Abstract

A comparison of the noise characteristics of χ⁽³⁾ and photorefractive coherent amplifiers reveals basic differences in their dependence on operating parameters. Unlike all types of χ⁽³⁾ amplifiers, which are shown to have a well-defined optimum working point in the region of the self-stimulated scattering threshold, the photorefractive amplifier can be made increasingly quieter by lowering the pump power. This is demonstrated by use of highly doped Co:BaTiO₃ in a tight-focus reflection grating geometry. It is shown that scattering from inhomogeneities in the crystal is the major limiting noise source and is significantly higher than predictions resulting from fundamental considerations such as random space-charge noise. An extremely high small-signal gain of 10⁷ was measured with this crystal and geometry. To our knowledge this is the highest photorefractive gain reported to date.

© 1995 Optical Society of America

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