X-Ray and Electron Generation in the relativistic Lambda-cubed Regime.

Over the last two decades, laser-plasma interactions at relativistic intensities have been carried out using large laser facilities producing at least several hundred millijoule pulses at a repetition rate of 10 Hz or lower. A less explored regime is when intensities in excess of 10sup18 W/cm2 are attained by focusing millijoule-level femtosecond pulses to a spot with a diameter comparable to the laser wavelength. This so-called relativistic λ3 regime allows the study of certain laser-plasma experiments at kilohertz repetition rate. The present dissertation contributes to the understanding of the x-ray source and hot electrons produced in this regime. The micron-sized λ3 focus engenders a comparably sized x-ray source that could be attractive for high resolution x-ray imaging applications. With this in mind, the source size is measured for various target materials using the knife-edge technique. Furthermore, the source spatial coherence properties are investigated by analyzing the diffraction pattern off a straight edge. Also investigated are the spatial and energy distributions of hot electrons escaping the plasma. In the case of an Al plasma, the electrons have a Maxwellian-like energy distribution with a temperature that scales with (I λ2)~0.6 in the 10sup17 − 2×10sup18 W/cm2 intensity range. On the other hand, in the case of an SiO2 plasma with λ/2 scale-length, the electrons are emitted in a collimated relativistic jet having a non-Maxwellian distribution with Ei = 675 keV. This is the first demonstration of laser-generated relativistic electron beams at kilohertz repetition rate. Additionally, this dissertation reports on two pioneering demonstrations in a related but fundamentally different regime, that of high-average power fiber lasers. In the first experiment, Ni Kα x-rays are produced using a fiber CPA system at the intensity of 2×10sup18 W/cm2, the highest reported to date from a fiber system. The conversion efficiency into the Kα photons is comparable to those obtained from Ti:sapphire lasers with similar pulse-energy. In another experiment, extreme UV radiation is generated from a bulk Sn target using a nanosecond fiber laser. This result has confirmed that fiber lasers are a potential contender to drive the source of the next generation EUV lithography instrument.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/58371/1/amordova_1.pd

Hard X-ray generation from solids driven by relativistic intensity in the lambda-cubed regime

Interaction of relativistic intensity laser pulses encompassed at focus by a volume of a few wavelengths cubed with solids is examined. Spectroscopy of hard X-rays of several metallic targets, including Cu, Ge, Mo, Ag, and Sn, irradiated in this regime at a high repetition rate (0.4 kHz), has been experimentally studied. The K α and K β peaks of all targets were obtained. Averaged electron temperatures of several tens of keV and total X-ray conversion efficiencies up to 0.02% are calculated. The X-ray source size is measured to be ∼10 micron with varying elliptical shape.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47054/1/340_2005_Article_2085.pd

Quasimonoenergetic electron beams with relativistic energies and ultrashort duration from laser-solid interactions at 0.5 kHz

International audienceWe investigate the production of electron beams from the interaction of relativistically-intense laser pulses with a solid-density SiO2 target in a regime where the laser pulse energy is -mJ and the repetition rate -kHz. The electron beam spatial distribution and spectrum were investigated as a function of the plasma scale length, which was varied by deliberately introducing a moderate-intensity prepulse. At the optimum scale length of λ/2, the electrons are emitted in a collimated beam having a quasimonoenergetic distribution that peaked at -0.8MeV. A highly reproducible structure in the spatial distribution exhibits an evacuation of electrons along the laser specular direction and suggests that the electron beam duration is comparable to that of the laser pulse. Particle-in-cell simulations which are in good agreement with the experimental results offer insights on the acceleration mechanism by the laser field. © 2009 The American Physical Society

High power fiber laser driver for efficient EUV lithography source with tin-doped water droplet targets

In this paper we report the development of nanosecond-pulsed fiber laser technology for the next generation EUV lithography sources. The demonstrated fiber laser system incorporates large core fibers and arbitrary optical waveform generation, which enables achieving optimum intensities and other critical beam characteristics on a laser-plasma target. Experiment demonstrates efficient EUV generation with conversion efficiency of up to 2.07% for in-band 13.5-nm radiation using mass-limited Sn-doped droplet targets. This result opens a new technological path towards fiber laser based high power EUV sources for high-throughput lithography steppers

High-order harmonic generation from solid targets with 2 mJ pulses

International audienceHarmonics up to the 18th order are generated from solid targets by focusing 2 mJ, 50 fs pulses at 800 nm to a spot size of 1:7 µm (FWHM). To our knowledge, this is the first demonstration of high-harmonic generation with a very short focal length paraboloid (f /1.4) and kilohertz laser system. The harmonics have a low divergence (10-7 per harmonic) comparable to gas harmonics. No contrast enhancement techniques are employed, and the system is capable of operating at 500 Hz. © 2010 Optical Society of America