Significant Increases in Light Extraction From YAP:Ce Scintillators With a Uniform Surface Taper Modification at the Exit Boundary

A technique for increasing light extraction out of scintillation crystals has been developed by introducing a uniform surface taper at the exit boundary of thin YAP:Ce scintillators. This taper was introduced by precision machining pyramidal structures on the scintillator´s surface on a scale significantly larger than the scale typical of surface roughness. Light extraction out of the crystal is increased because the surface modification significantly reduces the chance that light can be incident on the crystal´s exit boundary at an angle greater than the critical angle for total internal reflection. For the best case, a factor of 4.8 increase in light collection was measured without optical coupling, relative to the same crystal with a normal, polished exit boundary. The characteristics of the etched surfaces were precisely quantified, and measured increases in light collection relative to a polished surface are presented. Gains in light extraction are interpreted through detailed light transport simulations, and good agreement between predicted and measured light collection was observed.