快速雷射脈衝加熱金屬薄膜之光學特性及其對熱傳特性逆算影響之研究

Abstract

由於快速雷射加熱時間極為短暫而造成直接量測電子溫度變化的困難，以往研究都以量測薄膜的光學反射率變化來取代之，並設定光學反射率與電子溫度呈線性關係。本文探討此線性關係的適用性，重新建立光學反射率與電子溫度之間的關係式，並針對快速雷射加熱金屬薄膜的過程，帶入同時能夠量測金屬熱傳導係數與電子-聲子連結因子的逆運算程式，進一步分析其關係式對逆算結果之影響。逆運算結果顯示，當金屬薄膜愈薄，所得到的熱傳導係數與連結因子和原先設定反射率與電子溫度呈線性關係的結果相差愈大；顯示出此一光學反射率與電子溫度的線性關係在電子溫度變化愈大時，適用性愈低。此外，由於一段時間後薄膜內部電子溫度才會達到平衡，故達到平衡前，薄膜內部電子溫度將會影響到我們估測值而導致其逆運算的不合理。

This thesis investigates the applicability of the linear variation of the reflectivity with the electron temperature when the laser pulse duration is too short to measure the variation of electron temperature directly. A more exact relationship between optical reflectivity and electron temperature is derived, and is brought into an inverse analysis which is performed for simultaneous estimation of both thermal conductivity and the electron-phonon coupling factor for thin metal films subjected to ultra-fast laser heating. Results show that as the change range of the electron temperature is small the linear variation of the reflectivity with the electron temperature can be applied, while at small thickness the applicability of the linear relationship is questionable. Furthermore, the reflectance we get before electron temperature reaches balance between front surface and rear surface is too low at the front surface and is too high at the rear surface, the effect of electron temperature distribution on the reflectance should be addressed in order to obtain more accurate estimation of heat transfer characteristics. In the present study, the reflectivity distribution relates to the thickness of thin film, electron temperature, the photon energy and incident angle are also analyzed.