相长干涉：电磁诱导吸收

揭示修饰态原子相干对吸收的相长干涉产生电磁诱导吸收，这与修饰态原子相干对吸收的相消干涉导致电磁诱导透明的情形形成鲜明的对照. 以三个电偶极跃迁构成N型链的四能级系统为例，中间跃迁作为探测跃迁，在修饰态表象中分裂成四个相互耦合的跃迁. 这些耦合源于介质的自发辐射和介质激发态相干到基态相干的自发转移. 前者对所有四个探测跃迁产生相同符号的耦合，表现为对吸收的抑制. 而后者对其中两个跃迁产生正号的耦合，对另两个跃迁产生负号的耦合. 正是这些正负参半的耦合显著改变修饰态相干对吸收的贡献，使之由抑制吸收改变为增强吸 关键词： 电磁诱导吸收 相消干涉 相长干涉 原子相干的自发转移

Constructive interference: electromagnetically induced absorption

In this paper we reveal that the constructive interference of atomic coherence on absorption leads to electromagnetically induced absorption,which is in sharp contrast to the case in which destructive interference of atomic coherence gives rise to electromagnetically induced transparency. A four_level atomic system is employed in which three transitions are in N configuration and the middle transition is used as a probe transition. In the dressed states representation the probe transition is split into four transitions that are coupled to each other. The coupling originates from the spontaneous emission of the atomic medium and the spontaneous transfer from excited state coherence to ground state coherence. The former leads to couplings between all transitions with the same sign and to the absorption reduction. The latter results in couplings,of which two terms have positive sign and another two have negative sign. It is due to the couplings with positive and negative signs that significant modification of the contribution of dressed coherence to absorption occurs,i.e., absorption inhibition is changed to absorption enhancement.