N型四能级系统的原子吸收

The Atomic Absorption in N-Type Four-Level System

研究了在较强光低饱和限制下相干光场与N型四能级原子相互作用系统中原子的吸收性质。借助于数值计算,讨论了较强光失谐、探针光强、激发能级向低能级衰减的分配系数对原子吸收的影响。结果表明,抽运场失谐使原子吸收发生横向变化,信号场失谐使原子吸收发生纵向变化;探针光强影响非线性吸收,并通过它影响原子吸收,当探针光强远小于抽运和信号光强时,原子吸收与线性吸收一致,均表现为电磁感应透明特征,当信号光强增大,非线性吸收产生了增益,原子吸收也由透明变为增益;激发能级同时向两个低能级衰减,当对应探针光的原子衰减通道的衰减分配系数趋近零时,原子吸收随该系数变化非常强烈,当该分配系数等于零时,其增益在探针场共振处趋于无穷大。

In the low-saturation limit, the property of atomic absorption resulted from the interaction between coherent light and N-type four-level system is investigated. With the numerical method, the influences of the offset of stronger light, probe-field strength and branching ratio coefficient of spontaneous decay from excited level to lower levels to atomic absorption are discussed. The results exhibit that the coupling offset makes the atomic absorption modified in transverse orientation, and the signal offset in vertical orientation; the probe-field strength modifies the nonlinear absorption which modifies the atomic absorption, it is found that when the strength of the probe-field is far less than that of the coupling and signal field the atomic absorption is the same as the linear absorption, and it shows the characteristic of electromagnetically induced transparency; when the probe field strength continues to increase the gain emerges in the nonlinear absorption, and the atomic absorption begins to change from the transparency window to the gain one; as is known, an excited level in the system decays to two lower levels. When the branching ratio coefficient corresponding to the probe channel is near to zero, a rapid variety emerges in the atomic absorption, and when the branching ratio coefficient is equal to zero, the gain in the atomic absorption becomes infinite on the resonance of the probe field.