- 期刊
Laser Direct Writing of Diamond Micro-nozzle Using Q-Switched Nd:YAG Laser
脈衝式Nd:YAG雷射直寫加工鑽石微噴嘴研究
摘要
本研究探討脈衝式Nd: YAG雷射波長(1064 nm)以直寫方式對單晶鑽石進行微噴嘴結構直寫加工。當短脈衝雷射的高峰值功率能量密度達到材料臨界閥值時，即使擁有非常低的吸收係數，由於非線性光學效應，緊密的聚焦光束仍會被吸收導致後續的熱致燒蝕過程。因此我們考慮雷射燒蝕單晶鑽石為石墨化（溫度上升至1500K，鑽石層轉化為石墨層）與石墨昇華（後續溫度上升至4000K，石墨層昇華汽化）兩種過程。透過實驗，當雷射能量密度達到0.45J/平方公厘和1.14J/平方公厘分別達到石墨化與昇華化。同時開發CAD/CAM軟體，將欲加工的三維結構轉換成層狀二維平面圖案，進行雷射直寫加工，並經由拉曼光譜儀來確認加工後殘留的石墨層，最後驗證以脈衝式Nd: YAG雷射並透過argon輔助氣體可進行乾淨且低熱影響區的鑽石微噴嘴雷射直寫加工。
關鍵字
無資料並列摘要
In this work, a Q-switched Nd: YAG laser (1064 nm) with a pulse width of 170 ns was used to fabricate 3D geometric features on the type Ib single crystal diamond. The 3D geometric features were machined based on the laser direct writing method instead of photo-mask assisted technique (mask projection) to fabricate diamond nozzle for nano-powder spray devices. Diamond is difficult to machine because it is transparent in a wide wavelength range. However, under high laser power density, the absorption coefficient can be increased significantly due to the nonlinear absorption phenomenon. Therefore a conclusion of the laser ablation of diamonds using a Q-switched Nd:YAG laser is the laser fluence up to a threshold fluence that will cause the optical nonlinear absorption to form a thermally stimulated process. We considered the material removal mechanism of laser ablation of diamond as a two-step process which combines the chemical and physical reactions. The first step employs a transformation of the crystalline diamond structure to the layered graphite at a temperature around 1500K (called the graphitization process), and followed by the sublimation of the layered graphite at a temperature around 4000K (called the sublimation process). The laser irradiance thresholds for the graphitization and sublimation steps were experimentally identified as 0.45 J/mm^2 and 1.14 J/mm^2 respectively. Because of the laser direct writing method, it permits direct pattern generation of each layer by use of CAD/CAM software. Finally, we demonstrated that a diamond micro-nozzle was fabricated with clean and low HAZ (heat affected zone) surface appearance using the Nd-YAG laser of 170 ns pulse width and 1064 nm wavelength. The laser-treated diamond substrate was examined by a Raman spectroscopy. The result confirms that the residual graphite layer on the diamond is not significant. The substrate surface remained as single crystalline diamond state after the laser processing.