Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
  • G01B9/02056—Passive reduction of errors
  • G01B9/02057—Passive reduction of errors by using common path configuration, i.e. reference and object path almost entirely overlapping
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
  • G01B9/02056—Passive reduction of errors
  • G01B9/02058—Passive reduction of errors by particular optical compensation or alignment elements, e.g. dispersion compensation
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/0209—Low-coherence interferometers
  • G01B9/02091—Tomographic interferometers, e.g. based on optical coherence
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B21/00—Microscopes
  • G02B21/06—Means for illuminating specimens
  • G02B21/08—Condensers
  • G02B21/14—Condensers affording illumination for phase-contrast observation
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B21/00—Microscopes
  • G02B21/33—Immersion oils, or microscope systems or objectives for use with immersion fluids

Definitions

• the present invention relates to the field of interferometry.
• the present invention relates more particularly to an interferometry imaging device, specially adapted for performing tomographic imaging.
• interferometric tomographic imaging devices comprising an interferometric device, for example of the Mirau, Michelson, or Linnik type, in which the light source has a small coherence length making it possible to locate the interference fringes in a thin slice of space of the order of coherence length.
• interferometric device for example of the Mirau, Michelson, or Linnik type
• the light source has a small coherence length making it possible to locate the interference fringes in a thin slice of space of the order of coherence length.
• an offset between the focus plane of the objective and the plane corresponds to a zero path difference in the interferometer.
• an immersion objective is disclosed, for example, in application US-A-2005/008663. This document discloses a method of analyzing a signal provided by an interferometric microscope in white light for the study of structures under the surface of an object.
• the objective of the microscope may be an immersion microscope.
• the document does not disclose how to prevent, at the object to be imaged, a shift between the objective focusing plane and the plane corresponds to a zero path difference in the interferometer.
• the effects of chromatic dispersion differences between the two arms of the interferometer are taken into account in the analysis of the signals provided by the interferometric microscope, which means that these effects are not compensated.
• EP-A-0503236 discloses an apparatus for performing high-resolution near-infrared imaging of the internal semiconductor wafer structure.
• This apparatus comprises an optical device positioned near the plate.
• This optical device may comprise a plano-convex lens.
• the plano-convex lens can be separated from the plate by an optical coupling fluid to allow the plate to be moved under the lens.
• One of the embodiments of EP-A-0503236 teaches that the plano-convex lens can be used within a Linnik interferometer.
• the fluid disclosed by the application EP-A-0503236 does not compensate for differences between the two arms of the interferometer, and in particular the dispersion, and / or the difference in operation.
• One of the aims of the present invention is therefore to reduce the dispersion between the two arms of the interferometer in the case of tomographic imaging and to coincide at best, at the level of the object to be imaged, the plan of implementation. point and the plane corresponding to a difference of zero market.
• Another object of the present invention is also to allow better penetration of light into the object to be imaged.
• the present invention intends to achieve these goals by proposing a device for the tomographic imaging of an object to be imaged, comprising a light source of coherence length substantially equal to the thickness of an object slice to be imaged, and a interferometric imaging system comprising at least one objective, a reference mirror (1) and a light beam splitting means (2), characterized in that said interferometric system is arranged so that said objective defines a first plane at the level of the slice of the object to be analyzed, and a second focusing plane at said reference mirror, and in that said interferometric imaging system comprises at least a first compensating medium (3a , 3b) positioned between said second focusing plane and said separating means, the thickness and the optical index of said compensating medium being chosen so that the optical path of the light beam from said light source between said first plane of illumination point and said separation means is substantially equal to the optical path of the light beam between said second focusing plane and said separation means, and so that the dispersion between said first focus plane and said separation means is substantially equal to the disper
• said interferometric imaging system further comprises at least a third optical index and thickness medium chosen so that the optical path of the light beam coming from said light source between said first focusing plane and said separating means is substantially equal to the optical path of the light beam between said second focusing plane and said separating means, and so that the dispersion between said first focusing plane and said separating means is substantially equal to the dispersion of the light beam between said second focusing plane and said separating means.
• the interferometric imaging system further comprises at least a second medium positioned between said first plan of placing at the point and said separation means, said second medium having optical properties substantially equal to the optical properties of said object to be analyzed.
• said first medium has optical properties substantially equal to the optical properties of said object to be analyzed.
• the device is particularly suitable when the object to be imaged is essentially composed of water.
• the invention also relates to an interferometer for the tomographic imaging of a slice of an object, characterized in that it comprises a fixing means on an objective, a reference mirror, a light beam separation means, said interferometer being arranged such that said objective defines a first focusing plane at the level of the slice of the object to be analyzed, and a second focusing plane on the surface of said reference mirror, and in that said interferometer comprises at least a first compensating medium (3a, 3b) positioned between said second focusing plane and said separating means, the thickness and the optical index of said at least one compensating medium being chosen so that the optical path a light beam between said first focusing plane and said separating means is substantially equal to the optical path of the light beam between said second focusing plane and said means of separation, and such that the dispersion between said first focusing plane and said separating means is substantially equal to the dispersion of the light beam between said second focusing plane and said separating means.
• a first compensating medium 3a, 3b
• the fixing means allows adjustment of the interferometer on the lens, for example on a standard immersion lens.
• said interferometric imaging system further comprises at least one at least one third optical index and thickness medium selected so that the optical path of the light beam from said light source between said first shot plane at the point and said separating means is substantially equal to the optical path of the light beam between said second focusing plane and said separating means, and so that the dispersion between said first focusing plane and said separating means is substantially equal to the dispersion of the light beam between said second focusing plane and said separating means.
• FIGS. 1A, 1B and 1C illustrate devices interferometry according to the prior art
• FIG. 2 illustrates a known immersion objective according to the prior art
• Figure 3 illustrates an embodiment of the invention
• FIG. 4 illustrates an embodiment of the invention in which an interferometric device is positioned on an immersion objective
• FIG. 5 represents a schematic view of the compensating media according to the invention at the level of the reference arm and the object arm of the interferometer
• FIGS. 6A and 6B show a schematic view of the compensating media according to the invention at the reference arm and the object arm of FIG.
• the invention comprises an interferometric microscope.
• a source 5 produces a light signal carried by a beam 6.
• the light source 5 has a broad spectrum and therefore a short coherence length in order to observe interference for a difference in walk of the order of this length of coherence. This makes it possible to observe thin slices of the object 4 and thus to obtain a good axial resolution.
• the coherence length of the source is typically of the order of a micrometer or a few micrometers, and the source is for example a filament lamp, a Xenon type arc or Mercury, or a light emitting diode.
• the reference mirror 1 of the interferometric system according to the invention preferably has a reflection coefficient comparable to the overall reflectivity of the object to be observed in order to minimize the difference in amplitude of the signal coming from the mirror and the signal coming from the object.
• the signal-to-noise ratio of the interference observed is optimized in this way.
• a reflection coefficient mirror of the order of a percent or a few percent for the observation of living cells essentially composed of water, one chooses a reflection coefficient mirror of the order of a percent or a few percent.
• the reference arm consisting of the area between the reference mirror 1 and the plane of the separator 2, and the object arm constituted by the zone between the separator 2 and the focus plane in object 4, as shown in Figure 5.
• Z obj the position of the focus plane of the objective in the object arm. This plan is located in the object to be observed.
• Z ref is the position of the focus plane of the lens in the reference arm. This plane is located on the surface of the reference mirror.
• the compensating medium (s) is (are) then arranged (s) so that the optical paths in the two arms are identical, and that the two arms have substantially the same dispersion.
• the optical path of Z ref to Z sep must therefore be substantially equal to the optical path from Z sep to Z obj .
• the optical indices and the thicknesses of the media 3a, 3b, 3c, 3d are chosen so as to compensate for the dispersion and the optical path difference introduced by the passage of the light beam in the object at the object arm. in part 4a.
• These media are then chosen so as to respect equations 1, 2 and 3. At least one of these compensating media is positioned in the reference arm so as to compensate for the passage through the object 4a.
• At least one compensating medium that can vary in thickness when the lens moves and that the focus position is modified in order to maintain the equality of the dispersions and optical paths in both arms.
• the medium is not necessarily placed in contact with the object to be analyzed and the media selected may have different optical characteristics from those of the object to be analyzed.
• a first medium 3c is positioned in the object arm and in contact with the object, the optical characteristics of which are substantially identical to those of FIG. those of the object to be analyzed.
• the object is a biological object, water or another liquid whose optical properties are close to water, such as PBS (Phosphate Buffer Saline), will preferably be chosen.
• PBS Phosphate Buffer Saline
• M this medium corresponding to the object and the middle 3c positioned in the object arm.
• the medium 3a in the reference arm may for example simply be the same as the medium M, or any other compensating medium of fixed thickness to respect the equality of dispersions and optical paths between the object arm and the arm reference.
• Other compensating media can also be added to both arms of the interferometer.
• the two arms are thus immersed in water or a liquid with optical characteristics close to those of water, as in FIG. 4.
• the compensating medium may also be a gel or any other material satisfying the conditions of equations 1, 2 and 3.
• PBS Phosphate Buffer Saline
• equations 1, 2 and 3 can be solved by a suitable program, possibly adding other constraints such as the reduction of optical aberrations.
• the person skilled in the art is able to easily determine the indices and thicknesses of the materials to be used, as well as the position of the reference mirror in order to satisfy these conditions.
• the number of distinct media can also be variable and chosen by those skilled in the art.
• These compensating media may be liquids, gels, or special glasses.
• the interference images are recorded by a matrix detector (not shown), for example of the CCD or CMOS camera type, and several phase-shifted interference images are recorded by the displacement of an element of the interferometer, for example the mirror. reference 1, or the entire interferometer.
• the interferometer according to the invention is fixed, and for example screwed, on a microscope objective according to a variable height.
• This embodiment is particularly advantageous since standard immersion objectives exist in common. Such objectives are, for example, illustrated in FIG. 2.
• the purpose of the immersion medium used for these objectives is to avoid reflections on the surface of the object, as well as to increase the resolution of the objective.
• an interferometer comprising a reference mirror, a separator and one or more compensating media so as to verify the conditions of equations (1), (2) and
• a compensating medium is then positioned in the reference arm of the interferometer.
• the compensating media of the interferometer are preferably water or a medium with optical characteristics close to those of water.
• the invention is particularly suitable for optical coherence tomography ("Optical Coherence Tomography” or "OCT" in English).

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Optics & Photonics (AREA)
• Analytical Chemistry (AREA)
• Dispersion Chemistry (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• Radiology & Medical Imaging (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)
• Instruments For Measurement Of Length By Optical Means (AREA)
• Microscoopes, Condenser (AREA)
• Length Measuring Devices By Optical Means (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 2005
  • 2005-08-08 FR FR0508428A patent/FR2889584B1/fr not_active Expired - Fee Related
• 2006
  • 2006-08-04 WO PCT/FR2006/001909 patent/WO2007017589A1/fr active Application Filing
  • 2006-08-04 CA CA002617983A patent/CA2617983A1/fr not_active Abandoned
  • 2006-08-04 JP JP2008525598A patent/JP2009505051A/ja active Pending
  • 2006-08-04 US US11/997,929 patent/US20080246972A1/en not_active Abandoned
  • 2006-08-04 EP EP06794295A patent/EP1913331A1/fr not_active Withdrawn
  • 2006-08-04 CN CN200680029559.0A patent/CN101243298A/zh active Pending

Non-Patent Citations (1)

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