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標題: | 系統最佳化的低光雜訊原子測磁計 Low Optical Noise Atomic Magnetometer with System Optimization |
作者: | Chia-Teng Hsu 許家騰 |
指導教授: | 石明豐(Ming-Feng Shih) |
關鍵字: | 原子測磁計,拉莫徑動,不受自旋交換影響,自旋交換碰撞,光驅動, Atomic magnetometers,Larmor precession,spin exchange relaxation free (SERF),Spin exchanged collisions,optical pumping, |
出版年 : | 2012 |
學位: | 碩士 |
摘要: | 高靈敏度測磁計在很多領域中都有廣泛的應用,包括物理,生物以及地質等的磁場量測。低溫超導量子干涉儀是磁性測量領域中的紀錄保持者,但維持它的工作溫度需用到液態氦來降溫,也因而造成高額的花費,這個缺點局限了它的運用。近年來,鹼金屬原子測磁計的發展日新月異,到達了與低溫超導量子干涉儀同樣的靈敏度1 ft/√Hz,與此同時,卻沒有其高額花費的缺點。鹼金屬測磁計的原理主要是藉由測量金屬原子自旋極化於極小磁場下的拉莫徑動,進而了解環境磁場的大小。其靈敏度的主要限制是來自於量子雜訊。量子雜訊的大小跟垂直磁場的自旋緩和效率有關,又已知垂直磁場的自旋緩和效率主要是自旋交換碰撞導致。所以可以藉由製造零磁場環境來排除自旋交換碰撞的影響,使自旋緩和效率變的極小。在此條件下,我們稱該原子測磁計為不受自旋交換緩和影響的原子測磁計,這樣的雜訊約略為0.3 ft/√Hz。此論文是在這些理論的基礎之下,模擬以及實驗使系統參數最佳化藉以得到較佳的靈敏度。於驅動雷射的強度為 0.52 W/cm^2時,可得到探測光共振在此系統中的最小寬度是210 μG,此寬度比原有設定之下的寬度小了3倍。此外,藉由平衡偵測器的使用與探測雷射光極化角度的調整使光雜訊從mV變成μV的數量級。 High sensitivity magnetometers are applied in many fields including physics, biology, and geology. For detection of magnetic fields, low-temperature superconducting quantum interference device (SQUID) magnetometers give the most sensitive performance traditionally. However, to maintain SQUID working in the low temperature requires relatively high cost. Recently, alkali-metal magnetometers approach the same sensitivity level without this drawback. The principle of atomic magnetometers is based on the detection of Larmor spin precession in the magnetic fields. The fundamental sensitivity limit of atomic magnetometers comes from the shot noise which is associated with the transverse relaxation time. Spin exchanged collisions contributes to the transverse relaxation time mostly, and it can be reduced by operating in the environment with a near zero magnetic field. As the condition is introduced, it can reduce the noise limit down to 0.3 ft/√Hz. Such environment character is called spin exchange relaxation free (SERF). In this thesis, I analyze the system with simulations and experiments in an attempt to reach the optimization. The narrowest width 210 μG of the dispersion curves is read with the pump beam intensity 0.52 W/cm^2. Besides, the low optical noise system is built via applying a balance detector with appropriately adjusting the polarization of probe beam. The noise level decreases from mV to μV as compared from our previous system. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/66178 |
全文授權: | 有償授權 |
顯示於系所單位: | 應用物理研究所 |
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