Comparison of hard x-ray production from various targets in air using a   short pulse kHz laser with photon production from a high power multifilament   laser beam from the same targets in air
  Over the last few years there has been much interest in the production of hard X-rays from various targets using a kHz short pulse laser at intensities above 1014Wcm-2 (A). Most of these studies have been carried out in vacuum and very many fewer studies have been carried out in air. Recently this lack has been partially addressed with the development of femtosecond laser micromachining. Another similar although apparently unconnected field (B) deals with the channelling of high power laser beam in filaments after passage through long distances in air. This has been largely driven by the construction of a mobile terawatt laser beam (Teramobile) for atmospheric studies. The laser beams in these two cases (A and B) have very different pulse energies (mJ against J) although the filaments in (B) have similar energies to (A) and are clamped at intensities less than 1014 Wcm-2. This paper has been written to compare the production of hard X-rays in these two cases. The conclusion is interesting that a focused sub TW laser pulse in air reaches intensities sufficiently high that characteristic K and L X-rays are generated from a number of metal and non metal targets as well as a continuous bremsstrahlung spectrum. On the other hand the clamping of the multi-filaments in a 100 TW laser beam in air cannot generate hard Xrays especially when propagated over long distances. 
K.W.D. Ledingham, S. S. Abuazoum, T. McCanny, J.J. Melone, K. Spohr,   U. Schramm, S.D. Kraft, A. Wagner, A. Jochmann
physics.plasm-ph