Combining infrared- and green-laser stimulation sources in single-grain luminescence measurements of feldspar and quartz

A system designed for measurement of the optically stimulated luminescence (OSL) from individual sand-sized mineral grains has been constructed. Previously, this system was equipped only with a green laser emitting at 532 nm, but now an infrared (IR) laser at 830 nm has been added. It is now possible to interchangeably use the two laser sources for optical stimulation. This is especially valuable for the measurement of feldspars. The power density using the IR laser at the grain is ∼ 500 W cm^-2, and stimulation for 1 s reduces the OSL signal to near background level. Initial results on grains from two feldspar samples are described. These show that the ratio of the OSL signal under green and IR stimulation is similar for all the feldspar grains. As expected, the ratio for quartz grains is very different, with a much weaker signal when using IR stimulation. For the two feldspars, the distribution of OSL between the grains and the saturation of the dose response curve shows much less variability than is typically seen for quartz grains.