模擬超快脈衝雷射在電磁引發透明與光儲存的交互作用

Abstract

電磁引發透明是利用量子干涉機制，使得原本與原子因共振而被吸收的雷射光，在額外加入一道耦合光後，雷射光不再被原子吸收。在我們的研究中，使用超快雷射來研究電磁引發透明形成的機制，並實現儲存超短脈衝雷射於電磁引發透明介質。 本工作主要可分為理論計算和模擬實驗，理論計算從探討二能階與三能階的原子色散性質，來了解耦合光如何影響原子的光學性質，再從三能階的原子的漢米頓量的本徵態與本徵值了解耦合光促使原子能階改變，造成透明現象。並利用微擾計算電子在三能階原子的居量隨時間變化，再結合波動方程式推導出半古典暗態極化子，研究物質與光資訊的轉換；模擬實驗部分，利用有限差分方法解波動方程式和四階Runge-Kutta法計算物質與光作用後放出的散射光，藉以了解電磁引發透明現象與機制，再利用控制耦合光強度研究光資訊寫入電磁引發透明介質與光資訊讀出，其中影響的因素包括電子在激發態衰減速率、原子密度和控制耦合光開關速度。在模擬實驗結果中，我們注意到耦合光開關速度和各空間探測光電場隨時間變化，都必須遵守緩慢變化條件。

Electromagnetically induced transparency (EIT) is a quantum interference mechanism to make an opaque medium transparent to light at its resonance frequency in the presence of a coupling field. In our research, we study the mechanism of EIT and realize the storage of ultrafast laser pulse. Our work includes theoretical calculation and simulation. In theoretical part, the dispersion relations of the two-level and three-level model atom are studied by perturbation theory. To realize how the coupling field affects the optical properties of atoms and changes the energy levels of the three-level atom. We derive the population of the three-level atom varied with time and simplify the wave equation by the result of perturbation theory. In the simulation, the wave equation is solved by finite difference method and the polarization is solved by 4th-order Runge-Kutta method. The phenomenon and mechanism of EIT is demonstrated from the simulation results. The light storage and retrieval of ultra-fast laser pulse are accomplished by controlling the intensity of coupling field. Some important factors, including the decay rate of the excited state, atomic density and the turned-off time of the coupling field, affect the efficiency of light storage. It has been found that not only does the coupling field should follow the adiabatic condition but also the probe field.