We have demonstrated near-wavelength resolution microscopy in the extreme ultraviolet.Images of 50 nm diameter nanotubes were obtained with a single ~1 ns duration pulse from a desk-top size 46.9 nm laser. We measured the modulation transfer function of the microscope for three different numerical aperture zone plate objectives, demonstrating that 54 nm half-period structures can be resolved. The combination of near-wavelength spatial resolution and high temporal resolution opens myriad opportunities in imaging, such as the 2 ability to directly investigate dynamics of nanoscale structures. © 2007 Optical Society of America OCIS codes: 180.7460, 110.7440, 140.7240. Conventional visible light microscopy, the most convenient method to image small objects, is limited in resolution to about 200 nm [1]. A direct approach to overcome this limitation is the use of shorter wavelength extreme ultraviolet (EUV) or soft x-ray (SXR) light [2][3][4][5][6][7][8][9][10][11]. The highest spatial resolution achieved to date was obtained at the Advanced Light Source, a third generation synchrotron, where images with 15 nm half-period spatial resolution were acquired in exposure times of several seconds using 1.52 nm wavelength SXR light [2]. The need for compact and more broadly accessible full-field optical microscopes has motivated the development of microscopes based on high-harmonic light sources [5,6], plasma sources [7], and EUV/SXR lasers [8][9][10][11] . However, in all cases the spatial resolution achieved was several times the wavelength and/or required long exposures.In this letter we report what is to our knowledge the first EUV microscope that can obtain images with a spatial resolution approaching the wavelength of illumination, in this case λ = 46.9 nm (hν = 26.4 eV). Moreover, this microscope can obtain high spatial resolution images with a single laser shot, corresponding to ~1 ns temporal resolution, opening the possibility to investigate dynamics of nanoscale structures. This is possible due to the high brightness of the laser source, the high throughput of the optics, and the ability to tailor the spatial coherence of the laser to reduce coherence effects that can degrade single shot images. The entire microscope is extremely compact, occupying an area of 0.4 m × 2.5 m. The combination of these attributes 3 results in the demonstration of a high-resolution tool that can rapidly acquire full-field images for practical laboratory use in a broad range of applications.The microscope is schematically illustrated in Figure 1. Two spherical Sc/Si multilayer mirrors arranged in a Schwarzschild configuration with 13% throughput condense the light from the output of the laser onto the sample. A freestanding objective zone plate lens projects the image onto a charge-coupled device (CCD) detector with 13.5 µm pixels. The laser beam is created via a highly ionized plasma column that is generated by fast electrical discharge excitation of an argon-filled capillary [12]. It emits laser pulses with ~10 µJ of energy (2.4×...
We deal with the recent progress in the fabrication of the graded Co/C multilayer mirrors to be used in a 21x Schwarzschild objective (SO) operating at the wavelengths near 4.5 nm ("carbon window" region). The peak reflectivity of flat Co/C mirrors was measured to be 14.8% (wavelength of 4.48 nm, incidence angle of 5 degrees). The reflectivity curves of the spherical mirrors achieved 3%-6%, with the spectral matching accuracy being Deltad approximately 0.008 nm (Deltad/d approximately 0.3%). As a result the SO demonstrates a full working aperture (N(A) approximately 0.2) operation with the total throughput of 0.25%.
The extension of the Fresnel integral to tilted objects is studied using both analytical and numerical approaches. Exact solutions of the parabolic wave equation are used for this purpose. The wavefields produced by a beam propagating at an arbitrary angle θ = π/2 relative to the object surface are investigated. The diffraction patterns are simulated for 1 • ≤ θ ≤ 10 • . It is shown that the inverse problem for tilted objects can be reduced to a Fredholm-type integral equation. Both 2D and 3D geometries are considered. The results may be useful as a theoretical framework for the development of coherent reflection imaging of tilted objects and x-ray imaging of submicron footprints of relativistic electron beams for measurement of their size and shape.
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