The organization said it is recognizing Nilsen for his "pioneering contributions to the development and understanding of X-ray lasers and their applications."
Nilsen has been at the Lab for 33 years. He is currently working in the Weapons and Complex Integration directorate, leading a science campaign and doing research on high energy density physics.
His laser accomplishments include developing the pre-pulse techniques that are now the standard techniques used worldwide to drive X-ray lasers. This technology has allowed such lasers to be reduced in size from requiring large fusion laser facilities to operating as table-top lasers.
In his early research, Nilsen invented and led experiments to demonstrate a nuclear pumped X-ray laser. He also helped develop the X-ray imaging techniques used to diagnose and understand X-ray lasers, which are now used to diagnose other plasmas.
In all, Nilsen has published 240 papers on X-ray lasers, atomic physics, and non-linear optics.
OSA selected 64 new fellows this year, with about half of them working in the United States.
Nilsen becomes the seventh OSA fellow currently at LLNL. He also is a fellow of the American Physical Society (APS).