Ultra hard x rays from krypton clusters heated by intense laser fields

The interaction of ultrashort laser pulses with krypton clusters at intensity up to 1.3×1018 Wcm−2 has been investigated. Intense Kα and Kβ emission from krypton at 12.66 and 14.1 keV, respectively, has been observed using conventional solid state x-ray detectors. The measured x-ray spectra have broad bremsstrahlung continuum reaching to photon energies up to 45 keV, with evidence that approximately 10% of electrons that are heated to very high electron temperatures, which is consistent with a two-temperature electron distribution. This is ascribed to the presence of a hot electron population, similar to that found in laser-solid interactions. The highest laser energy to x-ray conversion efficiency observed is 9.2×10−7, which is equivalent to 45 nJ x-ray pulse energy from the 12.66 keV krypton Kα transition

Ionisation and fragmentation of polycyclic aromatic hydrocarbons by femtosecond laser pulses at wavelengths resonant with cation transitions

When femtosecond laser pulses irradiate hydrocarbon molecules, then many fragmentation channels evident in nanosecond irradiation are bypassed, providing a strong analytically useful parent ion. However a number of molecules show only a very small or indeed no parent ions and recent papers suggest that those that do not produce parent peaks have cation transitions in resonance with the femtosecond laser wavelength. This Letter shows that this resonance effect is not universal and some aromatic molecules not only show strong parent peaks but also doubly and triply ionised entities when their cation absorption spectrum is strongly resonant at either the 800 or 400 nm or indeed both

A tuneable ultra-compact high-power, ultra-short pulsed, bright gamma-ray source based on bremsstrahlung radiation from laser-plasma accelerated electrons

The laser driven plasma wakefield accelerator is a very compact source of high energy electrons. When the quasi-monoenergetic beam from these accelerators passes through dense material, high energy bremsstrahlung photons are emitted in a collimated beam with high flux. We show how a source based on this emission process can produce more than 109 photons per pulse with a mean energy of 10 MeV. We present experimental results that show the feasibility of this method of producing high energy photons and compare the experimental results with GEANT4 Montecarlo simulations, which also give the scaling required to evaluate its suitability as method to produce radioisotopes via photo-nuclear reactions or for imaging applications