An optical assembly for an analyzer instrument for analysis of elemental composition of a sample using optical emission spectroscopy includes: an exciter generating an excitation focused at a target position to produce optical emission from the sample; and an optical arrangement including a light collection arrangement transferring the optical emission from the target position to a detector assembly's detector interface. The light collection arrangement includes: an off-axis parabolic light collecting mirror including an aperture, a lens arrangement including converging and diverging axicon lens portions, the lens arrangement positioned so its optical axis is parallel to that of the light collecting mirror and intersects a surface of the light collecting mirror at the aperture, and an off-axis parabolic focusing mirror having its focal point at the detector interface, the optical axis of the lens arrangement being parallel to that of the focusing mirror and intersects the focusing mirror's surface.