Patent ID: 6771370
Filing Date: 2004-08-03
Classification: G01J,G01N

Abstract:
A method for characterizing a powder bed, comprising:generating a plurality of measurements of a powder bed comprising a plurality of particles by repeating the following for each location of a plurality of locations of the powder bed: illuminating a location of the powder bed with a light, the light having a time varying intensity with a resolution of less than one hundred nanoseconds, the particles scattering the light to alter the time varying intensity of the light; detecting the light received from the powder bed, the light having propagated through a portion of the particles, the portion of the particles defining a sampled volume interrogated by the propagating light; measuring the altered time-varying intensity of the light to generate a time-dependent signal, the time-dependent signal having a time-dependence less than or equal to a time-of-flight of a photon of the propagating light; determining a measurement of an optical property of the powder bed according to the time-dependent signal using a mathematical model describing light propagation; and determining a measurement of a characteristic of the powder bed in accordance with the optical property; determining the sampled volume interrogated by the propagating light; calculating a variance associated with at least a subset of the measurements; and determining a uniformity associated with the powder bed in accordance with the variance and the sampled volume.