Staring/focusing lobster-eye hard x-ray imaging for non-astronomical objects

Abstract

A new approach to hard X-ray imaging is proposed, based on staring optics consisting of a lobster-eye lens. This new Staring Imaging Lobster-Eye X-Ray approach is especially suited to X-ray lobster-eye imaging of non-astronomical objects at finite distances, because the staring optics replacing the standard scanning optics, result in an extremely efficient power budget, making possible not only the use of low-efficiency Compton backscattering but also operation with low-flux X-ray beams, increasing operator safety. The lobster-eye optics, consisting of square-cross-section microchannels, transmit an X-ray beam by total external reflection. This mode of operation has already been verified for viewing astronomical objects. Its major challenge is minimizing image defocusing by apodization. For this purpose, a new lens imaging equation is derived, and a new local optical axis concept is defined. Applications include medical imaging, cargo inspection, non-destructive testing, industrial and security safeguards, and surveillance. INTRODUCTIONThe nature of X-rays makes its impossible to create practical refractive elements to focus them. The only way to focus X-rays is to reflect them from smooth metal surfaces at low grazing angles of incidence. Classical X-ray reflection optics are large (meter scale), expensive, and hard to align, and -the most significant drawback, they have small fields of view (FOV). This has led to the development of Kumakov X-ray focusing optics, consisting of curved, circular capillaries [1,2] . Because of the very small critical grazing angles (≤3.6 arc-minutes for 60 keV X-rays), and relatively large inner capillary diameters, the capillaries must be extremely long. Such optics still have limited FOVs, and the thickness of the capillary elements and the dead space between them considerably reduce the fill factor of these capillary X-ray optics. The more advanced type of X-ray focusing optics is the lobster eye (LE). A lobster (including shrimp, crayfish, and other crustaceans) views the world through an array of square cross section ommatidia curved across the outside of its eye [3] . In a lobster eye, each square cell is short and rectangular, with its length about twice its width. Light is reflected over a wide range of angles of incidence to form a rather fast focus. For hard X-ray applications, the cell lengths must be >100 times their widths, but the optical principle remains the same as that in the eye of the crustacean. The eye of a lobster has an FOV of slightly more than 180°. Each ommatidium captures a small amount of light, which comes to the eye from all angles, and the light from numerous ommatidia is focused to form an image.Current X-ray LE optics are based on slumped lead-glass microchannel plates (MCPs) [4][5][6][7][8] , but the spectral range of operation of existing MCP-based LE optics is limited to X-rays with energies of ≤4 keV (or λ ≥3.1 Å) [4][5][6] . Harder X-rays with lower critical grazing angles cannot be focused efficiently by glass MCPs because of the inaccessibil...

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