Weak temporal ratchet effect by asymmetric modulation of a laser

Subjecting lasers to triangular modulations of the pump produces phenomena that drastically depend on the symmetry of the triangle. For instance, with slow up-rising triangles, a laser below threshold on average may deliver coherent pulses, while it does not deliver coherent pulses with fast up-rising triangles. This effect, which requires the presence of fluctuations in addition to the modulation, is reminiscent of the thermal ratchet with which a directed motion is extracted from a stochastic medium.