氬氣中雙波長激發之四波混頻訊號:相對相位效應

Four-Wave Mixing with Two Color Excitation in Argon: The Relative Phase Effect

陳韋帆(Wei-Fan Chen)

指導教授 ： 潘犀靈

國立清華大學/理學院/物理學系/碩士(2012年)

摘要

在此論文中，我們研究在氬氣中由Q-開關Nd:YAG雷射基頻(λ=1064nm)和其二倍頻(λ=532nm)所產生的三階諧波(λ=355nm)訊號，並且著重於討論相對相位和驅動雷射強度對非線性頻率轉換的影響。根據基頻與二倍頻光微擾非線性光學理論，三階諧波訊號的強度會隨著相對相位的改變而具有週期性的變化，三階諧波訊號的週期性振盪是由直接三倍頻轉換與四波混合這兩個轉換機制的干涉所產生。實驗趨勢與理論模擬吻合。另外，我們也研究基頻與二倍頻光雷射強度以及氣體壓力對於三階諧波訊號的影響。實驗結果指出，三階諧波訊號在二倍頻的強度為7.6×1012 W/cm2附近會出現飽和的現象，且與氬氣壓力密度平方成正比，正如理論所預期。

關鍵字

諧波產生 ； 相對相位 ； 四波混頻

並列摘要

In this thesis, we investigate the generation of (355nm) light by the fundamental output of the in Q-switched Nd:YAG laser (λ=1064nm) and its second harmonic (λ=532nm) in argon. The emphasis is on the influence of relative phases and intensities of the 2-color light. Based on our simulation of the 3rd harmonic of the Nd:YAG laser, the intensity of the 355nm light will oscillate periodically with the relative phases of the two-frequency driving electric fields. The periodic modulation of the 3rd-order harmonic can be attributed to the interference of third-harmonic signals generated from a direct THG channel (3ω = ω + ω + ω) and four-wave mixing (FWM) channel (3ω = 2ω + 2ω − ω). Our experimental results are in good agreement with the theoretical simulation. In addition, the dependence of the intensity of the 2-color exciting light and the gas pressure dependence of the 3rd-order harmonic signal are also presented. It was found out that the 3rd harmonic output exhibits saturation behavior as the intensity of the second harmonic reaches 7.6×1012 W/cm2. A square-law dependence on gas pressure is also in agreement with the prediction of the theory.

並列關鍵字

harmonic generation ； relative phase ； four wave mixing

參考文獻

1 L. E. Chipperfield, J. S. Robinson, J. W. G. Tisch, and J. P. Marangos, “ Ideal Waveform to Generate the Maximum Possible Electron Recollision Energy for Any Given Oscillation Period ,“ Phys. Rev. Lett. ,vol. 102, issue 6, 2009.

3 Dmitry A. Telnov, Jingyan Wang, Shih-I Chu, ‘‘Two-color phase control of high-order harmonic generation in intense laser fields,’’ Phys. Rev. A vol. 52 no. 5, pp. 3988-3996, 1995.

4 P. A. Franken, A. E. Hill, C. W. Peters, and G. Weinreich, “Generation of Optical Harmonics,” Phys. Rev. Lett. vol. 7, no. 4, pp. 118-119, 1961.

5 G. H. C. New and J. F. Ward, “Optical Third-Harmonic Generation in Gases, ” Phys. Rev. Lett. vol. 19, no. 10, pp. 556-559, 1967.

6 Armstrong, J. A., Bloembergen, N., Ducuing, J. & Pershan, P. S. “Interactions between light waves in a nonlinear dielectric, ” Phys. Rev. A, vol. 127, no. 6, pp. 1918–1939, 1962