Effects of the upper level coupling field on lasing without inversion in a V-type system

Driven by one upper level coupling field, a three-level V-type atomic system with a pair of upper levels is studied. With one strong coupling field and one weak probe field, it is found that, due to the effects of the upper level coupling field, the quantum coherence between the two upper levels can be induced, and the absorption of the probing field is very sensitive to the relative phase of the probe, the pumping and the upper level coupling fields. With proper parameters, lasing without inversion (LWI) can be realized.