X-Ray Nanointerferometer Based on Si Refractive Bilenses

We report a novel type of x-ray interferometer employing a bilens system consisting of two parallel compound refractive lenses, each of which creates a diffraction limited beam under coherent illumination. By closely overlapping such coherent beams, an interference field with a fringe spacing ranging from tens of nanometers to tens of micrometers is produced. In an experiment performed with 12 keV x rays, submicron fringes were observed by scanning and moiré imaging of the test grid. The far field interference pattern was used to characterize the x-ray coherence. Our technique opens up new opportunities for studying natural and man-made nanoscale materials.

Figure 1

(a) Schematic view of the x-ray bilens interferometer. (b) Scanning electron microscope micrograph of a single silicon bilens consisting of 6 individual parabolic lenses. (c) General view with five bilens systems fabricated on the same substrate.

Figure 2

An interference pattern (a) generated by a second bilens system, recorded at a 1 Å wavelength. The intensity variation (b) obtained for the line though the center of the fringe pattern and (c) insert showing a visibility of approximately 38%.

Figure 3

(a) Layout for measurements of interference patterns in the near field. (b) Intensity modulations recorded with a $p\mathrm{\text{−}}i\mathrm{\text{−}}n$ diode counter by scanning a Ta grid vertically. X-ray moiré patterns taken with a CCD camera for various distances between the bilens and the Ta grid: (c) 270, (d) 280, (e) 288, and (f) 291 mm.

Figure 4

Interference fringes for point (left) and $30\mu \mathrm{m}$ (right) source calculated for the parameters $E=50\mathrm{keV}$, $A=20\mu \mathrm{m}$, $d=A$, $R=1.2\mu \mathrm{m}$, $N=100$, $z_0=100\mathrm{m}$, and $z_d=6.7\mathrm{cm}$.