Alexopoulos N G, Uzunoglu N K
Appl Opt. 1978 Jan 15;17(2):235-9. doi: 10.1364/AO.17.000235.
The scattering properties of active particles are studied and compared with those of particles with a complex conjugate (passive) index of refraction. It is shown that the extinction cross section of active particles is zero at certain frequencies and that only at certain frequency bands it is amplified. For most frequencies, the interference between diffracted and refracted waves causes the extinction cross section to behave like that of passive particles. A comparison of backscattered and forwardscattered intensities between active and passive particles with n(a) = n(p) * shows that as +/- Im(n) ? + infinity the intensities converge to the same value. For nonsymmetric scatterers, such as cylindrical fibers of elliptic cross section, it is shown that in the resonance region the major portion of the scattered field is not in the forward direction. In addition, the ratio of backscattered to forward scattered intensity is found to be greater than unity for active media for certain frequencies beyond the low frequency region.
研究了活性粒子的散射特性，并与具有复共轭（无源）折射率的粒子的散射特性进行了比较。结果表明，活性粒子的消光截面在某些频率下为零，并且仅在某些频带中会增大。对于大多数频率，衍射波和折射波之间的干涉会导致消光截面的表现类似于无源粒子。对具有n(a) = n(p) *的活性粒子和无源粒子之间的后向散射强度和前向散射强度进行比较表明，当+/- Im(n)趋于正无穷时，强度会收敛到相同的值。对于非对称散射体，例如椭圆形横截面的圆柱形纤维，结果表明在共振区域中，散射场的主要部分不在向前方向。此外，发现在低频区域之外的某些频率下，活性介质的后向散射强度与前向散射强度之比大于1。
