A method for interferometric angle calibration under oblique incidence

Abstract

The present invention discloses a method for calibrating interference angles under oblique incidence, because the accuracy of the incident angle is directly related to the measurement accuracy. Especially in the case of large-angle oblique incidence (grazing incidence), a slight angle change will cause a large fluctuation in the result. Therefore, the present invention designs a calibrated prism standard, assisted by a high-precision angle alignment method based on interference, to achieve second-level incident angle calibration. The calibration method of the present invention only needs to be calibrated when the measuring instrument is first installed. Its principle is to calibrate and fix the angle between the grazing incident light beam and the reflected light beam, which has nothing to do with the measured object. During the sample measurement process, only the interference fringes of the measured object are adjusted to meet the requirements, and the incident angle can meet the requirements at the same time.

Description

Technical Field

[0001] The invention belongs to the field of optical measurement, and in particular relates to an interference angle calibration method under oblique incidence. Background Art

[0002] Plane surface detection is one of the essential basic technologies in the field of precision machining and optical manufacturing. The demand for detecting large components such as large-aperture optical flat crystals and large-aperture precision ceramic discs is growing. In the field of industrial production, contact measurement is usually used to detect the flatness of components, but it will cause certain damage to the sample surface. Optical interferometry is widely used due to its non-contact, sensitivity, accuracy and measurement speed advantages.

[0003] Compared with normal incidence measurement, oblique incidence interferometry has the following advantages: first, the oblique incidence angle can be selected to determine the corresponding detection sensitivity and expand the dynamic measurement range; second, oblique incidence can widen the detection aperture; third, the light beam is incident on the surface to be measured at an oblique incidence angle, and the reflectivity is improved compared with normal incidence, so low reflectivity surfaces and rough surfaces can be detected.

[0004] In oblique incidence measurement, the interference scale factor is different from 0.5 for normal incidence. It is related to the incident angle and is k = 1 / 2cos(θ), where k is the interference scale factor and θ is the oblique incidence angle. In the case of grazing incidence, a small angle change will cause a large fluctuation in the scale factor. For this reason, the incident angle needs to be accurately measured (calibrated) or calibrated to a specific angle value.

[0005] Han Linpei introduced two methods of angle calibration in the article "A Single Section Flatness Absolute Detection Method Based on Oblique Incidence". One is to obtain the angle through the graduation method, such as designing an adjustment frame with a degree plate to obtain the precise angle; the other is to use the imaging method to calculate the length of the measured plane on the x-axis based on the measurement data to obtain the incident angle. However, both methods have their own shortcomings. The graduation method can obtain precise angles, but it is expensive; the imaging method will increase errors due to pixel values ​​and image recognition, so it is difficult to obtain results with 10nm level accuracy. Summary of the invention

[0006] The invention proposes an interference angle calibration method under oblique incidence, and uses an angle standard to calibrate the incident angle.

[0007] The technical solution to realize the present invention is: a method for interferometric angle calibration under oblique incidence, the steps are as follows:

[0008] Step 1: Build an oblique-incidence interferometry system:

[0009] The oblique-incidence interference measurement system comprises an angle standard, an interferometer and a high-reflection mirror.

[0010] Step 2: Place the angle standard between the interferometer and the high reflector. The interferometer and the high reflector are respectively tilted and mounted by brackets. The angle standard and the two brackets are placed on a horizontal platform.

[0011] Step 3: Adjust the position of the prism so that the light beam forms interference fringes on the incident hypotenuse surface of the angle standard and minimizes the interference fringes.

[0012] Step 4: Continue to adjust the position of the prism so that the light beam reflected by the bottom surface of the prism is irradiated onto the high reflector, and adjust the two-dimensional tilt and pitch of the high reflector so that the light beam returns to the original path, interference fringes appear, and the interference fringes are minimized.

[0013] Step 5: Fix the angle position of the interferometer and the high reflector, and the calibration is completed.

[0014] Compared with the prior art calibration method, the calibration method has high calibration accuracy, low cost and can remain stable over a long period of time. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a diagram of the standard device components of the oblique incidence measuring device of the present invention.

[0016] Figure 2 This is a basic structural diagram of the present invention for interference angle calibration under oblique incidence.

[0017] Figure 3 This is the result diagram of the angle calibration method. DETAILED DESCRIPTION

[0018] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation" and the like should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; "connection" can be a mechanical connection or an electrical connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0019] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0020] The following will further introduce the specific implementation method, as well as the technical difficulties and inventive points of this invention in combination with this design example.

[0021] A method for interferometric angle calibration under oblique incidence, the steps are as follows:

[0022] Step 1: Build an oblique-incidence interferometry system:

[0023] Combination Figure 2 The oblique-incidence interferometry measurement system comprises an angle standard 1, an interferometer 2 and a high-reflection mirror 3.

[0024] The angle standard 1 is a trapezoidal prism, the top and bottom surfaces of which are rectangular, the length of the top surface is shorter than the length of the bottom surface, and the other four surfaces are all isosceles trapezoids, the areas of the left and right side surfaces are equal, the areas of the front and rear side surfaces are equal, and the area of ​​the left side surface is smaller than the area of ​​the front side surface. The right side surface is used as the incident bevel surface 1.1, the left side surface is used as the exit bevel surface 1.3, and the bottom surface is used as the total internal reflection long side bottom surface 1.2. The incident bevel surface 1.1, the total internal reflection long side bottom surface 1.2 and the exit bevel surface 1.3 constitute polished surfaces, and the top surface and the front and rear side surfaces do not need to be light-transmissive and can be frosted.

[0025] The angle between the incident bevel surface 1.1 and the total internal reflection long side bottom surface 1.2 is assumed to be the oblique incident angle θ.

[0026] Interferometer 2 adopts a dynamic interferometer.

[0027] Step 2: Place the angle standard 1 between the interferometer 2 and the high reflector 3. The interferometer 2 and the high reflector 3 are respectively tilted and mounted through adjustment frames. The angle standard 1 and the two adjustment frames are placed on a horizontal platform.

[0028] Step 3: Adjust the position of the prism so that the light beam forms interference fringes through the incident hypotenuse surface 1.1, and the interference fringes are minimized.

[0029] Step 4: Continue to adjust the position of the prism so that the light beam reflected by the bottom surface 1.2 of the prism irradiates the high reflector 3, and adjust the two-dimensional tilt and pitch of the high reflector 3 to produce interference fringes and minimize the interference fringes.

[0030] Step 5: Fix the interferometer 1 and the high reflective mirror 3, and the calibration is completed.

[0031] Embodiment 1:

[0032] Angle standard 1 accuracy: ±1', oblique incident angle θ is set to 85°, and the dimensions are 150mm (length L) × 50mm (height H) × 100mm (width W). The interference coefficient accuracy after angle calibration is approximately ±0.5.

[0033] The interferometer 2 used is a dynamic interferometer, and the beam exit aperture is Φ150 mm; the high reflective mirror 3 has a size of Φ180 mm×20 mm, and a reflectivity of R=98%@632.8 nm.

[0034] Combination Figure 1-2 The interference angle calibration method under grazing incidence of the present invention comprises the following steps:

[0035] Step 1: According to Figure 2 , build the oblique-incidence interferometry measurement system on the experimental platform, and turn on the power of interferometer 2 to make it enter normal working state.

[0036] Step 2: Place the angle standard 1 on the platform (between the interferometer 2 and the high reflector 3) along the optical axis, align the incident bevel surface 1.1 with the light outlet of the beam expander in the dynamic interferometer 2, and align the exit bevel surface 1.3 with the high reflector 3.

[0037] Step 3: Manually adjust the position of the angle standard 1 so that the reflected beam of the incident bevel surface 1.1 returns to the perforated light screen at the focus of the beam expander in the interferometer 2 and enters the hole. Observe the software's point display and continue to adjust the position of the angle standard 1 so that the reflected beam moves to the center of the cross scale of the point display. At this time, an interference pattern will appear in the software window. Fine-tune the inclination and rotation of the two adjustment frames of the interferometer 2 and the high reflector 3 to minimize the interference pattern fringes.

[0038] Step 4: Release the fixing screws on the adjustment frame of the high reflector 3 to make fine adjustments, and adjust its two-dimensional tilt / pitch, so as to change the relative position of the angle standard 1, so that its bottom surface 1.2 can return the light beam reflected on the high reflector 3 along the original optical path to the interferometer 2. At this time, superimposed interference fringes appear in the interference pattern, and continue to fine-tune the adjustment frame of the high reflector 3 to minimize the fringes.

[0039] Step 5: Lock the adjustment frame of the high reflective mirror 3 and the dynamic interferometer 2. During the locking process, the number of fringes needs to be kept stable. The final calibration result is as follows: Figure 3 As shown, the number of interference fringes is the least, and the angle calibration is completed.

Claims

1. A method for interferometric angle calibration under oblique incidence, characterized in that: Here are the steps: Step 1: Build an oblique-incidence interferometry system: The oblique-incidence interferometric measurement system comprises an angle standard (1), an interferometer (2) and a high-reflection mirror (3); The angle standard (1) is a trapezoidal prism, the top and bottom surfaces of which are rectangular, the length of the top surface is shorter than the length of the bottom surface, the remaining four surfaces are all isosceles trapezoids, the areas of the left and right side surfaces are equal, the areas of the front and rear side surfaces are equal, and the area of ​​the left side surface is smaller than the area of ​​the front side surface; Step 2: placing the angle standard (1) between the interferometer (2) and the high reflector (3); the interferometer (2) and the high reflector (3) are respectively tilted and mounted by brackets; and the angle standard (1) and the two brackets are placed on a horizontal platform; Step 3, adjusting the position of the prism so that the light beam forms interference fringes through the incident hypotenuse surface of the angle standard (1), and the interference fringes are minimized; Step 4, continue to adjust the position of the prism so that the light beam reflected by the bottom surface of the prism is irradiated onto the high reflector (3), and adjust the two-dimensional tilt and pitch of the high reflector (3) so that the light beam returns to the original path, interference fringes appear, and the interference fringes are minimized; Step 5: Fix the angle positions of the interferometer (2) and the high reflector (3) to complete the calibration.

2. The interference angle calibration method under oblique incidence according to claim 1, characterized in that: The right side surface is used as the incident bevel surface (1.1), the left side surface is used as the exit bevel surface (1.3), and the bottom surface is used as the total internal reflection long side bottom surface (1.2). The incident bevel surface (1.1), the total internal reflection long side bottom surface (1.2) and the exit bevel surface (1.3) constitute a polished surface. The top surface and the front and rear side surfaces do not need to be light-transmissive and can be frosted. The angle between the incident bevel surface (1.1) and the total internal reflection long side bottom surface (1.2) is set as the oblique incident angle .

3. The interference angle calibration method under oblique incidence according to claim 1, characterized in that: The interferometer (2) adopts a dynamic interferometer.

Images