We demonstrate the generation of axially modulated plasma waveguides using spatially patterned high-energy laser pulses. A spatial light modulator (SLM) imposes transverse phase front modulations on a low-energy (10 mJ) laser pulse which is interferometrically combined with a high-energy (130-450 mJ) pulse, sculpting its intensity profile. This enables dynamic and programmable shaping of the laser profile limited only by the resolution of the SLM and the intensity ratio of the two pulses. The plasma density profile formed by focusing the patterned pulse with an axicon lens is likewise dynamic and programmable. Centimeter-scale, axially modulated plasmas of varying shape and periodicity are demonstrated.

We examine the interaction of relativistic laser pulses with plasma channels formed in a nitrogen cluster jet. We observe creation of nearly pure N5+ plasma channels and ionization injected wakefield beams with energies >100 MeV.

The energy gain in laser wakefield acceleration is ultimately limited by dephasing, occurring when accelerated electrons outrun the accelerating phase of the wakefield. We apply quasi-phase-matching, enabled by axially modulated plasma channels, to overcome this limitation. Theory and simulations are presented showing that weakly relativistic laser intensities can drive significant electron energy gains.

Plasma guiding structures are generated with programmable axial density modulations using a Spatial Light Modulator (SLM). A coherent beam-combining scheme enables the sculpting of high power beams with modest energy passing through the SLM.

Ionization injection-assisted laser wakefield acceleration of electrons up to 120 MeV is demonstrated in a 1.5 mm long pure helium-like nitrogen plasma waveguide. The guiding structure stabilizes the high energy electron beam pointing and reduces the beam divergence. Our results are confirmed by 3D particle-in-cell simulations.

Two quasi-phasematching schemes are proposed for efficient acceleration of electrons to relativistic energies using moderate intensity laser pulses. In the first scheme, Direct Laser Acceleration (DLA) in a corrugated plasma waveguide is proposed for acceleration of relativistic electrons with sub-terawatt laser systems, using the laser field directly as the accelerating field. The second scheme uses the fact that a plasma wakefield generated by an intense guided pulse in a corrugated plasma waveguide can accelerate relativistic electrons significantly beyond the well-known dephasing limit. In each case, particle-in-cell (PIC) simulations are used to validate the acceleration concept, demonstrating linear acceleration by either the phase matched laser field or phase-matched wakefield. In the phase matched wakefield case, theory and PIC simulations demonstrate a significant increase in energy gain compared to the standard laser wakefield acceleration (LWFA) scheme. Corrugated plasma waveguides can be generated by the interaction between an ionizing laser pulse and an atomic cluster flow interrupted by an array of thin wires,. When the collisional mean free path of the clusters is greater than the wire diameter, shadows of the periodically located wires are imparted on the cluster flow, leading to the production of axially modulated plasma waveguides after laser heating of the flow. This occurs when the population ratio of clusters to monomers in the gas is high. At other limit, dominated by gas monomer flow, shock waves generated off the wires by the supersonic gas flow disrupts modulated waveguide generation. Lastly, we experimentally demonstrate LWFA with ionization injection in a N 5+ plasma waveguide. It is first shown that the plasma waveguide is almost completely composed of He-like nitrogen (N 5+). It is then shown that intense pulse channeling in the plasma waveguide drives stronger wakefields, while the ionization injection process is critical to lowering the laser intensity threshold for self-trapping.

We examine the generation of axially modulated plasmas produced from cluster jets whose supersonic flow is intersected by thin wires. Such plasmas have application to modulated plasma waveguides. By appropriately limiting shock waves from the wires, plasma axial modulation periods can be as small as 70 μm, with plasma structures as narrow as 45 µm. The effect of shocks is eliminated with increased cluster size accompanied by a reduced monomer component of the flow.

We examine the generation of plasma waveguides generated from cluster jets whose supersonic flow is intersected by a periodic array of wires. We find that the minimum modulation period is dictated by shock waves launched off the wires by residual monomer gas. This effect is reduced with increased cluster size accompanied by a reduced monomer component of the flow. By appropriately limiting shockwaves, the modulation period can be less than 100 μm.

A laser pulse propagating in a corrugated plasma channel is composed of spatial harmonics whose phase velocities can be subluminal. The phase velocity of a spatial harmonic can be matched to the speed of a relativistic electron resulting in direct acceleration by the guided laser field in a plasma waveguide and linear energy gain over the interaction length. Here we examine the fully self-consistent interaction of the laser pulse and electron beam using particle-in-cell (PIC) simulations. For low electron beam densities, we find that the ponderomotive force of the laser pulse pushes plasma channel electrons towards the propagation axis, which deflects the beam electrons. When the beam density is high, the space charge force of the beam drives the channel electrons off axis, providing collimation of the beam. In addition, we consider a ramped density profile for lowering the threshold energy for trapping in a subluminal spatial harmonic. By using a density ramp, the trapping energy for a normalized vector potential of a(0) = 0.1 is reduced from a relativistic factor gamma(0) = 170 to gamma(0) = 20.

We report electrically-induced, explosive atomization of metals and analytes at nanoscale. The phenomenon involves formation of highly-localized nanoscale leakage channels in the oxide layer of a metal-oxide-semiconductor (MOS) structure under pulsed drive, ballistic transport of injected electrons in the nanoscale void channels, impact ionization of metal atoms, and explosive atomization of metal and adjacent analyte materials. The fragmented atoms produce atomic luminescence from radiative transitions in the relaxation process. This electrically induced explosive atomization through nanochannels offers a potential for nanoscale elemental/trace analysis on a chip.

Two highly versatile experimental techniques are demonstrated for making preformed plasma waveguides with periodic structure capable of supporting the propagation of ultra-intense femtosecond laser pulses. These waveguides were made in hydrogen, nitrogen and argon plasmas with a length of 15 mm and modulation period as short as 35 mu m. Simulations show that these guides allow direct laser acceleration of electrons, achieving gradients of 80 MV/cm and 10 MV/cm for laser pulse powers of 1.9 TW and 30 GW, respectively. We also demonstrate a technique for making the required radially polarized pulses.

The Coulomb fragmentation phenomenon has been known to occur in matter at various different length scales, such as nuclei and atomic or molecular clusters, and microscopic droplets. In many cases, the Coulomb explosion is triggered by sudden ionization with high-intensity (>10²14 W/cm¹2) femto-second laser pulses. At this intensity level, the valence electrons are quickly ripped off and the ionized metal clusters fragment before thermalization occurs. In this thesis, we report Coulomb explosion of Ag atoms induced by electron impact ionization in a Si metal-oxide-semiconductor (MOS) structure (Ag/SiO2/Si). Under positive voltage pulses applied to the Ag gate, kinetic electrons are injected onto the gate through leakage channels formed in oxide and impact-ionize the metal atoms at the gate/dielectric interface. When the Coulomb repulsion among the ions becomes stronger than the binding force of metal atoms, the ions accumulated at the interface explode, atomizing the metal and also adjacent dielectrics. This explosive fragmentation results in atomic luminescence from neutral silver at 328 nm, 338 nm, 521 nm, 547 nm, 769 nm, and 827 nm. The mechanisms of oxide breakdown, localized injection of kinetic electrons, and atomization/luminescence are discussed.