Solid inspection apparatus and method of use

An inspection apparatus, comprising:

• an optical target including a solid host material and a fluorescing material embedded in the solid host material, the solid host material having a predetermined phonon energy HOSTPE;
• a body having a pocket to receive the optical target, wherein the body includes an inset region located at a top surface and surrounding the pocket;
• and
• a transparent layer mounted in the inset region and positioned above the optical target;
• wherein the body includes a channel at least partially surrounding the pocket, the channel to receive an adhesive to bond to a grating layer, wherein the channel includes a series of pressure relief pockets distributed about the channel, the pressure relief pockets to relieve stress induced onto the grating layer by the adhesive during a curing process;
• wherein the fluorescing material exhibits a select ground energy level and a target excitation (TE) energy level separated from the ground energy level by a first energy gap corresponding to a fluorescence emission wavelength of interest (FEWI), the fluorescing material having a next lower lying (NLL) energy level relative to the TE energy level, the NLL energy level spaced a second energy gap FMEG2 below the TE energy level wherein a ratio of the FMEG2/HOSTPE is three or more.