The Thermal Effect in Ablated Stainless Steel by Femtosecond Laser and Nanosecond Laser

雷射已被廣泛應用於不同特性材料之高精密加工製程，然而雷射加工對材料所產生的熱效應卻是非常難以避免，而限制了雷射加工的品質。在近年來許多應用與研究中，使用深紫外光的奈秒脈衝雷射以及近紅外光的飛秒脈衝雷射降低熱效應以及增加加工精密度，例如：抑制毛邊的產生、改善粗糙的表面結構、提升加工尺寸之重複性等等…。但究竟深紫外光的奈秒脈衝雷射與近紅外光的飛秒脈衝雷射對於材料所產生的熱有多少，至目前為止尚未被完全解決。大部分的研究僅使用模擬的方法分析加工時的溫度，鮮少有清楚地實驗證據證明於加工過程中雷射對於樣品所產生的溫度分佈。為了瞭解雷射加工時的溫度，本研究分析了加工區域內的生成物之材料特性。使用光學顯微鏡搭配拉曼光譜量測技術分析飛秒雷射及奈秒雷射於不鏽鋼加工完成後之樣品表面特性的改變，亦即使用不同型態的雷射於加工製程中在不同區域之不鏽鋼樣品表面產生破壞，並量測破壞區域內所生成的氧化物，進而，探討雷射加工過程中不鏽鋼所經歷的熱效應，使得雷射加工製程之機制可以被更清楚地瞭解。Laser was widely used in the high precision micro-machining of various materials. However, the thermal effect in the laser processing is not easy to be avoided. Therefore, many applications and researches, in recently, use ultraviolet laser with nanosecond duration and near-infrared laser with femtosecond duration. The both types of laser have the reduced thermal effect during laser processing and thereby increase the precision such as minimization of burr, improvement of surface roughness of structure, promotion of repeatability in dimension etc…. However, the thermal effect in the laser micro-machining was not understood yet. It is due to almost the explanation only depending on the simulation. Seldom researcher using the experimental evidence shows the temperature. This issue to uncover the machining mechanism is vital to understanding the limitation and advantage in application of laser micro-machining applications. In this thesis, the property to form the different type of oxide in the different condition will be used to disclose the temperature on the stainless steel surface during femtosecond laser processing and nanosecond laser processing. The experimental method is using optical microscope and Raman spectroscope to measure and to analyze the products on the stainless steel surface within the ablated region. Raman experiment shows that femtosecond and nanosecond lasers create different iron oxides during the micro-machining. These oxides provide a clear evidence of processing temperature which is important to understand the laser-machining mechanism