Department of Physics

Department News

Dr. Kapale's most recent PRL paper may open the door for the development of highly efficient X-ray and Gamma-Ray lasers.

May 5, 2008

Dr. Kishor Kapale, who joined the group of Atomic, Molecular and Optical Physics a year ago, has just published his second Physical Review paper during this academic year. The paper addresses a very important problem in Quantum Information, namely how to extract pure lasing without inversion contribution. In a nutshell, the results of the paper can be explained as follows:

Einstein's explanation of the stimulated emission gave rise to a concept of lasing and the devices we now call lasers. To obtain laser light the medium (atomic or molecular) that is emitting light need to be excited giving rise to a condition popularly known as population inversion. Population inversion means the higher energy states need to be more populated than lower energy states. This inversion condition makes it very difficult to obtain lasing in the high frequency region of the electromagnetic spectrum. This traditional requirement gets modified if there is an extra transition coupling with the lasing transition. There is a quantum interference between the coupled transitions and population inversion on the lasing transition is no longer necessary giving the phenomena of so-called lasing without inversion (LWI). There is a caveat here however. There are other competing processes and perhaps hidden Raman inversion present in the system when there are more than one transition taking part in the lasing process. Dr. Kapale's work with Dr. Kilin and Dr. Scully shows how to extract pure lasing without inversion contribution and show an accompanying capitalistic effect in the population dynamics in the involved three energy levels of the active medium. The population dynamics is such that an initially more populated ground state (as there is no inversion on any of the transitions) gets more populated with time and gives rise to lasing without inversion. The concept of LWI is the only hope to obtain highly efficient X-ray and gamma-ray lasers. Also in the context of quantum information generation of pure states as initial states of the quantum system is a necessity and the capitalistic population dynamics proposed can be used to generate such pure states.

Details can be found at Phys. Rev. Lett. 100, 173601 (2008).