Plasma characterization in the extreme ultraviolet spectral range

At Laser-Laboratorium Gottingen different laser-plasma sources were tested, which are going to be used for characterization of optical components and sensoric devices in the wavelength region from 11 to 13nm. In all cases EUV radiation is generated by focussing a Q-switched Nd:YAG laser into a gas puff target. By the use of xenon or oxygen as target gas, broadband as well as narrowband EUV radiation is obtained, respectively. Different types of valves and nozzles were tested in order to optimize the emitted radiation with respect to maximum EUV intensities, small source diameters and pointing stability. The investigation of these crucial source parameters was performed with specially designed EUV pinhole cameras, utilizing evaluation algorithms developed for standardized laser beam characterization. In addition, a rotatable pinhole camera was developed which allows spatially and angular resolved monitoring of the soft X-ray emission characteristics. With the help of this camera a strong angular dependence of the EUV intensity was found. The results were compared with fluorescence measurements for visualization of the target gas jet. To explain these results a theoretical model was developed, including the absorptance of the EUV radiation in the surrounding target gas.