Gain without inversion in a V-type system with low coherence decay rate   for the upper levels
  Inversionless gain is observed in a V-type inhomogeneously broadened system without introducing any incoherent pumping and only by changing the collisional dephasing decay rate. In this system sub-Doppler linewidth is achieved with off-resonance pump detuning. 
Dipankar Bhattacharyya, Biswajit Ray and Pradip N. Ghosh