Device and method for adjusting a laser interferometer

Abstract

Device for the relative coarse adjustment of a measuring head of a fiber optic laser interferometer and a reflective object to be measured, comprising: a beam splitter designed to split at least one light beam into a reference beam directed towards a reference mirror and an object beam directed towards the object to be measured, a detection surface that enables detection a) an object reflection beam reflected from the object to the beam splitter and b) of a reference reflective beam and / or the reference beam reflected from the reference mirror to the beam splitter, wherein the detection surface is arranged so that it is opposite either a reference mirror or an object to be measured, but not the measuring head where A) the beam splitter is part of a beam splitter cube and one surface of the beam splitter cube is provided with the detection surface, and / or B) the detection surface is designed to be photoluminescent, in particular fluorescent, and can be excited by the reference reflection beam and the object reference beam to emit light with at least one wavelength in the range of 380 nm to 780 nm from the respective point of impact.

Description

[0001] The invention relates to a device for the relative alignment of a fiber optic interferometer measuring head to a movable, reflective object and a corresponding alignment method, in particular a method and an alignment device for the relative alignment of the optical components of a sinusoidally phase-modulated, fiber optic laser interferometer.

[0002] Essentially, an interferometer works by splitting an emitted light beam into at least two parts that travel different optical paths (hereinafter referred to as paths) before being recombined. At the point of recombination, interference occurs due to the different path lengths and the resulting phase shift. In regions where the waves are in phase, their amplitudes add up, a phenomenon known as "constructive interference." Here, the intensity is particularly high. If the waves are out of phase, this is called "destructive interference."

[0003] Due to the movement of the object being measured, a change occurs in the interference pattern, which can be measured using appropriate detectors (e.g., photodetectors). It turns out that the measured intensities change periodically due to a displacement of the object, with a period that depends on the wavelength. Ideally, this results in a sine wave. However, this simple method of position detection has significant drawbacks. The sinusoidal measurement signal resulting from the displacement has areas with very low slopes near the extreme points, meaning that changes in the distance being measured result in only very small changes in the measurement signal. In the worst case, a small change in distance then causes no detectable change in the measurement signal. These are referred to as "blind spots."Another crucial disadvantage is that the direction of any shift cannot be determined from the simple sine signal.

[0004] To achieve high resolution across the entire range and to determine the direction of any shift, a second measurement signal is often generated. Ideally, this second signal is phase-shifted by 90° relative to the first sinusoidal measurement signal. In this case, the second signal exhibits a cosine-shaped dependence on the distance. Therefore, a (sin / cos) pair of values ​​is obtained at each measurement point. These measurement signals are also called quadrature signals. There are various methods for generating the second measurement signal. The simplest is to detect the interferometer light using a second detector positioned at a different location than the first. Due to the path difference between the detectors, a phase shift occurs between the two measurement signals. This path difference can then be adjusted so that the phase shift between the two signals is 90°, as described above.Plotting these quadrature signals on a common XY diagram results in a so-called "Lissajous figure." Such a plot involves mapping the value of the sine curve on the abscissa and the value of the cosine curve on the ordinate axis, ideally forming a circle. The result of such a plot is generally referred to as a "Lissajous figure," regardless of whether the "circle" is perfectly shaped or not. If a bright area (in the region of constructive interference) and a dark area (in the region of destructive interference) are completely traversed, the plot represents exactly one complete circle. This circle corresponds to an incremental shift by a distance proportional to the wavelength of the light. If the shift is continued, the measured signal continues to move along the circle.The direction in which the measurement signal travels along the circle allows the relative direction of the displacement to be determined. The resulting angle of the vector pointing from the origin of the circle to the current measurement reveals the range within one increment where the mirror, whose displacement is being measured, is located. In this way, the relative position of the mirror can be determined even over multiple periods of light-dark cycles by counting the circle's rotations (where the distance traveled per rotation is known as an increment) and adding the resulting value to the current measurement.

[0005] It is not absolutely necessary to work with two detectors. There are alternative approaches to achieving consistently high resolution and also to be able to determine direction. A particularly elegant class is represented by sinusoidally phase-modulated interferometers. This class is often referred to in the field as SPM interferometers, where "SPM" stands for "Sinusoidal Phase-Modulated." Therefore, the term "SPM interferometer" will be used in the following. With SPM interferometers, the sinusoidal modulation of the wavelength and suitable signal processing also produce sine and cosine curves, which can then be used for position determination as described previously. Their sine and cosine curves can also be plotted as a "Lissajous figure." A characteristic of SPM interferometers is that a reference wavelength is sinusoidally modulated (alternatively, the measurement distance can, of course, be used instead of the wavelength, e.g.,...).(modulated by a vibrating mirror), resulting in time-dependent interferences, from which the above sine and cosine signals can be calculated by suitable signal processing, by means of which the direction of displacement and position can be determined.

[0006] An early description of an SPM interferometer is given in the publication by O. Sasaki and H. Okazaki: “Sinusoidal phase modulating interferometry for surface profile measurement”, published in Applied Optics, Volume 25, No. 18, on September 15, 1986. In this description, the reference mirror is excited to vibrate in order to sinusoidally modulate the measurement signal.

[0007] It is possible to introduce the modulation before the optics of the interferometer, as described by G. Basile, A. Bergamin, G. Cacagnero and G. Mana in the publication “Phase Modulation in High-resolution Optical Interferometry”, published in Metrologia, 1991 / 1992, 28, 455-461, which makes the modulation less susceptible to disturbance by external influences.

[0008] A very fast phase modulation is described by the authors U. Minoni, E. Sardini, E. Gelmini, F. Doccio and D. Marioli in their publication “A high-frequency sinusoidal phase-modulation interferometer using an electro-optic modulator: Development and evaluation”, published in Rev. Sci. Instrum. 62, 2579-2583 (1991).

[0009] High-frequency modulation allows, for example, a high translation speed, which is important for technical applications of interferometers.

[0010] The use of so-called DFB diodes has become the dominant method for wavelength modulation. A first description was provided by O. Sasaki, K. Takahashi, and T. Suzuki in their publication "Sinusoidal phase modulating laser diode interferometer with feedback control system to eliminate external disturbance," published in Optical Engineering 29(12), 1511-1515, in December 1990. This publication explains how modulating the wavelength of a laser diode in a sinusoidally phase-modulated interferometer affects the interference signal. The diode current is modulated via its amplitude and frequency.

[0011] "DFB" stands for "Distributed Feedback." Interestingly, the wavelength of DFB diodes can be modulated simply by changing the diode current or the temperature. Firstly, a change in temperature causes the frequency-determining structure to expand or contract. This allows the wavelength range to be shifted over a wide area. Also important is the property that a change in the diode current affects the charge carrier density, which in turn changes the refractive index of the active medium and thus the optical path length in the diode. While this doesn't allow for shifts as wide as those achieved by temperature changes, it enables high-frequency modulation.

[0012] Fiber-based SPM interferometers are of particular interest for many applications. For example, they allow for a compact design in the area of ​​the sensor head. There are generally no active components in the sensor head, resulting in minimal heat input, which is very important for cryogenic applications, for instance. Fiber-based SPM interferometers have been described extensively, such as by S. Venkatesh and W.V. Sorin in "Fibre-Tip Displacement Sensor Using a Sinusoidal FM-Based technique," Electronic Letters, pages 1652-1654, Volume 27, Issue 18, from 1991. This article describes a so-called fiber-optic Fabry-Perot interferometer, explicitly with low finesse.

[0013] The authors X. Wang, X. Wang, Y. Liu, C. Zhang and D. Yu also describe a fiber-based SPM interferometer in the publication “A sinusoidal phase-modulating fiber-optic interferometer insensitive to the intensity change of the light source”, published in Optics & Laser Technology, Volume 3, Issue 3, pages 219 to 222, from April 2003.

[0014] In addition to fiber-based SMP interferometers, a number of other interferometers have been developed, such as the class of multi-wave laser interferometers as described in DE 10 2008 033 942.

[0015] US 6,219,146 B1 concerns a laser reflector alignment. A laser beam or other parallel light beam splits at a beam splitter into a measurement beam and a reference beam. The measurement beam is reflected from a reflecting surface back to the beam splitter, and the reference beam is reflected from a retroreflector back to the beam splitter. The beams are then directed into a telescope. The angle between the measurement and reference beams at the telescope is proportional to the angle between the laser beam and the normal of the reflecting surface. The telescope collects both the measurement and reference beams and transforms each beam into a sharply defined point image. The lateral distance between the two point images is proportional to the magnification of the telescope and the angle formed at the telescope between the measurement and reference beams.When the reflecting surface is precisely aligned relative to the laser beam, the two point images almost perfectly coincide. Alignment is achieved by adjusting the orientation of the reflecting surface until the lateral distance between the two point images is zero or a predetermined value.

[0016] A device for indicating the misalignment of the optical elements of an optical system according to US 4,621,924 B1 comprises an optical radiation source (generally unpolarized), a beam splitter, an optical plane plate, and an off-axis beam detector. The beam splitter divides an input beam from the source into a transmitted component, which travels along the optical axis of the optical system to the optical plane plate, and a reflected component, which travels to the beam detector off the optical axis. The beam detector splits the reflected component of the input beam into two angularly separated beams, which are returned to the beam splitter. The beam splitter transmits the components of the angularly resolved beams to a detector plane.When the optical elements of the system are correctly aligned, the optical plane reflects the transmitted component of the input beam back along the optical axis to the beam splitter. The splitter then reflects one component of the transmitted beam onto the detector plane, so that the components are deflected by equal amounts, but symmetrically opposite each other. If the optical elements of the system are significantly misaligned, the transmitted component is reflected by the optical plane along a path outside the optical axis of the system. Consequently, the beam splitter reflects the component of the transmitted beam to a different position on the detector plane than the position to which the component would be reflected if the optical elements were correctly aligned.Quadrant detectors on the detector plane detect any difference between the angular deviations of the components from the component and thus provide a measure of the misalignment of the optical elements of the system.

[0017] Wavelengths from 1200 nm to 1650 nm have become established for fiber-based interferometers, as components suitable for this wavelength range are relatively inexpensive.

[0018] In principle, with interferometers that use a wavelength outside the visible range, the user faces the difficulty of properly aligning the components, such as the reflective surface of the object to be moved, because the light, or its reflection on the surface, is not directly visible.

[0019] To simplify setup, SmarAct GmbH integrated a pilot laser, operating in the visible spectrum, into their fiber-based SPM interferometer "PicoScale" in 2014. This laser can be activated by the user for alignment purposes. This has significantly simplified the alignment process. However, even with this assistance, aligning the components is still more difficult than desired.

[0020] It is of great interest to simplify the use of fiber-based interferometers. In particular, the still difficult alignment of the components for setting up the interferometer should be simplified.

[0021] One of the objectives of the present invention is to present a device for aligning the optical components of a fiber optic laser interferometer and a corresponding method that enables rapid setup of the interferometer.

[0022] According to a first aspect of the present invention, a device for the relative coarse adjustment of a measuring head of a fiber optic laser interferometer and a reflective object to be measured is proposed, as defined in claim 1.

[0023] According to a second aspect of the present invention, a fiber optic laser interferometer is proposed, in particular a sinusoidally phase-modulated fiber optic laser interferometer, comprising a measuring head, a reference mirror and a coarse adjustment device according to the invention, wherein either the object to be measured or the reference mirror is opposite the detection surface of the device.

[0024] According to a third aspect of the present invention, a method for coarsely adjusting a fiber optic laser interferometer to a reflective object to be measured is proposed, as defined in claim 7.

[0025] The invention is based on the following insight: To simplify the setup of a fiber optic interferometer, it is very helpful for the user to have a visual indicator or other measurable signal to determine whether the interferometer components are reasonably aligned during the initial, "rough alignment"—that is, before the laser interferometer can measure signal changes due to interference. Ideally, this visual indicator or signal helps to bring the alignment into a range where the interferometer is able to perform initial, albeit not yet ideal, measurements, so that the interferometer's measurement signals can then be used for fine-tuning the components.

[0026] An astonishingly simple and effective approach, according to the invention, is to perform the "coarse alignment" using the beam splitter cube typically employed in Michelson interferometers, provided the interference detector is located on the same side as the beam coupling. Of course, a beam splitter cube is not strictly necessary; the components—beam splitter, fixed reference mirror, and alignment detection surface—can also be positioned freely in space, although this is not quite as straightforward as using a beam splitter cube. For the following explanations, it is assumed that a beam splitter cube consists of at least two prisms, the surface resulting from the intersection of one prism being partially transparent to light and acting as the beam splitter. This partially transparent surface is therefore referred to as the beam splitter in the following.

[0027] In a very simple implementation, the surface (e.g., on a beam splitter cube, which is used in this example) opposite the stationary reference mirror is made frosted but translucent. If visible light or a pilot laser operating in the visible wavelength range, as mentioned above, is used to align the reflecting surface of the object to be moved, then, in the case of misalignment, two luminous points will be visible on the frosted surface. These points simply need to be aligned to obtain a properly pre-aligned interferometer. The reasons for this and how it can be used for alignment are described below using an example.

[0028] Light is coupled into one side of the beam splitter cube, causing the light beam to strike the diagonally positioned beam splitter (a partially reflective mirror) inside the cube. The beam splitter splits the light beam into two partial beams. One portion of the light is directed onto a reference mirror fixed to the beam splitter. From there, the beam is reflected back onto the diagonal beam splitter, and a portion of it then returns to the area of ​​original light coupling. The remaining portion of the light passes through the beam splitter and strikes the aforementioned frosted surface opposite the reference mirror. A luminous point is then visible on this frosted surface, remaining stationary regardless of the orientation of the object being moved.

[0029] Of the light initially coupled into the beam splitter cube, a portion passes through the diagonal beam splitter and strikes the reflective surface of the object being aligned, moved, or measured. From there, the light is reflected and strikes the diagonal beam splitter again, so that part of it returns to the area of ​​original light coupling, while another portion is directed by the diagonal beam splitter onto the frosted surface. In the case of misalignment, this portion is visible as a second point on the frosted surface. This second point moves across the frosted surface as the orientation of the object being moved changes. In an ideally aligned system, the visible points of the reference mirror and the measuring mirror overlap. In the case of misalignment, the two visible points can be aligned by changing the orientation of the head relative to the reflecting object being measured.This is very easy to do due to the visible "wandering" of the second point on the matte surface with a change in orientation, provided the matte surface is designed and positioned so that the user can see or measure it during adjustment. Once this "rough alignment" has been achieved, fine adjustment can be carried out using the signals from the laser interferometer.

[0030] It should be noted here that for the simplified alignment process, it is irrelevant whether the measuring head and steel divider are fixed in position and the object to be measured is aligned, or whether the object is fixed and the measuring head and steel divider are aligned. What is important is that the relative orientation of the measuring head to the object being measured is changed and optimized.

[0031] Furthermore, the surfaces on which the points are visualized can also be advantageously designed to be fluorescent, adapted to the wavelength.

[0032] In principle, it is not absolutely necessary to make the surface(s) matte.

[0033] Furthermore, the positions of the surfaces on the beam splitter cube can of course be swapped arbitrarily, as long as the rays always hit at least one diagonal beam splitter.

[0034] This invention significantly simplifies the process of setting up a fiber optic interferometer compared to the prior art, where a first signal from the interferometer must be obtained by simply moving the mirror back and forth. This usual "blind" search can be very time-consuming. The technique according to the invention not only simplifies manual alignment but is particularly beneficial for automated alignment processes, as a signal can be used well before the interferometer is capable of measuring one.

[0035] If the beam splitter is part of a beam splitter cube and one surface of the beam splitter cube is provided with the detection surface, this results in easy handling and relative insensitivity of the actual beam splitter, which is protected to some extent from environmental influences by the cube.

[0036] If the detection surface is photoluminescent, especially fluorescent, and can be excited by the reference reflection beam and the object reference beam to emit light with at least one wavelength in the range of 380 nm to 780 nm from the respective point of impact, the advantage is that the resulting points are easy for the user to recognize, whereby the same detectability is in principle also given for a sensor (e.g. a camera or similar), which, however, can also be used beyond the visible wavelength range.

[0037] A combination of different approaches according to the invention, which are explained below, is possible. This enables a particularly quick and easy alignment of the components.

[0038] In a preferred embodiment, the detection surface is designed to scatter the reference reflex beam and the object reflex beam, so that the points of impact of the reference reflex beam and the object reflex beam on the detection surface are recognizable.

[0039] An alternative or supplementary possibility is to convert at least some of the rays into rays in the visible range, which can then be visually perceived by the user.

[0040] The possibility of scattering also has the advantage that the resulting points are easy for the user to recognize, whereby the same recognizability is in principle also given for a sensor (e.g. a camera or similar), which, however, can also be used beyond the visible wavelength range.

[0041] In one embodiment, the invention provides a photosensitive sensor for detecting the points of impact of the reference reflective beam and the object reflective beam on the detection surface, wherein in another embodiment the detection surface itself can also be designed as a photosensitive sensor with spatial resolution.

[0042] In a further preferred embodiment of the laser interferometer, the measuring head is designed to use a laser beam in a first wavelength range, in particular in the wavelength range of 1,200 nm to 1,650 nm, and to selectively emit a pilot laser beam parallel to the laser beam in a wavelength range of 380 nm to 780 nm.

[0043] Exemplary embodiments of the alignment devices according to the invention are presented below with reference to various illustrations. The alignment method according to the invention is explained with reference to one illustration.

[0044] Preferred and advantageous embodiments of the invention are defined in particular in the dependent claims, whereby it is understood that an embodiment described in connection with a method according to the invention is also to be understood as an embodiment of a device according to the invention, and vice versa.

[0045] The invention will now be explained in more detail using exemplary embodiments with reference to the accompanying figures. These are merely examples and are not intended to be limiting in any way.

[0046] This shows Fig. 1 a schematic representation of a first embodiment of an alignment device according to the invention in a misaligned position, Fig. 2 a schematic representation of a first embodiment of an alignment device according to the invention in an adjusted position, Fig. 3 a schematic representation of a second embodiment of an alignment device according to the invention with a fluorescent surface, Fig. 4 a schematic representation of a third embodiment of an alignment device with sensor according to the invention, Fig. 5 a schematic flowchart of an alignment method according to the invention.

[0047] Fig. Figure 1 shows a schematic diagram of a fiber-optic Michelson interferometer misaligned by an angle α, with an alignment device (as an example of a device for relative coarse adjustment) according to a first embodiment. For the sake of simplicity, a beam splitter cube is used in the example, comprising two prisms 101 and 10'1, where one of the surfaces 51 resulting from the intersection of the prisms has a partially transparent property and acts as a beam splitter. Instead of the cube, for example, a diagonally positioned glass plate (with or without a coating – depending on the wavelength of the light to be split) could also be used. Of course, the object 71 can be arbitrarily misaligned. The misalignment by the angle α is only used because it is easier to represent than a multidimensional misalignment.

[0048] In this example, a 2x2 coupler 31 is used to couple the light from a laser diode "LD" 11—or another light source—on the left side of the beam splitter cube shown in the diagram. After passing through two paths within the beam splitter cube, the light is coupled back into the fiber 111 and directed to a detector 121, such as a photodiode PD, which can then measure the interferences or intensities. It should be noted that many alternative approaches can be used instead of the 2x2 coupler 31. The specific coupling and uncoupling process is irrelevant to the inventive concept.

[0049] In the Fig. On the left side of the beam splitter cube, the collimated light beam 131 from the light source 11, exiting the fiber 111 via one or more lenses 41, is coupled out so that the light beam strikes the diagonally arranged beam splitter 51 inside the beam splitter cube. Part of the light is directed onto a reference mirror 61, which is fixed relative to the beam splitter 51. From there, the beam is reflected back onto the beam splitter 51, so that a portion of it again strikes the area of ​​the original light coupling on the left side of the beam splitter cube. A portion of the light beam reflected by the reference mirror 61 (reference reflection beam) passes through the beam splitter 51 and strikes a matte but translucent surface 81 (as an example of a detection surface) located opposite the reference mirror 61.Since the matte surface 81 scatters the light beam, if visible light is used, a luminous point or spot 91 can already be seen on the matte surface with the naked eye, which remains stationary regardless of the orientation of the object 71.

[0050] Of the light beam 131 originally introduced into the beam splitter cube, a portion passes through the diagonal beam splitter 51 (namely the object beam) and strikes the reflective surface of the object 71 to be aligned, moved, or measured. From there, the light is reflected (as the object reflection beam) and strikes the beam splitter 51 again, so that a portion returns to the side of the original light output. Re-coupling into the fiber 111 only occurs if the object 71 is correctly aligned. Fig. In the case shown, the beam is not coupled into fiber 111 due to the misalignment of object 71. Part of the light reflected by object 71 is also reflected by the beam splitter 51 onto the frosted surface 81. Due to the misalignment, this beam can be seen as a second point 9'1 on the frosted surface 81. This second point 9'1 moves on the frosted surface 81 as the orientation of the object 71 to be moved or measured changes. If the angle α of the misalignment is reduced, point 9'1 moves towards point 91. In order to achieve a "sufficiently good" alignment, in which the beams that hit the surface of the original light output to the left of the beam splitter cube also couple into fiber 111 so that their interference can be measured with detector 121, the object to be moved or measured must be adjusted accordingly.The object 71 to be measured only needs to be aligned so that points 91 and 9'1 are at least partially aligned. Once this is achieved, further fine-tuning can be carried out directly using the interferometer's measurement signals, if necessary.

[0051] Due to the visible "wandering" of point 9'1 on the matte surface 81, the effect of changing the orientation of object 71 is very easy to see if the matte surface 81 is designed and arranged in such a way that the user can see or measure the matte surface 81 during adjustment.

[0052] Fig. Figure 2 shows a schematic representation of a first embodiment of an alignment device according to the invention with a sufficiently well-aligned object 71. Points 91 and 9'1 are aligned one above the other, so that it is ensured that the rays which are to interfere with each other are coupled into the fiber 111.

[0053] Fig. Figure 3 shows a schematic representation of a second embodiment of the alignment device according to the invention. The structure is similar to the first embodiment. Instead of a matte surface, a fluorescent surface 83 (as another example of a detection surface) is provided, which is locally excited to luminescence when the light beams of the interferometer strike it, so that luminous spots or points appear: firstly, point 93, whose position is independent of the orientation of the object 71, and secondly, point 9'3, which moves with the orientation of the object 71. These points 93 and 9'3 are again sufficiently aligned when the object 71 is well aligned, as described in connection with Fig. 1 and Fig. 2. The fluorescent surface should be selected so that it is excited to luminescence by light with the wavelength of the interferometer. This eliminates the need for a pilot laser operating in the visible range, as the luminous points 93 and 9'3, which need to be aligned, are very easy to see. This is particularly helpful if the alignment process is to be carried out manually or using sensors that are not sensitive in the wavelength range of the interferometer.

[0054] Fig. Figure 4 shows a schematic representation of a third embodiment of the alignment device according to the invention. In this case, the points on the surface 84 are detected by a sensor 144. Various sensors can be used. One example is a CCD chip that can detect the position of the points. This allows for particularly simple automation of the alignment process. However, other sensors are also conceivable, up to and including complex cameras. When using sensors, depending on the choice of sensor 144, it is not absolutely necessary for the surface 84 to be matte or fluorescent, since some sensors can also directly detect the incident light. In this case, the sensors themselves can take over the function of the detection surface.

[0055] Fig. Figure 5 shows a schematic flowchart of an alignment method according to the invention.

[0056] The alignment procedure 100 comprises the following steps: Relative alignment 110 of a movable object with a reflective surface to a measuring head of a laser interferometer with integrated beam splitter and

[0057] Illuminate 120 with a light beam passing through the beam splitter, which is reflected from the surface of the movable object, so that the beam subsequently hits the beam splitter again, where part of the light beam hits a surface that also hits the part of the light beam that was reflected from the stationary reference mirror and passed through the beam splitter.

[0058] Visualization of 130 of the light rays striking the surface, either by scattering 140 of the light rays on the surface, by giving that surface a matte, translucent finish, or by fluorescence 150 in the areas of the surface where the light rays hit, by using materials that are stimulated to glow by the light rays, or by using a sensor that is sensitive in the wavelength range of light rays, so that the surface is not necessarily required, or combination 170 of all or parts of the steps from 140 to 160.

[0059] Subsequently, the spots or points are approximated by targeted changes in the position of the object or the measuring head by 180 degrees until the points are aligned.

[0060] Following step 180, further optimization 190 of the position of the moving object or the measuring head can be performed using the now available sensitive signals from the laser interferometer. Subsequently, the moving object can be moved (200) any number of times along the beam direction, while the laser interferometer regularly measures the distance of the displacement (210).

[0061] In one embodiment of the invention, a device is provided for the relative adjustment of a measuring head to a movable mirror or reflective object, the displacement of which is to be measured by the fiber-optic laser interferometer, wherein at least two light beams, of the originally at least one light beam which is split into several light beams by the beam splitter, are directed onto a surface where these are visualized by suitable means in the form of spots or points, wherein at least one of the spots or points is not influenced by the position of the movable mirror, while the second spot or point is not.The point moves when the orientation of the movable mirror on the surface is changed, so that a sufficiently good pre-adjustment of the mirror can be achieved by changing the position of the movable mirror so that at least one moving spot is aligned with the stationary spot, which is an indicator that the interferometer is able to perform measurements.

[0062] Preferably, the fiber optic laser interferometer is specifically a sinusoidally phase-modulated fiber optic laser interferometer.

[0063] In one embodiment, the surface on which the points of impact of the rays are visualized is part of a beam splitter cube comprising the beam splitter, wherein a stationary reference mirror is preferably also part of the beam splitter cube.

[0064] In one embodiment of the invention, the means for visualizing the points where the light rays hit the surface consists in the surface being designed to be matte and translucent, so that the light rays are scattered when they hit the surface, so that the points of impact appear as luminous spots or points when a light with wavelengths in the visible range or in the detectable range is selected.

[0065] In an alternative or supplementary variant, the means of visualizing the points where the light rays hit the surface consists in designing the surface in such a way that it is locally stimulated to fluoresce when one or more rays locally hit the surface.

[0066] With a suitable embodiment, the invention allows the spots produced on the surface by the light rays to be observed with the eye while the position of the movable mirror is changed to bring the spots into alignment.

[0067] It is also possible to observe the spots created on the surface by the light rays with a sensor while changing the position of the movable mirror to align the spots.

[0068] Another possibility is to observe the spots created on the surface by the light rays with a sensor while changing the position of the movable mirror to align the spots, with the surface being part of the sensor, as is possible with a CCD chip, for example.

[0069] Within the scope of the invention, it is particularly provided that when using a sensor to detect the position of the spots on the surface, an algorithm for automatically covering the spots is used and / or that when using a sensor to detect the position of the spots on the surface, an analog control loop for automatically covering the spots is used.

[0070] In one embodiment, the invention relates to a method for aligning the movable or measured object with a reflective surface within a fiber-optic laser interferometer, comprising the following steps: Relative alignment of a movable object with a reflective surface to a measuring head of a laser interferometer with an integrated beam splitter and illumination with a light beam passing through the beam splitter, which is reflected from the surface of the movable object, so that the beam subsequently hits the beam splitter again, where part of the light beam hits a surface that is also hit by the part of the light beam that is reflected from a stationary reference mirror and passes through the beam splitter;Visualization of the points of impact of light rays striking the surface, either by scattering the light rays on the surface by giving it a matte, translucent finish, or by fluorescence in the areas of the surface where the light rays strike, by using materials that are locally excited to glow by the locally striking light rays, or by using a sensor sensitive to the wavelength range of the light rays, thus eliminating the need for a matte or fluorescent surface; observation of the movement of the visualized points of impact, either visually and / or by a sensor, during targeted changes in the position of the movable object to be aligned; concealment of the visualized points of impact by adjusting the correct position of the movable object with a reflective surface;and optional further optimization of the position of the moving object with a reflective surface using the measurement data from the fiber optic laser interferometer.

Claims

[1] Device for the relative coarse adjustment of a measuring head of a fiber optic laser interferometer and a reflective object to be measured, comprising: a beam splitter designed to split at least one light beam into a reference beam directed towards a reference mirror and an object beam directed towards the object to be measured, a detection surface that enables detection a) an object reflection beam reflected from the object to the beam splitter and b) of a reference reflective beam and / or the reference beam reflected from the reference mirror to the beam splitter, wherein the detection surface is arranged so that it is opposite either a reference mirror or an object to be measured, but not the measuring head where A) the beam splitter is part of a beam splitter cube and one surface of the beam splitter cube is provided with the detection surface, and / or B) the detection surface is designed to be photoluminescent, in particular fluorescent, and can be excited by the reference reflection beam and the object reference beam to emit light with at least one wavelength in the range of 380 nm to 780 nm from the respective point of impact. [2] Device according to claim 1, wherein the detection surface is designed for scattering of the reference reflex beam and the object reflex beam, so that the points of impact of the reference reflex beam and the object reflex beam on the detection surface are recognizable. [3] Device according to aspect B) of claim 1 or claim 2, comprising a photosensitive sensor for detecting the points of impact of the reference reflective beam and the object reflective beam on the detection surface. [4] Device according to claim 1, wherein the detection surface is designed as a photosensitive sensor with spatial resolution. [5] Fiber optic laser interferometer, in particular sinusoidal phase-modulated fiber optic laser interferometer, comprising: a measuring head a reference mirror and a device for coarse adjustment according to one of claims 1 to 4, where either the object to be measured or the reference mirror is opposite the detection surface of the device. [6] Laser interferometer according to claim 5, wherein the measuring head is designed to use a laser beam in a first wavelength range, in particular in the wavelength range of 1,200 nm to 1,650 nm, and to selectively emit a pilot laser beam parallel to the laser beam in a wavelength range of 380 nm to 780 nm. [7] Method for coarsely adjusting a fiber optic laser interferometer to a reflective object to be measured, in particular a laser interferometer according to claims 5 and 6, comprising the steps: Provision of a measuring head, a reference mirror and a beam splitter for the interferometer, wherein the beam splitter is designed to split at least one light beam from the measuring head into a reference beam directed towards a reference mirror and an object beam directed towards the object to be measured, the provision also includes the provision of a detection area that enables detection a) an object reflection beam reflected from the object to the beam splitter and b) of a reference reflective beam and / or the reference beam reflected from the reference mirror to the beam splitter, Arrange the measuring head, the detection surface, the reference mirror, the beam splitter and the object to be measured in such a way that the detection surface and the measuring head are not opposite each other, Direction of at least one light beam from the measuring head into the beam splitter, Capturing the object's reflection beam using the detection surface, Capturing the reference reflex beam using the detection surface and at least a rough adjustment of the relative arrangement of the laser interferometer and the object to be measured, using the results of the acquisition steps, preferably by overlapping the light rays made visible on the detection surface, where A) the beam splitter is part of a beam splitter cube and one surface of the beam splitter cube is provided with the detection surface, and / or B) the detection surface is designed to be photoluminescent, in particular fluorescent, and can be excited by the reference reflection beam and the object reference beam to emit light with at least one wavelength in the range of 380 nm to 780 nm from the respective point of impact.

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