An official website of the United States government
The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before
sharing sensitive information, make sure you’re on a federal
government site.
The site is secure.
The https:// ensures that you are connecting to the
official website and that any information you provide is encrypted
and transmitted securely.
Oldenburg AL, Chhetri RK, Cooper JM, Wu WC, Troester MA, Tracy JB.Oldenburg AL, et al. Among authors: chhetri rk.Opt Lett. 2013 Aug 1;38(15):2923-6. doi: 10.1364/OL.38.002923.Opt Lett. 2013.PMID: 23903180Free PMC article.