Device and method for detecting and/or characterizing fluid-borne particles

Measurement method for the detection and/or characterization of fluid-borne particles, the measurement method comprising the steps of:

• producing a flow of fluid along a fluid flow path,
• emitting a pulse of laser light from a laser polarized in a first direction of polarization along a first optical path, in a measurement volume of the fluid flow path, said pulse having a pulse duration,
• collecting fluorescent light emitted by individual fluid-borne particles in said measurement volume when hit by said pulse of laser light polarized in said first direction of polarization and filtered by a linear polarizer, and measuring an intensity of said collected fluorescent light at at least one determined wavelength at a sampling rate of at least three samples per fluorescence decay duration,
• directing a pulse of laser light along a second optical path polarized in a second direction of polarization from a different position relative to said laser in said measurement volume, wherein said second direction of polarization is different from said first direction of polarization and said second optical path is different from said first optical path, such that a time delay between a moment of crossing said measurement volume by said pulse of laser light polarized in said first direction of polarization and a moment of crossing said measurement volume by said pulse of laser light polarized in said second direction of polarization is longer than said pulse duration and shorter than a travel time of the fluid in said measurement volume, wherein the step of directing comprises collecting said pulse of laser light polarized in a first direction of polarization after it crossed said measurement volume and redirecting it towards said measurement volume again, and rotating the polarization of the light of said pulse of laser light polarized in a first direction from said first direction of polarization to said second direction of polarization before said pulse reaches said measurement volume again,
• capturing fluorescent light emitted by individual fluid-borne particles in said measurement volume when hit by said pulse of laser light polarized in said second direction of polarization and filtered by a linear polarizer, and measuring an intensity of said captured fluorescent light, filtered with a linear polarizer, at said at least one determined wavelength at a sampling rate of at least three samples per said pulse duration.