2007 Conference on Lasers and Electro-Optics (CLEO)
DOI: 10.1109/cleo.2007.4452662
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Table top holography with EUV laser was demonstrated. The hologram recorded in a photoresist was digitized with an AFM. The image was reconstructed achieving 380 nm spatial resolution determined using wavelet analysis and image correlation. ©2007 Optical Society of America OCIS codes: (090.2890) Holographic optical elements; (100.2960) Image analysis Demonstration of highly coherent compact EUV sources [1-3] opens possibilities for an implementation of practical table-top coherent imaging systems with nanometer-scale resolution. In a recent experiment Gabor holographic imaging using a fully coherent table-top source of high order harmonic (HHG) radiation demonstrated a spatial resolution approximately 7 microns [3]. In this paper, we improve the spatial resolution of the table-top EUV holographic imaging by a factor ~17 to below 400 nm using a table top extreme ultraviolet laser. A wavelet analysis was used to evaluate the resolution of our system and is in excellent agreement with predicted resolution limited by spatial coherence of the source. The experimental set up is schematically illustrated in Figure 1. The 46.9 nm wavelength light used for illumination is produced by a table top discharge pumped capillary Ne-like Ar laser. Laser produced 0.1 µJ pulses at a repetition rate of 1 Hz [4] and occupies a compact 1 × 0.5 m 2 footprint. The EUV laser has a high temporal coherence with a fractional spectral bandwidth of ∆λ/λ ≈ 1×10 -4 , which corresponds to a coherence length of l c ≈ 470 µm. An AFM cantilever [5] served as the test object. Holograms were recorded in a 200 nm thick layer of polymethil metacrylate (PMMA MicroChem 950,000 molecular weight) spin-coated on a silicon wafer. The PMMA coated wafer was placed at a distance of z p ≈ 4 mm away from the AFM cantilever to record the hologram. Exposures were approximately 150 laser shots which correspond to ≈ 2×10 7 photons µm -2 . After the exposure, the photoresist was developed by immersing sample in a solution of MIBK-methyl isobutyl ketone (4-Methyl-2-Pentanone) with IPA-isopropyl alcohol 1:1 for 30 seconds and in a 1:3 solution for 30 seconds. After that the sample was dried using compressed nitrogen.