A confocal measurement structure for interference line spectrum

Abstract

The present invention provides an interference line spectrum confocal measurement structure, including a line light source, a spectroscopic prism, a dispersion prism, a dispersion objective lens, and a spectrum demodulation module. The line light source is used to generate a strip narrow light source. The spectroscopic prism is a polarization-insensitive prism, which divides the strip light source into two mutually perpendicular light paths. The strip light is then dispersed off-axis by the dispersion prism and axially by the dispersion objective lens, ultimately forming an illumination surface perpendicular to the horizontal. The illumination surfaces of the two light paths interfere with each other and enhance each other, and then return along the symmetrical light path again and enter the spectrum demodulation system. The spectrum demodulation system is composed of the dispersion prism and the dispersion objective lens, and can achieve high linearity in height and position. At the same time, the device can highly compress the detection signal width, thereby improving the measurement accuracy and repeatability of the device.

Description

Technical Field

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

[0002] Optical microscopes are widely used in industrial measurement due to their non-contact and non-destructive properties. With the rapid development of precision manufacturing, the demand for high-precision inspection is increasing. Spectral confocal sensors are a common sensor. They focus a broad spectrum light source onto different locations using a dispersive objective lens, and spectral demodulation enables rapid, high-precision displacement and thickness measurement without axial scanning.

[0003] In order to strike a balance between resolution and light source utilization, existing spectral confocal sensors mostly use light with a diameter of tens of microns as light-guiding devices. This makes the confocal structure less able to suppress off-focus light, causing the detected spectral signal to become wider, thereby reducing 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 address these issues, conventional techniques have employed methods such as increasing the accuracy of peak extraction algorithms to improve measurement accuracy and using peak separation algorithms to achieve smaller thickness measurements. These algorithms are only effective under specific conditions, such as a high signal-to-noise ratio and a well-defined peak shape. This limits the further development of spectral confocal technology. Therefore, it is necessary to improve the spectral confocal structure from a hardware perspective to enhance its measurement capabilities. Summary of the Invention

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

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solution: a coherent line spectrum confocal measurement device, comprising a line light source, a spectroscopic prism, a dispersive prism, a dispersive 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 spectroscopic prism separates the light source with equal intensity into two vertical optical paths, the dispersive prism disperses the wide-spectrum light source along the off-axis, the dispersive objective lens disperses the wide-spectrum light along the axial direction and receives light from another optical path, ensuring that the focused light interference near the focus is enhanced and the defocused light interference is cancelled, and the spectrum demodulation device is responsible for dispersing the return light to different detector positions.

[0007] Furthermore, the line light source is a broad spectrum light source, the bandwidth of which can be determined by a broadband filter. The line-shaped light is generated by a linear array LED light source passing 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] Furthermore, 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 reflecting mirror is included between the beam splitter prism and the dispersive prism, and there are two reflecting mirrors, each of which reflects the collimated light to the pupil of the dispersive objective lens;

[0011] Furthermore, the center line of the dispersion prism forms a certain angle with the axis of the dispersion objective lens, ensuring that the center wavelength coincides with the axial direction 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] Furthermore, the measuring device comprises two optical paths, and the optical path difference between the two optical paths from the light source to the focal point of the objective lens is exactly the same;

[0014] Furthermore, the spectral demodulation system includes a slit, a collimating mirror, a reflecting mirror, a dispersion prism, a dispersion objective lens, and a detector. The components of the spectral demodulation system are exactly the same as those 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 detection surface, thereby suppressing off-focus light. This compresses the width of the detected spectral signal, facilitates subsequent signal peak extraction, and effectively improves 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, thus enabling the device to measure smaller thicknesses;

[0018] 3. The present invention uses identical structures in the design of the illumination optical path and the spectral demodulation optical path, allowing each component to be reused, reducing component processing costs and system assembly difficulty;

[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 the 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 of the lighting light path of the invention 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 clearly and completely described 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 this specification of the present invention 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 conjunction with a transverse scanning stage.

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

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

[0033] When using this device 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, it passes through the dispersion prism 5 dispersion objective lens 6 and the dispersion prism 8 dispersion objective lens 7 respectively. The two light paths are simultaneously focused on a symmetrical plane to form coherence enhancement.

[0034] See 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 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 collimated by the collimator 12, reflected by the 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 dispersive prism 5, and the dispersive objective lens 6. Each optical element satisfies the following table:

[0038]

[0039]

[0040] Table 1 Parameters of optical components of lighting module

[0041] Where 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 end aperture is 12 mm. The preferred operating wavelengths are the design wavelengths of 530 nm, 560 nm, and 590 nm. Figure 6 、 Figure 7 、 Figure 8 The point diagrams are 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 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 by: An interference line spectrum confocal measurement structure includes two illumination light path modules and a spectrum demodulation module. Each illumination module includes a linear light, a collimator, a reflector, a dispersion prism, and a dispersion objective lens. 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 by a beam splitter to two illumination modules. After being dispersed off-axis and axially by a dispersion prism and a dispersion objective lens, it is focused on a symmetric plane to form interference enhancement. The reflected light is dispersed by a dispersion objective lens. The light is collected by the optical microscope and the dispersion prism and focused on the slit by the focusing mirror, and enters the spectral demodulation module and is uniformly imaged to the detector through the dispersion prism and the dispersion objective lens, thereby enhancing the interference of the focused light and suppressing the interference of the defocused light, and ultimately improving the measurement accuracy and resolution of the system. There are two illumination optical path modules and one spectral demodulation module. The device parameter structures of the three modules are completely consistent. The two illumination optical path modules and the spectral demodulation module are connected together through a beam splitter prism, and the splitting ratio of the beam splitter prism is 50:

50.

2. The interferometer line spectrum confocal measurement structure according to claim 1, characterized in that: The two illumination light path modules focus light onto a symmetric plane through a dispersion prism and a dispersion objective lens to form interference enhancement.

3. The interference line spectrum confocal measurement structure according to claim 2, characterized in that: The illumination light paths form an angle of 90 degrees with each other.

4. The interference line spectrum confocal measurement structure according to claim 2, characterized in that: The illumination light path module further includes linear light, a collimating mirror, a reflecting mirror, a dispersion prism, and a dispersion objective lens.

5. The interference line spectrum confocal measurement structure according to claim 2, 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.

6. The interference line spectrum confocal measurement structure according to claim 2, characterized in that: The dispersion prism in the illumination light path module can be fine-tuned to ensure that the central wavelength passes through the center line of the objective lens.

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

8. The interference line spectrum confocal measurement structure according to claim 1, characterized in that: The detector in the spectrum demodulation module forms an angle of 45 degrees with the central wavelength optical axis.

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