Effects of combined RF and optical fields on a laser medium

Modulation of a laser signal at radio frequencies ranging from 28 to 347 MHz is experimentally investigated by subjecting coherently emitting atoms of a Xe-He laser amplifier to simultaneous dc and RF magnetic fields. The sidebands are generated by a coherent nonlinear process that exhibits resonances when the Zeeman splitting of the laser levels equals the frequency of the magnetic field. A perturbational theory that is based on a simplified atomic model adequately describes the dependence of the modulation efficiency on the dc magnetic field, the signal frequency, and atomic parameters. A presently unexplained phenomenon is the absence of the upper sideband.