Spatial characterization of extreme ultraviolet plasmas generated by laser excitation of xenon gas targets

Abstract

At Laser-Laboratorium Göttingen 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 13 nm. In all cases extreme ultraviolet (EUV) radiation is generated by focusing a Q-switched Nd:YAG laser into a pulsed 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 positional 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 both 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 data were compared with fluorescence measurements for visualization of the target gas jet. The experimental observations can be explained by reabsorption of the generated EUV radiation in the surrounding target gas, as supported by semiempirical model calculations based on the attenuation in the three-dimensional gas density according to Lambert–Beer’s law. As a consequence of the presented investigations, an optimization of the EUV source with respect to intensity, plasma shape, and angular dependence is achieved, resulting in a spherical plasma of 200 μm diameter and a 50% increase of the EUV pulse energy.

Spatial and temporal evolution of argon sparks

“…8 Laserproduced sparks have many practical applications. Laser-induced sparks have been used as a source for producing high-intensity x rays 9 and extreme UV radiation in rare gases 10 and also for producing ultrafast shutters. 11 They are also capable of igniting gaseous mixtures or even of extinguishing a diffusion flame.…”

EUV damage threshold measurements of Mo/Si multilayer mirrors

“…Fig. 1) [10][11][12]. EUV radiation is generated by focusing a Nd:YAG laser (Innolas, wavelength 1064 nm, pulse energy 700 mJ, pulse duration 8.8 ns) onto a rotating solid Au target, yielding a plasma diameter of about 50 µm (FWHM) [9].…”

Ablation of polymers by focused EUV radiation from a table-top laser-produced plasma source

“…Fig. 1) [21][22][23]. EUV radiation is generated by focusing a Nd:YAG laser (Innolas, wavelength 1064 nm, maximum pulse energy 700 mJ, pulse duration 8.8 ns) onto gaseous or solid targets [26,28].…”