Spectral Radiant Power Measurements of VUV and Soft X-Ray Sources

Abstract

In the last decade the use of VUV and soft x-ray radiation has steadily been growing, not only in fields of basic research like atomic, molecular, solid state, surface and astrophysics, but also in applied physics and technology like controlled nuclear fusion research, x-ray microscopy and x-ray lithography. In principle, an electron storage ring dedicated to the generation of VUV and soft x-ray radiation meets nearly all requirements in the research areas mentioned above but disadvantages exist especially in the fields of applied physics and technology: (i) high capital and operating costs are disadvantageous, (ii) all instrumentation has to be transported to and operated at the site of the storage ring, (iii) the ultra-high vacuum requirements are incompatible with some types of applications, (iv) especially in the soft x-ray range the usable emission angle perpendicular to the plane of the electron orbit is rather limited. Therefore, different laboratories started with the development of alternative sources for VUV and soft x-ray radiation (particularly for x-ray lithography and microscopy) which are more compact, less expensive to construct and to operate and which are optimized for the specific application. The interest is concentrated mainly on pulsed plasma sources,e.g., [5.1–4] of small emitting areas having high spectral radiant power like vacuum sparks, laser-produced plasmas, plasma focus devices and plasma pinches. Presently the quoted radiant properties of the different sources can hardly be compared amd improvements can be judged only with certain reservations because reliable (absolute) spectral radiant power measurements are missing in the extreme VUV and soft x-ray range. Therefore, in the radiometric laboratory of PTB at the Berlin electron storage ring BESSY an instrumentation was developed particularly suited for spectral radiant power measurements under grazing incidence. In this paper we describe the method and the corresponding uncertainties. The quality of the method is studied by measuring the radiant properties of a laser-produced plasma.