Particle path determination system

An apparatus for determining a particle's position in a flow path comprising:

• means for transmitting to a focal plane in said flow path, first and second substantially parallel optical beams, said beams being initially mutually coherent but of different polarizations, said beams displaced from each other along said flow path, a particle in said flow path that passes through a beam inducing a phase shift and change in extinction of said beam;
• recombining means positioned in a path which said beams take after departing from said flow path for combining said beams, a phase shift in a said beam causing said combined beam to manifest an elliptical polarization exhibiting first and second polarization axes;
• detector means for sensing an intensity of at least one of said polarization axes to provide a phase shift signal;
• processing means for accumulating phase shift signals resulting from a particle's travel in said flow path, to derive a phase shift waveform therefrom, and for measuring a width characteristic of said phase shift waveform and deriving from said width characteristic an indication of the position of said particle relative to said focal plane.

An apparatus for determining a particle's position in a flow path having a determinable direction, comprising:

• means for transmitting to a flow path at least an optical beam;
• dither means for oscillating said optical beam across said flow path at a rate that is high in relation to a rate of travel of a particle in said flow path, a particle in said flow path causing a change in extinction in said optical beam when said beam intercepts said particle;
• sensor means for providing output signals indicative of the extinction of said beam and including a noise cancelling amplifier provided with an input from said transmitting means, whereby said amplifier provides a minimal signal output at times other than when a particle in said flowpath intersects said beam;
• and
• processor means for sampling said output signals and deriving an extinction signal profile resulting from a said particle's travel in said flow path.

An apparatus for determining a particle's position in a flow cell, said particle's flow direction path being indeterminate, comprising:

• means for transmitting to said flow cell, first and second substantially parallel optical beams, said beams being initially mutually coherent but of different polarizations, said beams displaced from each other along an axis, a particle in said cell that intercepts a beam inducing a change in intensity of said beam;
• dither means for cyclically moving said optical beams across said flow cell in a direction at an angle with respect to said axis;
• a pair of detector means, one said detector means responsive to said first beam's intensity to produce a first output, and another said detector means responsive to said second beam's intensity to produce a second output;
• means for combining said first and second outputs to provide a composite signal;
• and
• processing means for accumulating composite signals resulting from a particle's interception of said dithered beams to derive a waveform therefrom, and for determining said particle's position from said waveform.

An apparatus for determining a particle's position in a flow cell, said particle's flow direction being indeterminate, comprising:

• means for transmitting to said flow cell, a coherent optical beam, a particle in said cell that intercepts said beam inducing a change in extinction of said beam;
• dither means for cyclically moving said optical beam in said flow cell in a pattern that closes upon itself and encompasses an inspection region;
• detector means responsive to said beam's extinction to produce first output signals;
• and
• processing means for accumulating said first output signals resulting from a particle's interception of said dithered beam to derive a waveform therefrom and for determining said particle's position from said waveform.

An apparatus for determining a particle's position in a flow path, comprising:

• means for transmitting to said flow path, first and second optical beams, said beams being initially mutually coherent but of different polarizations, said second beam offset from said first beam along an axis that intersects said flow path at an acute twist angle, a particle that intersects a beam inducing a change in a said beam;
• recombining means positioned in a path which said beams take after departing from said flow path, for combining said beams, a change in a said beam causing said combined beam to manifest an elliptical polarization exhibiting first and second polarization axes;
• detector means for sensing an intensity of one of said polarization axes to provide a signal;
• and
• processing means for accumulating said signals resulting from a particle's travel in said flow path past said beams, and for determining an asymmetry value of said signal indicative of said particle s position in said flow path and a further value indicative of said particle's position relative to a focal plane in said flow path, said processor further determining from said values and from stored, allowed off-axis and out-of-focus distances, whether the particle resides in an allowed inspection volume.