We are interested in laser spectroscopy and magnetic resonance under high pressure. The derivative of free-energy vs. pressure is volume. Any change of state involving volume changes will have a pressure dependent equilibrium state, and a process having finite activation volume exhibits a pressure-dependent rate.
Pressure ranks with temperature as a useful thermodynamic parameter.
It exploits the superior mechanical strength of diamond. In a DAC, the sample is located in a small hole in a metal gasket. As the gasket is squeezed between two diamond anvils, extremely high pressure may be generated with a very compact apparatus, see Fig.1. Our DAC, reaching 100,000 atm, has a thermal mass of some 60 gram. Such a device may readily be cooled to liquid helium temperature.