The Ruby Scale at Megabar Pressures

ABSTRACTDiamond anvil cells revolutionized high pressure research because they provided easy to generate extremely high pressures with an optical window on the sample and an easy-to-use pressure gauge based on the shift with pressure of the ruby fluorescence spectrum. The ruby scale provides an accurate method of determining pressure distributions within samples. However, at pressures above 100 GPa measurement of the ruby fluorescence begins to become difficult due to weakening signals, interference from intense diamond fluorescence, and ultimately, strong absorption of the exciting laser by diamond itself. We shall discuss a number of methods which have been devised to extend the ruby pressure optical gauge to 500 GPa, including quasi-direct pumping of the ruby R-lines.