EUV Optics

For the production of high EUV energy densities a modified Schwarzschild objective for 13.5 nm radiation has been developed within the BMBF project KOMPASS ("Kompakte Strahlquelle hoher Brillanz für den weichen Röntgen-Spektralbereich").

A Schwarzschild objective was developed in the scope of a cooperative project KOMPASS („Kompakte Strahlquelle hoher Brillanz für den weichen Röntgen-Spektralbereich“) of the German Ministry of Research. It consists of two spheric mirrors (the substrate is ULE glass) which were each given a reflectivity of almost 70% using a Mo/Si multilayer-coating (Fraunhofer IOF). The aperture is 0.4, the magnification is 0.1. The diameter of the resulting EUV focus is < 30 µm at an energy density of ~ 100 mJ/cm² (cf. Table 1).

Magnification (M)	0.102
Spot size	~ 30 µm (source image)
NA	0.4
Acceptance angle (omega)	5.33 msr
Substrates	ULE glass (spherical)
Reflectivity of Mo/Si multi-layers (R)	> 65 % (per mirror / IOF)

Table 1: Charakteristics of the EUV Schwarzschild-Objektive

: Prototype of a compact EUV source with Schwarzschild objective (left). Focussing a Nd:YAG-laser in a pulses Xe gas jet leads to 13.5 nm emission by the highly excited plasma. The modified Schwarzschild object (right, cf. Fig. 1 in Adaptive Optics / Optics Design) was coated by our project partner IOF (Jena) in order to reach a high EUV reflectivity.

The Mo/Si multilayer coating allows the Schwarzschild objective to reflect light in a narrow range at 13.5 nm. A broadband beam guidance is possible by means of total reflection at grazing angles. In the scope of the InnoNet project SpeXUV, a Kirkpatrick-Baez configuration was designed (cf. Fig. 2) to be used as a broadband condensator in a spectral photometer in the range 10…20 nm (specifications cf. Table 2).

: Schematic representation of the principle of a Kirkpatrick-Baez configuration (left) and picture of the actual condensor.

Resolution	< 10 µm (1:1 imaging)
NA	0.007
Transmission (twofold reflection)	> 65 % (> 81 % per mirror)

Table 2: Specifications of the Kirkpatrick-Baez condensor