Patrick Egan (Fed)

Patrick began at NIST in 2006 as an NRC-NIST postdoc. At the time, his focus was on the development of an optical frequency comb metrology system for the calibration of vacuum-wavelength. In 2008 he began to investigate highly precise measurements of the refractive index of air using a Fabry-Perot cavity-based refractometer. The work culminated in one of the most accurate measurements of the refractive index of nitrogen and argon at 633 nm, and laid the groundwork for what developed into the 2012 Innovation in Measurement Science (IMS) project entitled "Reinventing pressure, temperature, and length". The IMS project was awarded the Department of Commerce Gold medal in 2017.

Throughout his career, Patrick has achieved several milestones in precision thermophysical measurement. He led an effort to determine the Boltzmann constant in 2017, via the equation of state and polarizability of helium. He has built some of the world's most stable Michelson interferometers as epoxy-free assemblies of fused silica glass. His work in refractometry has been foundational to the optical pressure scale, realizations of which are currently being investigated by several national metrology institutes around the world. His measurement of the thermal expansion coefficient of fused quartz glass was more accurate than anything before; a reference material for thermal expansion is essential to calibrate a dilatometer. He has contributed to the international effort to improve the temperature scale; his determination of the temperature scale error was one of the few above room temperature not based on the speed of sound. His procedure to calculate the effective area of a piston-cylinder assembly from dimensional characterization established the nation's current mechanical pressure scale.

Since 2015 Patrick has been a staff member of the Dimensional Metrology Group, and leader of the SI Length and Traceability project.