Lasing without inversion: The road to new short-wavelength losers

Lasing Without Inversion (LWI) is a novel technique in laser physics which holds the promise of a solution to one of the most fundamental problems in short-wavelength laser research. Making use of quantum coherence and interference effects, this technique allows lasing even if only a small fraction of population is in the excited state, i.e., even if the population of the active medium is not inverted. The intense theoretical work on the subject has been verified by several experiments which confirmed that LWI is indeed possible. The efforts of researchers are presently directed to demonstrate LWI in the UV and X-ray spectral regions.