACT Hot electron generation plays an important role in the fast ignition approach to inertial confinement fusion (ICF) and other applications with ultra-intense lasers. Hot electrons of temperature up to 10-20 MeV have been produced by high contrast picosecond duration laser pulses focussed to intensities of ̃1020 W cm-2 with a deliberate pre-pulse on solid targets using the Vulcan Petawatt Laser facility. We present measurements of the number and temperature of hot electrons obtained using an electron spectrometer. The results are correlated to the density scale length of the plasma produced by a controlled pre-pulse measured using an optical probe diagnostic. 1D simulations predict electron temperature variations with plasma density scale length in agreement with the experiment at shorter plasma scale lengths (<7.5μm), but with the experimental temperatures (13-17 MeV) dropping below the simulation values (20-25 MeV) at longer scale lengths. The experimental results show that longer interaction plasmas produced by pre-pulses enable significantly greater number of hot electrons to be produced.
We investigate dense relativistic electron mirror generation from a micro-droplet driven by circu... more We investigate dense relativistic electron mirror generation from a micro-droplet driven by circularly polarized Laguerre-Gaussian lasers. The surface electrons are expelled from the droplet by the laser's radial electric field and evolve into dense sheets after leaving the droplet. These electrons are trapped in the potential well of the laser's transverse ponderomotive force and are steadily accelerated to about 100 MeV by the longitudinal electric field. Particle-in-cell simulations indicate that the relativistic electron mirrors are characterized by high beam charge, narrow energy spread, and large angular momentum, which can be utilized for bright X/γ-ray emission and photon vortex formation.
Presented are results from experimental campaigns undertaken on the Gemini laser system at the Ce... more Presented are results from experimental campaigns undertaken on the Gemini laser system at the Central Laser Facility in the UK. In these experiments amorphous carbon targets ranging in thickness from 10nm to 100nm were irradiated with high contrast 40fs pulses with an intensity up to 1021 W/cm2, for both circular and linear polarisations and the resulting proton and ion spectra compared. Examining the highest energies achieved for a given polarisation and target thickness, allows to identify the transition from TNSA to LS. Observations of the optimal target thickness for ion acceleration are compared to analytical predictions from LS theory, in addition to results from Particle in Cell modelling.
David Neely was an internationally recognised scientist who formed collaborations and friendships... more David Neely was an internationally recognised scientist who formed collaborations and friendships across the world. His passion for his work always shone through. He always made time for early-career scientists and became a mentor and supervisor to many. He was an active Editorial Board Member of the international journal High Power Laser Science and Engineering. Sadly, David was taken from us much too early. In this Editorial we pay tribute to his work through his publications in the journal.
Relativistic electrons generated by the interaction of petawatt-class short laser pulses with sol... more Relativistic electrons generated by the interaction of petawatt-class short laser pulses with solid targets can be used to generate bright x-rays via bremsstrahlung. The efficiency of laser energy transfer into these electrons depends on multiple parameters including the focused intensity and pre-plasma level. This paper reports experimental results from the interaction of a high intensity petawatt-class glass laser pulses with solid targets at a maximum intensity of 1019 W cm−2. In-situ measurements of specularly reflected light are used to provide an upper bound of laser absorption and to characterize focused laser intensity, the pre-plasma level and the generation mechanism of second harmonic light. The measured spectrum of electrons and bremsstrahlung radiation provide information about the efficiency of laser energy transfer.
After a population of laser-driven hot electrons traverses a limited thickness solid target, thes... more After a population of laser-driven hot electrons traverses a limited thickness solid target, these electrons will encounter the rear surface, creating TV/m fields that heavily influence the subsequent hot-electron propagation. Electrons that fail to overcome the electrostatic potential reflux back into the target. Those electrons that do overcome the field will escape the target. Here, using the particle-in-cell (PIC) code EPOCH and particle tracking of a large population of macro-particles, we investigate the refluxing and escaping electron populations, as well as the magnitude, spatial and temporal evolution of the rear surface electrostatic fields. The temperature of both the escaping and refluxing electrons is reduced by 30%–50% when compared to the initial hot-electron temperature as a function of intensity between $10^{19}$ and $10^{21}~~\text{W}/\text{cm}^{2}$ . Using particle tracking we conclude that the highest energy internal hot electrons are guaranteed to escape up to a...
Journal of Physics B: Atomic, Molecular and Optical Physics, 2000
Elastic scattering of electrons by highly charged ions, in particular the measurements of differe... more Elastic scattering of electrons by highly charged ions, in particular the measurements of differential cross sections, is the focus of the present research. By using a 150° crossed beam method, we have successfully measured the angular distributions of electrons elastically scattered from Ar7+ and Ar8+ ions over a wide angular range, employing a novel toroidal electron energy analyser, which is capable of simultaneous determination of the angle and the energy of the scattered electrons over a wide range. Relative differential cross sections for the e + Ar7+ system have been derived by employing results of e + Ar8+, which can be treated as pure Rutherford scattering, as a calibration for the detection efficiency over the angular range. In the angular range studied, between 34°-85°, experimental data of the e + Ar7+ system agree with the Rutherford classical cross sections fairly well, indicating that the Coulombic interaction dominates over this angular range, at a collision energy of 100 eV. Some small deviations from the Rutherford cross sections are considered to be due to the influences of the ionic structure to the scattering cross sections.
Laser-produced plasmas are bright, short sources of x-rays commonly used for time-resolved imagin... more Laser-produced plasmas are bright, short sources of x-rays commonly used for time-resolved imaging and spectroscopy. Their usage implies accurate knowledge of laser-to-x-ray conversion efficiency (CE), spectrum, photon yield and angular distribution. Here, we report on soft x-ray emission in the direction close to the target normal from a thin Si foil irradiated by a sub-PW picosecond laser pulse. These absolute measurements cover a continuous and broad spectral range that extends from 4.75 to 7.3 Å (1.7–2.6 keV). The x-ray spectrum consists of spectral line transitions from highly charged ions and broadband emission with contributions from recombination and free-free processes that occur when electrons decelerate in plasma electromagnetic fields. Angular distribution of the emission was investigated via particle-in-cell simulations, which allowed to estimate the yield into the full solid angle. We find that experimental and simulation estimations of laser to free-free emission CE a...
A novel scheme of staged laser-plasma accelerators produces extremely brilliant γ-rays with photo... more A novel scheme of staged laser-plasma accelerators produces extremely brilliant γ-rays with photon energies up to GeV level.
ABSTRACT Hot electron generation plays an important role in the fast ignition approach to inertia... more ABSTRACT Hot electron generation plays an important role in the fast ignition approach to inertial confinement fusion (ICF) and other applications with ultra-intense lasers. Hot electrons of temperature up to 10-20 MeV have been produced by high contrast picosecond duration laser pulses focussed to intensities of ̃1020 W cm-2 with a deliberate pre-pulse on solid targets using the Vulcan Petawatt Laser facility. We present measurements of the number and temperature of hot electrons obtained using an electron spectrometer. The results are correlated to the density scale length of the plasma produced by a controlled pre-pulse measured using an optical probe diagnostic. 1D simulations predict electron temperature variations with plasma density scale length in agreement with the experiment at shorter plasma scale lengths (<7.5μm), but with the experimental temperatures (13-17 MeV) dropping below the simulation values (20-25 MeV) at longer scale lengths. The experimental results show that longer interaction plasmas produced by pre-pulses enable significantly greater number of hot electrons to be produced.
We investigate dense relativistic electron mirror generation from a micro-droplet driven by circu... more We investigate dense relativistic electron mirror generation from a micro-droplet driven by circularly polarized Laguerre-Gaussian lasers. The surface electrons are expelled from the droplet by the laser's radial electric field and evolve into dense sheets after leaving the droplet. These electrons are trapped in the potential well of the laser's transverse ponderomotive force and are steadily accelerated to about 100 MeV by the longitudinal electric field. Particle-in-cell simulations indicate that the relativistic electron mirrors are characterized by high beam charge, narrow energy spread, and large angular momentum, which can be utilized for bright X/γ-ray emission and photon vortex formation.
Presented are results from experimental campaigns undertaken on the Gemini laser system at the Ce... more Presented are results from experimental campaigns undertaken on the Gemini laser system at the Central Laser Facility in the UK. In these experiments amorphous carbon targets ranging in thickness from 10nm to 100nm were irradiated with high contrast 40fs pulses with an intensity up to 1021 W/cm2, for both circular and linear polarisations and the resulting proton and ion spectra compared. Examining the highest energies achieved for a given polarisation and target thickness, allows to identify the transition from TNSA to LS. Observations of the optimal target thickness for ion acceleration are compared to analytical predictions from LS theory, in addition to results from Particle in Cell modelling.
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Papers by Paul McKenna