在屏蔽磁場下使用紅外線加熱的鉀原子測磁計

Abstract

理論上，鹼金屬原子測磁計的高敏感度可和現今最敏感測磁計的超導量子干涉磁量儀（Superconducting Quantum Interference Device）媲美。在本實驗中，利用溫度約 的高密度鉀原子氣體，在外圍以μ合金（mu-metal）圍住使其可以在微小磁場下進行作用，再將原子共振態的半導體雷射光照射在原子上，使得原子在磁場下和光產生了非線性的磁光效應，接著利用量測原子自旋角動量的拉馬旋進（Larmor Precession），我們就可以得知磁場大小。在高原子密度和微小磁場下，原子和原子之間碰撞所產生的自旋角動量互相交換且衰減的情況並不明顯，所以稱為不受自旋交換衰弛影響（Spin-Exchange Relaxation Free）的鉀原子測磁計。 在這套系統，為了改善以熱空氣加熱使得荷姆霍茲線圈和 合金會過熱的情形，我們改善了加熱系統，利用375W紅外線燈泡為熱源，以石英棒為熱源傳輸，成功將原子氣體加熱到160±10℃左右，而且荷姆霍茲線圈和 合金保持在室溫狀態。此外，我們設計新的方法來找零點磁場，進而得到幾十個 頻寬的共振分佈曲線，但是此訊號並不穩定，接著我們做了一連串的測試排除各種原因和對此系統做分析。

Theoretically, Alkali-metal magnetometers can be accurate as SQUID which is currently the most sensitive magnetic field sensors. We use high density Potassium atom vapor as our measurement sample, which is heated to 160±10℃, and is shielded by mu-metal for near zero magnetic field operation condition to reduce the noise from the spin exchange collision. The principle of the magnetometer is based on the resonant nonlinear magneto-optical effect that Larmor precession can be used to measure the spins of polarized atoms under the influence of the magnetic field. In order to eliminate the overheating problem of the Helmholtz Coils and mu-metal caused by the hot-air heating method, we use an infrared light bulb as a thermal source and a quartz bar to transfer the heat to the Potassium cell. The temperature of the cell has been successfully raised up to 160±10℃ with no overheating problem and the system is more stable. Furthermore, a new method of finding zero magnetic fields is presented, in which the resonant signal with around 10μG width is observed. However, the signal drifts over time. To solve this problem, we have assumed some causes and target to solve them one by one.