Methods and apparatus for molecular characterization

A beam dump for attenuating a light beam without substantial reflection, comprising:

• an enclosure having an inlet for receiving a light beam parallel to an optical axis and a light absorbing interior wall;
• a surface located within said enclosure and positioned for intercepting the light beam received through said inlet, said surface being oriented relative to said light beam at an angle selected to cause said light beam to undergo multiple reflections within said enclosure downstream of a point at which said surface intercepts said light beam and in a direction along said optical axis;
• and
• means for guiding said light beam to the inlet of said enclosure, said means for guiding comprising a truncated conical, light-absorbing surface having a first opening that is larger than said inlet for receiving said light beam and a second opening that defines the inlet of said enclosure.

A molecular characterization instrument comprising:

• a scattering cell containing a sample for molecular characterization;
• means for directing a polarized light beam through said cell so that the light beam is scattered by said sample, said light beam defining an optical axis;
• means for detecting a first measurement beam comprising light from the light beam that is scattered by said sample in a predetermined range of angles relative to said optical axis and providing a first electrical signal representative of said first measurement beam for characterization of said sample;
• means for detecting a second measurement beam comprising light from the light beam that is scattered by said sample in a direction perpendicular to said light beam and perpendicular to a direction of polarization of said light beam and providing a second electrical signal representative of said second measurement beam for characterization of said sample;
• means for detecting a third measurement beam comprising light from the light beam that is scattered by said sample in a direction perpendicular to said light beam and parallel to the direction of polarization of said light beam and providing a third electrical signal representative of said third measurement beam for characterization of said sample;
• means for detecting a fourth measurement beam comprising fluctuations in light from the light beam that is scattered by said sample in a direction perpendicular to said light beam and providing a fourth electrical signal representative of said fourth measurement beam for characterization of said sample;
• means for determining the difference between the refractive index of the sample and a reference fluid by measuring a deviation angle of a light beam passing through a two chamber cell and providing a fifth electrical signal representative of said sample;
• and
• means for processing said first, second, third, fourth and fifth electrical signals to provide a molecular characterization of said sample.

A method for generating a signal for molecular characterization of a liquid sample comprising the steps of:

• directing a light beam through a scattering cell having a window at each end and containing a liquid sample for molecular characterization so that the light beam is scattered by the sample, the light beam defining an optical axis;
• selecting from the scattered light a measurement beam comprising light from the light beam that is scattered by the sample from a predetermined portion of the scattering cell in a predetermined range of angles relative to the optical axis, the step of selecting a measurement beam including the steps of selecting light within said predetermined range of angles with an annular aperture and blocking light from the light beam that is scattered by the window at each end of said scattering cell with axially spaced apart irises located downstream of said annular aperture;
• and
• detecting the measurement beam and providing an output electrical signal representative of the measurement beam for characterization of the sample.

A molecular characterization detector comprising:

• a scattering cell containing a sample for molecular characterization;
• means for directing a light beam through said cell so that the light beam is scattered by said sample, said light beam defining an optical axis;
• means for selecting from the scattered light a measurement beam comprising light from the light beam that is scattered by said sample in a predetermined range of angles relative to said optical axis, said means for selecting a measurement beam comprising means for defining an annular aperture for passing said measurement beam and optical means for focusing light scattered by said sample on said annular aperture, said means for defining an annular aperture comprising a first iris for blocking light scattered by said sample at angles greater than said predetermined range of angles and a second iris for blocking light scattered by said sample at angles less than said predetermined range of angles, said optical means comprising a lens having a single spherical surface, said first iris and said second iris being axially spaced apart on said optical axis;
• and
• means for detecting said measurement beam and providing an output electrical signal representative of said measurement beam for characterization of said sample.