Hard X-rays (no vacuum required)

The conventional x-ray tube that has been around for more than a century works on the principle of driving electrons from a cathode into an anode material. The repulsion these electrons exhibit for each other limits the brightness of such tubes, the number of x-rays that can be emitted from a given area in a given amount of time.  These same materials, on the other hand, are replete with their own electrons and need only a driver to push the electrons with weakly relativistic velocities in order to emit x-rays.  When we focus our ultrafast laser light onto materials we make a very bright x-ray source with application to phase contrast imaging, crystal diffraction and time resolved x-ray studies. Such as source was used to make the image above.  In this source the relativistic lambda cubed laser is focused onto various metals, semiconductors, and dielectrics to generate x-rays both in a vacuum vessel and in the open laboratory with an small flow of helium gas. The chart to the right shows the spectra and efficiency of a number of these sources.

In addition to the short duration of the x-rays from these laser-solid interaction (between 100fs and a few ps) the sources also have small lateral dimensions. This gives them sufficient coherence to produce images with enhanced edges due to phase contrast. In the image below the wings of a damselfly are shown with the effects of diffraction from their fine support structure. The fine structure of materials in another target of our research.  Owing to their very short wavelength, x-rays can probe both the well-ordered atomic structure of materials such as the silicon crystal whose diffraction is shown below and the defects in materials as is illustrated by the crack that was imaged by femtosecond-laser based x-rays.

Our papers on hard x-ray generation can be found at:

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