Low-dispersion reflector

Abstract

Low dispersion reflector. A retroreflector comprising a front boundary surface configured for incoming measurement light into the retroreflector, a back boundary surface configured for reflecting the measurement light as reflected measurement light. The front boundary surface and the back boundary surface are arranged on opposite sides of the retroreflector and define an optical axis by the arrangement of the front boundary surface and / or the back boundary surface, wherein an angle of incidence of the measurement light relative to the optical axis is equal to an angle of exit of the reflected measurement light relative to the optical axis. A first optical element comprising the front boundary surface and a second optical element comprising the back boundary surface are provided. The front boundary surface and the back boundary surface are of a curved shape, the first optical element and the second optical element have different shapes and / or sizes, the first optical element is connected to the second optical element, and the retroreflector is configured such that the measurement light entering the retroreflector at the front boundary surface is focused at the back boundary surface.

Description

Technical Field

[0001] This invention generally relates to a retroreflector for accurately measuring the distance and position of a target or target point using a metrology system and / or industrial measurement system. Background Technology

[0002] In metrology, a common goal is to determine the geometric properties of one or more target objects relative to a measuring device, such as coordinates, distance, and orientation. In most cases, these properties must be determined relative to a known reference system, such as by one or more known reference points.

[0003] Methods and systems for measuring target coordinates are used in many applications, such as very precise measurements in geodesy, measurement problems in building installation, or for controlling industrial processes.

[0004] Metrological instruments designed for continuously tracking a target point and coordinating its location are generally referred to as trackers or laser trackers, particularly in industrial metrology. In this context, the target point can be represented by a retroreflective unit (e.g., a corner cube prism) that uses an optical measuring beam, specifically a laser beam, from the measuring instrument for aiming. The laser beam is reflected back to the measuring device in a parallel manner, and the reflected beam is sensed by the device's sensing unit. In this context, the emission and reception directions of the beam are determined, for example, by an angle measuring sensor associated with the system's deflection mirror or aiming unit. Furthermore, by sensing the beam, the distance from the measuring device to the target point can be determined, for example, through propagation time measurements or phase difference measurements.

[0005] Furthermore, laser trackers according to existing technology can be equipped with an optical image capture unit with a two-dimensional photosensitive array, such as a CCD camera or a CMOS array-based camera, or a pixel array sensor, and an image processing unit. In this case, the laser tracker and camera can be specifically mounted vertically so that their relative positions are immutable. Alternatively, the camera can be arranged to rotate with the laser beam. The camera can be integrated with the laser system in a common housing.

[0006] By capturing and evaluating images of a so-called auxiliary measuring instrument (probe) with markers of known relative positions (using an image capture and image processing unit), the orientation of the probe relative to the tracking unit can be inferred. Combined with the determined spatial position of the target point, the position and orientation of an object with six degrees of freedom (6DoF) can be accurately determined.

[0007] The probe can be embodied in a so-called contact sensing tool or tactile probe, which is positioned at a point on the object to be measured by its point of contact. The contact sensing tool has a marker (e.g., a light spot) and a retroreflector representing a target point on the contact sensing tool, which can be aimed by a laser beam emitted from a tracker. The positions of the marker and reflector relative to the point of contact of the contact sensing tool are precisely known. It is known to those skilled in the art that the probe can also be a scanner, such as a handheld scanner, equipped with distance measurement capabilities for non-contact surface measurement operations. The direction and position of the scanner's measuring beam for distance measurement are precisely known relative to the positions of the light spot and reflector arranged on the scanner. Such a scanner is described, for example, in EP 0 553 266.

[0008] For distance measurement, existing laser trackers have at least one distance measuring device, which is typically in the form of a laser interferometer, for example. Due to their relatively long coherence length and the range they allow for measurement, interferometers used for distance measurement primarily utilize a helium-neon gas laser (HeNe laser) as the light source. This is known, for example, in WO 2007 / 079600 A1 or WO 2010 / 148525 A1.

[0009] To reflect the measurement beam of a laser tracker, retroreflectors known in the prior art are typically provided either as solid glass retroreflective prisms or as hollow pyramidal cube retroreflectors.

[0010] For solid glass prisms, measuring the 3D position of the tripoints depends on the measurement angle of refraction within the glass. Therefore, it is difficult to achieve high-precision absolute position measurements in industrial measurement tasks using solid glass prisms. Consequently, solid glass prisms are typically used only for monitoring applications where measuring relative position changes is sufficient.

[0011] Hollow prisms used as retroreflectors typically consist of three reflective surfaces, in which incident light is reflected back in the opposite direction to its incident direction. Reflection is usually provided by direct reflection across the three reflective surfaces of the hollow prism. One advantage of hollow prism retroreflectors over solid glass prism retroreflectors is that the back reflection of incident light is unaffected by refraction. On the other hand, this also limits the usable angular range (field of view, FOV) of hollow prisms compared to glass prisms. However, the three reflective surfaces need to be precisely oriented relative to each other to avoid dihedral errors. Furthermore, the three reflective surfaces need to have a high degree of flatness. Hollow retroreflectors are also known as pyramidal cube retroreflectors.

[0012] The aforementioned typical reflectors must provide a highly precise arrangement of their components to deliver accurate retroreflective characteristics. Therefore, manufacturing such a reflector requires relatively considerable effort. Furthermore, due to its design, this reflector contains a relatively complex structure and is typically heavy. Moreover, the accuracy of this reflector depends on (external) thermal conditions, as the reflector's optical properties change with temperature.

[0013] Furthermore, a typical drawback of retroreflectors known in the prior art, such as hollow prisms, is the significant limitation on the reception angle (i.e., the angle at which the measuring light can be received and retroreflected with sufficient intensity for proper distance measurement).

[0014] For other retroreflectors, such as spherical lenses, their spectral behavior has a particular effect on their retroreflection characteristics. For example, a retroreflector can provide perfect reflection conditions for measurement light with a wavelength of about 650 nm, but if the same reflector is used for measurement light with a wavelength of about 900 nm or even about 1500 nm, the reflection conditions deteriorate. Summary of the Invention

[0015] Therefore, one object of the present invention is to provide a retroreflector that provides accurate retroreflection characteristics while providing an improved structural configuration, for example, one that is less complex.

[0016] A further object of the present invention is to provide a retroreflector that offers more reliable measurement characteristics and more flexible applicability.

[0017] This invention relates to a novel retroreflector that can be used in most laser trackers on the market. Current retroreflectors are limited in terms of receiving angle range (e.g., + / - 30°), maximum measurement distance (e.g., 18 m), or wavelength range (e.g., 633 nm to 792 nm).

[0018] The present invention relates to a retroreflector with a sufficient angular range (+ / - 50°), a measurement distance of up to 50 m, and spectral applicability to all laser trackers (e.g., 633 nm to 1550 nm). The wavelength problem in optical systems is typically solved by replacing a single lens with a doublet (achromatic lens) consisting of two lenses with different dispersions. This approach is relatively complex in terms of required space, weight, and proper integration.

[0019] The present invention provides a retroreflector design with a curved front surface and a curved rear surface to provide general retroreflective characteristics of a reflector. The rear surface may be coated with a reflective layer. To compensate for deviations or divergences caused by the use of different wavelengths (e.g., in the range of 500 nm to 1600 nm) in the retroreflector, at least one optical element of the retroreflector may be made of low-dispersion glass, and intermediate components may be incorporated into the reflector design. This design can be constructed relatively compactly and with less complexity.

[0020] Therefore, in one method for a retroreflector described herein, low-dispersion glass can be used in the first step. In a further method, wavelength-dependent dispersion can be further reduced by using an additional diffraction element placed on the intermediate surface of two (low-dispersion) glass hemispheres. Thus, the present invention proposes a retroreflector consisting of only two glass hemispheres, in a compact and inexpensive manner, wherein achromaticity is achieved by using low-dispersion glass and / or a diffraction element between the glass hemispheres.

[0021] The present invention relates to a retroreflector, comprising: a front boundary surface configured for measurement light to enter the retroreflector, and a rear boundary surface configured for reflecting the measurement light as a reflective measurement light.

[0022] The front and rear boundary surfaces are arranged on opposite sides of the retroreflector, and the arrangement of the front and / or rear boundary surfaces of the retroreflector defines the optical axis, wherein the angle of incidence of the measurement light relative to the optical axis is equal to the angle of exit of the reflected measurement light relative to the optical axis. Therefore, the propagation axes (directions) of the incident and reflected measurement lights are parallel. Due to possible offset between the incident and reflected measurement lights, the corresponding angles of incidence and exit at the curved front boundary surface may differ. However, the angles of incidence and exit relative to the optical axis are equal. In other words, the directions of the measurement light and the reflected light are antiparallel.

[0023] The retroreflector includes a first optical element comprising the front boundary surface and a second optical element comprising the rear boundary surface. The front and rear boundary surfaces are curved. The first and second optical elements have different shapes and / or sizes. The retroreflector includes an intermediate member disposed between the first and second optical elements, and the first and second optical elements are connected to each other via the intermediate member. The intermediate member may be, for example, an adhesive, such as glue or optical adhesive.

[0024] The retroreflector is configured such that the measuring light entering the retroreflector at the front boundary surface is focused at the rear boundary surface (and in particular reflected back).

[0025] The measuring light is preferably provided as a collimated laser, particularly emitted by measuring devices such as measuring apparatuses (e.g., total stations or laser scanners) or metrological devices (e.g., laser trackers). The laser may have a specific wavelength, such as a wavelength with the visible spectrum (VIS) (e.g., 633 nm) or the infrared spectrum (IR). However, the wavelength of the measuring light depends on the measuring device used with the retroreflector and therefore varies from device to device.

[0026] In one embodiment, the first optical element and / or the second optical element may comprise low-dispersion glass having an Abbe number V > 80.

[0027] Low-dispersion glass is a type of glass with reduced chromatic aberration. The refractive index of this glass does not change drastically with different wavelengths of light. In other words, light passing through the glass diffuses or disperses less between its constituent colors, resulting in a reduced "rainbow effect" at high-contrast edges. The wavelength dispersion in a particular material is characterized by its Abbe number, V—the higher the Abbe number, the lower the wavelength dispersion in the material. Low-dispersion glass has a higher Abbe number than conventional types (e.g., crown glass).

[0028] In one embodiment, the first and second optical elements may be made of the same material and have the same Abbe number V. Using low-dispersion glass for both optical elements further improves insensitivity to the wavelength of the measurement light used.

[0029] According to one embodiment, the front boundary surface may have a radius of curvature different from that of the rear boundary surface, and in particular, the radius of curvature of the front boundary surface is smaller than that of the rear boundary surface.

[0030] In one embodiment, the front boundary surface and the rear boundary surface may be spherical. According to some embodiments, at least one boundary surface, the front and / or rear boundary surface, may be formed as a sphere, an ellipsoid, a parabola, or a hyperboloid.

[0031] In one embodiment, each of the two optical elements may include a center point, particularly an optical or geometric center, and the optical elements are arranged such that the center points of the optical elements coincide. This provides a single center distance between the front boundary surface and the rear boundary surface.

[0032] In one embodiment, the intermediate component may comprise or may consist of an adhesive, particularly an optical adhesive.

[0033] In one embodiment, the intermediate component may comprise a diffractive structure, particularly a diffractive optical element. The intermediate component may be provided as a specific element providing an intermediate layer. Alternatively, the intermediate component may be provided as an optical element integrated into one of the optical elements.

[0034] Specifically, the intermediate component may include a first intermediate element comprising a varnish, particularly wherein the shape or structure of the first intermediate element defines the diffraction structure. The varnish may be an optical varnish that provides specific optical properties in terms of transmittance. For example, a varnish providing a refractive index of about 1.5 and sufficient transmittance in the relevant wavelength region.

[0035] In one embodiment, the intermediate component may include a second intermediate element comprising an optical adhesive. The optical adhesive provides specific optical properties in terms of transmittance. For example, an optical adhesive providing a refractive index of about 1.7 and sufficient transmittance of over 99% in the relevant wavelength region.

[0036] In one embodiment, the first intermediate element may contain a refractive index different from that of the second intermediate element.

[0037] According to one embodiment, the diffraction structure may include a blaze height h, where 3.5 µm < h < 15 µm. The blaze height is preferably adjusted according to the materials used for the first and second intermediate elements. Specifically, the diffraction structure may be constructed and provide a blaze height adapted to the refractive index of the varnish and the optical adhesive.

[0038] The plane forming one side of the grooves etched on a diffraction grating can be called the blaze surface. Blaze height is typically a parameter within the context of a diffraction grating, which is an optical device composed of a series of closely spaced parallel grooves or slits. Blaze height can be a key characteristic of a diffraction grating and is associated with the profile of the grooves. The blaze height can represent the depth or height of the grooves on the grating. In a diffraction grating, light incident on the surface diffracts as it interacts with the periodic structure of the grooves. The blaze height can be optimized to improve diffraction efficiency at a specific wavelength or set of wavelengths. By designing the blaze height, the intensity of diffracted light at the desired spectral order can be maximized. Choosing an appropriate blaze height helps improve the performance of the diffraction grating in terms of dispersion, resolution, and efficiency at the desired wavelength of interest.

[0039] The present invention also relates to a method for providing a retroreflector. The method includes: providing a first optical element having a first boundary surface with a curved shape and a second boundary surface with a planar shape; and applying a varnish layer to the second boundary surface, the varnish layer being provided with a defined thickness. The varnish may provide a support structure to construct the diffraction structure.

[0040] In the next step, a stamping element (stamping tool) is pressed into the varnish layer. The stamping element contains a negative image of a structure to be defined by the varnish, wherein a recess of defined shape and size is provided in the varnish layer. The structure and its negative image are preferably defined optical diffraction structures. The varnish layer is cured to provide mold support. Curing can be performed using ultraviolet light.

[0041] Now, optical adhesive is applied to the recess, and in particular, also to the varnish layer. The optical adhesive then flows into the provided negative image structure, thereby constructing a corresponding (positive) image structure. Diffraction structures, particularly diffractive optical elements, can be provided through the optical adhesive.

[0042] A second optical element is provided, having a curved third boundary surface and a planar fourth boundary surface, with the fourth boundary surface disposed on one side of the optical adhesive. This can be done before or after curing the optical adhesive. This means the optical adhesive can cure after contacting the fourth boundary surface, thereby providing adhesion between the two optical elements. Alternatively, the optical adhesive can be cured first, and the fourth boundary surface can be connected to the intermediate member using an adhesive to provide fixed positioning of the optical element. The intermediate member is provided by the varnish layer and the optical adhesive.

[0043] In one embodiment, a reflective layer may be provided on the first boundary surface and / or the third boundary surface, wherein the reflective layer provides reflection of measurement light, particularly measurement light with wavelengths outside the range of 600 nm to 1600 nm.

[0044] The present invention also relates to a retroreflector for determining the location and / or marking target points, particularly for industrial or geodetic surveying. The retroreflector is obtained by performing any of the methods described above. Attached Figure Description

[0045] Various aspects of the invention are described or explained below purely by way of example, with reference to the working examples schematically illustrated in the accompanying drawings. Identical elements are labeled with the same reference numerals in the drawings. The described embodiments are generally not shown to scale and should not be construed as limiting the invention. Specifically,

[0046] Figure 1 This describes a metering system using the retroreflector according to the present invention;

[0047] Figure 2 An exemplary embodiment of the retroreflector according to the present invention is shown;

[0048] Figures 3a to 3b An exemplary embodiment of the retroreflector according to the present invention is shown;

[0049] Figure 4 : Referring to the expected or desired optical behavior, it is shown that according to Figure 2 and Figure 3a The optical characteristics of the retroreflector implementation; and

[0050] Figures 5a to 5b The following are exemplary embodiments of how to manufacture the structure and method of the retroreflector according to the present invention. Detailed Implementation

[0051] Figure 1 A metrology system 1 using the retroreflector 20 according to the invention is illustrated exemplarily. The figure shows an exemplary use case, such as measurement and quality control of workpiece 5 in industrial automobile or aircraft production.

[0052] A typical metrology system for determining the 3D coordinates of object 5 includes a coordinate measuring device 2 with tracking capabilities, hereinafter also referred to as a laser tracker, configured to automatically track a movable accessory device 3 and generate coordinate measurement data indicating the position (and usually orientation) of the movable accessory device. For example, the tracking capability of the tracker can be provided by at least one of the following: a video tracking unit, a radio frequency tracking unit, and optical tracking based on emitting a tracking beam toward a cooperative target (i.e., retroreflector 20).

[0053] The movable attachment device 3 is configured to scan the object 5, for example by tactile scanning, and / or laser-based scanning, and / or camera-based scanning, and / or the movable attachment device is configured to perform interventions on the object 5, such as for manufacturing and / or marking the object 5. For example, the movable attachment device 3 can be implemented as a scanning device configured to approach the object and perform coordinate measurements autonomously, for example, the movable attachment device is a handheld scanner 3. Alternatively, the device can be a tactile detection or scanning device, an articulated robot, an X-ray inspection device, or a stereoscopic imaging device. The movable attachment device can also be a marking device or tool and / or manufacturing instrument for marking objects. Furthermore, the attachment device can also be another laser tracker, for example, a laser tracker configured with scanning capabilities.

[0054] Measurement systems are typically configured such that coordinate measurement data of accessory devices are generally referenced to the coordinate system of one of the coordinate measuring devices (e.g., one of the fixed laser trackers), or the external coordinate system of a group of coordinate measuring devices.

[0055] For example, the movable accessory device 3 is implemented as a handheld scanner configured to emit a local scanning beam to scan the surface of an object in a local coordinate system, wherein the position of the handheld scanner 3 is tracked and measured by a laser tracker 2, and the measurement points of the handheld scanner 3 (typically coordinate measurement data in the local coordinate system) can be referenced to the coordinate system of the laser tracker 2.

[0056] Both the movable attachment device 3 and the tracker 2 can be mounted on the robot, for example, as a UGV (“unmanned ground vehicle”) carrying the tracker 2 or a UAV (“unmanned aerial vehicle”) carrying sensor devices and providing the movable attachment device 3.

[0057] For example, the tracker is implemented as an industrial laser tracker 2, which provides high-precision coordinate measurement and tracking of a cooperative target 20 on a probe 3, such as a passive reflection unit with defined reflection characteristics of a retroreflection unit 20, wherein at least a portion of the laser beam emitted by the laser tracker 2 is reflected back, for example, parallel to the laser tracker. In other words, in the context of this application, the term "cooperative target" refers to a target specifically anticipated for use in conjunction with a tracking unit in order to generate a tracking signal. Thus, the cooperative target "cooperates" with the tracking unit because it has at least one unique reflection characteristic, a unique emission characteristic, a known shape, and a known size.

[0058] The basic structure of a typical laser tracker 2 includes an electro-optical rangefinder for determining the distance to an object based on a laser measurement beam 11 (measuring beam), wherein the aiming direction of the laser measurement beam 11 can be varied under motor drive, for example, relative to one or more independent spatial directions.

[0059] Optical and photoelectric laser rangefinders have now become the standard solution in many fields, where various principles and methods are known in the field of electronic or electro-optical distance measurement. One approach is to use interferometric ranging principles, particularly absolute (i.e., frequency scanning) interferometry, frequency modulated continuous wave (FMCW, especially C-FMCW), Fizeau's principle, and / or frequency comb principle.

[0060] Furthermore, the laser tracker 2 includes a tracking unit for automatically adjusting the aiming direction of the laser measurement beam 11, enabling the measurement beam 11 to continuously track the target point. The emission direction of the laser measurement beam 11 is determined by an angle measurement sensor (e.g., an angle encoder). As the tracking sensor, a position-sensitive detector (PSD), such as a surface sensor operating in an analog manner, can be used, by means of which the centroid of the light distribution on the sensor surface can be determined.

[0061] The movable accessory device 3 includes a cooperative objective implemented as a retroreflector 20 according to the invention.

[0062] Figure 2 An exemplary embodiment of a retroreflector 20 according to the present invention is shown. The retroreflector 20 includes a first optical element 21 having a front boundary surface 22 and a second optical element 23 having a rear boundary surface 24. The front boundary surface 22 and the rear boundary surface 24 are curved. The first optical element 21 and the second optical element 23 are connected to each other. In the illustrated embodiment, the first optical element 21 is a hemisphere, and the second optical element 23 comprises an object having a rear boundary surface 24 having a partially spherical shape. In particular, the second optical element 23 is part of a hemisphere or includes a spherical cap. The first optical element 21 and the second optical element 23 are bonded together. The bonding is provided by an adhesive, such as a layer of optical glue between the first optical element 21 and the second optical element 23, which represents an intermediate component. The optical glue may be provided with a defined thickness, for example, 10 µm.

[0063] The front boundary surface 22 is configured for the measurement light 11 to enter the retroreflector 20. The rear boundary surface 24 is configured to reflect the measurement light into reflected measurement light 12. The rear boundary surface 24 may be covered by a corresponding reflective layer. It can be seen that the front boundary surface 22 and the rear boundary surface 24 are arranged on opposite sides of the retroreflector 20.

[0064] The optical axis 13 is defined by the arrangement of the front boundary surface 22 and / or the rear boundary surface 24. The incident angle of the measurement light 11 relative to the optical axis 13 is equal to the exit angle of the associated reflected measurement light 12 relative to the optical axis 13. The reflected measurement light 12 propagates parallel to the incident measurement light 11 in the opposite direction, i.e., substantially antiparallel.

[0065] The retroreflector 20 is configured such that the measuring light 11 entering the retroreflector 20 at the front boundary surface 22 is focused at the rear boundary surface 24, and in particular the first optical element 21 and the second optical element 23 are shaped accordingly.

[0066] In this embodiment, the first optical element 21 and the second optical element 23 comprise low-dispersion glass with an Abbe number V > 80. In another embodiment, at least one of the first optical element 21 and the second optical element 23 comprises low-dispersion glass.

[0067] By using low-dispersion glass, the retroreflector 20 provides wavelength insensitivity over a wide range of measurement light 11 wavelengths. This means that even when using different wavelengths, the retroreflector 20 still provides sufficient reflection quality for the reflected measurement light 12 (e.g., related to reflected light intensity, angular consistency, reflected beam divergence, etc.). This still holds true for measurement ranges up to 50 m or even larger (distance between the laser tracker and the retroreflector).

[0068] In the illustrated embodiment, each optical element 21, 23 defines a center point, specifically an optical or geometric center, and the two optical elements are arranged such that the center points of the two optical elements 21, 23 coincide. This design ensures that the principal ray from any field of view passes through the same center point of the system. Therefore, due to spherical symmetry, the focusing and retroreflection performance is constant throughout the entire field of view (FOV).

[0069] Figure 3a Another exemplary embodiment of a retroreflector 20 according to the present invention is shown. The retroreflector 20 includes a first optical element 21 having a front boundary surface 22 and a second optical element 23 having a rear boundary surface 24. The front boundary surface 22 and the rear boundary surface 24 are curved. In the illustrated embodiment, the first optical element 21 is a hemisphere, and the second optical element 23 comprises an object having a rear boundary surface 24 having a partially spherical shape. Specifically, the second optical element 23 is part of a hemisphere or includes a cap.

[0070] However, it should be understood that in the context of this invention, the first optical element and / or the second optical element may provide any other geometry or shape of surface, the boundary surface of which is curved.

[0071] The retroreflector 20 further includes an intermediate member 30 disposed between the first optical element 21 and the second optical element 23. The intermediate member 30 includes a diffraction structure. In the illustrated embodiment, the intermediate member includes a diffractive optical element. Furthermore, the intermediate member 30 provides adhesion between the first optical element 21 and the second optical element 23.

[0072] By arranging this intermediate component, specifically by integrating a diffraction structure (DOE) between the two glass half-shells, the design and reflection characteristics of the retroreflector 20 can be further improved. Thus, the diffraction structure contributes to or even takes over wavelength correction. Here, the first optical element 21 and / or the second optical element 23 can be made of standard (optical) glass (e.g., crown glass).

[0073] In one embodiment, at least one of the first optical element 21 and the second optical element 23 comprises or is made of low-dispersion glass. This further improves the wavelength insensitivity of the retroreflector 20.

[0074] The DOE reduces divergence, particularly at medium wavelengths, due to the wavelength dependence of its structure. This provides a corresponding design based on two glass hemispheres and a diffractive intermediate layer 30, meeting the required specifications over an extended wavelength range.

[0075] Figure 3b An exemplary embodiment of the intermediate member 30 used in the retroreflector embodiment of the present invention is shown.

[0076] The intermediate component 30 includes a first intermediate element 31 containing an optical varnish and provides the diffraction structure. The intermediate component also includes a second intermediate element 32 containing an optical adhesive. The first intermediate element 31 and the second intermediate element 32 have a (slight) difference in diffraction capability.

[0077] The intermediate member 30 in this embodiment has a scintillation height ranging from 3.5 µm to 15 µm.

[0078] Figure 4 An example is shown according to Figure 2 and Figure 3a The optical characteristics of the retroreflector implementation are shown with reference to the desired or required optical behavior. The optical characteristics reference divergence as a function of wavelength are illustrated.

[0079] Curve 40 represents the desired or required optical performance of the retroreflector. It shows the maximum permissible wavelength-dependent divergence requirement of the retroreflector at a maximum distance of 50 m (e.g., when used with a laser tracker).

[0080] according to Figure 2 The performance of the retroreflector is shown by curve 41. It can be seen that, according to... Figure 2 The retroreflector provides sufficient divergence behavior over a wide wavelength range to satisfy several typical applications. In other words, the reflector already provides adequate characteristics, but exhibits a slight deviation at a medium wavelength λ1. This may result in a reduction in the maximum measurement distance, for example, from 50 m to approximately 35 m.

[0081] Furthermore, curve 42 shows the results based on... Figure 3a The optical performance of the retroreflector, i.e., the retroreflector including the intermediate member 30 with DOE, fully meets the required wavelength independence criterion.

[0082] Figure 5a and Figure 5b An exemplary embodiment of a structure and an embodiment of a method for manufacturing a retroreflector according to the invention are shown. Here, the retroreflector should provide an intermediate member 30 comprising a diffraction structure.

[0083] Precise achievement of the correct thickness of the intermediate components and their assemblies is crucial. The tolerances here are in the micrometer range to provide accurate and sufficient optical properties. To meet these requirements, a so-called support structure, such as a varnish layer, is first coated on the (second) optical element 23 to a defined thickness. This support structure represents the first intermediate element 31 (the black area in the figure).

[0084] It should be understood that the step of coating the support structure can be alternatively applied to another (first) optical element 21. The invention is not limited to any of these procedures.

[0085] from Figure 5b As can be seen, an outer thick interruption ring with a defined thickness (e.g., 30 µm height) was constructed to protect the central DOE. This ring also has a clearly defined layer thickness. The interruption is provided to optimize subsequent material flow (optical adhesive) and to remove air from the recess.

[0086] Next, a stamping tool is used to press the negative image of the diffraction structure (DOE) to be provided by the varnish into the varnish. The structure of the DOE is pressed into the varnish. Accordingly, recesses defining the shape and size are provided in the support structure 31 (varnish). Specifically, after the support structure has cured, the recesses are filled with optical adhesive 32 (shown as dots in the figure).

[0087] To provide a stable and accurate diffraction structure, optical adhesive 32 is cured. This can be done before or after the upper boundary layer of intermediate member 30 is attached to another optical element. This means that the other optical element is attached to the supporting optical element 23 via optical adhesive 32, i.e., bonded by optical adhesive 32, or the two optical elements are bonded together using an additional adhesive.

[0088] By stamping the diffractive structure into a varnish layer with a defined outer thickness and using a precision-manufactured stamping tool, a diffractive structure with a well-defined geometry and / or distance from at least one optical element can be precisely constructed. Therefore, this arrangement provides sufficient wavelength sensitivity correction for beam propagation in the retroreflector.

[0089] Although the invention has been described above with reference to some preferred embodiments, it must be understood that numerous modifications and combinations of different features of the embodiments can be made. All such modifications fall within the scope of the appended claims.

Claims

1. A retroreflector (20), the retroreflector comprising: - A front boundary surface (22), configured to measure the light (11) entering the retroreflector (20), and - A rear boundary surface (24) configured to reflect the measurement light as a reflected measurement light (12). in, - The front boundary surface (22) and the rear boundary surface (24) are arranged on opposite sides of the retroreflector (20), and - The optical axis (13) is defined by the arrangement of the front boundary surface (22) and / or the rear boundary surface (24) of the retroreflector (20), wherein the incident angle of the measurement light (11) relative to the optical axis (13) is equal to the exit angle of the reflected measurement light (12) relative to the optical axis (13). Its features are, - A first optical element (21), the first optical element comprising the front boundary surface (22), and - Second optical element (23), the second optical element includes the rear boundary surface (24). in, - The front boundary surface (22) and the rear boundary surface (24) are curved. - The first optical element (21) and the second optical element (23) have different shapes and / or sizes. - The retroreflector (20) includes an intermediate member (30) disposed between the first optical element (21) and the second optical element (23). - The first optical element (21) is connected to the second optical element (23) via the intermediate member (30), and - The retroreflector (20) is configured such that the measurement light (11) entering the retroreflector (20) at the front boundary surface (22) is focused at the rear boundary surface (24).

2. The retroreflector (20) according to claim 1. Its features are, The first optical element (21) and / or the second optical element (23) comprises low-dispersion glass having an Abbe number V > 80.

3. The retroreflector (20) according to claim 1 or 2. Its features are, The first optical element (21) and the second optical element (23) are made of the same material and have the same Abbe number V.

4. The retroreflector (20) according to any one of the preceding claims. Its features are, The front boundary surface (22) has a radius of curvature different from that of the rear boundary surface (24), and in particular, the radius of curvature of the front boundary surface is smaller than that of the rear boundary surface.

5. The retroreflector (20) according to any one of the preceding claims. Its features are, The front boundary surface (22) and the rear boundary surface (24) are spherical.

6. The retroreflector (20) according to any one of the preceding claims. Its features are, The first optical element (21) and the second optical element (23) have their respective center points, and the first optical element (21) and the second optical element (23) are arranged such that the center points of the first optical element (21) and the second optical element (23) coincide, and provide a single center distance between the front boundary surface (22) and the rear boundary surface (24).

7. The retroreflector (20) according to any one of the preceding claims. Its features are, The intermediate component (30) contains or is composed of adhesives, particularly optical adhesives.

8. The retroreflector (20) according to any one of the preceding claims. Its features are, The intermediate component (30) includes a diffraction structure, particularly a diffraction optical element.

9. The retroreflector (20) according to any one of the preceding claims. Its features are, The intermediate component (30) includes a first intermediate element (31) containing paint, and in particular, the shape or structure of the first intermediate element (31) defines the diffraction structure.

10. The retroreflector (20) according to any one of the preceding claims. Its features are, The intermediate component (30) includes a second intermediate element (32), which includes optical adhesive.

11. The retroreflector (20) according to claim 10. Its features are, The first intermediate element (31) has a refractive index that is different from that of the second intermediate element (32).

12. The retroreflector (20) according to any one of claims 8 to 11. Its features are, The diffraction structure includes a blaze height h, where 3.5 µm < h < 15 µm.

13. A method of providing a retroreflector (20), the method comprising: - Provide a first optical element (21) having a first boundary surface (22) of a curved shape and a second boundary surface of a planar shape. - Apply a paint layer (31) to the second boundary surface, the paint layer being provided with a defined thickness. - A stamping element is pressed into the paint layer (31), the stamping element comprising a negative image of the structure to be provided by the paint, wherein recesses defining shape and size are provided in the paint layer. - Curing the paint layer (31). - Apply optical adhesive (32) to the depression, particularly to the paint layer. - Provide a second optical element (23) having a curved third boundary surface (24) and a planar fourth boundary surface. - Arrange the fourth boundary surface on one side of the optical adhesive, and - Curing the optical adhesive (32). The intermediate component (30) is provided by the paint layer (31) and the optical adhesive (32).

14. The method according to claim 13, Its features are, A reflective layer is provided on the third boundary surface (24), wherein the reflective layer provides reflection of measurement light (11), particularly measurement light with wavelengths outside the range of 600 nm to 1600 nm.

15. A retroreflector (20) for determining location and / or marking target points, particularly for industrial or geodetic surveying, said retroreflector being obtained by performing the method according to claim 13 or 14.

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