Due to the high absorption of all materials in the XUV region all windows and filters have to be thin membranes with thicknesses in the 0.1- to 10-Î¼m range. We see from Fig. 2.5 that Be, C, Al, and Mg have low absorption coefficients. However, a material which can be made thinner might give higher transmission, even if it has a larger absorption coefficient. The art of fabricating such thin membranes has evolved over the last 30 years and has been reviewed [1â3]. Several suppliers can provide standard membranes and are able to provide customized structures [4â6].
The main function of a window is to separate two environments but transmit the desired radiation. Examples are:
- Protect the ultrahigh vacuum of a synchrotron source from the vacuum or atmosphere in the instrument of a user;
- Separate the atmosphere in a flow-proportional counter from the vacuum of the experiment;
- Support an absorber pattern in a mask for x-ray lithography;
- Protect an experiment from the debris of a laser plasma x-ray source.
Windows should have the highest possible transmission for the desired radiation. However, because all materials have absorption, and the absorption changes with wavelengths, each window will also have a filter function. It will transmit some wavelengths more than others.
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