Browse Prior Art Database

Optical Method for the Detection of Particles with Increased Tolere

IP.com Disclosure Number: IPCOM000113399D
Original Publication Date: 1994-Aug-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Taubenblatt, MA: AUTHOR

Abstract

Particle sizing (and refractive index measurement) using optical methods is usually affected by the shape and orientation of a particle. By using circularly polarized light in the optical system the shape of the particle is averaged over all orientations, making the detection system more tolerant of non-spherical shapes with random orientations.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Optical Method for the Detection of Particles with Increased Tolere

      Particle sizing (and refractive index measurement) using
optical methods is usually affected by the shape and orientation of a
particle.  By using circularly polarized light in the optical system
the shape of the particle is averaged over all orientations, making
the detection system more tolerant of non-spherical shapes with
random orientations.

      Particle detection using optical methods usually involves the
detection of light scattered from a particle.  In many schemes two
beams are used with different linear polarizations to determine and
compensate for the particle path when the beam is  non-uniform in
intensity (1).  When the particles being detected are not spherical
they will scatter light differently depending on the orientation of
the particle.  For example, a cigar shape particle will scatter more
light when the polarization is along the cigar length than when it is
perpendicular to it.  This can cause erroneous measurements when the
detection system assumes an isotropic response.  Specifically this
invention addresses a problem with the invention discussed in (2) in
which a laser based Nomarski microscope is used to determine the
particle size and refractive index by measuring the phase shift
extinction in a focused laser beam caused by a particle.  The path is
determined by the response of the detector to a particle passing
first through an s-polarized and then through a p-polarized beam.
Because the beams are offset with regard to the particle flow
direction, the asymetry in the signals is a measure of the particle
trajectory offset with regard to the beams.  However, a non-isotropic
response as would be obtained from a non-spherical particle would
cause an erroneous path to be computed, since the asymetry would be
strongly influenced by the particle shape and orientation as well.

      The invention is to modify the optics by modifying the Nomarski
optical system to employ rather than linearly polarized beams (i.e.,
the s and p polarized beams) circularly polarized beams (i.e., right
and left).  This may be easily accomplished by the insertion of two
qua...