Abstract

We report tests of a holographic microscope with submicrometer resolution. We used the microscope to record Fourier-transform holograms of gold test patterns (50 nm finest dimension) with 3.4 nm wavelength radiation from the soft-x-ray undulator at the National Synchrotron Light Source. The high-brightness undulator source enabled us to generate holograms of sufficient contrast to be numerically reconstructed from exposures of 10-30 min obtained with a chargecoupled-device (CCD) detector. The coherent x-ray flux through the 100 µ² test objects was 9 × 10⁵ photons/s and was 2 × 10⁶ photons/s in the reference source. The microscope used a 90 µm diameter zone plate as a beam splitter (50 nm finest zone width) both to illuminate the object and to form a focused reference spot. A low-noise integrating CCD camera recorded the interference between the reference and object wavefields, which had a mean spatial period of ~200 µm. After making background corrections, we performed discrete Fourier-transform reconstructions of 512 × 512 pixel arrays of the hologram data, which yielded images of the test patterns having features resolved to better than 1 µm. This approach to Fourier-transform holography demonstrates high-resolution x-ray microscopy by using a relatively coarse-grained detector; this permits fast turnaround from hologram acquisition to wave-front reconstruction.

© 1990 Optical Society of America