In accordance with an example embodiment of the invention, a detector assembly for an analyzer device for analysis of elemental composition of a sample using optical emission spectroscopy is provided. The detector assembly comprises an exciter for generating an excitation focused at a target position to invoke an optical emission from a surface of the sample at the target position; and a light collection arrangement for transferring the optical emission to a spectrometer. The light collection arrangement comprises a concave spherical mirror, an optical receiver arranged in an image point in the principal axis of the concave spherical mirror and a folding mirror including at least one aperture. The exciter is arranged with respect to the light collection arrangement such that the excitation is transferred towards the target position through said at least one aperture, and the folding mirror is arranged between the concave spherical mirror and the optical receiver such that the folding mirror folds the principal axis of the concave spherical mirror towards the target position and such that said at least one aperture is aligned with the principal axis of the concave spherical mirror to allow transferring optical emission reflected from the concave spherical mirror therethrough towards the optical receiver.