Shadow monochromatic backlighting: Large-field high resolution X-ray shadowgraphy with improved spectral tunability

The shadow monochromatic backlighting (SMB) scheme, a modification of the well-known soft X-ray monochromatic backlighting scheme, is proposed. It is based on a spherical crystal as the dispersive element and extends the traditional scheme by allowing one to work with a wide range of Bragg angles and thus in a wide spectral range. The advantages of the new scheme are demonstrated experimentally and supported numerically by ray-tracing simulations. In the experiments, the X-ray backlighter source is a laser-produced plasma, created by the interaction of an ultrashort pulse, Ti:Sapphire laser (120 fs, 3-5 mJ, 10¹⁶ W/cm² on target) or a short wavelength XeCl laser (10 ns, 1-2 J, 10¹³W/cm² on target) with various solid targets (Dy, Ni + Cr, BaF₂). In both experiments, the X-ray sources are well localized spatially (∼20 μm) and are spectrally tunable in a relatively wide wavelength range (λ = 8-15 Å). High quality monochromatic (δλ/λ ∼ 10^-5-10^-3) images with high spatial resolution (up to ∼ 4 μm) over a large field of view (a few square millimeters) were obtained. Utilization of spherically bent crystals to obtain high-resolution, large field, monochromatic images in a wide range of Bragg angles (35° < Θ < 90°) is demonstrated for the first time.