We report the demonstration of scanning-probe coherent diffractive imaging method (also known as ptychographic CDI) using a compact and partially-coherent gas-discharge plasma source of extreme ultraviolet (EUV) radiation at 17.3 nm wavelength. Until now, CDI has been mainly carried out with coherent, highbrightness light sources, such as 3rd generation synchrotrons, X-ray free-electron lasers and high harmonic generation. Here we performed ptychographic lensless imaging of an extended sample using a compact, labscale source. The CDI reconstructions were achieved by applying constraint relaxation to the CDI algorithm. Experimental results indicate that our method can handle the low spatial coherence, broadband nature of the EUV illumination as well as the residual background due to visible light emitted by the gas-discharge source. The ability to conduct ptychographic imaging with labscale and partially coherent EUV sources is expected to significantly expand the applications of this powerful CDI method. © Coherent diffractive imaging (CDI) is a rapidly emerging imaging technique to achieve diffraction-limited resolution without using imaging optics [1][2][3]. This makes CDI very attractive for imaging in the extreme ultraviolet (EUV) and X-ray spectral range, where the use of focusing optics is limited. In CDI, a coherent wave illuminating a sample produces a diffraction pattern related to the Fourier transform of the sample structure. While the magnitude of the Fourier transform (i.e. the square root of the diffraction intensity) can be collected by a detector, the phase information is lost, which constitutes the wellknown phase problem. If the diffraction intensity is properly measured, the phase information can be retrieved with an iterative algorithm and the sample structure can then be reconstructed [4]. With the rapid development of coherent X-ray sources worldwide, various CDI methods have been demonstrated and have found broad applications in both physical and biological sciences.One of the powerful CDI methods is termed ptychography (also known as scanning probe CDI) [5], in which an object is scanned relative to a structured illumination probe and a sequence of diffraction patterns is collected with an overlap between adjacent illuminated areas. In contrast to conventional CDI [1][2][3], ptychography uses the overlapping areas as a real space constraint, allowing the reconstruction of extended objects [5]. For high-resolution imaging, CDI and ptychography experiments typically employ large scale X-ray facilities, such as 3rd generation synchrotrons and X-ray free-electron lasers (XFELs) [1][2][3]. In the last decade, CDI and ptychography have also been successfully implemented with highly coherent tabletop femtosecond lasers generating EUV high harmonics [6][7][8][9][10].In this letter, we present an example of ptychographic imaging with a partially coherent compact gas-discharge EUV light source operating at 17.3 nm wavelength (Li-like oxygen, 1s 2 2p-1s 2 3d transition). In our gas-discharge light...

Extreme ultraviolet (EUV) spectroscopy is a powerful tool for studying fundamental processes in plasmas as well as for spectral characterization of EUV light sources and EUV optics. However, a simultaneous measurement covering a broadband spectral range is difficult to realize. Here, we propose a method for interferometric broadband Fourier spectroscopy connecting soft x ray and visible spectral ranges with moderate spectral resolution. We present an analytical model to recover the spectrum from a double-slit interferogram. We apply our model for spectral characterization of a partially coherent gas-discharge EUV light source operated with different gases in the spectral range between 10 and 110 nm wavelengths. Our approach allows a simple and fast broadband spectroscopy with fully or partially spatially coherent light sources, for instance, to characterize out-of-band radiation in EUV lithography applications.

Coherent diffractive imaging (CDI) and related techniques enable a new type of diffraction-limited high-resolution extreme ultraviolet (EUV) microscopy. Here, we demonstrate CDI reconstruction of a complex valued object under illumination by a compact gas-discharge EUV light source emitting at 17.3 nm (O VI spectral line). The image reconstruction method accounts for the partial spatial coherence of the radiation and allows imaging even with residual background light. These results are a first step towards laboratory-scale CDI with a gas-discharge light source for applications including mask inspection for EUV lithography, metrology and astronomy

We report on high-resolution lens-less imaging experiments based on ptychographic scanning coherent diffractive imaging (CDI) method employing compact plasma sources developed for extreme ultraviolet (EUV) lithography applications. Two kinds of discharge sources were used in our experiments: a hollow-cathode-triggered pinch plasma source operated with oxygen and for the first time a laser-assisted discharge EUV source with a liquid tin target. Ptychographic reconstructions of different samples were achieved by applying constraint relaxation to the algorithm. Our ptychography algorithms can handle low spatial coherence and broadband illumination as well as compensate for the residual background due to plasma radiation in the visible spectral range. Image resolution down to 100 nm is demonstrated even for sparse objects, and it is limited presently by the sample structure contrast and the available coherent photon flux. We could extract material properties by the reconstruction of the complex exit-wave field, gaining additional information compared to electron microscopy or CDI with longer-wavelength high harmonic laser sources. Our results show that compact plasma-based EUV light sources of only partial spatial and temporal coherence can be effectively used for lens-less imaging applications. The reported methods may be applied in combination with reflectometry and scatterometry for high-resolution EUV metrology.