高階諧波產生是一種高相干性Extreme-UV/X-ray光源，過去三年來，我們的實驗團隊一直在努力提升高階諧波的輸出效率與能量，在我接手之前，利用810-nm雷射脈衝入射Ar氣體，所產生高階諧波的第23階脈衝輸出能量可達到1.2 nJ，轉換效率為1.6×〖10〗^(-7)。由於在相位匹配條件下，使用較短波長的激發光源可以有效提升高階諧波產生的轉換效率，因此，在本論文中，我使用由810 nm二倍頻至405 nm的超短脈衝，做為高階諧波的激發光源，實驗結果顯示此方法成果顯著，在40-nm波段附近，405-nm激發光源的第9階高階諧波輸出能量提升至280.6 nJ，轉換效率達到 2.3×〖10〗^(-5)。 本論文紀錄我提升高階諧波輸出效率的方法，並比較使用不同激發光源波長、與使用不同氣體所產生高階諧波的差異，得到與理論預期相符的結果。其次，為了得到高階諧波的絕對輸出能量，我量測了高階諧波對鋁箔膜的穿透率，結果顯示，鋁箔膜對35-nm與45-nm 高階諧波的穿透率分別為13.9 % 與 4.0 %，這讓我們得以計算高階諧波的絕對輸出能量與絕對轉換效率。最後，我觀測激發雷射脈衝穿過交互作用氣體時的Thomson Scattering，測得高階諧波產生過程中，自由電子的相對密度，驗證了不同波長產生高階諧波的相位匹配條件。 ;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.
