Acceleration of electrons in a self-modulated laser wakefield

Acceleration of electrons in a self-modulated laser-wakefield is investigated. The generated electron beam is oberved to have a multi-component beam profile and its energy distribution undergoes discrete transitions as the conditions are varied. These features can be explained by simple simulations of electron propagation in a 3-D plasma wave. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87719/2/333_1.pd

Electron acceleration by self-modulated laser wakefield in a relativistically self-guided channel

The relativistic self-focusing of an intense laser pulse (I ∼ 4×1018 W/cm2,I∼4×1018W/cm2, λ = 1 μm,λ=1μm, τ = 400 fsτ=400fs) in a gas jet 750 μm in length was observed using sidescattering imaging. A self-modulated laser wakefield was generated to accelerate self-trapped electrons. The energy distribution and transverse emittance of the electron beam changed due to the onset of the relativistic self-guiding. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87563/2/408_1.pd

Nonlinear optics in relativistic plasmas

We discuss various nonlinear optical processes that occur as an intense laser propagates through a relativistic plasma. These include the experimental observations of electron acceleration driven by laser-wakefield generation, relativistic self-focusing, waveguide formation and laser self-channeling. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87450/2/103_1.pd

Mechanism and Control of High‐Intensity‐Laser‐Driven Proton Acceleration

We discuss the optimization and control of laser‐driven proton beams. Specifically, we report on the dependence of high‐intensity laser accelerated proton beams on the material properties of various thin‐film targets. Evidence of star‐like filaments and beam hollowing (predicted from the electrothermal instability theory) is observed on Radiochromic Film (RCF) and CR‐39 nuclear track detectors. The proton beam spatial profile is found to depend on initial target conductivity and target thickness. For resistive target materials, these structured profiles are explained by the inhibition of current, due to the lack of a return current. The conductors, however, can support large propagating currents due to the substantial cold return current which is composed of free charge carriers in the conduction band to neutralize the plasma from the interaction. The empirical plot shows relationship between the maximum proton energy and the target thickness also supports the return current and target normal sheath acceleration (TNSA) theory. We have also observed filamentary structures in the proton beam like those expected from the Weibel instability in the electron beam. Along with the ion acceleration, a clear electron beam is detected by the RCF along the tangent to the target, which is also the surface direction of target plate. © 2004 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87542/2/595_1.pd

High harmonic generation in relativistic laser–plasma interaction

High harmonics generated due to the scattering of relativistic electrons from high intensity laser light is studied. The experiments are carried out with an Nd:Glass laser system with a peak intensity of 2×1018 W cm−22×1018Wcm−2 in underdense plasma. It is shown that, at high intensities, when the normalized electric field approaches unity, in addition to the conventional atomic harmonics from bound electrons there is significant contribution to the harmonic spectrum from free electrons. The characteristic signatures of this are found to be the emission of even order harmonics, linear dependence on the electron density, significant amount of harmonics even with circular polarization and a much smaller spatial region over which these harmonics are produced as compared to the atomic case. Imaging of the harmonic beam shows that it is emitted in a narrow cone with a divergence of 2 to 3 degrees. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70961/2/PHPAEN-9-5-2393-1.pd

Control of Bright Picosecond X-Ray Emission from Intense Subpicosecond Laser-Plasma Interactions

Using temporally and spectrally resolved diagnostics, we show that the pulse duration of laser-produced soft x rays emitted from solid targets can be controlled, permitting a reduction to as short as a few picoseconds. To enable this control, only a single parameter must be adjusted, namely, the intensity of the high-contrast ultrashort laser pulse (400 fs). These results are found to be in qualitative agreement with a simple model of radiation from a collisionally dominated atomic system

Evidence of Ionization Blue Shift Seeding of Forward Raman Scattering

We report on the results of spectroscopic experiments that were conducted by focusing an intense ultra‐short laser pulse onto a helium gas target. The scattered light from the interaction region was measured spectrally and spatially from various directions as a function of laser intensity and plasma density. The experimental data showed that forward Stimulated Raman Scattering (SRS) was sensitive to the focus position of laser relative to the nozzle. Together with the plasma channel that was imaged by a CCD camera, the measurements indicate that SRS is seeded by the ionization blue‐shifted light. The cross‐phase modulation between the SRS and laser beam was also observed in the experiment. © 2004 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87541/2/585_1.pd

Laser-triggered ion acceleration and table top isotope production

We have observed deuterons accelerated to energies of about 2 MeV in the interaction of relativistically intense 10 TW, 400 fs laser pulse with a thin layer of deuterated polystyrene deposited on Mylar film. These high-energy deuterons were directed to the boron sample, where they produced ~105 atoms of positron active isotope 11C from the reaction 10B(d,n)11C. The activation results suggest that deuterons were accelerated from the front surface of the target

Swarm of ultra-high intensity attosecond pulses from laser-plasma interaction

We report on the realistic scheme of intense X-rays and γ-radiation generation in a laser interaction with thin foils. It is based on the relativistic mirror concept, i.e., a flying thin plasma slab interacts with a counterpropagating laser pulse, reflecting part of it in the form of an intense ultra-short electromagnetic pulse having an up-shifted frequency. A series of relativistic mirrors is generated in the interaction of the intense laser with a thin foil target as the pulse tears off and accelerates thin electron layers. A counterpropagating pulse is reflected by these flying layers in the form of a swarm of ultra-short pulses resulting in a significant energy gain of the reflected radiation due to the momentum transfer from flying layers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85400/1/jpconf10_244_022029.pd

Bright picosecond x‐rays from intense sub‐picosecond laser‐plasma interactions

Short‐pulse, high‐intensity laser‐plasma interactions are investigated experimentally with temporally and spectrally resolved soft x‐ray diagnostics. The emitted x‐ray spectra from solid targets of various Z are characterized for a range of laser intensities (I<5×1017 W/cm2) and pulse widths (η∼400 fs). With low contrast (105), the x‐ray spectrum in the λ=40–100 Å spectral region is dominated by line emission, and the x‐ray pulse duration is found to be long, τx≳100 ps, characteristic of a long‐scale‐length, low‐density plasma. Bright, picosecond, continuum emission, characteristic of a short‐scalelength, high‐density plasma, is produced only when a high laser contrast (1010) is used. It is demonstrated experimentally that the pulsewidth of laser‐produced x‐ray radiation may be varied down to the picosecond time‐scale by adjusting the incident ultrashort‐pulse laser flux. This controls the peak electron temperature relative to the ionization potential, corresponding to the emitted x‐ray photon energy of interest. The results are found to be consistent with the predictions of a hydrodynamics code coupled to an average atom model only if non‐local thermodynamic equilibrium (NLTE) is assumed. © 1994 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87587/2/473_1.pd