An apparatus for detection of a fluid borne particle comprising i. a pair of coaxially opposed concave reflective surfaces having the same focal length wherein only one of the reflective surfaces comprises a central aperture, the reflective surfaces separated at their common axis by three times the focal length of the concave reflective surfaces about a zone, and a flow means provided for delivering a fluid flow comprising the fluid borne particle through the zone; ii. a continuous wave laser arranged to illuminate the fluid flow in the zone to identify the presence of the fluid borne particle in the zone; iii. a first and second detector wherein the first detector is arranged to detect scattered and/or emitted light of a first wavelength band emanating from the zone, and the second detector is arranged to detect scattered and/or emitted light of a second wavelength band emanating from the zone; iv. a first and second light source wherein the first source is arranged to illuminate the zone with light of a third wavelength band and the second source is arranged to illuminate the zone with light of a fourth wavelength band; and v. a third detector arranged to detect forward scattered light as a result of illuminating the particle by the laser and/or the first or second light source whereby the continuous wave laser, first light source and second light source are configured to sequentially illuminate the fluid borne particle in the zone, and are each arranged in a plane substantially orthogonal to the direction of the fluid flow provided for by the flow means, the first and second detectors are present on a single side of the laser beam and arranged to detect light focussed through the central aperture, the second detector is arranged to detect back or side scattered light, and the apparatus further comprises feedback means between the second detector and the third detector configured to combine the forward scattered light response detected at the third detector with the back or side scattered light response detected at the second detector in order to reduce the effect of Mie oscillations in a sizing response curve. i. a pair of coaxially opposed concave reflective surfaces having the same focal length wherein only one of the reflective surfaces comprises a central aperture, the reflective surfaces separated at their common axis by three times the focal length of the concave reflective surfaces about a zone, and a flow means provided for delivering a fluid flow comprising the fluid borne particle through the zone; ii. a continuous wave laser arranged to illuminate the fluid flow in the zone to identify the presence of the fluid borne particle in the zone; iii. a first and second detector wherein the first detector is arranged to detect scattered and/or emitted light of a first wavelength band emanating from the zone, and the second detector is arranged to detect scattered and/or emitted light of a second wavelength band emanating from the zone; iv. a first and second light source wherein the first source is arranged to illuminate the zone with light of a third wavelength band and the second source is arranged to illuminate the zone with light of a fourth wavelength band; and v. a third detector arranged to detect forward scattered light as a result of illuminating the particle by the laser and/or the first or second light source