Abstract
幾何雜訊指的是經由雷射光束的幾何性質改變所引入的雜訊,常見的幾何 雜訊源有光路跳動(beam jitter),光腰位置(大小)的漂動等,光束幾何性 質的改變將會耦合著各種的高階模態,而且各模態的耦合比率也不盡相同; 對於精密度要求甚高的大型干涉儀而言,所有的雜訊源都必須嚴密控制,一 般而言,降低幾何雜訊都使用模態純化的方法。我們為了3.5 m真空雙折射 原型干涉儀所架設的0.67 m光學模態純化共振腔(Optical mode cleaner) 就是為了要降低幾何雜訊,藉由高精細度Fabry- Perot共振腔的模態選擇 特性,可使得通過模態純化共振腔的雷射光為高純化的單一模態(通常為 TEM00)的光源,我們使用精細度為1500的反射鏡,並利用雙擺減振系統懸吊 鏡子而形成一組懸吊式Fabry-Perot共振腔,我們使用Pound-Drever穩頻法 來對雷射做穩頻的工作,同時也對FP共振腔體進行腔長鎖定,使得雷射的頻 率鎖定在FP共振腔的縱模上。 For measurement of the vacuum birefringence predicted by quantum electrodynamics, we are currently building a 3.5 m prototype Fabry-Perot interferometer. The presence of various noise sources limits the sensitivity of our experiment. For experiments which require high-sensitivity,e.g., laser interferometric gravitational wave detection and vacuum- birefringence measurement, best sensitivity can only be achieved after considerable reduction in various noise sources. Geometric fluctuation is one of the important noises. The mode cleaner cavity is essentially a high finesse Fabry Perot cavity which could serve both as a mode selector and and as a frequency reference to frequency stablize the laser using Pound- Drever scheme.