Generation of Coherent X-rays in the Water Window Using 5-Femtosecond Laser Pulses

Abstract

Coherent extreme-ultraviolet radiation extending to wavelengths below the carbon K edge at 4.37 nanometers (nm) has been generated at a repetition rate of 1 kilohertz by focusing 5-femtosecond near-infrared (780 nm) laser pulses into a helium gas jet. The incident light field performs just a few oscillations, which results in the emission of an x-ray supercontinuum rather than discrete harmonics. Owing to the extremely short rise time of the driving pulses, neutral atoms can be exposed to high fields before they are depleted by ionization. As a result, the observed x-ray radiation extends well into the water window and is delivered in a well-collimated beam (divergence less than 1 milliradian). The high repetition rate and spatial coherence result in a brightness of about 5 x 1 O8 photons per square millimeter per square milliradian per second in a I -percent bandwidth at 4.37 nm, the carbon edge of the water window. The compact laboratory system holds promise as a source for biological holography and nonlinear optics in the x-ray regime.

Acquisition of photoelectron diffraction patterns with a two-dimensional wide-angle electron analyzer

“…With the currently fast progressing development of pulsed light sources based on higherharmonic generation (HHG) [5], reaching photon energies in the uv and soft x-ray region, there is also a potential to use photoelectron diffraction in a pumpprobe scheme for studying structural dynamics at surfaces. Such experiments have already been successfully performed for laser-aligned molecules in the gas phase using free-electron laser pulses [6].…”

Low-order harmonic generation in metal ablation plasmas in nanosecond and picosecond laser regimes

“…1,2 On the other hand, high-order harmonic generation 3 (HHG) requires pulses of higher intensities (typically 10 14 -10 15 W/cm 2 ) which can easily be achieved with femtosecond (fs) driving lasers. Although the phenomenon of HG is universal and can be generalized to any material with sufficient non linear response, mostly atomic, 4,5 or in some cases, molecular 6,7 gas jets have been investigated as nonlinear media. In practical applications of coherent short wavelength HG sources, a high conversion efficiency and thus high photon flux of the harmonic radiation are essential.…”

Hydrodynamic Simulation of the Femtosecond Laser Processing of Metals

“…Molecular dynamics (MD) is a suitable tool for studying phase change and material removal. (13)(14)(15) As the fundamental input in MD simulations, the potential function must be obtained through the quantum mechanics method. The particle-in-cell method solves the equations of motion and Maxwell's equations for particles in order to determine the forces among these particles, (16)(17)(18) which is very similar to the description of plasma from first principles as a system of charged particles.…”