PatentDe  


Dokumentenidentifikation EP0676629 28.03.2002
EP-Veröffentlichungsnummer 0676629
Titel Brechungsindexmessung von Brillenglas
Anmelder Carl Zeiss, 89518 Heidenheim, DE;
Carl-Zeiss-Stiftung Trading as Carl Zeiss, 89518 Heidenheim, DE
Erfinder Hellmuth, Dr., Thomas, D-73431 Aalen, DE;
Campbell, Charles E., Berkeley, US
DE-Aktenzeichen 69525481
Vertragsstaaten DE, ES, FR, GB, IT
Sprache des Dokument EN
EP-Anmeldetag 28.03.1995
EP-Aktenzeichen 951045277
EP-Offenlegungsdatum 11.10.1995
EP date of grant 20.02.2002
Veröffentlichungstag im Patentblatt 28.03.2002
IPC-Hauptklasse G01M 11/02

Beschreibung[en]
Technical Field of the Invention

The present invention pertains to method and apparatus for measuring a refractive index of spectacle lenses.

Background of the Invention

There are various methods in the prior art which are used to measure the index of refraction of glass. One method entails utilizing an Abbe refractometer to measure the critical angle of total reflection. In accordance with this method, the index of refraction is derived from the measured value of the critical angle. This method is illustrated in a book entitled "Optics" by Eugene Hecht and Alfred Zajac, published by Addison-Wesley Publishing Company, Inc. February, 1979 (Copyright 1974), pp. 81-84.

Another method utilized to measure the index of refraction of glass entails measuring the reflectivity of glass, which reflectivity depends on the index of refraction. The relation between index of refraction and reflectivity is described, for example, by the Fresnel formula shown on p. 75 of the above -identified reference.

Yet another method utilized to measure the index of refraction of glass entails measuring the deflection angle of a light beam passing through a sample block of glass. This method is illustrated on pp. 62-63 of the above identified reference.

All of the above methods suffer from drawbacks. For example, all of the above methods require the surface geometry of the glass whose index of refraction is to be measured to be known. For example, the radii of curvature of the surfaces must be measured to an accuracy of about 0.1% to obtain a measurement of index of refraction of comparable accuracy. In addition, the first two methods are measurements of reflection. This is a drawback when measuring the index of refraction of spectacles since spectacles are often antireflection coated.

In EP-0 277 496-A2 a Laserinterferometer-Refractometer for measuring the refractive index of gases is known. The devices comprises a two beam interferometer with a fixed reflector in the reference beam path and a chamber which can be evacuated and which is passed by the measuring beam twice by reflecting the measuring beam back after the first passage of through the chamber. For determining the refractive index of the gas the length of the chamber can be varied. This device in unsuited for measuring the refractive index of glasses.

In light of the above, there is a need for a method and apparatus for measuring the index of refraction of glass such as the glass of spectacle lenses without measuring the surface geometry of the glass.

This object is solved by apparatus according to the features of claims 1 and 12 and by methods having the features of claims 11 and 16.

Embodiments of the present invention advantageously satisfy the above-identified need in the art and provide a method and apparatus for measuring the index of refraction of glass such as the glass of spectacle lenses without measuring the surface geometry of the glass.

A first embodiment of the invention refers to an apparatus for measuring the index of refraction of a sample material which comprises:

  • a source of a substantially spatially coherent beam of radiation,
  • a beamsplitter for providing a sample beam and a reference beam;
  • reflecting means for reflecting the sample beam back through the sample material
  • a translatable reflector,
  • a detector, disposed to detect the reflected reference beam and the reflected sample beam for producing a detector output signal in response thereto, and
  • an analysis means in response to the detector output signal, for determining the index of refraction of the sample material,
characterised in, that
  • the translatable reflector reflects the reference beam,
  • a sample thickness measuring means determines the thickness of the sample material where the sample beam passes through,
  • the analysis means, in response to the detector output signal, determines a position of the translatable reflector and, in response to the position of the translatable reflector and the thickness of the sample material, determines the index of refraction of the sample material.

In a specific instance of the first embodiment of the present invention, the source is a light emitting diode whose output is collimated and focused through a pinhole; the means for providing a sample and a reference beam is a beamsplitter; the translatable reflecting means is a retroreflector mounted on a stepper motor; the holder for the material is a caliper which holds the material at a predetermined distance from the beamsplitter and a retrorefelctor; and the detector means comprises a detector whose output is bandpass filtered, root means square filtered, and applied to a trigger.

A second embodiment of the invention refers to an apparatus for measuring the index of refraction of a sample material which comprises:

  • a source of a substantially specially coherence beam of radiation,
  • beamsplitter means for providing a sample beam and a first reference beam and a second reference beam,
  • a reflecting means for reflecting the sample beam back through the sample material,
  • a translatable reflector,
  • means for reflecting the second reference beam, wherein the means for reflecting the second reference beam are in a position which is fixed with respect to the reflecting means for reflecting the sample beam,
  • a detector, disposed to detect the reflected reference beams and the reflected sample beam, for producing a detector output signal in response thereto, and
  • an analysis means in response to the detector output signal, for determining the index of refraction of the sample material,
characterised in, that
  • the translatable reflector is disposed to reflect the first reference beam,
  • and that the analysis means, in response to the detector output signal, determines a first and a second position of the translatable reflector and, in response to the first and a second positions, determines the index of refraction of the sample material.

In a specific instance of the second embodiment of the present invention, the source is a light emitting diode whose output is collimated and focused through a pinhole; the means for providing a sample and a first and second reference beam is a first and a second beamsplitter; the translatable reflecting means is a retroreflector mounted on a stepper motor; the holder for the material is a caliper which holds the material and a first and a second retroreflector, and the detector means comprises a detector whose output is bandpass filtered, root means square filtered, and applied to a trigger.

A complete understanding of the present invention may be gained by considering the following detailed description together with the accompanying drawings, in which:

  • Fig. 1 shows, in pictorial form, a preferred embodiment of the present invention which is apparatus for measuring the index of refraction of glass such as the glass of spectacle lenses without measuring the curvature of the surface of the glass;
  • Fig.2 shows, in graphical form, a signal produced by a detector in accordance with the present invention;
  • FIG. 3 shows, in pictorial form, an alternate embodiment of the present invention; and
  • FIG. 4, shows, in graphical form, a signal produced by a detector in accordance with the alternative embodiment of the present invention.

Corresponding elements in each of the drawings have the same reference numbers.

Detailed Description

FIG. 1 shows, in pictorial form, embodiment 200 of the present invention which is apparatus for measuring the index of refraction of glass such as the glass of spectacle lens 8 without measuring the curvature of the surface of the glass.

In the embodiment of the present invention shown in FIG. 1, a beam of light 205 output by light source 1 is collimated as beam 210 by collimator lens 2. In accordance with the present invention, output 205 from light source 1 has a short coherence length, which coherence length is preferably on the order of a few microns. A suitable light source may be, for example, a light emitting diode ("LED").

Collimated output 210 from lens 2 is focused by lens 21 having focal length f as beam 220 onto small pinhole 22 having a diameter substantially given by the following formula: d = 1.22λf/a where λ is the wavelength of the output from LED 1 and a is the radius of collimated beam 210 formed by lens 2. The result is that beam 230 output from pinhole 22 is spatially coherent. In other embodiments, beam 230 may be provided as the output from a superluminescent light source such as a superluminescent diode. Although a superluminescent diode is a diffraction limited source, it requires more critical alignment than does the extended LED source arrangement shown in FIG. 1.

Beam 230 is again collimated, this time by collimator lens 23, into beam 240. Beam 240 impinges upon beamsplitter 3 to form sample beam 4 and reference beam 5.

As shown in FIG. 1, reference beam 5 is directed to impinge upon reference mirror 6 which is mounted on movable stage 7. Reference mirror 6 can be, for example, a retroreflector such as a retroreflecting prism.

As further shown in FIG. 1, sample beam 4 is directed to impinge upon spectacle lens 8 at its vertex point. Sample beam 4 passes through spectacle lens 8 and impinges upon retroreflecting prism 9 which is mounted on a movable arm of caliper 27. Retroreflected sample beam 4 and retroreflected reference beam 5 are superimposed in detector path 91 and the combined signal is detected by light detector 92.

In accordance with the present invention, reference mirror 6 is moved back and forth by movable stage 7 at a constant linear speed v. In accordance with the present invention, as soon as the optical length of reference beam 5 is equal to the optical length L of sample beam 4, the signal at detector 92 is modulated with a frequency f which is given by the following: f = 2v/λ where λ is the wavelength of source 1.

FIG. 2 shows, in graphical form, detector signal 300 produced by detector 92. In FIG. 2, vertical axis 400 represents the amplitude of detector signal 300 and horizontal axis 410 represents the displacement of reference mirror 7. As shown in FIG. 2, the signal length is about equal to the coherence length of light source 1 and, in an embodiment where light source 1 is an LED, the signal length is on the order of microns.

The optical length L of sample beam 4 is given by: L = 2 (d1 + nd + d2) where d1 is the distance from the upper surface of spectacle lens 8 to beamsplitter 3, n is the index of refraction of the glass material of spectacle 8, d is the thickness of spectacle lens 8, and d2 is the distance from the lower surface of spectacle lens 8 to retroreflector 9. In accordance with the present invention, n, the index of refraction of spectacle lens 8, is determined by solving eqn. 3 for n; this is done in accordance with the embodiment as described below.

Part of the setup steps in carrying out the inventive method entails measuring thickness d of spectacle lens 8. Caliper 27 having pins 10 and 11 is utilized for this purpose. As shown in FIG. 1, retroreflector 9 is fixed to movable pin 11 of caliper 27 and pin 10 of caliper 27 is fixed to interferometer platform 101. The use of a fixed distance between pin 11 and retroreflector 9 and a fixed distance between pin 10 and interferometer platform 101 provides d1 and d2 of eqn. 3 as known, predetermined values. Then, in accordance with the present invention, the thickness d of spectacle lens 8 is measured by displacement sensor 12. Displacement sensor 12 measures the displacement of pin 11 of caliper 27 which holds retroreflector 9.

Electrical readout signal 310 from displacement sensor 12 is transmitted to control unit 13 which outputs signal 320 to drive stepper motor 7. In accordance with the present invention, signal 300 from detector 92 is bandpass filtered by bandpass filter 14. Output signal 330 from bandpass filter 14 is an oscillating signal pulse with a frequency given by eqn. (2) and a pulse length which corresponds to the coherence length of light source 1. Output 330 from bandpass filter 14 is further filtered by root mean square filter 15 to obtain the envelope of the signal pulse produced by detector 92, i.e., signal 340.

Next, output signal 340 from root mean filter 15 is applied as input to trigger unit 16, for example, a Schmitt trigger, to derive timing signal 350 from signal pulse 340. Timing pulse 350 is applied as input to control unit 13.

In accordance with the present invention, in response to timing signal 350 from trigger 16, control unit 13 stores the position of stepper motor 7 at the moment of trigger pulse 350. The position of stepper motor 7 corresponds to the reference arm length which is equal to the optical path length of sample beam 4. This optical length is equal to L of eqn. 2 above.

At this point, control unit 13 has the values needed to solve eqn. 3 for the index of refraction n: (a) d1 and d2 (as discussed above, d1 and d2 are obtained as predetermined values); (b) d (as discussed above, d is obtained from signal 310 output by displacement sensor 12); and (c) L (as discussed above, L is obtained from the position of stepper motor 7). Control unit 13 solves eqn. 3 for n, the index of refraction of the material of spectacle lens 8, and displays the value, for example, on display 17. Many methods and apparatus should be well known to those of ordinary skill in the art for providing control unit 13. For example, control unit 13 may be fabricated utilizing readily available microprocessor apparatus.

FIG. 3 shows, in pictorial form, alternate embodiment 500 of the present invention which is apparatus for measuring the index of refraction of glass such as the glass of spectacle lens 8 without measuring the curvature of the surface of the glass.

The following will concentrate on the matters which are different from embodiment 200 shown in FIG. 1 and described above. As shown in FIG. 3, beam 240 is a spatially coherent, collimated beam which is divided by beamsplitter 3 into sample beam 4 and reference beam 5. As further shown in FIG. 3, reference beam 5 is further split by beamsplitter 24 into a first reference beam 25 and a second reference beam 26. First reference beam 25 is reflected by reference retroreflector 6 which is mounted on stepper motor driven, movable stage 7.

Second reference beam 26 is reflected by retroreflector 127 which is mounted on platform 28. As shown in FIG. 3, retroreflector 9 and caliper pin 11 are also mounted on platform 28. Backreflected, second reference beam 26 is reflected by beamsplitter 24 and beamsplitter 3 and, finally, is superposed with backreflected, first reference beam 25 and backreflected, sample beam 4 in detector beam path 91.

The inventive measurement process takes place as follows. Spectacle lens 8 is brought between caliper pins 10 and 11 so that they are in close contact with spectacle lens 8. The geometrical path between beamsplitter 3, beamsplitter 24 and retroreflector 127 is chosen to be the same as the geometrical path between beamsplitter 3 and retroreflector 9. As described above, retroreflector 6 is moved back and forth by movable stage 7 at a constant liner speed v and detector 92 produces detector signal 600 shown in FIG. 4.

In FIG. 4, vertical axis 610 represents the amplitude of detector signal 600 and horizontal axis 620 represents the displacement of reference mirror 7. The position of signal peak 1001 in FIG. 4 marks the position of retroreflector 127 relative to a zero point of caliper 27, i.e., the zero point of caliper 27 corresponds to a point where caliper pins 10 and 11 in FIG. 3 are in contact (no spectacle 8). As a result, the position of peak 1001 in FIG. 4 measures the thickness d of spectacle lens 8. The position of signal peak 2001 in FIG. 4 depends on the optical thickness nd of spectacle lens 8. Peaks 1001 and 2001 are determined by control 13 from signal 350 output from trigger 16 as described above in connection with FIG. 1. Then, control 13 uses peaks 1001 and 2001 to obtain the position of retroreflector 6 and, thereby, d and nd. Using these two numbers, d and nd, control 13 solves for n and displays the result on display 17. Alternative embodiment 500 shown in FIG. 3 is advantageous in that there is no need for displacement sensor 12 shown in FIG. 1 and there is no need to know d1 (the distance from the upper surface of spectacle lens 8 to beamsplitter 3) or d2 (the distance from the lower surface of spectacle lens 8 to retroreflector 9).

In alternative embodiment 500 of FIG. 3, signal 300 from detector 92 is bandpass filtered by bandpass filter 14. Output signal 330 from bandpass filter 14 is two oscillating signal pulses, each with a frequency given by eqn. (2) and a pulse length which corresponds to the coherence length of light source 1. Output 330 from bandpass filter 14 is further filtered by root mean square filter 15 to obtain the envelope of the signal pulse produced by detector 92, i.e., signal 340.

Next, output signal 340 from root mean filter 15 is applied as input to trigger unit 16, for example, a Schmitt trigger, to derive timing signal 350 from signal pulse 340. Timing pulse 350 is applied as input to control unit 13.

In accordance with the present invention, in response to timing signal 350 from trigger 16, control unit 13 stores the position of stepper motor 7 at the moment of each of the pulses in timing pulse 350. As set forth above, the position of stepper motor 7 corresponding to peak 1001 produces d and the position of stepper motor 7 corresponding to peak 2001 produces nd.


Anspruch[de]
  1. Vorrichtung (200) zum Messen des Brechungsindexes eines Probematerials (8), die folgendes umfaßt:
    • eine Quelle (1, 2, 21, 22) für einen im wesentlichen räumlich kohärenten Strahlungsstrahl (240),
    • einen Strahlteiler (3) zum Bereitstellen eines Meßstrahls (4) und eines Vergleichsstrahls (5);
    • ein Reflexionsmittel (9), um den Meßstrahl (4) durch das Probematerial (8) zurückzureflektieren;
    • einen verschiebbaren Reflektor (6),
    • einen Detektor (92), der so angeordnet ist, daß er den reflektierten Vergleichsstrahl (5) und den reflektierten Meßstrahl (4) erfaßt, um als Reaktion darauf ein Detektorausgangssignal (300) zu erzeugen, und
    • ein Analysemittel (14, 15, 16, 13), um als Reaktion auf das Detektorausgangssignal (300) den Brechungsindex des Probematerials (8) zu bestimmen,
    dadurch gekennzeichnet, daß
    • der verschiebbare Reflektor (6) den Vergleichsstrahl (5) reflektiert,
    • ein Probedickenmeßmittel (10, 11, 12) die Dicke des Probematerials (8) dort bestimmt, wo der Meßstrahl (4) hindurchtritt,
    • das Analysemittel (14, 15, 16, 13) als Reaktion auf das Detektorausgangssignal (300) eine Position des verschiebbaren Reflektors (6) bestimmt und als Reaktion auf die Position des verschiebbaren Reflektors (6) und die Dicke des Probematerials (8) den Brechungsindex des Probematerials (8) bestimmt.
  2. Vorrichtung nach Anspruch 1, wobei die Quelle (1, 2, 21, 22) eine Kohärenzlänge in der Größenordnung einiger weniger Mikrometer aufweist.
  3. Vorrichtung nach Anspruch 2, wobei die Quelle (1) eine Leuchtdiode umfaßt.
  4. Vorrichtung nach Anspruch 2, wobei die Quelle (1, 2, 21, 22) eine Superlumineszenzdiode umfaßt.
  5. Vorrichtung nach Anspruch 3 oder 4, wobei die Quelle weiterhin ein Mittel (2) zum Kollimieren der Ausgabe der Leuchtdiode (1) und ein Mittel (21) zum Fokussieren der kollimierten Ausgabe durch eine Lochblende (22) umfaßt.
  6. Vorrichtung nach einem der Ansprüche 1 bis 5, wobei der verschiebbare Reflektor (6) ein an einem Schrittmotor (7) montierter Rückstrahler (6) ist.
  7. Vorrichtung nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß zum Halten des Probematerials (8) ein Dickenmesser (27) vorgesehen ist, der eine erste Fläche des Probematerials (8) in einer vorbestimmten Entfernung (d1) von dem Strahlteiler (3) und eine zweite Fläche des Probematerials (8) in einer vorbestimmten Entfernung (d2) von dem den Meßstrahl (4) reflektierenden Reflexionsmittel (9) hält.
  8. Vorrichtung nach Anspruch 7, wobei das den Meßstrahl (4) reflektierende Reflexionsmittel (9) ein Rückstrahler ist und wobei die Probedickenmeßeinrichtung (10, 11, 12) ein Mittel (12) zum Bestimmen von Verschiebungen des Dickenmessers (27) umfaßt.
  9. Vorrichtung nach einem der Ansprüche 1 bis 8, dadurch gekennzeichnet, daß die Ausgabe des Detektors (92) an ein Bandpaßfilter (14), ein RMS-Filter (15) (root mean square = quadratischer Mittelwert) und an einen Auslöser (16) angelegt wird.
  10. Vorrichtung nach Anspruch 6, wobei der Rückstrahler (6) mit einer im wesentlichen konstanten Geschwindigkeit bewegt wird.
  11. Verfahren zum Messen des Brechungsindexes eines Probematerials (8), mit den folgenden Schritten:
    • Bilden eines im wesentlichen räumlich kohärenten Strahlungsstrahls (240),
    • Teilen des Strahls (240) in einen Meßstrahl (4) und einen Vergleichsstrahl (5),
    • Halten des Probematerials (8) in dem Weg des Meßstrahls und Reflektieren des Meßstrahls (4) zurück durch das Probematerial (8);
    • Reflektieren des Vergleichsstrahls (5),
    • Erfassen des reflektierten Vergleichsstrahls (5) und des reflektierten Meßstrahls (4) und Erzeugen eines Detektorausgangssignals (300),
    gekennzeichnet durch
    • Reflektieren des Vergleichsstrahls (5) von einem verschiebbaren Reflektor (6);
    • Bestimmen der Dicke des Materials (8) dort, wo der Meßstrahl (4) hindurchtritt,
    • Bestimmen einer Position des verschiebbaren Reflektors (6) als Reaktion auf das Detektorausgangssignal (300) und
    • Bestimmen des Brechungsindexes des Probematerials (8) als Reaktion auf die Position des verschiebbaren Reflektors (6) und die Dicke des Probematerials (8).
  12. Vorrichtung (500) zum Messen des Brechungsindexes eines Probematerials (8), die folgendes umfaßt:
    • eine Quelle (1, 2, 21, 22) für einen im wesentlichen räumlich kohärenten Strahlungsstrahl (240),
    • ein Strahlteilermittel (3, 24) zum Bereitstellen eines Meßstrahls (4) und eines ersten Vergleichsstrahls (25) und eines zweiten Vergleichsstrahls (26),
    • ein Reflexionsmittel (9), um den Meßstrahl (4) durch das Probematerial (8) zurückzureflektieren;
    • einen verschiebbaren Reflektor (6),
    • Mittel (127) zum Reflektieren des zweiten Vergleichsstrahls (26), wobei sich die Mittel (127) zum Reflektieren des zweiten Vergleichsstrahls (26) in einer Position befinden, die bezüglich der Position des Reflexionsmittels (9) zum Reflektieren des Meßstrahls (4) fixiert ist,
    • einen Detektor (92), der so angeordnet ist, daß er die reflektierten Vergleichsstrahlen (25, 26)
    • und den reflektierten Meßstrahl (4) erfaßt, um als Reaktion darauf ein Detektorausgangssignal (300) zu erzeugen, und
    • ein Analysemittel (14, 15, 16, 13), um als Reaktion auf das Detektorausgangssignal (300) den Brechungsindex des Probematerials (8) zu bestimmen,
    dadurch gekennzeichnet, daß
    • der verschiebbare Reflektor (6) so angeordnet ist, daß er den ersten Vergleichsstrahl (25) reflektiert,
    • und das Analysemittel (14, 15, 16, 13) als Reaktion auf das Detektorausgangssignal (300) eine erste und eine zweite Position des verschiebbaren Reflektors (6) bestimmt und als Reaktion auf die erste und eine zweite Position den Brechungsindex des Probematerials (8) bestimmt.
  13. Vorrichtung nach Anspruch 12, wobei die Quelle (1, 2, 21, 22) eine Kohärenzlänge in der Größenordnung einiger weniger Mikrometer aufweist.
  14. Vorrichtung nach Anspruch 13, wobei die Quelle (1, 2, 21, 22) eine Superlumineszenzdiode umfaßt.
  15. Vorrichtung nach einem der Ansprüche 12 bis 14, wobei der Rückstrahler (6) mit einer im wesentlichen konstanten Geschwindigkeit bewegt wird.
  16. Verfahren zum Messen des Brechungsindexes eines Probematerials (8), mit den folgenden Schritten:
    • Bilden eines im wesentlichen räumlich kohärenten Strahlungsstrahls (240),
    • Teilen des Strahls (240) in einen Meßstrahl (4) und einen ersten Vergleichsstrahl (25) und einen zweiten Vergleichsstrahl (26),
    • Halten des Probematerials (8) in dem Weg des Meßstrahls und Reflektieren des Meßstrahls (4) zurück durch das Probematerial (8);
    • Reflektieren des ersten und zweiten Vergleichsstrahls (25, 26), wobei die Position, in der der zweite Vergleichsstrahl (26) reflektiert wird, bezüglich der Position, in der der Meßstrahl (4) reflektiert wird, fixiert ist,
    • Erfassen des ersten und zweiten reflektierten Vergleichsstrahls (25, 26) und des reflektierten Meßstrahls (4) und Erzeugen eines Detektorausgangssignals (300),
    gekennzeichnet durch
    • Reflektieren des ersten Vergleichsstrahls (25) von einem verschiebbaren Reflektor (6);
    • Bestimmen der Dicke des Materials (8) dort, wo der Meßstrahl (4) hindurchtritt,
    • Bestimmen einer ersten und einer zweiten Position des verschiebbaren Reflektors (6) als Reaktion auf das Detektorausgangssignal (300) und
    • Bestimmen des Brechungsindexes des Probematerials (8) als Reaktion auf die erste und die zweite Position des verschiebbaren Reflektors (6).
Anspruch[en]
  1. Apparatus (200) for measuring the index of refraction of a sample material (8) which comprises:
    • a source (1, 2, 21, 22) of a substantially spatially coherent beam of radiation (240),
    • a beamsplitter (3) for providing a sample beam (4) and a reference beam (5);
    • reflecting means (9) for reflecting the sample beam (4) back through the sample material (8)
    • a translatable reflector (6),
    • a detector (92), disposed to detect the reflected reference beam (5) and the reflected sample beam (4) for producing a detector output signal (300) in response thereto, and
    • an analysis means (14, 15, 16, 13), in response to the detector output signal (300), for determining the index of refraction of the sample material (8),
    characterised in, that
    • the translatable reflector (6) reflects the reference beam (5),
    • a sample thickness measuring means (10, 11, 12) determines the thickness of the sample material (8) where the sample beam (4) passes through,
    • the analysis means (14, 15, 16, 13), in response to the detector output signal (300), determines a position of the translatable reflector (6) and, in response to the position of the translatable reflector (6) and the thickness of the sample material (8), determines the index of refraction of the sample material (8).
  2. Apparatus of claim 1, wherein the source (1, 2, 21, 22) has a coherence length in the order of a few microns.
  3. Apparatus of claim 2, wherein the source (1) comprises light emitting diode.
  4. Apparatus of claim 2, wherein the source (1,2,21,22) comprises a superluminescent diode.
  5. Apparatus of claim 3 or 4, wherein the source further comprises means (2) for collimating the output of the light emitting diode (1) and means (21) for focusing the collimated output through a pinhole (22).
  6. Apparatus of one of the claims 1 to 5, wherein the translatable reflector (6) is a retroreflector (6) mounted on a stepper motor (7).
  7. Apparatus of one of the claims 1 to 6, characterised in that for holding the sample material (8) a caliper (27) is provided which holds a first surface of the sample material (8) at a predetermined distance (d1) from the beamsplitter (3) and s second surface of the sample material (8) at a predetermined distance (d2) from the reflecting means (9) reflecting the sample beam (4).
  8. Apparatus of claim 7, wherein the reflecting means (9) reflecting the sample beam (4) is a retroreflector and wherein the sample thickness measuring device (10, 11, 12) comprises means (12) for determining displacements of the caliper (27).
  9. Apparatus of one of the claims 1 to 8, characterised in that the output of the detector (92) is applied to a bandpass filter (14), a root means square filter (15) and applied to a trigger (16).
  10. Apparatus of claim 6, wherein the retroreflector (6) is moved at a substantially constant speed.
  11. Method for measuring the index of refraction of a sample material (8) comprising the steps of:
    • forming a substantially spatially coherent beam of radiation (240),
    • splitting the beam (240) into a sample beam (4) and a reference beam (5),
    • holding the sample material (8) in the path of the sample beam (4) and reflecting the sample beam (4) back through the sample material (8),
    • reflecting the reference beam (5),
    • detecting the reflected reference beam (5) and the reflected sample beam (4) and producing a detector output signal (300),
    characterised by
    • reflecting the reference beam (5) from a translatable reflector (6);
    • determining the thickness of the material (8) where the sample beam (4) passes through,
    • determining a position of the translatable reflector (6) in response to the detector output signal (300), and
    • determining the index of refraction of the sample material (8) in response to the position of the translatable reflector (6) and the thickness of the sample material (8).
  12. Apparatus (500) for measuring the index of refraction of a sample material (8) which comprises:
    • a source (1,2,21,22) of a substantially spatially coherence beam of radiation (240),
    • beamsplitter means (3, 24) for providing a sample beam (4) and a first reference beam (25) and a second reference beam (26),
    • a reflecting means (9) for reflecting the sample beam (4) back through the sample material (8),
    • a translatable reflector (6),
    • means (127) for reflecting the second reference beam (26), wherein the means (127) for reflecting the second reference beam (26) are in a position which is fixed with respect to the position of the reflecting means (9) for reflecting the sample beam (4),
    • a detector (92), disposed to detect the reflected reference beams (25, 26) and the reflected sample beam (4), for producing a detector output signal (300) in response thereto, and
    • an analysis means (14, 15, 16, 13), in response to the detector output signal (300), for determining the index of refraction of the sample material (8),
    characterised in, that
    • the translatable reflector (6) is disposed to reflect the first reference beam (25),
    • and that the analysis means (14, 15, 16, 13), in response to the detector output signal (300), determines a first and a second position of the translatable reflector (6) and, in response to the first and a second positions, determines the index of refraction of the sample material (8).
  13. Apparatus of claim 12, wherein the source (1, 2, 21, 22) has a coherence length in the order of a few microns.
  14. Apparatus of claim 13, wherein the source (1, 2, 21, 22) comprises a superluminescent diode.
  15. Apparatus of one of the claims 12 to 14, wherein the retroreflector (6) is moved at a substantially constant speed.
  16. Method for measuring the index of refraction of a sample material (8) comprising the steps of
    • forming a substantially spatially coherent beam of radiation (240),
    • splitting the beam (240) into a sample beam (4) and a first reference beam (25) and a second reference beam (26),
    • holding the sample material (8) in the path of the sample beam (4) and reflecting the sample beam (4) back through the sample material (8),
    • reflecting the first and the second reference beam (25, 26), wherein the position at which the second reference beam (26) is reflected is fixed with respect to the position at which the sample beam (4) is reflected,
    • detecting the first and second reflected reference beams (25, 26) and the reflected sample beam (4) and producing a detector output signal (300),
    characterised by
    • reflecting the first reference beam (25) from a translatable reflector (6);
    • determining the thickness of the material (8) were the sample beam (4) passes through,
    • determining a first and a second position of the translatable reflector (6) in response to the detector output signal (300), and
    • determining the index of refraction of the sample material (8) in response to the first and second positions of the translatable reflector (6).
Anspruch[fr]
  1. Appareil (200) pour mesurer l'indice de réfraction d'un échantillon de matériau (8) comprenant :
    • une source (1, 2, 21, 22) d'un faisceau de radiation (240) relativement cohérent dans l'espace,
    • un fractionneur de faisceau (3) pour fournir un faisceau d'échantillon (4) et un faisceau de référence (5),
    • un moyen de réflexion (9) pour réfléchir le faisceau d'échantillon (4) en arrière à travers l'échantillon de matériau (8),
    • un réflecteur (6) pouvant effectuer un mouvement de translation,
    • un détecteur (92) disposé de manière à détecter le faisceau de référence (5) réfléchi et le faisceau d'échantillon (4) réfléchi pour produire un signal de sortie du détecteur (300) en réaction à ceux-ci, et
    • des moyens d'analyse (14, 15, 16, 13) en réaction au signal de sortie du détecteur (300) pour déterminer l'indice de réfraction de l'échantillon de matériau (8),
    caractérisé en ce que
    • le réflecteur (6) pouvant effectuer un mouvement de translation réfléchit le faisceau de référence (5),
    • des moyens de mesure de l'épaisseur de l'échantillon (10, 11, 12) déterminent l'épaisseur de l'échantillon de matériau (8) à l'endroit où le faisceau d'échantillon (4) le traverse,
    • les moyens d'analyse (14, 15, 16, 13), en réaction au signal de sortie du détecteur (300), déterminent une position du réflecteur (6) pouvant effectuer un mouvement de translation et, en réaction à la position du réflecteur (6) pouvant effectuer un mouvement de translation et à l'épaisseur de l'échantillon de matériau (8), déterminent l'indice de réfraction de l'échantillon de matériau (8).
  2. Appareil selon la revendication 1, dans lequel la source (1, 2, 21, 22) a une longueur de cohérence de l'ordre de quelques microns.
  3. Appareil selon la revendication 2, dans lequel la source (1) comprend une diode électroluminescente.
  4. Appareil selon la revendication 2, dans lequel la source (1, 2, 21, 22) comprend une diode superluminescente.
  5. Appareil selon la revendication 3 ou 4, dans lequel la source comprend en plus des moyens (2) pour collimater la sortie de la diode électroluminescente (2) et des moyens (21) pour concentrer la sortie collimatée à travers un trou de visée (22).
  6. Appareil selon l'une des revendications 1 à 5, dans lequel le réflecteur (6) pouvant effectuer un mouvement de translation est un rétroréflecteur (6) fixé sur un moteur pas à pas (7).
  7. Appareil selon l'une des revendications 1 à 6, caractérisé en ce qu'un palpeur (27) est prévu pour maintenir l'échantillon de matériau (8), lequel maintient une première surface de l'échantillon de matériau (8) à une distance prédéterminée (d1) du fractionneur de faisceau (3) et une deuxième surface de l'échantillon de matériau (8) à une distance prédéterminée (d2) du moyen de réflexion (9) qui reflètent le faisceau d'échantillon (4).
  8. Appareil selon la revendication 7, dans lequel le moyen de réflexion (9) reflétant le faisceau d'échantillon (4) est un rétroréflecteur et dans lequel le dispositif de mesure de l'épaisseur de l'échantillon (10, 11, 12) comprend des moyens (12) pour déterminer les déplacements du palpeur (27).
  9. Appareil selon l'une des revendications 1 à 8, caractérisé en ce que la sortie du détecteur (92) est appliquée à un filtre passe-bande (14), un filtre à moyenne quadratique (15) et appliquée à un déclencheur (16).
  10. Appareil selon la revendication 6, dans lequel le rétroréflecteur (6) est déplacé à une vitesse relativement constante.
  11. Méthode pour mesurer l'indice de réfraction d'un échantillon de matériau (8) comprenant les étapes suivantes :
    • formation d'un faisceau de radiation (240) relativement cohérent dans l'espace,
    • fractionnement du faisceau (240) en un faisceau d'échantillon (4) et un faisceau de référence (5),
    • maintien de l'échantillon de matériau (8) dans le trajet du faisceau d'échantillon (4) et réflexion du faisceau d'échantillon (4) en arrière à travers l'échantillon de matériau (8),
    • réflexion du faisceau de référence (5),
    • détection du faisceau de référence (5) réfléchi et du faisceau d'échantillon (4) réfléchi et production d'un signal de sortie du détecteur (300),
    caractérisée par
    • la réflexion du faisceau de référence (5) par un réflecteur (6) pouvant effectuer un mouvement de translation,
    • la détermination de l'épaisseur de l'échantillon de matériau (8) à l'endroit où le faisceau d'échantillon (4) le traverse,
    • la détermination d'une position du réflecteur (6) pouvant effectuer un mouvement de translation en réaction au signal de sortie du détecteur (300),et
    • la détermination de l'indice de réfraction de l'échantillon de matériau (8) en réaction à la position du réflecteur (6) pouvant effectuer un mouvement de translation et à l'épaisseur de l'échantillon de matériau (8).
  12. Appareil (200) pour mesurer l'indice de réfraction d'un échantillon de matériau (8) comprenant :
    • une source (1, 2, 21, 22) d'un faisceau de radiation (240) relativement cohérent dans l'espace,
    • des moyens de fractionnement du faisceau (3, 24) pour fournir un faisceau d'échantillon (4) et un premier faisceau de référence (25) et un deuxième faisceau de référence (26),
    • un moyen de réflexion (9) pour réfléchir le faisceau d'échantillon (4) en arrière à travers l'échantillon de matériau (8),
    • un réflecteur (6) pouvant effectuer un mouvement de translation,
    • des moyens (127) pour réfléchir le deuxième faisceau de référence (26), dans quel cas les moyens (127) pour réfléchir le deuxième faisceau de référence (26) se trouvent dans une position qui est fixée par rapport à la position des moyens de réflexion (9) pour réfléchir le faisceau d'échantillon (4),
    • un détecteur (92) disposé de manière à détecter les faisceaux de référence (25, 26) réfléchis et le faisceau d'échantillon (4) réfléchi pour produire un signal de sortie du détecteur (300) en réaction à ceux-ci, et
    • des moyens d'analyse (14, 15, 16, 13) en réaction au signal de sortie du détecteur (300) pour déterminer l'indice de réfraction de l'échantillon de matériau (8),
    caractérisé en ce que
    • le réflecteur (6) pouvant effectuer un mouvement de translation réfléchit le premier faisceau de référence (5), et
    • les moyens d'analyse (14, 15, 16, 13), en réaction au signal de sortie du détecteur (300), déterminent une première et une deuxième positions du réflecteur (6) pouvant effectuer un mouvement de translation et, en réaction aux première et deuxième positions, déterminent l'indice de réfraction de l'échantillon de matériau (8).
  13. Appareil selon la revendication 12, dans lequel la source (1, 2, 21, 22) a une longueur de cohérence de l'ordre de quelques microns.
  14. Appareil selon la revendication 13, dans lequel la source (1, 2, 21, 22) comprend une diode superluminescente.
  15. Appareil selon l'une des revendications 12 à 14, dans lequel le rétroréflecteur (6) est déplacé à une vitesse relativement constante.
  16. Méthode pour mesurer l'indice de réfraction d'un échantillon de matériau (8) comprenant les étapes suivantes :
    • formation d'un faisceau de radiation (240) relativement cohérent dans l'espace,
    • fractionnement du faisceau (240) en un faisceau d'échantillon (4) et un premier faisceau de référence (25) et un deuxième faisceau de référence (26),
    • maintien de l'échantillon de matériau (8) dans le trajet du faisceau d'échantillon (4) et réflexion du faisceau d'échantillon (4) en arrière à travers l'échantillon de matériau (8),
    • réflexion des premier et deuxième faisceaux de référence (25, 26), dans quel cas la position à laquelle est réfléchi le deuxième faisceau de référence (26) est fixée par rapport à la position à laquelle est réfléchi le faisceau d'échantillon (4),
    • détection des premier et deuxième faisceaux de référence (25, 26) réfléchis et du faisceau d'échantillon (4) réfléchi et production d'un signal de sortie du détecteur (300),
    caractérisée par
    • la réflexion du premier faisceau de référence (25) par un réflecteur (6) pouvant effectuer un mouvement de translation,
    • la détermination de l'épaisseur de l'échantillon de matériau (8) à l'endroit où le faisceau d'échantillon (4) le traverse,
    • la détermination des première et deuxième positions du réflecteur (6) pouvant effectuer un mouvement de translation en réaction au signal de sortie du détecteur (300), et
    • la détermination de l'indice de réfraction de l'échantillon de matériau (8) en réaction aux première et deuxième positions du réflecteur (6) pouvant effectuer un mouvement de translation.






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