All-optical magnetic resonance in semiconductors

A scheme is proposed wherein nuclear magnetic resonance (NMR) can be induce d and monitored using only optical fields. In analogy to radio-frequency fi elds used in traditional NMR, circularly polarized Light creates electron s pins in semiconductors whose hyperfine coupling could tip nuclear moments. Time-resolved Faraday rotation experiments were performed in which the freq uency of electron Larmor precession was used as a magnetometer of Local mag netic fields experienced by electrons in n-type gallium arsenide. Electron spin excitation by a periodic optical pulse train appears not only to prepa re a hyperpolarized nuclear moment but also to destroy it resonantly at mag netic fields proportional to the pulse frequency. This resonant behavior is in many ways supportive of a simple model of optically induced NMR, but a curious discrepancy between one of the observed frequencies and classic NMR values suggests that this phenomenon is more complex.