Dual beam maximum intensity laser sizing system

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

• laser generation means for generating a second laser beam, said second laser beam having a smaller diameter than said first beam;
• light directing means for directing said laser beams along an axis and for causing said pair of laser beams to cross said axis at a known angle to establish an interference pattern within the area defined by the intersection of said first and second beams;
• sensing means for sensing the scattered signal of said beams caused by a particle, droplet or the like passing through said interference pattern;
• filtering means coupled to said sensing means for filtering said signal such that only signal components having frequencies within a predetermined range are permitted to pass;
• detecting means coupled to said filtering means for detecting the presence of Doppler fringes in said filtered signal, thereby indicating that said particle, droplet or the like has crossed the central portion of said first laser beam.

An apparatus for determining the size of particles, droplets or the like, employing laser scattering, comprising:

• laser generation means for providing first and second laser beams, said first beam having a greater diameter than said second beams;
• light directing means for directing said laser beams along an axis and for causing said pair of laser beams to cross said axis at a given angle to establish an interference pattern between said pair of beams;
• collection means for sensing the scattered signal of said beams caused by a particle, droplet or the like in said interference pattern;
• filter means coupled to said collection means for filtering said scattered signal and for providing a pedestal (DC) signal representative of the intensity of said scattered signal;
• sizing means coupled to receive said pedestal signal to establish the size of said particle, droplet or the like;
• whereby the size of said particle, droplet or the like is determined.

An apparatus for determining the velocity of particles, droplets and the like, employing laser scattering, comprising:

• laser generation means for providing first and second laser beams, said first beam having a greater diameter than said second beam;
• light directing means for directing said laser beams along an axis and for causing said pair of laser beams to cross said axis at a given angle to establish an interference pattern between said pair of beams;
• collection means for sensing the scattered signal of said beams caused by a particle, droplet or the like in said interference pattern;
• filter means coupled to said collection means for filtering said scattered signal and providing a high frequency signal representative of high frequency Doppler (AC) signal components of said scattered signal;
• velocity means coupled to receive said high frequency Doppler signal for determining the velocity of said particle, droplet or the like;
• whereby the velocity of said particle, droplet or the like is determined.

An apparatus for determining the size and velocity of particles, droplets and the like, employing laser scattering, comprising:

• laser generation means for providing first and second laser beams, said first beam having a greater diameter than said second beam;
• light directing means for directing said laser beams along an axis and for causing said pair of laser beams to cross said axis at a given angle to establish an interference pattern between said pair of beams;
• collection means for sensing the scattered signal of said beams caused by a particle, droplet or the like in said interference pattern;
• filter means coupled to said collection means for filtering said scattered signal and providing high frequency signals representative of the high frequency Doppler (AC) signal components of said scattered signal, and a pedestal (DC) signal representative of the intensity of said scattered signal;
• sizing means coupled to receive said pedestal signal to establish the size of said particle, droplet or the like;
• velocity means coupled to receive said high frequency Doppler signal for determining the velocity of said particle, droplet or the like;
• whereby both the size and velocity of said particle, droplet or the like is determined.

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

• generating first and second laser beams, said first beam having a greater diameter than said second beam;
• directing and focusing said first and second laser beams along an axis and causing said first and second beams to cross said axis to establish an interference pattern between said beams the intensity of said mixed beams being described by the following relationship;
• ##EQU5## where, B=phase angle of said interference pattern,
• I.sub.12 =intensity of first laser beam,
• I.sub.14 =intensity of second laser beam,
• sensing resulting scattered signals of said first and second laser beams caused by a particle, droplet or the like passing through said interference pattern;
• low pass filtering said scattering signal to determine the intensity of the pedestal signal;
• determining the size of said particle, droplet or the like from said pedestal signal.

A method for determining the velocity of a particle, droplet or the like employing laser scattering, which comprises the steps of:

• generating first and second laser beams, said first beam having a greater diameter than said second beam;
• directing and focusing said first and second laser beams along an axis and causing said first and second beams to cross said axis to establish an interference pattern between said beam the intensity of said mixed beams being described by the following relationship;
• ##EQU6## where, B=phase angle of said interference pattern,
• I.sub.12 =the intensity of the first laser beam,
• I.sub.14 =the intensity of the second laser beam,
• sensing resulting scattered signals of said first and second laser beams caused by a particle, droplet or the like passing through said interference pattern;
• high pass filtering said scattered signals to determine the Doppler (AC) component of said intensity from the following relationship;
• ##EQU7## where, V=signal visibility, determining the velocity of said particle, droplet or the like from said Doppler component;
• whereby the velocity of the particle, droplet or the like passing through said interference pattern is determined.

A method for determining the size and velocity of a particle, droplet or the like, employing laser scattering which comprises the steps:

• generating first and second laser beams, said first beam having a greater diameter than said second beam;
• directing and focusing said first and second laser beams along an axis and causing said first and second beams to cross said axis to establish an interference pattern between said beams;
• the intensity of said mixed beams being described by the following relationship;
• ##EQU8## where, I.sub.12 =intensity of first laser beam,
• I.sub.14 =intensity of second laser beam,
• B=phase angle of said interference pattern,
• sensing resulting scattered signals of said first and second laser beams caused by a particle, droplet and the like passing through said interference pattern;
• high pass filtering said scattered signals to determine the Doppler (AC) component of said intensity from the following relationship;
• ##EQU9## where, V=signal visibility determining the velocity of said particle, droplet or the like from said Doppler component;
• low pass filtering said scattering signal to determine the intensity of the pedestal signal;
• determining the size of said particle, droplet or the like from said pedestal signal.