Color confocal measurement system for high speed ranging

Abstract

A chromatic confocal measuring device is disclosed which uses a strong broadband light source achieved by optical pumping of a luminescent body. The illumination of the luminescent body is chosen in such a way that the optical output power of the light source is maximized using the properties of the luminescent body.

Description

Technical Field

[0001] This invention relates to a color confocal measurement apparatus comprising a broadband light source in the visible wavelength range up to the near-infrared range, particularly in the wavelength range between 400 nm and 900 nm, using a pump light source in the wavelength range of 350 nm to 500 nm, and a first optical device for imaging the pump light source onto a light-emitting body. The invention also relates to a second optical device for imaging the light-emitting body onto a facet of an optical fiber or fiber bundle (8a), wherein at least a portion of the broadband light is coupled into the optical fiber or fiber bundle, and wherein the light coupled into the optical fiber or fiber bundle is used as the measurement light of the color confocal measurement apparatus. Furthermore, the invention relates to a light source used in such a color confocal measurement apparatus. Background Technology

[0002] A color confocal multipoint measuring device is known from patent FR 3006758 B1, which is capable of providing distance or thickness information along a line.

[0003] A method for using a light source based on a light emitter for a color confocal sensor is known from patent US2010 / 009779A1.

[0004] Patent US10180355 B2 describes a color confocal sensor using a broadband light source, which is realized by optical pumping of a light-emitting element.

[0005] US10731965 B1 describes a broadband light source based on a light emitter and having a slit-shaped light-emitting surface.

[0006] According to Volker Hagemann, Albrecht Seidl, and Günter Weidmann's "Static ceramic phosphor assembly for high-power, high-brightness SSL light sources for digital projection and professional lighting," Proc. SPIE 11302, Light-emitting devices, materials and applications XXIV, 113021N (hereinafter referred to as NPL1), the illumination limit, i.e., the maximum power of the light emitted by the phosphorescent conversion ceramic, is limited by thermal quenching.

[0007] The journal article “Spot size limitation associated with phosphorescent materials in laser illumination” Opt. Express 285578-55767 (2020) (hereinafter referred to as NPL2), co-authored by Anastasiia Krasnoshchoka, Anders Kragh Hansen, Anders Thorseth, Dominik Marti, Paul Michael Petersen, Xu Jian, and Ole Bjarlin Jensen, describes the confinement characteristics of the luminescent material and its dependence on the spot size of the excitation light.

[0008] High-resolution optical circuit scanners require long-life, high-intensity broadband light sources. Phosphorescent converters are increasingly being used as high-power broadband light sources, for example, in automotive microscopes.

[0009] The use of such broadband sources in metrology is also increasing compared to US10180355 B2 and US2010 / 009779 A1. However, the heat generated is a problem, leading to a preference for dynamic solutions that reduce localized high temperatures by moving the phosphor to distribute heat. Higher intensities can theoretically be achieved, as described in US2010 / 009779A1. However, mechanical movement causes some wear, shortening the lifespan. Furthermore, a thicker phosphor layer must be used to achieve better mechanical stability, which leads to a reduction in the radiation limit (see NPL1), thus negating any increase in intensity gained through movement. Additionally, movement and the resulting motion artifacts increase the effective emission area, which in light-limited systems such as color confocal measurements results in either reduced intensity or a decrease in resolution if the intensity remains constant.

[0010] In summary, it can be said that, to date, only a small fraction of the emitted radiation has been used in the measurement system. However, unused photons also contribute to heating, thus limiting the intensity and lifespan of the white light source. Summary of the Invention

[0011] Therefore, the objective of this invention is to provide a color confocal measurement apparatus using a high-efficiency and durable broadband light source, which has emission characteristics optimized for color confocal sensors. The light source must have high optical power because it limits the measurement rate of the color confocal unit and the measurement device due to the availability of high-speed hardware and software, especially in the visible spectrum where the measurement rate is limited by a high-efficiency detector.

[0012] According to the present invention, the objective is achieved by using focused illumination from a light source in a color confocal measurement apparatus and by using the resulting broadband measurement light. The imaging beam path of the pump source on the light source and the imaging beam path of the light source at the end of the optical fiber or fiber bundle partially overlap; that is, the light incident on the light source and the light emitted by the light source and used as the measurement light partially follow the same path in opposite directions. A dichroic mirror is used to decouple or separate the light used as the measurement light and, for the aforementioned objective, couples the measurement light from the beam path of the pump source into the optical fiber or fiber bundle.

[0013] In a preferred embodiment, the beam path of the pump source imaging on the light emitter is made to coincide with the beam path of the light emitter imaging on the end of the optical fiber or fiber bundle by including at least one common imaging optical element, in particular a lens, in the first and second optical devices.

[0014] This invention claims protection for the color confocal measuring device according to claim 1 and the light source used in the device according to claim 14 or 15.

[0015] A color confocal single-point or multi-point measurement device is proposed, featuring a durable and powerful broadband light source in the visible to near-infrared wavelength range for measuring the distance / thickness of objects. Many optical measurement devices based on color confocal or interferometric principles are known.

[0016] A light source based on a luminescent material is understood as a light source in which fluorescence (the luminescent material) is excited by a pump source (usually a laser or LED), emitting light through physical processes, particularly phosphorescence, fluorescence, or scintillation. In this context, a luminescent material generally refers to a radiation-converting substance.

[0017] In a preferred embodiment, the pumping of the luminescent body is optimized in such a way that, taking into account volume scattering and the relevant changes in the irradiated and luminescent surfaces (see NPL2), it produces optimal radiation characteristics for coupling into the measurement system.

[0018] The advantage of this preferred embodiment is that, in the light emitter, the light-emitting surface is typically larger than the surface illuminated by the pump light (see NPL 2). Therefore, the optical elements in this embodiment are selected such that the illuminated surface of the light emitter is smaller than or equal to the lateral dimension of the facet of the fiber bundle or fiber, and / or the image of the illuminated surface of the light emitter on the facet of the fiber is smaller than its lateral dimension.

[0019] This ensures that heat generation is reduced by using a small illuminated area of ​​the light source, thereby achieving a long lifespan for the light source and high optical performance for the broadband light source.

[0020] At the same time, it is ensured that the lateral dimensions of the emitting surface do not limit, or only slightly limit, the amount of light that can be coupled into the optical fiber or fiber bundle. In order to couple emitted light over a wide angular range, the optics in the receiving path of the light source and the individual fibers of the optical fiber or fiber bundle are typically selected with high numerical apertures, where, in most cases, the numerical aperture of the fiber is a limiting factor.

[0021] In another embodiment of the color confocal measurement apparatus, a light source is provided by appropriately selecting a first optical element or by placing an additional optical element in front of a dichroic mirror, wherein the additional optical element is used to introduce spherical aberration into the wavefront.

[0022] The following embodiments are particularly preferred:

[0023] The first optical element (specifically including a lens) is selected such that it produces spherical aberration at the dominant wavelength of the pump light source.

[0024] Spherical aberration can also be generated by inserting a glass plate before the first optical element.

[0025] In addition, spherical aberration can also be generated by additional optical elements such as lenses or compensating plates.

[0026] The aforementioned possibilities also include, in particular, arrangements in which spherical aberration is generated only in conjunction with a second optical element in the plane of the luminescent surface.

[0027] Furthermore, spherical aberration can be generated solely by the second optical element.

[0028] Additionally or alternatively, the light source may be moved axially relative to the focal point of the illumination path, especially to increase the light spot size, or to optimize the beam profile by means of the propagation invariance of optical aberrations, especially to make the illuminated area of ​​the light source have a beam profile with uniform intensity, or the beam profile has a rotationally symmetric intensity distribution that depends on the radial position, especially an annular beam profile, an intensity profile consisting of several rings, or a flat-topped profile.

[0029] In another embodiment of the color confocal measurement apparatus, diffractive optical elements are introduced into the light source, dichroic mirror, or beam splitter, so that the irradiated area of ​​the light source has a rotationally symmetric intensity distribution that depends on the radial position, especially an annular beam profile, an intensity profile composed of several rings, or a flat-topped profile.

[0030] In another embodiment of the color confocal measuring device, one or more axial cones in the light source are used as optical elements to generate a Bessel-Gaussian beam in the region of the light source.

[0031] In another embodiment of the color confocal measurement apparatus, the light source is operated by multiple pumped light sources that illuminate non-overlapping or only partially overlapping areas on the light-emitting body. In such... Figure 2 In the illustrated embodiment, the pump sources are arranged such that they pass through the same optical element, wherein the beam paths differ in position and angle. Similarly, a beam splitter can be used to converge the beam paths of the pump sources used, such that all beam paths pass through the second optical element to a certain extent. Likewise, a polarization-dependent beam splitter can be used to converge the beam paths of multiple polarized pump sources together with minimal optical power loss.

[0032] In a similar manner, multiple non-overlapping or only partially overlapping regions on a light source can be illuminated by using a single pump source whose beam is split into multiple beam paths by optical elements, especially diffractive optical elements, beam splitters, or gratings.

[0033] In a preferred embodiment of the invention, broadband light is coupled into an optical fiber bundle, and the sides of the optical fibers in the bundle opposite to the coupling side are arranged to measure multiple thicknesses or thicknesses at different locations of the object being measured. The coupling side refers to the facet of the optical fiber into which light from the light source is coupled. On this side, the optical fibers are preferably arranged as close together in space as possible to effectively capture the light imaged thereon. The opposite side is the side of the measurement head.

[0034] Particularly preferably, the optical fibers are arranged in a row on one side of the measuring head so that measurements can be taken along a line.

[0035] In an alternative embodiment of the color confocal measurement apparatus, the light source is illuminated in the same manner as described above, but the converted light is coupled into a multimode fiber instead of a fiber bundle. The light guided in the multimode fiber is split into a line, discrete points, or another arrangement outside the light source and applied to measure multiple thicknesses or thicknesses at different locations on the object being measured. Splitting the light guided in the multimode fiber into a line can be achieved, for example, by a cylindrical lens of the measuring head. Splitting into discrete points can be achieved, for example, by inserting an aperture mask into the beam path after the multimode fiber. Alternatively, the cylindrical lens of the measuring head can be combined with an aperture mask to obtain a row of discrete points.

[0036] An alternative implementation is designed as a color confocal single-point measuring device for measuring the distance or thickness of a measuring object, wherein the light source is implemented in the manner described above, except that a single optical fiber with a diameter of less than 300 μm, preferably less than 50 μm, is used.

[0037] One possible implementation of the color confocal single-point measurement device is characterized in that the luminescent area of ​​the light-emitting body is smaller or slightly larger than the facet of the optical fiber.

[0038] Another possible implementation of the color confocal measurement apparatus includes an apparatus according to a previously unpublished patent application DE10 2020 116215. This patent application describes an optical measurement apparatus comprising a measurement head with imaging optics and an evaluation unit, wherein the measurement head is connected to the evaluation unit via two optical fibers. The evaluation unit includes a light source whose light is guided into the measurement head via a first optical fiber, and wherein light reflected from the object being measured is guided back into a second optical fiber via the measurement head and by means of a beam splitter, such that the forward and backward light are separated, wherein the fiber ends are in a mutually conjugate position. The beam splitter and the fiber ends serving as apertures are arranged together in a connector detachably connected to the measurement head.

[0039] The aforementioned device can be combined with techniques for reducing speckle, such as using a pump source with a wider bandwidth or reducing the coherence length by introducing frequency or phase modulation into the pump source, for example by changing the ambient temperature or diode current.

[0040] The aforementioned device can be extended with the aid of a cylindrical lens to correct the astigmatism prevalent in light sources. This is especially true when the pump source has asymmetrical radiation characteristics, such as in LEDs, where the divergence angle is strongly direction-dependent; this effect can be at least partially compensated for by the cylindrical lens. Here, the cylindrical lens can be placed at different positions in the beam path between the pump source and the light emitter, but in a preferred embodiment, it is placed between the first optical element and the dichroic beam splitter. Preferably, the cylindrical lens is oriented such that its axis with a smaller divergence angle is parallel to the pump source.

[0041] The aforementioned device can be designed as an alternative embodiment such that the measuring light is guided from the light source to the measuring head by means of a free-beam optics device rather than an optical fiber or fiber bundle.

[0042] The present invention also relates to a light source for use in a color confocal measurement apparatus, wherein the beam path of the pump light source (1) imaged on the light source (5) partially coincides with the beam path of the light source (5) imaged on the end of an optical fiber or fiber bundle (8a), and wherein the light source includes a dichroic mirror (3) arranged such that it decouples the beam path of the light source (5) imaged on the end of the optical fiber or fiber bundle (8a) from the beam path of the pump light source (1) imaged on the light source (5).

[0043] In an alternative embodiment of a light source for a color confocal measurement device, a pump light source is projected onto a combination of multiple light emitters. The combination of light emitters is achieved by stacking two or more light emitters on top of each other, or by splitting the beam path by a dichroic mirror or beam splitter and illuminating the first and second light emitters, and then recombining the light emitted by the first and second light emitters through the dichroic mirror or beam splitter.

[0044] Further features and advantages of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawings. Attached Figure Description

[0045] The diagram shows:

[0046] Figure 1 This is a first advantageous embodiment of the color confocal measuring device;

[0047] Figure 2 This is a second advantageous embodiment of the color confocal measuring device. Detailed Implementation

[0048] Figure 1 A first advantageous embodiment of the color confocal measuring device is shown.

[0049] The color confocal measurement device includes, for example, a broadband light source in the visible light wavelength range up to the near-infrared range.

[0050] The light source includes a pump light source 1 with a wavelength range of 350 nm to 500 nm, which is collimated by a first optical element 2, reflected by a dichroic mirror or beam splitter 3, and focused onto or near a light-emitting body 5 by a second optical element 4. The first optical element 2 and the second optical element 4 together constitute a first optical device for imaging the pump light source 1 onto the light-emitting body 5.

[0051] The luminescent surface 102 of the light-emitting body is preferably larger than the illuminated surface 101. Accordingly, broadband light from the light-emitting body is emitted across the entire luminescent surface 102.

[0052] The broadband light emitted by the light-emitting element 5 is collimated again by the second optical element 4. Therefore, the emitted light returns to the same path as the incident light. After passing through the dichroic mirror or beam splitter 3 again, and being transmitted rather than reflected based on the dichroism of the beam splitter 3 and the shifted spectral distribution of the light, it is decoupled and then coupled into the fiber bundle or fiber 8 via the third optical element 7. Optical elements 4 and 7 together constitute a second optical device that images the light-emitting element 5 onto the fiber facet 8a. Therefore, the entire light-emitting surface 102 is imaged onto the fiber facet 8a. Advantageously, the image extension of the light-emitting surface 102 on the fiber facet 8a is approximately equal to the extension of the fiber facet. This ensures that not only is the entire fiber facet illuminated, but light loss during coupling is minimized. Correspondingly, the image of the illuminated surface 101 (which in a preferred embodiment is smaller than the light-emitting surface 102) is also smaller than that of the fiber facet 8a.

[0053] The fiber facet 8a refers to the case where all the facets of the individual fibers of the fiber bundle 8 are combined together using the fiber bundle 8. Figure 1 A small facet of such an optical fiber bundle is shown.

[0054] The optical elements can typically consist of a single lens or a group of lenses or equivalent elements (e.g., an imaging mirror).

[0055] Figure 2 Another exemplary embodiment of a color confocal measurement apparatus is shown. This color confocal measurement apparatus includes, for example, a broadband light source in the visible wavelength range up to the near-infrared range. The light source includes, for example, two pump light sources 1, which are imaged onto a light emitter 5 via a dichroic mirror using a first optics and a second optics (each comprising a first optical element 2 and a common second optical element 4). The light emitter is located on a heat sink 6. Light emitted by the light emitter 5 is imaged onto a facet 8a of an optical fiber bundle 8 by means of a second optics comprising a second optical element 4 and a third optical element 7. The optical fibers of the optical fiber bundle 8 are exemplarily arranged within a circular surface at the first fiber end 8a and exemplarily arranged along a line at the other fiber end. Light emitted on the fiber facet 8b propagates exemplarily in a homogenizer 9, is reflected at a beam splitter 10, and is then focused onto the measurement object 12 by an optical element 11, wherein the optical element 11 exhibits dispersive behavior and produces different focal points depending on the wavelength of the light.

[0056] Other exemplary embodiments of the color confocal measurement device are provided by Figure 1 and Figure 2 The combination of the various features shown is constituted.

Claims

1. A color confocal measurement device, comprising: In the case of using a broadband light source in the visible light wavelength range up to the near-infrared range, and a pump light source in the wavelength range of 350 nm to 500 nm (1), A first optical device for imaging the pump light source (1) onto the light emitter (5), A second optical device for imaging the light source onto a small facet (8a) of an optical fiber or fiber bundle, such that at least a portion of the broadband light is coupled into the optical fiber or fiber bundle. The light coupled into the optical fiber or fiber bundle (8) is used as the measuring light of the color confocal measuring device. The characteristic feature is that the beam path of the pump light source (1) imaging on the light emitter (5) and the beam path of the light emitter imaging on the small facet (8a) of the optical fiber or optical fiber bundle partially overlap. Furthermore, the color confocal measurement device includes a dichroic mirror (3), which decouples the beam path of the light source (5) imaged on the facet (8a) of the optical fiber or fiber bundle from the beam path of the pump light source (1) imaged on the light source (5). By introducing spherical aberration into the wavefront through another optical element positioned in front of the dichroic mirror (3), and / or By introducing spherical aberration into the wavefront through another optical element located behind the dichroic mirror (3), and / or The light source (5) moves axially relative to the focal point of the illumination path.

2. The color confocal measuring device according to claim 1, characterized in that, The first optical device and the second optical device include at least one common imaging optical element.

3. The color confocal measuring device according to claim 1 or 2, characterized in that, The illuminated surface (101) of the light emitter (5) is equal to the lateral dimension of the coupling side of the fiber bundle or fiber (8), and The image of the illuminated surface of the light source on the facet (8a) of the fiber bundle or fiber (8) is smaller than the lateral dimension of the coupling side of the fiber bundle or fiber.

4. The color confocal measuring device according to any one of claims 1 or 2, characterized in that, The optical element is a lens or a glass plate.

5. The color confocal measuring device according to any one of claims 1 or 2, characterized in that, Multiple pump light sources (1) were used to illuminate the light source (5) without overlapping or with only partial overlap.

6. The color confocal measuring device according to any one of claims 1 or 2, characterized in that, The pump light is split into multiple beam paths by optical elements to illuminate the light source (5) without overlap or with only partial overlap.

7. The color confocal measuring device according to any one of claims 1 or 2, characterized in that, The broadband light is coupled into the fiber bundle (8), and the opposite sides of the small facet (8a) of the fiber bundle are suitably arranged at positions for measuring the thickness of multiple thicknesses or the thickness at different positions of the object being measured.

8. The color confocal measuring device according to any one of claims 1 or 2, characterized in that, Coupled in a single multimode fiber, and a coupled light is split into a line, discrete points or another spatially extended arrangement after leaving the fiber (8) for measuring multiple thicknesses or the thickness at different locations of a measurement object.

9. The color confocal measuring device according to any one of claims 1 or 2, characterized in that, A single optical fiber with a diameter of less than 300 μm is used to measure a single point of the object being measured.

10. The color confocal measuring device according to any one of claims 1 or 2, characterized in that, A device comprising a first optical fiber, a second optical fiber, and a beam splitter is used, wherein the first optical fiber is used to couple a broadband measurement light (8) such that the first optical fiber guides the measurement light from the broadband light source toward the measurement head of the color confocal measurement device, wherein the measurement head guides the measurement light toward the measurement object and guides the light reflected or scattered from the measurement object back to the dichroic beam splitter, and the dichroic beam splitter collects the measurement light and the light propagating back from the measurement object, and the second optical fiber guides the light from the measurement object propagating through the dichroic beam splitter to the spectrometer of the color confocal measurement device.

11. The color confocal measuring device according to any one of claims 1 or 2, characterized in that, Spot reduction technology was used.

12. The color confocal measuring device according to any one of claims 1 or 2, characterized in that, The astigmatism at the pump light source (1) is corrected by a cylindrical lens.

13. The color confocal measuring device according to any one of claims 10, characterized in that, The measurement light from the broadband light source to the measuring head is guided by free-beam optics, rather than optical fibers or fiber bundles (8).

14. A light source for use in a color confocal measuring apparatus, emitting light in the visible wavelength range up to the near-infrared range, comprising: Pump light source with a wavelength range of 350nm to 500nm (1). A first optical device for imaging the pump light source (1) onto the light emitter (5), A second optical device for imaging the light source onto a small facet (8a) of an optical fiber or fiber bundle, such that at least a portion of the broadband light is coupled into the optical fiber or fiber bundle. Its features are, The beam path of the pump light source (1) imaging on the light emitter (5) and the beam path of the light emitter imaging on the small facet (8a) of the optical fiber or fiber bundle partially overlap. Furthermore, the color confocal measurement device includes a dichroic mirror (3), which decouples the beam path of the light source (5) imaged on the facet (8a) of the optical fiber or fiber bundle from the beam path of the pump light source (1) imaged on the light source (5), wherein, By introducing spherical aberration into the wavefront through another optical element positioned in front of the dichroic mirror (3), and / or By introducing spherical aberration into the wavefront through another optical element located behind the dichroic mirror (3), and / or The light source (5) moves axially relative to the focal point of the illumination path.

15. A light source for use in a color confocal measuring apparatus, emitting light in the visible wavelength range up to the near-infrared range, comprising: Pump light source in the wavelength range of 350nm to 500nm (1). A first optical device for imaging the pump light source (1) onto the light emitter (5), Dichroic mirror or beam splitter (3). A second optical device for imaging the light source onto a facet (8a) of an optical fiber or fiber bundle, such that at least a portion of the broadband light is coupled into the optical fiber or fiber bundle. Its features are, in, By introducing spherical aberration into the wavefront through another optical element positioned in front of the dichroic mirror (3), and / or By introducing spherical aberration into the wavefront through another optical element located behind the dichroic mirror (3), and / or The light-emitting element (5) moves axially relative to the focal point of the illumination path. The combination of light-emitting bodies is achieved by stacking two or more light-emitting bodies on top of each other. or The combination of the light emitters is achieved in the following manner: the beam path is split by a dichroic mirror or beam splitter and illuminates the first and second light emitters, and the light emitted by the first and second light emitters is combined again by the dichroic mirror or the beam splitter.

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