Effect of dephasing collisions on amplification without inversion

We have analyzed amplification without inversion (AWI) in the presence of c ollisions in V and Lambda three-level systems. We have found that collision s cause a very important contribution to the quantum interference that redu ces absorption in the case of the V system. In the Lambda system the effect of collisionally induced quantum interference on AWI is smaller than in th e V system but the Lambda system offers new interesting possibilities of in coherent pumping on a low-energy transition. This possibility allows obtain ing frequency up-conversion of the amplified radiation with respect to both pumps, the coherent as well as the incoherent one.