We describe the design and implementation of a vacuum compatible laser-based absolute distance measurement system with subnanometer resolution. The presented system is compatible with operation in the range, and with some minor modifications it could be used in the range. The system is based on glancing incidence reflection and dual segmented diode detection. The system has been implemented as a focus sensor for extreme ultraviolet interferometry and microlithography experiments at Lawrence Berkeley National Laboratory’s Advanced Light Source synchrotron radiation facility. A 3σ operational noise floor of 0.78 nm has been demonstrated. © 2005 Society of Photo-Optical Instrumentation Engineers.