Intense High-Harmonic Generation in Extreme-Ultraviolet and Its Nonlinear Wave-Mixing

In this project, we plan to use the 100-TW laser we built in National Central University to drive intense extreme-ultraviolet (EUV) high-harmonic generation (HHG). By incorporating the frequency-doubled driving pulse and the gas-filled capillary technique, we expect that the output pulse energy can reach 1-10 |iJ within 30—50-nm wavelength range, close to the output of EUV free electron laser. Then we plan to use such intense HHG pulse for the research of EUV nonlinear optics.We plan to focus the intense EUV pulse with an intense near-infrared (NIR) pulse onto an Ar gas jet. The Ar atoms are ionized to Ar3+ ions by the intense NIR pulse through tunneling-ionization process. Then the Ar3+ ions serve as the nonlinear medium to achieve the sum-frequency generation (SFG) of one EUV photon and two NIR photons. We calculate the nonlinear polarizability of such process. The result is about 3.16 x 10-63 coul-m4/volt3. Then we propose an experiment by using 1-^J EUV pulse and 48-mJ NIR pulse. The calculated output energy reaches 1 nJ, corresponding to a conversion efficiency of 10-3. Such SFG process is a new technique for EUV wave manipulation.By incorporating the SFG of EUV and NIR pulses, we plan to develop a single-shot, all-optical cross-correlation frequency resolve optical gating (FROG) for EUV waveform measurement. Compared to the existing methods, our method needs no high-vacuum time-of-flight electron spectrometer, no delay scanning, and no data accumulation. The EUV waveform can be measured in one shot, which should be an important breakthrough of EUV waveform characterization.