Apparatus for sizing particles, droplets or the like with laser scattering

An apparatus for sizing particles, droplets or the like, employing laser scattering comprising:

• laser generation means for generating a pair of first laser beams of the same wavelength;
• focusing means situated to receive said pair of first laser beams for causing said pair of leaser beams to cross and thereby establish an interference pattern between said pair of beams;
• first collection means for sensing scattering of said pair of first laser beams caused by said particles, droplets or the like in said interference pattern, said collection means having a focal volume extending into said interference pattern;
• a second laser beam narrower than said first beams and distinguishable from said first beams, focused within said interference pattern;
• second collection means for sensing scattering of said second laser beam caused by said particles, droplets or the like in said focal volume of said first laser beam, said second collection means coupled to said first collection means for controlling output signals from said first collection means;
• whereby better fringe control within said interference pattern is achieved.

In an apparatus for measuring or sensing parameters associated with particles, droplets, or the like, employing the scattering of a light beam, an improvement for determining when a particle, droplet, or the like has crossed the central portion of a first light beam comprising:

• light generation means for generating a second light beam, said second beam being disposed co-axially within said central portion of said first beam;
• and,
• sensing means for sensing the scattering of said second beam, said sensing means being substantially unaffected by the scattering of said first beam;
• whereby the passage of a particle, droplet, or the like through said central portion of said first beam which includes said second beam is detected by sensing the scattering of said second beam.

A method for sizing a particle, droplet or the like, employing laser scattering which comprises:

• generating first and second laser beams of the same wavelength;
• focusing said first and second laser beams along a first axis and causing said first and second laser beams to cross said first axis to establish an interference pattern between said beams;
• sensing resulting scattered rays of said first and second laser beams caused by said particles, droplets or the like in said interference pattern, at an axis being off-axis from said first axis;
• determining the signal visibility associated with said scattering from the following relationship, ##EQU14## where, V=signal visibility
• E.sub.s1 =field scattered from said first beam
• E.sub.s2 =field scattered from said second beam
• A=aperture area of collecting means
• .sigma.=phase angle between scattered fields E.sub.s1 and E.sub.s2, which is given by,
• .sigma.=.pi. /2+2.alpha. (sin.tau.-msin.tau.')
• where,
• .alpha.=.pi.d/.lambda.:
• .lambda.=wavelength of said pair of laser beams
• d=diameter of said particle, droplets or the like
• .tau.=incident angle of said first beam measured with respect to a surface tangent at the point of contact with said particle, droplet or the like
• .tau.'=angle of said first beam passing through said particle, droplet or the like with respect to said tangent
• m=index of refraction of said particle, droplet or the like
• determining the size of said particle, droplet or the like from said signal visibility;
• whereby the size of a particle, droplet or the like is determined by sensing scattered rays from a point off-axis from said first axis.