By combining the time-of-flight or LIDAR principle with a Thomson backscatter diagnostic, spatial profiles of the electron temperature and density can be measured with a single set of detectors for all spatial points. The technique was demonstrated for the first time on the JET tokamak and has been in routine operation since July 1987. Originally a ruby laser (3J pulse energy, 300ps pulse duration, 0.5Hz repetition rate) was used together with a 700MHz bandwidth detection and registration system which yielded a spatial resolution of about 12cm. A large filter spectrometer with 6 spectral channels covering the wavelength range 400–800nm gives a dynamic range for the temperature measurements of 0.2–20keV. The original system is described, examples of measurements are given and compared with the results of other diagnostics. The system is being upgraded to make measurements at 10Hz and a major component of the new system is an Alexandrite laser (1–2J pulse energy, 350+/–50ps pulse duration, 10Hz repetition rate) which is currently being constructed. The new laser and other technological improvements being incorporated into the upgraded diagnostic will also be described.