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Narrow-linewidth, single longitudinal mode operation is demonstrated in an erbium-doped fibre laser with an intracavity nonlinear absorptive wave mixing of the counterpropagating beams. An unpumped length of erbium-doped fibre serves as the saturable absorber. Linewidths of the order of a few kilohertz are obtained.
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Horowitz et al. (1994) studied this question.
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