Ultrabright multikilovolt coherent tunable x-ray source at λ ∼ 2.71–2.93Å

Abstract

Detailed molecular structural information of the living state is of enormoussignificance to the medical and biological communities. Since hydrated biologicallyactive 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 functioningspecimens in order to faithfully reveal their full molecular architectures. Anx-ray holographic microscope equipped with an x-ray laser as the illuminatorwould be uniquely capable of providing these images. A quantitative interlockingconcordance of physical evidence, that includes (a) the observation ofstrong enhancement of selected spectral components of several Xeq+ hollow-atomtransition 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 theamplified transitions, (c) evidence for spectral hole-burning in thespontaneous emission, a manifestation of saturated amplification, thatcorresponds spectrally with the amplified lines, and (d) the detection ofan intense narrow (δθx ∼ 0.2 mrad)directed beam of radiation, (1) experimentally demonstratesin the λ ∼ = 2.71–2.93 Årange (ℏωx ∼ = 4230–4570 eV)the operation of a new concept capable of producing the ideal conditions foramplification of multikilovolt x-rays and (2) proves the feasibility of acompact x-ray illuminator that can cost-effectively achieve the missionof biological x-ray microholography. The measurements also (α) establish theproperty of tunability in the quantum energy over a substantial fraction of the spectralregion exhibiting amplification (Δℏωx ∼ 345 eV) and(β)demonstrate the coherence of the x-ray output through the observation of acanonical spatial mode pattern. An analysis of the physical scaling revealed bythese results indicates that the capability of the x-ray source potentially includessingle-molecule microimaging, the key for the in situ structural analysis ofmembrane proteins, a cardinal class of drug targets. An estimate of the peakbrightness 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-foldhigher than presently available synchrotron technology.