We show from ab initio laser theory that by choosing an appropriate spatialpump profile, many different spatial modes of a typical microlaser can beturned on at the same pump energy, substantially increasing the number, N, ofsimultaneous lasing modes. The optimal pump profile can be obtained simply fromknowledge of the space-dependent saturated gain profile when the system isuniformly pumped up to the Nth modal threshold. We test this general result byapplying it to a two-dimensional diffusive random laser and a microdisk laser.Achieving highly multimode lasing at reasonable pump powers is useful forreducing the spatial coherence of laser sources, making them suitable for usein speckle-free imaging and other applications.
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