| Summary: | 碩士 === 國立中央大學 === 物理學系 === 104 === High-order harmonic generation (HHG) is a kind of ultrashort coherent EUV/x-ray source. In this thesis, I report the frequency-doubling of 810-nm ultrashort laser pulses, and then use these 405-nm pulses to drive HHG. Comparing with the HHG yield driven by 810-nm pulses, the conversion efficiency is significantly increased with 405-nm pumping. The output pulse energy of the 9th harmonic (about 45-nm wavelength) from Ar gas reaches 280.6 nJ, corresponds to a conversion efficiency of about 2.3 × 10−5.
In the experiment, the HHG output is filtered by aluminum filters to block the driving pulse. In order to obtain the absolute HHG yield, I design an aluminum filter pair to calibrate the filter transmittance. The results show that the transmittances for 35-nm and 45-nm HHGs are 13.9% and 4.0%, respectively. These values are essential for the calculation of HHG pulse energy. Furthermore, I measured the Thomson scatterings from the interacting medium with different pump wavelengths. Comparing these Thomson scattering intensities, the relative electron densities and the ionization ratios are obtained. The results consist with the theoretical calculation of the phase-matching conditions with different pumping wavelengths.
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