An inspection apparatus (100, 250), comprising: an optical target (120, 270) including a solid host material and a fluorescing material embedded in the solid host material, the solid host material having a predetermined phonon energy HOST PE; a body (102, 202) having a pocket (114, 214, 264) to receive the optical target (120, 270), wherein the body includes an inset region (118, 218, 268) located at a top surface (104, 204) and surrounding the pocket (114, 214, 264); a transparent layer (272, 122) mounted in the inset region (118, 218, 268) and positioned above the optical target (120, 270); a grating layer comprising microstructures formed on a bottom surface of the transparent layer (272, 122) above the optical target (120, 270); and an adhesive bonding the grating layer to the body (102, 202); wherein the body (102, 202) includes a channel (116, 216, 266) at least partially surrounding the pocket (114, 214, 264), the channel (116, 216, 266) being arranged to receive the adhesive bonded to the grating layer and to the body (102, 202), wherein the channel (116, 216, 266) includes a series of pressure relief pockets (221, 271) distributed about the channel (116, 216, 266), the pressure relief pockets (221, 271) being arranged 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 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 energy level relative to the TE energy level, the NLL energy level spaced a second energy gap FM EG2 below the TE energy level wherein a ratio of the FM EG2 /HOST PE is three or more. an optical target (120, 270) including a solid host material and a fluorescing material embedded in the solid host material, the solid host material having a predetermined phonon energy HOST PE; a body (102, 202) having a pocket (114, 214, 264) to receive the optical target (120, 270), wherein the body includes an inset region (118, 218, 268) located at a top surface (104, 204) and surrounding the pocket (114, 214, 264); a transparent layer (272, 122) mounted in the inset region (118, 218, 268) and positioned above the optical target (120, 270); a grating layer comprising microstructures formed on a bottom surface of the transparent layer (272, 122) above the optical target (120, 270); and an adhesive bonding the grating layer to the body (102, 202); wherein the body (102, 202) includes a channel (116, 216, 266) at least partially surrounding the pocket (114, 214, 264), the channel (116, 216, 266) being arranged to receive the adhesive bonded to the grating layer and to the body (102, 202), wherein the channel (116, 216, 266) includes a series of pressure relief pockets (221, 271) distributed about the channel (116, 216, 266), the pressure relief pockets (221, 271) being arranged 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 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 energy level relative to the TE energy level, the NLL energy level spaced a second energy gap FM EG2 below the TE energy level wherein a ratio of the FM EG2 /HOST PE is three or more.