Ruby films as surface temperature and pressure sensors.

Epitaxial films of chromium doped alumina, 0.3 microns in thickness, were grown on single crystal sapphire substrates for use as surface thermometers. Curve fitting was performed on the R1 and R2 fluorescence peaks, and the line widths and peak shifts were used to determine the temperature of the surface during sliding contact with a variety of plastic bearings. Temperatures could be determined with a repeatability of 2 degrees C, and adequate signal for temperature determination could be obtained in 30-100 msec. in dots that were 200 microns in diameter, using a 0.25 watt argon laser. Both average (nominal) and local temperature increases were measured. Pressure-induced shifts could be treated as an error to the temperature determination.