A picometer measurement system and method based on picometer optical comb

Abstract

The invention discloses a picometer measurement system and method based on a picometer light comb. The measurement method process is as follows: light emitted by a laser is divided into two beams of light through a beam splitter, and each beam of light sequentially passes through a reflector, a microscope objective lens, a pinhole filter and a collimating lens to generate a collimated and expanded light field; the light field generated by the two beams of light converges on an interference plane to generate an interference field with a period of d; a holographic dry plate is placed on the interference plane for a first exposure; displacement information Δd of the picometer scale is loaded to cause a periodic change in the interference field; the holographic dry plate is exposed for a second time to obtain a picometer light comb. The axial moiré effect of the picometer light comb is utilized: the picometer light comb is irradiated with a collimated and expanded plane wave to generate moiré interference fringes. The moiré interference fringes are collected by a photoelectric detector, and the moiré interference fringes are calculated. Finally, the picometer scale information Δd to be measured is inversely deduced by a formula.

Description

Technical Field

[0001] The present invention relates to the technical field of picometer measurement, and in particular to a picometer measurement system and method based on a picometer optical comb. Background Art

[0002] With the rapid development of the precision machining industry, the machining accuracy has reached the nanometer level. For example, the chip manufacturing process has been advanced to the 1nm level. Therefore, the required measurement resolution has also increased accordingly, reaching the picometer level. Laser interferometer is a widely used displacement measurement device, but for picometer-level displacement information, it is very difficult to manufacture a picometer-level laser interferometer. It requires the most advanced optical, mechanical and electronic technologies, as well as extremely high environmental requirements, and precise control of factors such as temperature, humidity, and air cleanliness. In addition, picometer-level laser interferometers are also susceptible to laser wavelength drift, measurement platform isolation factors, and other factors. Therefore, it is necessary to seek other picometer-level displacement measurement methods.

[0003] Zhou Changhe et al. [Prior technology 1: C. Zhou, comb, picometer fabrication apparatus and method, Chinese Patent CN 110187424 A[P](2019)] first proposed and manufactured a picometer comb and observed the axial moiré interference effect of the picometer comb. It was found that the period of the moiré interference fringes generated by the picometer comb after being irradiated by a plane wave is inversely proportional to the period difference between the two exposures of the picometer comb, which is very suitable for small-scale displacement information measurement. Summary of the invention

[0004] The first purpose of the present invention is to solve the above-mentioned defects in the prior art and to provide a picometer measurement system and method based on a picometer optical comb, which avoids the high investment in manufacturing picometer-level laser interferometers while ensuring the accuracy of the measurement and greatly reducing the cost of the measurement system.

[0005] Another object of the present invention is to provide a method for implementing measurement using the above system.

[0006] The first object of the present invention can be achieved by adopting the following technical solutions:

[0007] A picometer measurement system based on a picometer light comb, the picometer measurement system comprising: a laser 1, a beam splitter 2, a reflector 3, a microscope objective 4, a pinhole filter 5, a collimating lens 6, a holographic dry plate 7, a photodetector 8, and a computer 9; wherein the laser 1 emits a laser beam which is split into two beams of light through the beam splitter 2, and the two beams of light are controlled at an angle by the reflector 3 so that the two beams of light can converge on a plane to form a double-beam exposure system. Each beam of light is filtered and collimated and expanded in turn through the microscope objective 4, the pinhole filter 5, and the collimating lens 6, and converges on an interference plane to generate interference fringes, the holographic dry plate 7 is set on the interference plane for the first exposure, and then the displacement information of the picometer scale is loaded on the interference field to cause periodic changes; the holographic dry plate 7 is exposed for the second time, and at this time, a picometer light comb is formed on the holographic dry plate 7;

[0008] The light beam emitted by the laser 1 passes through the microscope objective 4, the pinhole filter 5, and the collimating lens 6 in sequence to form a collimated and expanded plane wave to illuminate the picometer light comb on the holographic dry plate 7. Due to the axial moiré effect, moiré interference fringes are generated along the propagation direction of the light beam; the moiré interference fringes are collected by the photoelectric detector 8 and transmitted to the computer 9 to calculate the period of the moiré interference fringes, and the displacement information of the picometer scale is obtained according to the formula.

[0009] Furthermore, the power of the laser 1 determines the maximum detection distance of the moiré interference fringes.

[0010] Furthermore, the light beam emitted by the laser 1 is incident on the beam splitter 2. The beam splitter is a semi-transparent and semi-reflective mirror, which can evenly split the laser beam emitted by the laser 1 into two beams propagating in different directions, one of which passes through the beam splitter 2 and propagates in the transmission direction, and the other is reflected by the beam splitter 2 and propagates in the reflection direction.

[0011] Furthermore, the two light beams generated by the beam splitter 2 are reflected by the reflector 3 and converged on the interference plane. The reflector has an adjustment knob, which can fine-tune the deflection direction of the reflector and can be used to control the angle between the two light beams, thereby controlling the period d of the interference field.

[0012] Furthermore, the holographic dry plate 7 is a substrate coated with photoresist, and the substrate 7 is placed on an interference plane for exposure to record interference field information.

[0013] Furthermore, the picometer light comb is formed by exposing the holographic dry plate 7 twice and then developing, fixing and baking. Since the periods of the two exposures differ by picometers, the periods of the interference fields of the two exposures need to be measured with picometer accuracy.

[0014] Furthermore, the interference fringes generated by the picometer light comb on the holographic dry plate 7 after being irradiated by the laser beam are caused by the axial moiré interference effect. The picometer light comb is formed by two interference fields with a small period difference, and can therefore be regarded as two very close slits. When the laser beam irradiates the two slits, the overlapping part of the diffracted light fields of the two slits will produce an interference area due to the small distance between the two slits, and the moiré interference fringes propagate along the diffraction direction. Therefore, the diffraction effect of the picometer light comb is called the axial moiré effect.

[0015] Furthermore, the moiré interference fringes generated by the picometer light comb on the holographic dry plate 7 are obtained by the following formula:

[0016] Assume that the reference light can be expressed as The target beams for the first exposure and the second exposure are expressed as and When two exposures are made, two target beams are recorded on the hologram. O2(x,y) and reference beam The interference field after interference is generated:

[0017]

[0018]

[0019] Where R(x, y), O1(x, y), and O2(x, y) represent the intensities of the reference light, the first exposure, and the second exposure target light, respectively. represents the phase of the reference beam, the target beam of the first and second exposures, and x and y represent the positions of the abscissa and ordinate, respectively, during the propagation of the beam;

[0020] Therefore, the light field recorded by the picometer light comb is:

[0021]

[0022] In the formula is the background light intensity, and the last term is the phase information of the interference field. The light field periods of the two exposures differ by △d. Because △d is controlled by the incident angle of the target light beam, there is an angle difference △θ between the two exposures. △θ is a very small angle, so the phase difference between the two exposure fields is Very small, then This means that when the picometer light comb is irradiated by a laser beam, a series of moiré interference fringes with a large period will be generated due to the axial moiré effect. This is conducive to the collection and calculation of moiré interference fringes.

[0023] Furthermore, the moiré interference fringes have the characteristics of strong stability and high contrast, which is conducive to measuring and calculating the period of the fringes.

[0024] Furthermore, the period T of the axial moiré interference fringes generated by the picometer light comb on the holographic dry plate 7 is defined by the following formula:

[0025]

[0026] Where d is the exposure interference field period during the first exposure, and △d is the difference in the light field period between the two exposures.

[0027] Furthermore, the period T of the Moire interference fringes is inversely proportional to the difference △d between the periods of two exposures. When the loaded displacement △d is smaller, the period T of the Moire interference fringes is larger, and the sensitivity of the measurement system is higher.

[0028] Another object of the present invention can be achieved by adopting the following technical solutions:

[0029] A measurement method of a picometer measurement system based on a picometer optical comb comprises the following steps:

[0030] S1, laser 1 emits a laser beam which is split into two beams by beam splitter 2, and the two beams are controlled at an angle by reflector 3 so that the two beams can converge onto a plane;

[0031] S2, the two beams of light pass through the microscope objective 4, the pinhole filter 5, and the collimating lens 6 in sequence to form a collimated and expanded plane wave, which converges on the interference plane to produce interference fringes with a period of d;

[0032] S3, placing the holographic dry plate 7 on the interference plane for the first exposure;

[0033] S4, adjusting the angle between the two beams of light by controlling the reflector 3 to load picometer-scale displacement information Δd on the interference field, so that the interference field period changes to d+Δd;

[0034] S5, placing the holographic dry plate 7 on the interference plane for a second exposure, and then developing, fixing, and baking, so that a picometer light comb is formed on the holographic dry plate 7;

[0035] S6, the light beam emitted by the laser 1 passes through the microscope objective 4, the pinhole filter 5 and the collimating lens 6 in sequence to form a collimated and expanded plane wave to illuminate the picometer light comb on the holographic dry plate 7, generating moiré interference fringes;

[0036] S7, collecting the moiré interference fringes through the photoelectric detector 8, transmitting them to the computer 9 to calculate the period T of the moiré interference fringes;

[0037] S8, according to the formula Calculate the displacement information Δd of the picometer scale to be measured.

[0038] Compared with the prior art, the present invention has the following advantages and effects:

[0039] 1. The optical path structure required for the picometer measurement system based on the picometer optical comb disclosed in the present invention is simple and convenient for debugging. The various devices required are common in the market and low in cost.

[0040] 2. Due to the relationship between the period T of the moiré interference fringes in the axial moiré interference effect and the displacement Δd of the load: It can be seen that the displacement Δd is inversely proportional to the period T of the moiré interference fringes. When the displacement Δd is in the picometer level, the period T reaches the millimeter level, which is easy to detect. Therefore, the measurement method based on this principle is very suitable for picometer-scale measurements. The smaller the measured displacement, the higher the sensitivity of the measurement system. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0042] Figure 1 is a schematic diagram of making a picometer light comb in the present invention;

[0043] Figure 2 is a schematic diagram of measuring the moiré interference fringes generated by the picometer light comb in the present invention;

[0044] Figure 3 It is the test principle diagram of the present invention;

[0045] Figure 4 is a schematic diagram of the moiré interference fringes collected by the photoelectric detector in the present invention;

[0046] Figure 5 It is a schematic diagram of the moiré interference field fringes calculated in the computer in the present invention. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution 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 part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] Example 1

[0049] This embodiment discloses a picometer measurement system based on a picometer light comb. Figure 1 is a schematic diagram of making a picometer light comb in this embodiment, Figure 2The schematic diagram of measuring the moiré interference fringes generated by the picometer light comb in the present invention. A picometer measurement system based on the picometer light comb comprises: a laser 1, a beam splitter 2, a reflector 3, a microscope objective 4, a pinhole filter 5, a collimating lens 6, a holographic dry plate 7, a photodetector 8, and a computer 9; wherein the laser beam emitted by the laser 1 is divided into two beams of light by the beam splitter 2, and the two beams of light are controlled at an angle by the reflector 3 so that the two beams of light can converge on a plane to form a double-beam exposure system. Each beam of light is filtered and collimated and expanded by the microscope objective 4, the pinhole filter 5, and the collimating lens 6 in turn, and converges on the interference plane to generate interference fringes with a period of d. The holographic dry plate 7 is set on the interference plane for the first exposure, and then the displacement information Δd of the picometer scale is loaded on the interference field by the fine-tuning reflector 3 to cause a period change, and the period of the interference fringes becomes d+Δd, and the holographic dry plate 7 is exposed for the second time, and at this time, a picometer light comb is formed on the holographic dry plate 7;

[0050] The light beam emitted by the laser 1 passes through the microscope objective 4, the pinhole filter 5, and the collimating lens 6 in sequence to form a collimated and expanded plane wave to illuminate the picometer light comb on the holographic dry plate 7. Figure 3 The test principle diagram of the present invention is as follows. According to the axial moiré effect of the picometer light comb, moiré interference fringes are generated along the propagation direction of the light beam. The moiré interference fringes are collected by the photoelectric detector 8 and transmitted to the computer 9 to calculate the period T of the moiré interference fringes. According to the formula Obtain picometer-scale displacement information.

[0051] Example 2

[0052] This embodiment discloses a method for performing picometer measurement using a picometer measurement system based on a picometer optical comb, comprising the following steps:

[0053] S1. Use laser 1 to emit a laser beam which is split into two beams through beam splitter 2. The two beams are controlled at an angle by reflector 3 so that the two beams can converge on a plane. Each beam is filtered and collimated and expanded by microscope objective 4, pinhole filter 5, and collimating lens 6 in turn, and converges on the interference plane to generate an initial interference field with a period of d=833.333nm.

[0054] S2. Place the holographic dry plate 7 on the interference plane for the first exposure.

[0055] S3, changing the angle of the double light beams by the reflector 3, so that the interference field fringe period changes by Δd compared with the initial value. Placing the holographic dry plate 7 on the interference plane for the second exposure.

[0056] S4, developing, fixing and baking the holographic dry plate 7 after the double exposure, and then generating a picometer light comb on the holographic dry plate 7.

[0057] S5, the light beam emitted by the laser 1 passes through the microscope objective 4, the pinhole filter 5, and the collimating lens 6 in sequence to form a collimated and expanded plane wave to illuminate the picometer light comb on the holographic dry plate 7. Due to the axial moiré effect of the picometer light comb, moiré interference fringes are generated along the propagation direction of the light beam. The photodetector 8 collects the Figure 4 Moire interference fringes shown.

[0058] S6, transmitting the collected moiré interference fringes to the computer 9 to calculate the period T of the moiré interference fringes, Figure 5 Schematic diagram of the moiré interference fringes calculated by computer, and the period T of the moiré interference fringes is calculated.

[0059] S7. Substitute the period T of the moiré interference fringes and the period d of the interference field during the first exposure into the formula Finally, the picometer-scale displacement Δd to be measured is calculated.

[0060] Table 1 shows a series of parameters in this embodiment 2, wherein the period of the first exposure is d=833.333 nm, the picometer scale displacement to be measured is Δd, and the period of the moiré interference fringes is T.

[0061] The displacement Δd on the picometer scale is calculated by the following formula:

[0062]

[0063] Table 1. Comparison of displacement Δd corresponding to the period T of different moiré interference fringes

[0064] T(μm) d(nm) Δd(pm) 3.473 833.333 200 3.859 833.333 180 4.341 833.333 160 4.961 833.333 140 5.788 833.333 120 6.945 833.333 100

[0065] It can be seen from Table 1 that the period T of the measured moiré interference fringes increases rapidly as the displacement Δd to be measured decreases, which means that the sensitivity of the measurement system is very high, that is, for smaller changes, the period of the detected moiré interference fringes becomes more obvious. In summary, the picometer measurement system based on the picometer optical comb disclosed in the above embodiment has a simple structure, convenient measurement and high sensitivity, is very suitable for measuring picometer scale information, and has important application prospects.

[0066] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A picometer measurement system based on a picometer optical comb, characterized in that: The picometer measurement system comprises: a laser (1), a beam splitter (2), a reflector (3), a microscope objective lens (4), a pinhole filter (5), a collimating lens (6), a holographic dry plate (7), a photodetector (8), and a computer (9); wherein the laser (1) emits a laser beam which is split into two beams of light through the beam splitter (2); the two beams of light are controlled at an angle by the reflector (3) so that the two beams of light can converge onto a plane; each beam of light is sequentially converged onto an interference plane through the microscope objective lens (4), the pinhole filter (5), and the collimating lens (6) to generate interference fringes; the holographic dry plate (7) is set on the interference plane for a first exposure, and displacement information of the picometer scale is loaded on the interference field to cause periodic changes; the holographic dry plate (7) is exposed for a second time, and a picometer light comb is formed on the holographic dry plate; The light beam emitted by the laser (1) passes through the microscope objective lens (4), the pinhole filter (5), and the collimating lens (6) in sequence to form a collimated and expanded plane wave to illuminate the picometer light comb on the holographic dry plate (7) to generate moiré interference fringes; the moiré interference fringes are collected by the photoelectric detector (8), transmitted to the computer (9) to calculate the period of the moiré interference fringes, and the displacement information of the picometer scale is obtained according to the formula; the moiré interference fringes generated by the picometer light comb on the holographic dry plate (7) are obtained by the following formula: Assume the reference light is , the target beams for the first exposure and the second exposure are and ;in , , represent the intensities of the reference light, the target light beam for the first and second exposures, respectively. , , represents the phase of the reference beam, the target beam of the first and second exposures, and Respectively represent the positions of the abscissa and ordinate when the light beam propagates; When two exposures are performed, two target beams are recorded on the hologram. , and the reference beam The interference field after interference is generated: Therefore, the light field recorded by the picometer light comb is: In the formula is the background light intensity, and the last item is the phase information of the interference field. The period difference of the light field of the two exposures is ,because It is controlled by the incident angle of the target beam, so there is an angle difference between the two exposures. .

2. The picometer measurement system based on the picometer optical comb according to claim 1, characterized in that: The beam splitter (2) is a semi-transparent and semi-reflective mirror.

3. The picometer measurement system based on the picometer optical comb according to claim 1, characterized in that: The reflector (3) controls the period d of the interference field by controlling the angle between the two beams of light.

4. The picometer measurement system based on the picometer optical comb according to claim 1, characterized in that: The holographic dry plate (7) is a substrate coated with photoresist.

5. The picometer measurement system based on the picometer optical comb according to claim 1, characterized in that: The picometer light comb is formed by double exposure, and is formed after the holographic dry plate (7) is exposed twice and then developed, fixed, and baked. Since the period of the two exposures differs by the picometer level, the period of the interference field of the two exposures needs to be measured with picometer accuracy.

6. The picometer measurement system based on the picometer optical comb according to claim 1, characterized in that: The interference fringes generated by the picometer light comb on the holographic dry plate (7) after being irradiated by the laser beam are due to the axial moiré interference effect.

7. A measurement method of a picometer measurement system based on a picometer optical comb according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. A laser (1) emits a laser beam which is split into two beams by a beam splitter (2). The two beams are controlled at an angle by a reflector (3) so that the two beams converge onto a plane. S2, the two beams of light pass through the microscope objective (4), the pinhole filter (5), and the collimating lens (6) in sequence to form a collimated and expanded plane wave, which converges on the interference plane to generate interference fringes with a period of d; S3, placing the holographic dry plate (7) on the interference plane for the first exposure; S4. By controlling the reflector (3), the angle between the two beams of light is adjusted to load picometer-scale displacement information on the interference field. , so that the interference field period changes to d+ ; S5, placing the holographic dry plate (7) on the interference plane for a second exposure, and then developing, fixing, and baking, so that a picometer light comb is formed on the holographic dry plate (7); S6, the light beam emitted by the laser (1) passes through the microscope objective (4), the pinhole filter (5) and the collimating lens (6) in sequence to form a collimated and expanded plane wave, which illuminates the picometer light comb on the holographic dry plate (7) to generate moiré interference fringes; S7, collecting the moiré interference fringes through the photoelectric detector (8), transmitting the moiré interference fringes to the computer (9) to calculate the period T of the moiré interference fringes; S8, according to the formula Calculate the displacement information of the picometer scale to be measured .

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