以空間與時間解析光譜研究鎳薄膜微結構超快動力學

Abstract

本論文利用空間與時間解析光譜研究不同幾何形狀的鎳薄膜在外加磁場下瞬時反射率變化(∆R/R)之二維分布。從瞬時反射率變化的信號，我們清楚觀察到兩個弛緩過程，一個為較快的電子-聲子散射過程；另一個為較慢的自旋-晶格散射過程。實驗結果顯示，在改變外加磁場強度下，電子-聲子散射過程並不受影響，但自旋-晶格散射過程卻與外加磁場有密切的關係，隨著外加磁場越強，則自旋-晶格散射時間即越長。除此之外，在不同幾何形狀與尺寸下，也可經由空間與時間解析光譜觀測其磁矩在受磁場極化後的動力學行為。

In this thesis, we study the ultrafast dynamics of Nickel thin films with various microstructures using spatially and time-resolved femtosecond spectroscopy under different magnetic fields. From the transient reflectivity changes (∆R/R) in Nickel thin films, we observed two relaxation processes, one is the electron-phonon scattering process with ~10 ps, the other is the spin-lattice scattering process with ~100 ps. The electron-phonon scattering process is independent of the magnetic field. On the contract, the spin-lattice scattering process is strongly dependent on the magnetic field. Moreover, the microstructure-dependent ultrafast dynamics of Nickel thin films also can be revealed by this spatially and time-resolved femtosecond spectroscopy.