强光与自由电子的相互作用——半导体中载流子的多光子过程

本文讨论了半导体中载流子与laser光的相互作用。把电子运动分成带内运动与带间跃迁两部分后,我们证明了在强光下,电子在带内运动的状态仍可用准动量p来标志,但不再是通常的稳定态,波函数中包含一个描述强迫运动的因子。进一步以带间跃迁或其他带内过程作为微扰,由于在跃迁过程中强迫运动部分也改变,因此伴随着有多光子的吸收或发射。根据一般的讨论,我们计算了由电声子作用引起的自由载流子吸收及由价带到导带的直接多光子跃迁的吸收系数。粗略估计表明,在一些材料中,上述过程引起的双光子吸收是可以被观察到的,特别是Ge中的直接双光子吸收。我们还指出,利用一束laser光射到晶体上后,可以在红外区域看到激子吸收线,从而提高了分辨率,并具体地分析了CdSe中激子吸收的情况。

INTERACTION BETWEEN FREE ELECTRONS AND INTENSIVE LIGHT BEAM——MULTI-PHOTON PROCRSSES OF THE CARRIERS IN SEMICONDUCTORS

In the present article the interaction between carriers in semi-conductors and a laser beam has been discussed. The influence of intensive light on the intraband motion of an electron was treated, with the conclusion reached that the states of the electron withinone band can still be characterized by a set of quantum numbers-the quasi-momentump and that the wave function contains a factor describing the forced motion in the extremely strong electromagnetic field. The interband transition and other intraband scattering processes were then treated as perturbations. During the transition process, the forced motion changes with the absorption or emission of a number of photons.Following the above discussions, the absorption constants for multi-photon processes of free carrier absorption (with the partipation of the electron-phonon coupling) and the direct transition from valent band to conduction band were calculated. It was estimated that in some materials the two-photon process of the type discussed can be observed easily, especially the direct absorption of two photons in Ge. It was pointed out that using the laser light (the frequency of which is nearly equal to the forbidden energy gap), the absorption lines of the exciton may be shifted to the infrared region, so that the resolving power may be improved. As an example, the case of CdSe was discussed.