An analysation instrument including: a first reflector having a partial ellipsoidal shape; a near focal point of the partial ellipsoidal shape of the first reflector; a distant focal point of the partial ellipsoidal shape of the first reflector; a central axis of the partial ellipsoidal shape defined by the near focal point and distant focal point of the partial ellipsoidal shape of the first reflector; a source of electromagnetic radiation disposed at the near focal point of the partial ellipsoidal shape capable of emitting electromagnetic radiation toward the first reflector; a second reflector having a partial ellipsoidal shape oriented relative to the first reflector so as to be capable of receiving electromagnetic radiation reflected by the first reflector; a near focal point of the partial ellipsoidal shape of the second reflector; a distant focal point of the partial ellipsoidal shape of the second reflector wherein the distant focal point of the partial ellipsoidal shape of the first reflector and the distant focal point of the partial ellipsoidal shape of the second reflector overlap; a central axis of the partial ellipsoidal shape defined by the near focal point and distant focal point of the partial ellipsoidal shape of the second reflector; a flow source to produce a flow of particles to be analysed; an inspection zone of the flow of particles located at the near focal point of the partial ellipsoidal shape of the second reflector, wherein fluorescence from illuminated particles in the inspection zone is collected by the second reflector; and a dichroic filter positioned to direct fluorescence, which is reflected back by the said second reflector, to a detector in a detector housing. a first reflector having a partial ellipsoidal shape; a near focal point of the partial ellipsoidal shape of the first reflector; a distant focal point of the partial ellipsoidal shape of the first reflector; a central axis of the partial ellipsoidal shape defined by the near focal point and distant focal point of the partial ellipsoidal shape of the first reflector; a source of electromagnetic radiation disposed at the near focal point of the partial ellipsoidal shape capable of emitting electromagnetic radiation toward the first reflector; a second reflector having a partial ellipsoidal shape oriented relative to the first reflector so as to be capable of receiving electromagnetic radiation reflected by the first reflector; a near focal point of the partial ellipsoidal shape of the second reflector; a distant focal point of the partial ellipsoidal shape of the second reflector wherein the distant focal point of the partial ellipsoidal shape of the first reflector and the distant focal point of the partial ellipsoidal shape of the second reflector overlap; a central axis of the partial ellipsoidal shape defined by the near focal point and distant focal point of the partial ellipsoidal shape of the second reflector; a flow source to produce a flow of particles to be analysed; an inspection zone of the flow of particles located at the near focal point of the partial ellipsoidal shape of the second reflector, wherein fluorescence from illuminated particles in the inspection zone is collected by the second reflector; and a dichroic filter positioned to direct fluorescence, which is reflected back by the said second reflector, to a detector in a detector housing.