Patent Number: 
Section: claims

1. A window transparent to electron rays comprising: a foil transparent to electron rays and separated from a carrier substrate;  a retaining element connected to a peripheral region of the foil for supporting in the operational state a central region of the foil that is transparent to electron rays, the foil transparent to electron rays and the retaining element being constructed as two separate parts and the retaining element being made of a material which has a linear thermal expansion coefficient adapted to the linear thermal expansion coefficient of the foil material; and  a connecting layer interposed between the foil and the retaining element for connecting the foil to the retaining element. 2. A window transparent to electron rays as claimed in  claim 1 , wherein the foil transparent to electron rays is made of diamond. claim 1 3. A window transparent to electron rays as claimed in  claim 1 , wherein the foil transparent to electron rays is made of molybdenum. claim 1 4. A window transparent to electron rays as claimed in  claim 2 , wherein the retaining element is made of a material having a linear thermal expansion coefficient smaller than 9xc3x9710 xe2x88x926 /K. claim 2 5. A window transparent to electron rays as claimed in  claim 1 , wherein the retaining element is made from a material selected from a group comprising the following materials: metals such as molybdenum, tungsten, titanium, tantalum an their alloys, diamond, glasses, and ceramic materials having correspondingly low linear thermal expansion coefficients. claim 1 6. A window transparent to electron rays as claimed in  claim 1 , wherein the interposed connecting layer is a fusion layer of an active metal solder or a glass fusion layer or a combined adhesion-fusion layer. claim 1 7. A window transparent to electron rays as claimed in  claim 1 , wherein at least one surface of the foil transparent to electron rays comprises at least one thickening whose thickness is at least 10% of the foil thickness, the at least one surface being a surface facing away from the retaining element. claim 1 8. A window transparent to electron rays comprising: thickness (xcexcm) less than 0.7L(cm)xc3x97xcex94p(bar)  a foil transparent to electron rays and separated from a carrier substrate, the foil transparent to electron rays being made of diamond; and  a retaining element connected to a peripheral region of the foil for supporting in the operational state a central region of the foil that is transparent to electron rays,  wherein the retaining element is made of a material which has a linear thermal expansion coefficient adapted to the linear thermal expansion coefficient of the foil material and the following holds for the thickness of the diamond foil:  xe2x80x83with xcex94p (bar) representing the pressure difference between the two sides of the window, and L being the greatest longitudinal dimension of the window opening. 9. An X-ray device with an electron source for the emission off electrons, with a target made of a liquid metal circulating in an operational state of the X-ray device and emitting X-ray radiation when hit by the electrons, and with a window transparent to electron rays serving as a separation element between the electron source and the target; the window comprising: a foil transparent to electron rays and separated from a carrier;  a retaining element connected to a peripheral region of the foil for supporting in the operational state a central region of the foil that is transparent to electron rays, the foil transparent to electron rays and the retaining element being constructed as two separate parts and the retaining element being made of a material which has a linear thermal expansion coefficient adapted to the linear thermal expansion coefficient of the foil material; and  a connecting layer interposed between the foil and the retaining element for connecting the foil to the retaining element.