Thicket high Z wavelength-scale structured target: advantages and limitations for laser-driven hard x-ray source and phase contrast imaging

Abstract

The hard x-ray copper K α source formed by the interaction of a high intensity laser pulse with flat and thicket sub-micron structured copper targets is thoroughly characterized. It is shown that the flux of quanta can be increased up to several times using the structured target instead of the flat one. The maximal conversion efficiency into K α reaches 1.4 × 10−4 corresponding to >109 photons with a high contrast ratio over the bremsstrahlung radiation at the peak intensity ∼1018 W cm−2. The efficient use of the thicket target at higher intensity (2 × 1018 W cm−2) is limited by temporal contrast of the laser pulse and the few-fold lowered damage threshold of the modified target. Measurements of the x-ray source size revealed that the lateral coherence is similar both for the flat and thicket target. The estimated source size of ∼15 μm makes it suitable for the x-ray phase contrast imaging with reasonable geometry and short time object exposure. A simple concept of the image acquisition correction is proposed in order to account for the x-ray source lateral shifts, which is based on measurements in each shot instead of long exposure. Image post-processing allowed us to enhance source lateral coherence and retrieve phase contrast effects when the x-ray source shifts exceed its size.