Article at Next Big Future website here: http://nextbigfuture.com/2016/05/femtosecond-clock-synchronization-for.html The link to the source paper is broken at the website. Google the title of the paper and you will get the link - be sure to click on the link that indicates a PDF document. https://www.google.com/search?q=Tight+real-time+synchronization+of+a+microwa ve+clock+to+an+optical+clock+across+a+turbulent+air+path The PDF was the second link from the top.