Interference methods and interference microscopes for measuring energy path length differences, path length between two locaitons or for determiing refractive index

A method for determining the path length between two locations in an object, wherein said object is a partially energy transparent object with known refractive index between first and second locations in said object by measuring the difference between two energy path lengths, said method comprising:

• coherently directing a portion of an illuminating energy beam from a coherent energy source through a first coherent energy guide to an energy exit port denoted the first exit;
• coherently directing a second portion of said illuminating energy beam through a second coherent energy guide to an energy exit port denoted the second exit:
• wherein said first and second portions of said illuminating energy beam are at least partly coherent with respect to one another on emerging from said first and second exits respectively;
• focussing coherently at least a portion of illuminating energy emerging from said first exit into a first spot intersecting an object;
• spatially filtering confocally and coherently directing at least a portion of a first coherent signal energy beam resulting from interaction between said illuminating energy beam in said first spot and said object to an interferometer, said first signal beam being coherent with respect to said illuminating energy beam;
• focussing coherently at least a portion of illuminating energy emerging from said second exit into a second spot intersecting said object;
• coherently directing at least a portion of a second coherent signal energy beam resulting from interaction between said illuminating energy beam in said second spot and said object to said interferometer, said second signal beam being coherent with respect to said illuminating energy beam;
• wherein said first spot is at a first location in said object, said second spot is formed by focussing through said object via said first location to a second location in said object;
• whereby said first and second signal beams interfere thereby producing an output signal;
• and
• calculating from said output signal said energy path length difference between said first energy path from said energy source, through said first energy guide to the intersection of said first spot with said object to said interferometer and said second energy path from said energy source, through said second energy guide to the intersection of said second soot with said object to said interferometer;
• and
• determining the path length between said first and second locations from said energy path length difference with said known refractive index.

A method for determining refractive index of an object with known path length between first and second locations in said object, comprising:

• (a) coherently directing a portion of an illuminating energy beam from a coherent energy source through a first coherent energy guide an energy exit port denoted the first exit;
• (b) coherently directing a second portion of said illuminating energy beam through a second coherent energy guide to an energy exit port denoted the second exit;
• wherein said first and second portions of said illuminating energy beam are at least partly coherent with respect to one another on emerging from said first and second exits respectively;
• (c) focussing coherently at least a portion of illuminating energy emerging from said first exit into a first spot intersecting said object at a first location;
• (d) coherently directing at least a portion of a first coherent signal energy beam resulting from interaction between said illuminating energy beam in said first spot and said object at said first location to an interferometer, said first signal beam being coherent with respect to said illuminating energy beam;
• (e) directing coherently at least a portion of said first portion of said illuminating energy beam, denoted the first reference beam, from said first exit to said interferometer whereby said first reference beam and said first signal beam interfere thereby producing a first output signal;
• (f) calculating from a first output signal said first energy path length difference between a first energy path from said energy source, through said first energy guide to the intersection of said first spot with said object at said first location and from said first location to said interferometer and a second energy path from said energy source, through said second energy guide to said interferometer;
• (g) repeating steps (a) and (b);
• (h) focussing coherently at least a portion of illuminating energy emerging from said first exit through said object via said first location into a second spot intersecting said object at a second location;
• (i) coherently directing at least a portion of a second coherent signal energy beam resulting from interaction between said illuminating energy beam in said second spot and said object at said second location to the interferometer, said second signal beam being coherent with respect to said illuminating energy beam;
• (j) directing coherently at least a portion of said second portion of said illuminating energy beam, denoted the second reference beam, from said second exit to said interferometer whereby the second reference beam and said second signal beam interfere thereby producing a second output signal;
• and
• (k) calculating from said second output signal said second energy path length difference between a third energy path from said energy source, through said first energy guide to the intersection of said second spot with said object at said second location and from said second location to said interferometer and a fourth energy path from said energy source, through said second energy guide to said interferometer;
• (l) determining the refractive index of said object between said first and second locations in said object by comparing said first and second energy path length differences with said known path length.

A method for determining path length between two locations in an object, wherein the object is a partially energy transparent object with known refractive index between first and'second locations in the object, comprising;

• (a) coherently directing a portion of an illuminating energy beam from a coherent energy source through a first coherent energy guide to an energy exit port denoted the first exit;
• (b) coherently directing a second portion of the illuminating energy beam through a second coherent energy guide to an energy exit port denoted the second exit;
• wherein the first and second portions of the illuminating energy beam are at least partly coherent with respect to one another on emerging from the first and second exits respectively;
• (c) focussing coherently at least a portion of illuminating energy emerging from the first exit into a first spot intersecting the object at a first location;
• (d) coherently directing at least a portion of a first coherent signal energy beam resulting from interaction between the illuminating energy beam in the first spot and the object at the first location to an interferometer, the first signal beam being coherent will respect to the illuminating energy beam;
• (e) directing coherently at least a portion of the first portion of the illuminating energy beam, denoted the first reference beam, from the first exit to the interferometer whereby the first reference beam and the first signal beam interfere thereby producing a first output signal;
• and
• (f) calculating from the first output signal a first energy path length difference between a first energy path from the energy source, through the first energy guide to the intersection of the first spot with the object at the first location and from the first location to the interferometer and a second energy path from the energy source, through the second energy guide to the interferometer;
• (g) repeating steps (a) and (b);
• (h) focussing coherently at least a portion of illuminating energy emerging from the first exit through the object via the first location into a second spot intersecting the object at a second location;
• (i) coherently directing at least a portion of a second coherent signal energy beam resulting from interaction between the illuminating energy beam in the second spot and the object at the second location to said interferometer, the second signal beam being coherent with respect to the illuminating energy beam;
• (j) directing coherently at least a portion of the second portion of the illuminating energy beam, denoted the second reference beam, from the second exit to the interferometer whereby the second reference beam and the second signal beam interfere thereby producing a second output signal;
• and
• (k) calculating from the second output signal the second energy path length difference between a third energy path from the energy source, through the first energy guide to the intersection of the second spot with the object at the second location and from the second location to the interferometer and a fourth energy path from the energy source, through the second energy guide to the interferometer;
• (l) determining the path length between the first and second locations in the object by comparing the first and second energy path length differences with the known refractive index.

A microscope for measuring the difference between two energy path lengths comprising:

• an energy source which emanates an illuminating energy beam wherein at least a portion of the illuminating energy beam is substantially coherent;
• a first coherent energy guide operatively associated with the energy source to receive coherently a first portion of the coherent illuminating energy beam, the first coherent energy guide having an energy exit port denoted the first exit;
• a second coherent energy guide operatively associated with the energy source to receive coherently a second portion of the coherent illuminating energy beam, the second coherent energy guide having an energy exit port denoted the second exit;
• wherein the illuminating energy beams are coherent with respect to one another on emerging from the first and second exit;
• an energy focusser operatively associated with the first exit for focussing coherently at least a portion of illuminating energy emerging from the first exit into a spot intersecting an object;
• a first energy director operatively associated with the first exit and the focusser for spatially filtering confocally and coherently directing at least a portion of a signal energy beam resulting from interaction between the illuminating energy beam in the spot and the object to an interferometer, the signal beam being coherent with respect to the illuminating energy beam;
• a second energy director operatively associated with the second exit and the interferometer to direct coherently at least a portion of the second portion of the illuminating energy beam, denoted the reference beam, from the second exit to the interferometer whereby the reference beam and the signal beam interfere thereby producing an output signal;
• and
• a calculator operatively associated with the interferometer to calculate from the output signal the energy path length difference between a first energy path from the energy source, through the first energy guide to the intersection of the spot with the object via the focusser and from the intersection to the interferometer via the first energy director and a second energy path from the energy source, through the second energy guide to the interferometer via the second energy director.

A microscope for measuring the difference between two energy path lengths comprising:

• an energy source which emanates an illuminating energy beam wherein at least a portion of the illuminating energy beam is substantially coherent;
• a first coherent energy guide operatively associated with the energy source to receive coherently a first portion of the coherent illuminating energy beam, the first coherent energy guide having an energy exit port denoted the first exit;
• a second coherent energy guide operatively associated with the energy source to receive coherently a second portion of the coherent illuminating energy beam, the second coherent energy guide having an energy exit port denoted the second exit;
• wherein the illuminating energy beams are coherent with respect to one another on emerging from the first and second exits;
• a first energy focusser operatively associated with the first exit for focussing coherently at least a portion of illuminating energy emerging from the first exit into a first spot intersecting an object;
• a first energy director operatively associated with the first exit and the first focusser for spatially filtering confocally and coherently directing at least a portion of a first signal energy beam resulting from interaction between the illuminating energy beam in the first spot and the object to an interferometer, the first signal beam being coherent with respect to the illuminating energy beam;
• a second energy focusser operatively associated with the second exit for focussing coherently at least a portion of illuminating energy emerging from the second exit into a second spot intersecting said object;
• a second energy director operatively associated with the second exit and the second focusser for coherently directing at least a portion of a second signal energy beam resulting from interaction between the illuminating energy beam in the second spot and the object to the interferometer, the second signal beam being coherent with respect to the illuminating energy beam;
• whereby the first and second signal beams interfere thereby producing an output signal;
• and
• a calculator operatively associated with the interferometer to calculate from the output signal the energy path length difference between a first energy path from the energy source, through the first energy guide to the intersection of the first spot with the object via the first focusser and from the intersection of the first spot with the object to the interferometer via the first energy director and a second energy path from the energy source, through the second energy guide to the intersection of the second spot with the object via the second focusser and from the intersection of the second spot with the object to the interferometer via the second energy director.

A microscope for measuring the difference between two light path lengths comprising:

• a light source which emanates an illumination light beam having at least one wavelength in the range of far UV to far IR wherein at least a portion of the illuminating light beam is substantially coherent;
• a first optical fibre operatively associated with a first light splitter to receive coherently a first portion of the coherent illuminating light beam, the first optical fibre having a second light splitter and a light exit port denoted the first exit;
• a second optical fibre operatively associated with the light source to receive coherently a second portion of the coherent illuminating light beam via the first light splitter, the second optical fibre having a light exit port denoted the second exit and having a light path length changer;
• wherein the illuminating light beams are coherent with respect to one another on emerging from the first and second exits;
• a light focusser operatively associated with the first exit for focussing coherently at least a portion of illuminating light emerging from the first exit into a diffraction limited spot intersecting an object;
• wherein the focusser is operatively associated with the first exit for coherently directing at least a portion of a signal light beam resulting from interaction between the spot and the object to the first exit and thereby to the first light splitter which acts as an interferometer, via the first optical fibre and the second light splitter, the signal beam being coherent with respect to the illuminating light beam;
• wherein the numerical aperture NA, of the signal beam originating from the central portion of the spot, the wavelength of the signal light beam, .lambda., and average diameter, d, of the light guiding core of the first optical fibre at the first exit are related by the equation:
• NA<or.apprxeq.0.6.times..lambda./d
• a light reflector operatively associated with the second exit and the interferometer to direct coherently at least a portion of the second portion of the illuminating light beam, denoted the reference beam, to the first light splitter via the second exit and the second optical fibre whereby the reference beam and the signal beam interfere thereby producing an output signal;
• a first detector operatively associated with the first splitter to detect the output signal;
• a scanner operatively associated with the first and second exits whereby the first and second exits are movable relative to the focusser and the reflector, which focusser and reflector are stationary with respect to the object, but which exits are not movable with respect to each other;
• a second detector operatively associated with the second splitter to detect signal light from the first optical fibre;
• and
• a calculator operatively associated with the light path length changer, the first detector and the first light splitter to maintain the interference between the reference and signal beams in quadrature, to calculate the light path length difference between a first light path from the light source, through the first optical fibre to the intersection of the spot with the object via the first exit and the focusser and from the intersection back to the first light-splitter via the focusser, the first exit and the first optical fibre and a second light path from the light source, through the second optical fibre back to the first light splitter via the second exit, the light reflector and the second exit and back through the second optical fibre, and determine via the second detector when the spot is substantially focussed on the surface of the object.

A microscope for measuring the difference between two light path lengths comprising:

• a light source which emanates an illuminating light beam having at least one wavelength in the range of far UV to hr IR wherein at least a portion of the illuminating light beam is substantially coherent;
• a first optical fibre operatively associated with a first light splitter to receive coherently a first portion of the coherent illuminating light beam, the first optical fibre having a second light splitter and a light exit port denoted the first exit;
• a second optical fibre operatively associated with the light source to receive coherently a second portion of the coherent illuminating light beam via the first light splitter, the second optical fibre having a light exit port denoted the second exit and having a light path length changer;
• wherein the illuminating light beams are coherent with respect to one another on emerging from the first and second exits;
• a light focusser operatively associated with the first exit for focussing coherently at least a portion of illuminating light emerging from the first exit into a first diffraction limited spot intersecting an object;
• wherein the focusser is operatively associated with the first exit for coherently directing at least a portion of a first signal light beam resulting from interaction between the first spot and the object to the first exit and thereby to the first light splitter which acts as an interferometer, via the first optical fibre and the second light splitter, the first signal beam being coherent with respect to the illuminating light beam;
• wherein the numerical aperture NA, of the first signal beam originating from the central portion of the first spot, the wavelength of the first signal light beam, .lambda., and average diameter, d, of the light guiding core of the first optical fibre at the first exit are related by the equation:
• NA<or.apprxeq.0.6.times..lambda./d
• said light focusser being operatively associated with the second exit for focussing coherently at least a portion of illuminating light emerging from the second exit into a second diffraction limited spot intersecting the object;
• wherein the focusser is operatively associated with the second exit for coherently directing at least a portion of a second signal light beam resulting from interaction between the second spot and the object to the second exit anti thereby to the first light splitter which acts as an interferometer, via the second optical fibre, the second signal beam being coherent with respect to the illuminating light beam:
• wherein the numerical aperture NA, of the second signal beam originating from the central portion of the second spot, the wavelength of the second signal light beam, .lambda., and average diameter, d of the light guiding core of the second optical fibre at the second exit are related by the equation:
• NA<or.apprxeq.0.6.times..lambda./d
• whereby the first and second signal beams interfere thereby producing an output signal;
• a first detector operatively associated with the first splitter to detect the output signal:
• a scanner operatively associated with the first and second exits whereby the first and second exits are movable relative to the focusser, which is stationary with respect to the object, but are not movable with respect to each other;
• a second detector operatively associated with the second splitter to detect signal light from the first optical fibre;
• and
• a calculator operatively associated with the light path length changer, the first detector and the first light splitter to maintain the interference between the first and second signal beams in quadrature, to calculate light path length difference between a first light path from the light source, through the first optical fibre to the intersection of the first spot with the object via the first exit and the focusser and from the intersection back to the first light splitter via the focusser, the first exit and the first optical fibre a the second light path from the light source, through the second optical fibre back to the first light splitter via the second exit, the focusser and from the intersection back to the first light splitter via the focusser, the second exit and the second optical fibre, and determine via the second detector when the first spot is substantially focussed on the surface of the object.