Photon-Spin Controlled Lasing Oscillation in Semiconductor Lasers

Hiroaki Ando, Tetsuomi Sogawa, and Hideki Gotoh
Physical Science Laboratory

　We have succeeded in manipulating the spin, or rotation, of electrons to control the polarization state of the lasing output from a vertical cavity surface emitting laser (VCSEL). It is known that there are special polarization states of light, right-handed and left-handed circularly polarized light, in addition to usual linear polarizations. We have shown experimentally that the electron-spin alignment, created by optical pumping with circularly polarized light, drastically changes the polarization state of the lasing output, causing circular polarized lasing emission at room temperature[1].
In the experiment, a GaAs VCSEL is irradiated with either right-handed or left-handed circularly polarized light, and lasing is achieved by optical pumping. It was confirmed in the experiment that lasing of right-handed circularly polarized light actually occurs when irradiating the laser with right-handed circularly polarized light, and likewise for left-handed circularly polarized light. This polarization property is explained by an optical process; optical pumping by circularly polarized light creates a large number of spin-aligned electrons, and these electrons, in turn, emit the same circularly-polarized light. Thus the electron-spin alignment greatly affects the polarization characteristics of the lasing output.
A new research area called "spin electronics" has recently opened up placing particular attention on "electron rotation". The purpose of spin electronics is to control electron-spin states with the goal of creating novel optical functions. The present results are significant because they demonstrate that two types of circularly polarized light can be produced at will by manipulating electron spin. We expect that the new degree of freedom, that is, electron spin-state, will offer new possibilities for optical information processing and communication.
[1] H. Ando, T. Sogawa, and H. Gotoh, Appl. Phys. Lett. 73(1998) 566.

Fig. 1: GaAs surface emitting laser

Fig. 2: Lasing emission spectra

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