以雙色飛秒雷射合成波行研究聚甲基丙烯酸甲酯的光熔蝕現象

在這篇論文中, 我們研究甲基丙烯酸甲酯(壓克力)之單色與雙色飛秒雷射熔蝕現象。光源是鈦藍寶石雷射產生之基頻()與倍頻(2)光，我們量測樣品上熔蝕之面積並計算熔蝕過程之臨界閾值分別為2.53和1.86焦耳每平方公分；在雙色熔蝕之實驗中，我們設計並架設了一個同軸實驗架構，且著重於熔蝕洞面積對基頻與倍頻光間相對相位之變化，其中，基頻與倍頻光之脈衝在時域與空間上都是重疊的，我們發現，當基頻與倍頻光之偏振態相互平行時，熔蝕洞面積之變化和相對相位有強烈之對應關係，當基頻與倍頻之比例為8%時，我們可觀察到面積調制深度達到31%，此現象可解釋為合成電場波形對熔蝕之多光子吸收效率的影響，此外，我們也發現，當倍頻光相對於基頻光之比例越來越高時，這種調制現象則變的不明顯，而此種現象可解釋為，倍頻2之雙光子吸收激發相對於基頻之三或四光子吸收激發，逐漸主導了熔蝕現象。

關鍵字

熔蝕；飛秒

並列摘要

In this dissertation, we report the experiment and results of single color and two color femtosecond ablation of Polymethylmethacrylate(PMMA). The ablation threshold of PMMA by fundamental () and second harmonic (2) of a femtosecond Ti:sapphire laser amplifier are 2.53 J/cm2 and 1.86 J/cm2 respectively. For two color ablation, we designed and built an in-line system. We studied the effect of relative phase between the two wavelengths on the ablation hole area. The pulses of two colors are overlapping in both time and spatial domain. When the polarizations of two color are parallel, the ablation hole area depends strongly on the relative phase between the fundamental and second harmonic beams. A modulation depth of (31%) in the ablated area was observed with a 2/ power ratio of 8%. This phenomenon could be explained by the dependence of ablation on multiphoton ionization rate, which is related to the synthesized waveform. We also found that when the 2/ power ratio becomes higher, the modulation depth or contrast of ablated holes becomes unclear. This characteristic could be explained as the two photon-ionization rate of the second harmonic beam of PMMA dominates over that of the fundamental beam which is due to three or four-photon ionization.

並列關鍵字

Ablation ； Femtosecond

參考文獻

[1] M. D. F. B.C. Stuart, A. M. Rubenchik, B.W. Shore, M. D. Perry, "Laser-Induced Damage in Dielectrics with Nanosecond to Subpicosecond Pulses," Physical Review Letters, vol. 74, 1994.

[2] D. Ashkenasi, M. Lorenz, R. Stoian, and A. Rosenfeld, "Surface damage threshold and structuring of dielectrics using femtosecond laser pulses: the role of incubation," Applied Surface Science, pp. 101–106, 1999.

[3] J. Z. Sandra Zoppel, Georg A. Reider, "Two color laser ablation: Enhanced yield, improved machining," Applied Surface Science, vol. 253, pp. 7692–7695, 2007.

[4] n. i. m. okoshi, "Laser ablation of polymers using 395 nm and 790 nm femtosecond lasers," Appl. Phys. A, vol. 79, pp. 841–844, 2004.

[5] G. A. R. E. Schwarz, "Laser-induced plasma by two-color excitation," Applied Physics B, 2011.

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以雙色飛秒雷射合成波行研究聚甲基丙烯酸甲酯的光熔蝕現象

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