Quantum Electronics 25(9) 919-922 (1995) ©1995 Kvantovaya Elektronika and Turpion Ltd PACS numbers: 07.85. Yk; 41.50.+h;52.25.Nr;52.50.Jm Reflective soft x-ray microscope for the investigation of objects illuminated by laser-plasma radiation I A Artyukov*, V E Asadchikov, A V Vinogradov, Yu S Kas'yanov, V V Kondratenko, R V Serov, A I Fedorenko, S A Yulin Abstract. Multilayer mirrors were used in a soft x-ray optical system which formed magnified images of micro- scopic objects with a resolution of ~0.2 um at the wave- length 20 nm. The system consisted of a laser-plasma source, an x-ray condenser, a Schwarzschild objective with a magnification 20, a set of filters, and a detector. The quality of the x-ray optics and the precision of align- ment of the system components made it possible to attain a resolution of ~ 0.2 um when the full aperture of the objec- tive was used. A single shot in the form of the second harmonic of an Nd laser, generating pulses of ~0.5 J energy and ~ 1.5 ns duration, was sufficient for exposure. 1. Introduction An important task in modern x-ray microscopy is the attain- ment of spatial resolution of the order of the radiation wavelength, which corresponds to the diffraction limit in optical systems with a large numerical aperture. In the wave- length range 3-30 nm the most promising are the systems with x-ray optical components of two types: normal- incidence multilayer mirrors and zone plates. Particularly convenient are sliced zone plates fabricated by the method of multilayer sputtering on a thin wire or filament from which a zone plate of the required thickness is then cut [1 - 3]. For physical and technological reasons, the working areas of such mirrors and zone plates differ by six orders of mag- nitude. A mirror diameter is usually 50-150 mm and that of a zone plate is 100-300 um. Naturally, mirrors and zone plates have their own ranges of application and the method of their use is different. On the other hand, there is some com- petition between them in the attainment of the best resolution. However, in many applications other characteris- tics are as important as the resolution: they include the field view, the effective area, the focal length, etc. "This author's name is sometimes spelt Artioukov in some English- language publications. I A Artyukov, A V Vinogradov P N Lebedev Physics Institute, Russian Academy of Sciences, Leninskil prospekt 53, 117924 Moscow; V E Asadchikov Institute of Crystallography, Russian Academy of Sciences, Leninskil prospekt 59, 117333 Moscow; Yu S Kas'yanov, R V Serov Institute of General Physics, Russian Academy of Sciences, ul. Vavilova 38, 117942 Moscow; V V Kondratenko, A I Fedorenko, S A Yulin Polytechnic Institute, ul. Frunze 21, 310002 Kharkov, Ukraine Received 31 January 1995 Kvantovaya Elektronika 22 (9) 951 -954 (1995) Translated by A Tybulewicz We shall now give a description, and report studies, of a Schwarzschild microscope with the magnification M « 21 at wavelengths ~ 20 nm. Our aim was to develop a technology for the fabrication of components of such an x-ray microscope and for its alignment, and to test experi- mental methods in which reflection x-ray optics is used in imaging of small nonluminous objects with features of sub- micron size. 2. Schwarzschild x-ray objective Our microscope included a laser-plasma source, an x-ray condenser for the illumination of an object, a Schwarzschild objective, a set of filters, and a detector (Fig. 1). The Schwarzschild objective consisted of two spherical mirrors and was capable of compensating for third-order axial aber- rations when an object occupied a certain position. A = 0.53 um Figure 1. Schematic diagram of the soft x-ray microscope: (]) bulk rhenium target; (2) laser plasma; (3) condenser; (4) aluminium filters, 0.4-0.5 um thick; (5) test object; (6) UF-4 photographic film; (7) Schwarzschild objective; (8) focusing objective. In spite of the fact that work on the Schwarzschild x-ray objectives has been going on for over a decade [4-6], the spa- tial resolution achieved so far is still considerably greater than the x-ray wavelength. This is due to the stringent requirements in respect of the precision of fabrication of mir- rors of spherical shape, their alignment, and quality of multilayer coatings. At present the development and applications of the Schwarzschild x-ray objectives are proceeding along several directions. The first direction is the development of scanning microscopes [7 - 9] in which the most important characteris- tic is the resolution on the optic axis (representing the size of the spot), which is of the order of 0.1 um.