Abstract

The present work represents a detailed study of the properties of prompt multi-keV X-ray emission induced from Xe clusters irradiated with ultra-intense stable relativistic/ponderomotive laser channels. Recent experimental studies indicate the selective enhancement of certain Xe(L) and Xe(M) lines in the case of stable channel formation. Stable self-channeling of ultra-powerful (P₀ ~ 1 TW - 1 PW) laser pulses in dense plasmas is a key process for many applications requiring controlled power compression. Theoretical modeling predicts that the transition zone between stable and highly unstable modes of self-channeling can be characterized by a weakly unstable behavior involving bifurcation of the laser beam into two (or more) powerful channels. Recent observations of channel instability reveal a mode of bifurcation that corresponds well to theoretical computations. It is experimentally shown that the use of a suitable longitudinal gradient in plasma density can eliminate this unstable behavior and restore the stable formation of single high-power laser channels. Recent measurements of the anisotropy of prompt multi-keV Xe(L) emission induced from a Xe target irradiated in stable laser channels can be correlated with this analysis. Our latest experiments confirm the anisotropy and collimation of Xe(L) emission from the stable channels and indicate the possibility of strong amplification of certain Xe(L) lines at~2.9 Å, a wavelength shorter than the DNA base-pair spacing. This x-ray source can be a key component of a new form of biological microimaging applicable to living matter. An estimate of the peak brightness which can be achieved from this source gives a value of ~ 10²⁹ γ·s⁻¹·mm⁻²·mr⁻² (0.1% Bandwidth)⁻¹.

© 2001 EPS