Time-resolved spectroscopy of solid-state materials using an x-ray laser (Thesis)

X-ray laser is a characteristic extreme ultraviolet (EUV) source with short pulse duration of several pico-seconds, narrow spectral width, and high coherence. In particular, x-ray laser with the wavelength of around 13 nm is expected as a powerful tool of various research fields such as EUV lithography because the multilayer mirror with high reflectance is commercially prepared. However, spectroscopic studies of materials optically excited with x-ray laser are few while imaging and interference measurements are intensively studied. In this study, the beam divergence and spatial coherence of x-ray laser was improved and applied to the measurement of time resolved emission spectroscopy of a solid-state material. The beam divergence of the x-ray laser was improved by double target configuration using two gain media. The nickel-like silver x-ray laser at the wavelength of 13.9 nm was improved to be spatially fully coherent beam with the divergence of 0.20 mrad. The number of coherent photons of this beam was 108 per pulse. The narrow divergence allowed us the beam transported by use of a simple mirror system with a small diameter of 1 inch. As an application of the x-ray laser, the UV emission from the zinc oxide (ZnO) single crystal excited by the 13.9 nm x-ray laser was observed and evaluated for EUV scintillator. The time-resolved emission spectra were observed for 13.9 nm excitation and 351 nm excitation. In both the excitation conditions, a prominent fluorescence peak of the ZnO exciton transition was observed at around 380 nm. The time profile at the peak of the spectra could be expressed by a double exponential decay with time constants of 1 ns and 3 ns in the both cases. The lifetimes and intensity ratio of the two decay components in the both cases were almost similar in spite of the huge difference in the excitation photon energy. The response time is sufficiently short for characterizing EUV lithography light sources having several nanoseconds duration. It is also shown that the x-ray laser is an excellent tool for time-resolved spectroscopy and characterization of materials intended for next-generation lithography applications. Especially for time-resolved measurement, high-speed phenomenon can be observed with resolution of several pico-seconds using the x-ray laser. (author)