Interference line spectrum confocal measurement structure

Abstract

The invention provides an interference line spectrum confocal measurement structure, which comprises a line light source, a beam splitter prism, a dispersion prism, a dispersion objective lens and a spectrum demodulation module, and is characterized in that the line light source is used for generating a strip-shaped narrow light source, the beam splitter prism is a polarization insensitive prism, and the strip-shaped light source is equally divided into two mutually vertical light paths; the strip-shaped light is then subjected to off-axis dispersion by the dispersion prism and is axially dispersed by the dispersion objective lens, finally an irradiation surface perpendicular to the horizontal direction is formed, the illumination surfaces of the two light paths interfere with each other and are enhanced, and the strip-shaped light returns along the symmetrical light paths and enters the spectrum demodulation system; the spectrum demodulation system is composed of the dispersion prism and the dispersion objective lens, high linearity of the height and the position can be achieved, meanwhile, the device can conduct high compression on the width of a detection signal, and the measurement precision and repeatability of the device can be improved at the same time.

Description

Technical Field

[0001] The present invention relates to the field of ultra-precision measurement, and mainly to an interference spectrum confocal measurement structure. Background Art

[0002] Optical microscopes are widely used in the field of industrial measurement due to their non-contact and non-destructive advantages. With the rapid development of precision manufacturing, the demand for high-precision detection is increasing. Spectral confocal sensors are the most commonly used sensors. The broad spectrum light source is focused to different positions through a dispersive objective lens, and spectral demodulation is used to achieve fast, high-precision displacement and thickness measurement without axial scanning.

[0003] In order to balance resolution and light source utilization, existing spectral confocal sensors mostly use light with a diameter of tens of microns as light guides. This makes the confocal structure less able to suppress defocused light, causing the detected spectral signal to become wider, thereby resulting in a decrease in measurement accuracy. At the same time, the wider spectral signal also makes it easier for spectral signals to overlap when measuring the thickness of transparent samples, making it difficult to measure thinner samples.

[0004] To solve the above problems, traditional technologies are to improve the measurement accuracy by improving the accuracy of the peak extraction algorithm and use the peak separation algorithm to achieve small thickness measurement. These algorithms are effective only under certain conditions, such as high signal-to-noise ratio and good signal peak shape, which limits the further development of spectral confocal technology. Therefore, it is necessary to improve the spectral confocal structure from the hardware perspective and enhance its measurement capabilities. Summary of the invention

[0005] The object of the present invention is to provide a high-precision coherence line spectrum confocal measuring device capable of measuring extremely small thickness.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a coherent line spectrum confocal measurement device, comprising a line light source, a beam splitter prism, a dispersion prism, a dispersion objective lens, and a spectrum demodulation module distributed in sequence along a vertical optical path, wherein the line light source is used to generate a strip light source, the beam splitter prism separates the light source with equal intensity into two vertical optical paths, the dispersion prism disperses the wide spectrum light source along the off-axis, the dispersion objective lens disperses the wide spectrum light along the axial direction and receives light from another optical path to ensure that the focused light interference near the focus is enhanced and the defocused light interference is destructive, and the spectrum demodulation device is responsible for dispersing the return light to different detector positions.

[0007] Further, the line light source is a wide spectrum light source, and its bandwidth can be determined by a broadband filter. The line-shaped light is generated by a linear array LED light source through a slit. The linear light source can also be generated by collimating a point light source and then passing through a cylindrical mirror.

[0008] Further, the linear light is collimated by a collimator in a direction perpendicular to the linear light, and the collimated light is incident on the beam splitter prism in a parallel manner;

[0009] Furthermore, the beam splitter prism divides the collimated light into two light paths, and the angle between the two light paths is 90 degrees;

[0010] Furthermore, a reflector is included between the beam splitter prism and the dispersion prism, and the number of the reflectors is two, and each of the reflectors reflects the collimated light to the pupil of the dispersion objective lens;

[0011] Furthermore, the center line of the dispersion prism forms a certain angle with the axis of the dispersion objective lens, so as to ensure that the center wavelength coincides with the axis of the objective lens after passing through the dispersion objective lens;

[0012] Furthermore, the number of the dispersive objective lenses is two, the axes of the two dispersive objective lenses are perpendicular to each other, and the focal lengths thereof are greater than half of the aperture;

[0013] Further, the measuring device comprises two optical paths, and the optical path difference from the light source to the focal point of the objective lens of the two optical paths is exactly the same;

[0014] Furthermore, the spectral demodulation system comprises a slit, a collimating mirror, a reflecting mirror, a dispersion prism, a dispersion objective lens, and a detector, and the components of the spectral demodulation system are completely consistent with the components described above.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. The present invention uses two mutually perpendicular illumination and detection light paths to enhance the coherence of illumination on the illumination surface and the detection surface, thereby suppressing the defocused light, thereby compressing the width of the detected spectral signal, which is beneficial to the subsequent signal peak extraction and effectively improves the measurement accuracy;

[0017] 2. Since the width of the detected spectral signal is greatly compressed, the peak values ​​of the two spectral signals can be extracted at a smaller interval, so that the device can measure smaller thickness;

[0018] 3. The present invention uses exactly the same structure in the design of the illumination optical path and the spectrum demodulation optical path, so that each part of the device can be reused, reducing the device processing cost and the difficulty of system assembly and adjustment;

[0019] 4. The spectral demodulation part uses the same design as the illumination optical path, which ensures a high correlation between the illumination point and the detection point, and effectively improves the linearity of the measurement device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic structural diagram of an interference line spectrum confocal measurement device in an embodiment of the present invention.

[0021] Figure 2 Schematic diagram of the illumination surface of the dispersion prism and dispersion objective lens on the object surface.

[0022] Figure 3 This is the spectral distribution diagram of the traditional spectral confocal detection signal.

[0023] Figure 4 This is a spectrum distribution diagram of a detection signal of a correlation line spectrum confocal measurement device of the present invention.

[0024] Figure 5 The figure is a light path design diagram for the lighting light path of the invented device.

[0025] Figure 6 This is a diagram of the focused light spots when the optical path working wavelength is 530nm.

[0026] Figure 7 This is a diagram of the focused light spots when the optical path working wavelength is 560nm.

[0027] Figure 8 This is a diagram of the focused light spots when the optical path working wavelength is 590nm. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0030] The invention discloses a coherent spectrum confocal measuring device for displacement and thickness measurement, and can realize three-dimensional profile measurement in cooperation with a lateral scanning platform.

[0031] See also Figure 1 , is a schematic structural diagram of a coherent spectral confocal measurement device of the present invention, the measurement device comprises two illumination optical path modules and a spectral demodulation module, and the three modules have the same structure.

[0032] The left illumination light path module includes linear light 1, collimator 2, beam splitter prism 3, reflector 4, dispersion prism 5 and dispersion objective lens 6. The right illumination light path module includes linear light 1, collimator 2, beam splitter prism 3, reflector 9, dispersion prism 8 and dispersion objective lens 7. The spectrum illumination module includes slit 11, collimator 12, reflector 13, dispersion prism 14, dispersion objective lens 15 and detector 16. The three modules are connected together through dispersion prism 3.

[0033] When the device is used for measurement, the line light source 1 is first collimated by the collimator 2, and then equally divided by the beam splitter 3 to the reflector 4 and the reflector 9. After being reflected by the reflector 4 and the reflector 9, the line light source 1 passes through the dispersion prism 5, the dispersion objective lens 6 and the dispersion prism 8, the dispersion objective lens 7 respectively, and the two light paths are simultaneously focused on a symmetric plane to form coherence enhancement.

[0034] See also Figure 2 After the parallel light passes through the dispersion prism 5 and the dispersion objective lens 6, the light with wavelengths of λ1, λ2, and λ3 are focused at different positions on the symmetry plane respectively. The illumination mirror groups of the two optical paths are symmetrically distributed and collect the light from the symmetrical optical paths respectively.

[0035] The reflected light passes through the dispersion objective lens 6, dispersion prism 5, reflecting mirror 4 and the dispersion objective lens 7, dispersion prism 8, reflecting mirror 9, and is respectively transmitted and reflected by the beam splitter 3, and then is focused by the condenser 10 to the slit 11, and then is collimated by the collimator 12, reflected by the reflecting mirror 13, enters the dispersion prism 14, dispersion objective lens 15, and is finally detected by the detector 16.

[0036] refer to Figure 3 and Figure 4 For a specific plane, the intensity distribution of the detected light after coherent suppression is as follows: Figure 4 As shown, compared with the traditional Figure 3 The intensity distribution shown is extremely compressed.

[0037] Preferred Figure 5 is the parameter form of the collimator 2, the dispersion prism 5, and the dispersion objective lens 6, and each optical element satisfies the following table:

[0038]

[0039]

[0040] Table 1 Lighting module optical device parameters

[0041] Wherein, R is the radius of curvature of the lens surface, T is the air gap, and Nd is the refractive index of the lens at wavelength d. The working distance of the dispersion lens is 16.5 mm, and the terminal aperture is 12 mm. The preferred working wavelengths are the design wavelengths of 530 nm, 560 nm, and 590 nm. Figure 6 , Figure 7 , Figure 8 They are the point diagrams for working wavelengths of 530nm, 560nm and 590nm respectively. It can be seen from the figures that all the focused spots reach the diffraction limit, can meet the coherence requirements, and have good imaging quality.

[0042] In summary, the interference line spectrum confocal measurement structure of the present invention splits the linear light into two optical paths, and uses a dispersion prism and a dispersion objective lens to perform off-axis axial dispersion respectively, so that the light of the two optical paths forms a stable coherent enhancement on the symmetry plane, and the return light is also coherently enhanced in the detector, effectively suppressing the out-of-focus light, compressing the signal width, and achieving higher linearity and measurement accuracy.

Claims

1. An interference line spectrum confocal measurement structure, characterized in that: The interference line spectrum confocal structure includes two illumination light path modules and a spectrum demodulation module, each illumination module includes linear light, a collimator, a reflector, a dispersion prism, and a dispersion objective lens, and the spectrum demodulation module includes a slit, a collimator, a reflector, a dispersion prism, and a dispersion objective lens. The linear light is formed by a linear array LED through a slit, collimated by a collimator, and then equally divided into two illumination modules by a beam splitter prism, and is focused on a symmetric plane after being dispersed off-axis and axially by a dispersion prism and a dispersion objective lens to form interference enhancement. The reflected light is collected by a dispersion objective lens and a dispersion prism, and is focused on a slit through a focusing lens, and enters the spectrum demodulation module and is uniformly imaged to a detector through a dispersion prism and a dispersion objective lens, thereby achieving interference enhancement of the focused light and interference suppression of the defocused light, and ultimately improving the measurement accuracy and resolution of the system.

2. The interferometric spectroscopy confocal measurement structure according to claim 1, characterized in that: There are two illumination light path modules, one spectrum demodulation module, and the device parameter structures of the three modules are completely consistent.

3. The interferometric spectroscopy confocal measurement structure according to claim 1, characterized in that: The two illumination optical path modules and the spectrum demodulation module are connected together through a beam splitter prism, and the beam splitting ratio of the beam splitter prism is 50:

50.

4. The interferometric spectroscopy confocal measurement structure according to claim 1, characterized in that: The two illumination optical path modules focus the light onto the symmetric plane through a dispersion prism and a dispersion objective lens to form interference enhancement.

5. The interferometric spectroscopy confocal measurement structure according to claim 4, characterized in that: The illumination light paths are at a certain angle to each other, preferably 90 degrees.

6. The interferometric spectroscopy confocal measurement structure according to claim 4, characterized in that: The illumination optical path module also includes linear light, a collimator, a reflector, a dispersion prism, and a dispersion objective lens.

7. An interference spectrum confocal measurement structure according to claim 4, characterized in that: The product of the off-axis dispersion angle of the dispersion prism in the illumination optical path module and the focal length of the dispersion objective lens and the axial dispersion ratio of the dispersion objective lens is close to 1:

1.

8. The interferometric spectroscopy confocal measurement structure according to claim 4, characterized in that: The mirror in the illumination optical path module can be fine-tuned to ensure that the central wavelength passes through the center line of the objective lens.

9. An interference spectrum confocal measurement structure according to claim 1, characterized in that: The spectrum demodulation module comprises a slit, a collimating mirror, a dispersion prism, a dispersion objective lens and a detector.

10. The interferometric spectroscopy confocal measurement structure according to claim 1, characterized in that: The detector in the spectrum demodulation module forms a certain angle with the central wavelength optical axis, preferably 45 degrees.

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