A particle size analyzer that measures the intensity of light scattered by moving particles passing through the probe of a crossed beam laser anemometer, verifies that the measured signal was produced by a particle passing through a region near the center of the probe, and stores count values related to the number of particles producing the same scattered light intensity value is disclosed. Since scattered light intensity values are related to particle size, the stored count values equal the number of particles of the same size detected by the analyzer. In the preferred form of the invention, the measured light intensity determines the address of a particular intensity bin of a storage system. After verification to determine if a measured intensity value was produced by a particle passing through a region near the center of the probe, the count value stored in an intensity bin related to the measured value is updated by one. When any bin reaches the maximum value that can be stored therein, the particle light intensity measuring mode of operation ends and the particle size analyzer is placed in a readout mode of operation. In the readout mode of operation, the intensity bin count values are sequentially read out, converted into analog form, and displayed.

Method and apparatus for determining the width of an elongated element, such as a filament or slit which comprise producing a moving interference fringe zone by converging two beams of coherent light of the same intensity but slightly different frequency; positioning the element within the fringe zone in such manner that the longitudinal axis of the element is substantially normal to the plane of the convergent beams, namely, parallel to the plane of the fringes; maintaining the element substantially spatially stationary relative to the zone, whereby the moving fringe pattern continuously sweeps across the element; and determining the ratio of the AC to DC signal components of the radiation scattered or transmitted by the element. The method and system include respectively the step and means therefor of adjusting or scanning the fringe period value around the element to determine the size capable of producing a minimum AC/DC ratio. In the case of a system substantially free from noise, including non-compensating optical noise factors introduced by the element being measured, a zero ratio indicates that the filament diameter or slit width equals the known fringe period, and a non-zero ratio indicates diameter or slit width deviation from the fringe period, the degree of which can be determined from the signal ratio with the use of known means by adjusting the fringe period until the AC component of the signal becomes zero. In the case of a system having a substantial amount of noise, the AC/DC minimum ratio obtained at a given fringe period may have a finite value and indicates an element width equal to the given fringe period times a constant, the constant being the ratio of the width of the given element and the given fringe period. The element, though spatially stationary in the fringe zone, can be continuously moving longitudinally. The process and system are particularly useful for monitoring the width of manufactured elements and, by automatic feedback, correcting deviations. In some applications where change in the magnitude of the DC signal component during the fringe period scan is sufficiently nominal with respect to permissible width-sensing error, the AC/DC ratio measurement can be dispensed with and determination of the AC signal component minimum alone can be employed.

Method and apparatus for analyzing blood or other biological fluids containing cells or particles of interest by passing them sequentially through a narrow flow chamber where a repetitive physical stimulus, such as a plurality of beams of light, is spaced at intervals to form a code along the length of the flow chamber to elicit responses from the particles. These responses are then decoded and used to classify the particles according to type.

A multiple detection volume laser doppler velocimeter for continuously monitoring an aerosol for particle velocities and sizes is disclosed. A source of coherent light producing light beams at selected wavelengths is directed through: a beam separator separating the beams into a plurality of beams at selected wavelengths, beam splitters orienting and dividing at least two of the plurality of beams into two beams each at the selected wavelengths; and phase gratings for producing multiple beams of each beam received. The multiple beams are then converged to form at their intersections a plurality of detection volumes. Aerosols pass through the detection volumes and scatter light of the selected wavelengths. The scattered light is detected by transducers to produce electrical signals which are processed to produce signals representative of the horizontal and vertical components of particle velocity and size, and of the time it takes the particle to pass through the detection volume (duration signal). The duration signal is combined with a particle velocity signal to produce a signal indicative of particle size.

Method and apparatus for sensing the effective magnitude and/or number and/or position of individual depression and/or protrusion defects on a high-precision smooth surface of an article which may have said defects randomly distributed and relatively spatially distant each from the other, comprising continuously scanning the surface with a laterally-moving interference fringe pattern adjusted in size to have a cross-sectional area substantially smaller than the surface and no larger than an area which includes about an average predetermined spatial incidence of about one defect per pattern area; adjusting the fringe period to a size substantially larger than the effective cross-sectional dimension of a predetermined, maximum size defect; continuously sensing the AC and DC or AC signal components of the backscattered light; and substantially determining the effective magnitude and/or number and/or surface position of said defects by determining the magnitude of the AC or AC and DC signals obtained at each instantaneous relative position of the fringe pattern and the smooth surface. Said scan can thus provide information as to effective magnitude, number of defects, and topography of the defects on the surface. By the use of appropriate electronics, the information can be recorded and/or displayed.