Measurement of size and refractive index of particles using the complex forward-scattered electromagnetic field

An apparatus for classifying particles comprising:

• means for transmitting to a focal plane that includes at least one said particle, two substantially parallel optical beams, said beams being initially mutually coherent but of different polarizations, said beams displaced and focused in said focal plane, said particle inducing a phase shift and change in intensity in one beam;
• Nomarski optical means positioned in a path which said beams take after departing from said focal plane for combining said beams, a phase shift in said one beam causing said combined beam to manifest an elliptical polarization;
• a first Wollaston optical means for separating said elliptically polarized combined beam into a first pair of beams, one having a first polarization axis and a second having a second orthogonal polarization axis, said axes being displaced by 45.degree. from axes of said beams from said Nomarski optical means;
• a second Wollaston optical means for separating said elliptically polarized combined beam into a second pair of polarized beams, the axes of said second pair of polarized beams coincident with polarization axes of said beams from said Nomarski optical means;
• a first pair of detector means responsive to said first pair of polarized beams, one said detector means responsive to one beam's intensity to produce a first output, and another said detector means responsive to another second beam's intensity to produce a second output;
• a second pair of detector means responsive to said second pair of polarized beams, one said detector means responsive to one beam's intensity to produce a third output, and another said detector means responsive to another beam's intensity to produce a fourth output;
• means for subtracting said first and second outputs to provide a phase shift signal;
• means for subtracting said third and fourth outputs to provide an extinction signal;
• and
• processing means for classifying said particle in accordance with said extinction and phase shift output signals.

A method for classifying particles by reference to their refractive index, said method employing an optical system which focuses a pair of orthogonally polarized, adjacent, coherent beams into a focal plane containing said particles, a particle causing a change in phase and intensity of one said beam with respect to another said beam, said beams being recombined into an elliptically polarized beam which is subsequently analyzed by respectively subtracting and adding optical energy aligned along one polarization axis and optical energy aligned along an orthogonal polarization axis, said subtracted energies being representative of a phase shift value and said added energies being representative of an extinction value, all as created by a said particle, the method comprising:

• establishing a phase shift/extinction space;
• determining a point in said space for said particle in accordance with said phase shift and extinction values;
• allocating portions of said space to refractive index value ranges;
• and
• identifying a respective index of refraction range for said particle from said particles determined point in said space.