A projection optical system of an image display apparatus that includes a lens system and a concave reflection surface. The lens system is has a positive refractive power as a whole. The concave reflection surface reflects the image light emitted from the lens system toward an object. The projection optical system is configured such that a relationship 0<|(hmax) (0.9.Math.hmax)|/(hmax)<0.056 is satisfied, where a light beam height from the reference axis is h, an angle with respect to an optical axis height direction of a tangent line of a function Z(h) representing a shape of the concave reflection surface corresponding to the light beam height h is (h), an amount of change in the angle (h) is (h), and the light beam height h of a reflection point farthest from the reference axis of the concave reflection surface for reflecting the image light is hmax.

A compact photoluminescence hyperspectral imaging apparatus comprises a fore-optics module and a spectrometer module. The fore-optics module has a line laser for line scanning a sample. The fore-optics module comprises optical components forming an emission light signal pathway to guide a line scan emission light signal from the sample into the spectrometer module. The spectrometer module comprises a plurality of optical components forming a folded optical light signal pathway between an emission light signal entrance and a deflection mirror. The plurality of optical components including a diffraction element and the deflection mirror are arranged in a single optical plane. The deflection mirror is arranged to deflect a diffracted light signal from the diffraction element out of the optical plane into a detector positioned above or below the optical plane.