In 1971, Hall was awarded a National Academy of Sciences Fellowship at NASA Goddard Space Flight Center where he worked on for space-based optical communication systems. He then moved to Avco Everett Research Laboratory in Boston, where he worked on electron beam laser technology and high pulse energy modelocked lasers, laser radar and atmospheric optical propagation.
Hall moved to the Royal Signals and Radar Establishment in 1976 working on lasers and infrared systems, before transferring to the University of Hull in 1979. At Hull he led the UK national project to design and construct the Satellite Laser Ranging Facility at Royal Greenwich Observatory, Herstmonceux. At the same time Hall developed techniques for laser excitation using transverse radiofrequency discharges to produce a range of compact sealed CO2 lasers for medical, industrial and laser radar applications.
Since 1987, Hall has been Professor of Photonics at Heriot-Watt University, Edinburgh, where his research interests have continued in laser device physics and applications. He has been concerned with the design of ultracompact high power waveguide lasers, exploiting concurrent research in RF discharge physics and planar optical waveguides to develop new laser concepts based on 2-D laser power scaling and novel laser resonators. Planar waveguide CO2 lasers are now successful products manufactured by major international companies for applications in industry and medicine. More recently, the planar waveguide 'thin laser' concept has been extended to other gas lasers and to solid state lasers pumped by diode bars. This work, part of a general industrial orientation involving partnership in many industry/university collaborative research projects, has resulted in a series of new commercial laser devices and industrial laser-based systems. He has been involved in the creation of three successful start-up companies producing lasers and laser systems.