by apertures, e.g. pin-holes or knife-edges

Full Title

Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range (semiconductors lasers H01S5/00) > Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium > Construction or shape of optical resonators or components thereof > Mode suppression > Transverse or lateral modes > by apertures, e.g. pin-holes or knife-edges