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Filtering behavior of a self-induced three-mirror cavity formed by intracavity wave mixing in a saturable absorber.

Wave mixing with a self-induced grating in a saturable absorber, which is inserted into a resonator, gives special filtering behavior. In a linear Fabry-Perot cavity with gain, the grating forms a self-matched, threemirror laser cavity that can discriminate between modes whose frequency difference is much lower than the grating bandwidth. The effect was used to obtain single-mode lasers with narrow linewidths. The selfinduced grating can dynamically adjust itself to small disturbances and changes in the cavity parameters.