According to an example embodiment, a detector assembly for use in analysis of elemental composition of a sample by using optical emission spectroscopy is provided, the detector assembly including a rotatable element that is rotatable about an axis and that has attached thereto a laser source for generating laser pulses for invoking optical emission on a surface of the sample, the laser source arranged to generate laser pulses focused at a predefined distance from said axis at a predefined distance from a front end of the detector assembly, and a detector element for capturing optical emission invoked by said laser pulses.