Soft X-ray emission generated by the interaction of intense, femtosecond laser with gas, solid, and cluster targets

Abstract

This thesis is devoted to experimental study of the interaction of femtosecond laser pulse at terawatt power level with various forms of matter. The soft X-ray emission form laser-irradiated gases, solids, and gaseous clusters has been investigated by means of time-integrated spectroscopy in the wavelength region 40-500 Å. Spectroscopic study of optical-field-ionized Ar, Kr, Xe, and oxygen plasmas is presented. By focusing 20-fs laser pulse at intensity of $\sim7\times10^16W/cm^2$ into high-pressure gas jet and/or low-density static gas cell, emission on lines originating from ions up to Ar IX, Kr IX, and Xe IX was observed. The feasibility of using the powerful, femtosecond Ti:Sapphire laser system developed at KAIST for pumping of collisional-excitation and recombination soft X-ray lasers is investigated. Spectra from highly charged ions of up to F VII, Al XI, Ti XII, Fe XVI, and Cu XIX are presented, and the effect of femtosecond prepulse on the X-ray emission from solid target is examined. The interaction of intense, 25-100 fs pulses with Ar and Ne clusters from a cryogenically-cooled gas jet target is explored. New spectral lines from charge states as high as Ar XI and Ne VIII appeared with decreasing temperature, and significant enhancement of X-ray line emission was observed with cooling, demonstrating efficient collisional heating of near-solid-density expanding clusters by 25-100 fs laser pulses.