Population Inversions in Lightning Discharges?

William Silfvast

LaserFest provides a fitting opportunity to reflect on whether one of the hallmarks of the laser—population inversion—may have long predated its invention. Could these highly unstable and seemingly unnatural phenomena be part of the normal atmospheric process of lightning discharge?


figureA man-made lightning flash showing narrower streamers occurring adjacent to the main flash.

In reflecting on this year’s 50th anniversary of the first demonstration of the laser, I decided to raise a question that has been on my mind for about 30 years: When were the first population inversions, which are commonly associated with lasers, produced here on Earth? For those of you who aren’t familiar with how lasers operate, a population inversion involves generating an inverted distribution of population in the excited states of matter—an arrangement that is very difficult to achieve.

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