Detailed molecular structural information of the living state is of enormous significance to the medical and biological communities. Since hydrated biologically active structures are small delicate complex three-dimensional (3D) entities, it is essential to have molecular scale spatial resolution, high contrast, distortionless, direct 3D modalities of visualization of naturally functioning specimens in order to faithfully reveal their full molecular architectures. An x-ray holographic microscope equipped with an x-ray laser as the illuminator would be uniquely capable of providing these images. A quantitative interlocking concordance of physical evidence, that includes (a) the observation of strong enhancement of selected spectral components of several Xeq+ hollow-atom transition arrays (q = 31, 32, 34, 35, 36, 37) radiated axially from confined plasma channels, (b) the measurement of line narrowing that is spectrally correlated with the amplified transitions, (c) evidence for spectral hole-burning in the spontaneous emission, a manifestation of saturated amplification, that corresponds spectrally with the amplified lines, and (d) the detection of an intense narrow (δθx ∼ 0.2 mrad) directed beam of radiation, (1) experimentally demonstrates in the λ ∼ = 2.71–2.93 Å range (ℏωx ∼ = 4230–4570 eV) the operation of a new concept capable of producing the ideal conditions for amplification of multikilovolt x-rays and (2) proves the feasibility of a compact x-ray illuminator that can cost-effectively achieve the mission of biological x-ray microholography. The measurements also (α) establish the property of tunability in the quantum energy over a substantial fraction of the spectral region exhibiting amplification (Δℏωx ∼ 345 eV) and (β) demonstrate the coherence of the x-ray output through the observation of a canonical spatial mode pattern. An analysis of the physical scaling revealed by these results indicates that the capability of the x-ray source potentially includes single-molecule microimaging, the key for the in situ structural analysis of membrane proteins, a cardinal class of drug targets. An estimate of the peak brightness achieved in these initial experiments gives a value of ∼1031–1032 photons s−1 mm−2 mrad−2/(0.1% bandwidth), a magnitude that is ∼107–108-fold higher than presently available synchrotron technology.

Comparison of Xe(L)/Kr(L) emission spectra generated from Xe and Kr clusters by ultraviolet (248 nm) and infrared (800/1060 nm) excitation reveals sharply different wavelength scalings. An interpretation of these contrasting scalings based on L-shell Auger widths explains this difference and supports the theoretical attribution of the strong hollow-atom Xe(L) emission produced with 248 nm irradiation to an ordered phase-dependent coupling. These results indicate that clusters of Yb, Ta and W may produce comparably strong hollow atom L-shell emission at ∼8 keV with 248 nm excitation.

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