CN103454249B - Based on optical glass homogeneity detection method and the device of white light interference - Google Patents

Abstract

The invention discloses a method and a device for detecting the uniformity of optical glass based on white light interference. The device includes a white light interferometer and two dual-frequency laser feedback displacement measurement systems, and the two dual-frequency laser feedback displacement measurement systems and the white light interferometer are linked structures, combining the two dual-frequency laser feedback displacement measurement systems with the white light interferometer One-piece structure for mobile scanning. The detection method is: calibrate the white light interferometer to obtain the proportional coefficient of the optical path difference and the fringe offset; obtain the optical path difference change introduced by the optical glass to be tested, and use the displacement measurement system to measure the same measured position of the optical glass to be tested According to the optical path difference obtained by the white light interferometer and the thickness deviation obtained by the displacement measurement system, the refractive index deviation of the optical glass to be tested is determined; the entire optical glass to be tested is scanned to complete the uniformity detection of the optical glass to be tested. The invention has high precision and low cost for detecting the uniformity of optical glass, and the testing process is simple and convenient.

Description

Optical glass uniformity detection method and device based on white light interference

technical field

The invention belongs to the technical field of light interference measurement, in particular to a method and device for detecting the uniformity of optical glass based on white light interference.

Background technique

The uniformity of optical glass refers to the inconsistency of the refractive index inside the material, which can affect the imaging quality of the optical system and is one of the important indicators to measure the quality of optical glass processing. At present, the interferometer is mainly used to measure the uniformity of optical glass. The difference is that the means of eliminating the surface error of optical glass are different:

One method is to improve the measurement accuracy by using the mounting board. A pair of high-precision parallel flat plates are used as the mounting plates, and the refractive index liquid is pasted on both sides of the measured optical glass to eliminate the influence of the measured glass surface shape on the uniformity measurement. However, due to the high processing cost of large-size mounting plates and the difficulty in loading and unloading, it is not suitable for the uniformity testing of large-diameter flat glass. Generally, small-size mounting plates are used for splicing measurements in different areas, but this method needs to be used in the measurement process. Constantly moving the position of the mounting plate to measure different areas of the glass, resulting in cumbersome measurement steps and difficult to guarantee accuracy.

Another method is the absolute measurement method. Place the optical glass between the reference mirrors, measure the wave surface data including uniformity information, optical glass surface information and reference mirror shape information, and then measure the reference mirror shape and optical glass surface shape separately, combined with several interferometric measurements The wavefront data eliminates the influence of reference mirror shape and optical glass surface shape on uniformity measurement. This method requires the use of a high-precision reference mirror to assist measurement, especially when measuring large-diameter optical glass, a large-diameter interferometer equipped with a large-diameter reference mirror must be used, and the manufacturing cost of a large-diameter interferometer is very high, resulting in the cost of this measurement method. too high.

Contents of the invention

The object of the present invention is to provide a high-precision, low-cost optical glass uniformity detection method and device based on white light interference.

The technical solution to achieve the purpose of the present invention is: a method for detecting the uniformity of optical glass based on white light interference, using a white light interferometer to measure the optical path difference change introduced by the optical glass to be tested, and using a dual-frequency laser feedback displacement measurement system to measure the optical path difference to be tested. Measure the thickness deviation of the optical glass, and combine these two measurement data to detect the uniformity of the optical glass to be tested. The specific steps are as follows:

Step 1. Calibrate the white light interferometer: Use a monochromatic LED and two identical compensating mirrors to calibrate the white light interferometer to obtain the proportional coefficient C between the optical path difference and the fringe offset. Replace the monochromatic LED with a white light source, and The central stripe is adjusted to the zero position of the scale x ₀ ;

Step 2. Obtain the change in optical path difference introduced by the optical glass to be tested: After replacing the compensating mirror in the test optical path of the white light interferometer with the optical glass to be tested, the optical glass to be tested is obtained according to the offset Δx of the central fringe of the white light interferometer The optical path difference Λ introduced by the measured position, and the thickness deviation Δd of the same measured position of the optical glass to be measured is measured by a dual-frequency laser feedback displacement measurement system;

Step 3. Determine the refractive index deviation of the measured position of the optical glass to be tested: through the optical path difference Λ obtained by the white light interferometer at the same measured position and the thickness deviation Δd obtained by the displacement measurement system, determine the deviation of the measured position of the optical glass to be measured Refractive index deviation Δn _e ;

Step 4. Change the measured position of the optical glass to be tested, and repeat steps 2 to 3 until the entire optical glass to be tested is scanned to complete the uniformity detection of the optical glass to be tested.

An optical glass uniformity detection device based on white light interference, including a white light interferometer and two dual-frequency laser feedback displacement measurement systems; the white light interferometer adopts a Michelson interferometer structure, including light sources arranged coaxially along the optical path direction , collimating objective lens, beam splitter, first compensation mirror, first reflecting mirror, optical glass to be tested, second reflecting mirror, imaging objective lens, CCD, signal processing system, wherein the light source is located at the focus position of the collimating objective lens, the first compensating The mirror, the first reflector, the optical glass to be tested, and the second reflector are respectively perpendicular to their respective optical axes, the signal processing system is connected to the CCD, and all optical components are coaxial with the substrate at the same height, that is, relative to the optical platform or instrument The base is coaxial and equal in height; the two dual-frequency laser feedback displacement measurement systems are coaxially arranged on both sides of the optical glass to be tested, and the emitted light of the two dual-frequency laser feedback displacement measurement systems is vertically incident on the optical glass to be tested. glass surface.

Compared with the prior art, the present invention has the following remarkable advantages: (1) the interferometer uses short-coherent white light as the light source, which can effectively reduce the interference of reflected light from other surfaces in the optical path system; (2) it does not need to manufacture high-precision stickers A high-precision reference mirror with a built-in board or a larger diameter reduces the test requirements and test costs; (3) The test process is simple, easy to adjust, and has low environmental requirements, making the test easier to implement.

Description of drawings

Fig. 1 is a schematic diagram of the optical glass to be tested in the present invention, wherein (a) is a circular optical glass to be tested, and (b) is a rectangular optical glass to be tested.

Fig. 2 is a schematic structural diagram of an optical glass uniformity detection device based on white light interference of the present invention.

Fig. 3 is a schematic diagram of a white light interferometer in the optical glass uniformity detection device based on white light interference of the present invention.

Fig. 4 is a schematic diagram of measuring the local thickness deviation of the optical glass to be measured by the dual-frequency laser feedback displacement measurement system of the present invention.

FIG. 5 is a schematic diagram of the interference light path of the white light interferometer in FIG. 3 .

Figure 6 is the interferogram collected by the CCD during the process of calibrating the interferometer, where (a) is the interferogram when a monochromatic LED is used, and (b) is the interferogram when a white light source is used.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

The principle of the present invention is as follows: the amount of change in the optical path difference in the optical glass uniformity detection device is a comprehensive reflection of the optical glass uniformity and local thickness, and satisfies the following conditions:

Λ=(n _e +Δn _e )(d+Δd)

In the formula, Λ is the optical path difference, d is the reference thickness of the optical glass to be tested, _ne is the refractive index of the white light source passing through the optical glass to be tested, Δd is the local thickness deviation of the front and rear surfaces of the optical glass to be tested at a certain position, Δn _e is the refractive index deviation at this position. Therefore, knowing the reference thickness d and the refractive index _ne of the optical glass to be tested, and determining the optical path difference Λ while measuring the local thickness deviation Δd, the uniformity measurement of the optical glass to be tested can be realized.

The method for detecting the uniformity of optical glass based on white light interference in the present invention uses a white light interferometer to measure the optical path difference variation introduced by the optical glass to be tested, and uses a dual-frequency laser feedback displacement measurement system to measure the thickness deviation of the optical glass to be tested. Two measurement data are used to detect the uniformity of the optical glass to be tested. The specific steps are as follows:

Step 1. Calibrate the white light interferometer: Use a monochromatic LED and two identical compensating mirrors to calibrate the white light interferometer to obtain the proportional coefficient C between the optical path difference and the fringe offset. Replace the monochromatic LED with a white light source, and The central stripe is adjusted to the zero position of the scale x ₀ ;

Step 2. Obtain the change in optical path difference introduced by the optical glass to be tested: After replacing the compensating mirror in the test optical path of the white light interferometer with the optical glass to be tested, the optical glass to be tested is obtained according to the offset Δx of the central fringe of the white light interferometer The optical path difference Λ introduced by the measured position, and using the dual-frequency laser feedback displacement measurement system to measure the thickness deviation Δd of the same measured position of the optical glass to be tested; the specific formula of the optical path difference Λ is as follows:

Λ=Δx·C

Among them, C is the proportional coefficient between the optical path difference and the fringe offset obtained by the calibration in step 1, and Δx is the offset of the central fringe position x ₁ of the white light interferometer relative to the scale zero position x ₀ in step 2, that is, Δx=x ₁ -x ₀ ;

Step 3. Determine the refractive index deviation of the measured position of the optical glass to be tested: through the optical path difference Λ obtained by the white light interferometer at the same measured position and the thickness deviation Δd obtained by the displacement measurement system, determine the deviation of the measured position of the optical glass to be measured Refractive index deviation _Δne , the formula is as follows:

${\mathrm{<span\; class="notranslate">\; \&Delta;\; n</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}$

Among them, d is the reference thickness of the optical glass to be tested, and _ne is the refractive index of the white light source passing through the optical glass to be tested.

Step 4. Change the measured position of the optical glass to be tested, and repeat steps 2 to 3 until the entire optical glass to be tested is scanned to complete the uniformity detection of the optical glass to be tested.

Referring to Figure 1, the optical glass to be tested is a circular or rectangular optical glass plate, and its surface is close to a plane after rough grinding and fine grinding.

In conjunction with Fig. 2, the optical glass uniformity detection device based on white light interference of the present invention includes a white light interferometer and two dual-frequency laser feedback displacement measurement systems, and the two dual-frequency laser feedback displacement measurement systems and the white light interferometer are linked structures , combining two dual-frequency laser feedback displacement measurement systems and a white light interferometer into an integrated structure for mobile scanning. 3, the white light interferometer adopts a Michelson interferometer structure, including a light source 1, a collimating objective lens 2, a beam splitter 3, a first compensating mirror 4, a first reflecting mirror 5, a waiting Measuring optical glass 6, second reflecting mirror 7, imaging objective lens 8, CCD 9, signal processing system 10, wherein light source 1 is positioned at the focus position of collimating objective lens 2, first compensating mirror 4, first reflecting mirror 5, optical glass to be measured 6. The second mirrors 7 are respectively perpendicular to their respective optical axes, the signal processing system 10 is connected to the CCD9, and all optical elements are coaxially equal to the base, that is, coaxially equal to the optical platform or the instrument base; combined with the figure 4. The two dual-frequency laser feedback displacement measurement systems are coaxially arranged on both sides of the optical glass 6 to be tested, and the emitted light of the two dual-frequency laser feedback displacement measurement systems is vertically incident on the surface of the optical glass 6 to be tested. . The glass plate to be tested in the figure is the optical glass 6 to be tested.

In conjunction with FIG. 5, the optical path of the white light interferometer is as follows: the white light emitted from the light source 1 passes through the collimating objective lens 2, and enters the beam splitter 3 in the form of parallel light; the beam splitter 3 divides the optical path into two beams perpendicular to each other: The path of light that is incident on the first compensating mirror 4 and reflected back to the beam splitter 3 by the first mirror 5 is called the reference light path, and is incident on the optical glass 6 to be tested and reflected back to the beam splitter 3 by the second mirror 7 The light is called the test light path; the test light reflected by the beam splitter 3 and the reference light transmitted by the beam splitter 3 converge on the target surface of the CCD9 through the imaging objective lens 8 and interfere. During the test, the first reflector 5 and its plane perpendicular to the optical axis are set at an angle θ, where θ satisfies the following formula:

$\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; tan</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}\frac{{\mathrm{<span\; class="notranslate">\; n\&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; D.</span>}}$

In the formula, n is the number of interference fringes on the entire surface of the optical glass to be tested and n=5-10, λ _e is the equivalent wavelength of the white light source, and D is the diameter or width of the optical glass to be tested.

The present invention will be further described in detail below in conjunction with specific embodiments.

Example 1

The present invention combines the white light interferometry and the displacement sensor measurement method to scan and detect the method for the uniformity of the glass plate shown in Fig. 1, comprising the following steps:

Step 1: First calibrate the white light interferometer. After installing and adjusting the instruments as shown in Figure 2, use a monochromatic LED as the light source of the interferometer with a wavelength of λ, and place a standard compensation mirror at the position of the glass plate to be tested in Figure 2 for calibration; as shown in the figure 5, adjust the front and rear positions of the standard compensation mirror and the first compensation mirror 4 in the optical path, so that the reflected light r ₁ and r ₂ '/r ₃ ', r ₂ and r ₁ '/r ₂ '/r ₃ ', The optical path difference between r ₃ and r ₁ '/r ₂ '/r ₃ ' is not zero, then r ₁ and r ₂ '/r ₃ ', r ₂ and r ₁ '/r ₂ '/r ₃ ', There will be no interference between r ₃ and r ₁ '/r ₂ '/r ₃ '. At this time, the interferogram and scale readings of r ₁ and r ₁ ' are obtained in the CCD, as shown in Figure 6(a). Read out on the dial that there are N fringes within the length range of ΔL, then find the proportional coefficient of the optical path difference Λ and the fringe offset Δx:

$\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; L</span>}}$

Replace the white light source and obtain a new interferogram in the CCD, as shown in Figure 6(b). At this time, read the position of the central fringe from the scale on the monitor, that is, the zero position of the scale x ₀ .

Step 2: Replace the standard compensating mirror in the test optical path with the optical glass to be tested as the glass plate to be tested. The center of the interference fringe deviates from the position of the starting point. Read the position x ₁ of the center fringe at this time, and the fringe offset Δx=x ₁ -x ₀ , then the optical path difference Λ is:

Λ=Δx·C

At the same time, use a dual-frequency laser feedback displacement measurement system to obtain the local thickness deviation Δd of the front and rear surfaces of the optical glass to be tested at the same position: Referring to Figure 4, each dual-frequency laser feedback displacement measurement system uses two detectors to detect two frequency lasers respectively The light intensity is determined by the interference superposition of the inner cavity laser and the outer cavity laser. The orthogonal dual-frequency laser emitted by it is reflected by the surface of the measured glass plate and returns to the inside of the laser, thus establishing two resonant cavities inside and outside, and using the optical feedback effect to convert the displacement change into a light intensity change. Every half-wavelength movement of the measured target corresponds to a cycle of light intensity change. It uses a non-contact measurement method, which can accurately and quickly obtain the radial displacement of the measured point, that is, the local thickness deviation of the measured glass plate, with an accuracy better than 20nm.

Step 3: Determine the refractive index deviation of the measured position of the optical glass to be tested: through the optical path difference Λ obtained by the white light interferometer at the same measured position and the thickness deviation Δd obtained by the displacement measurement system, determine the deviation of the measured position of the optical glass to be tested Refractive index deviation _Δne , the formula is as follows:

${\mathrm{<span\; class="notranslate">\; \&Delta;\; n</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}$

Among them, d is the reference thickness of the optical glass to be tested, and _ne is the refractive index of the white light source passing through the optical glass to be tested.

Step 4: The scanning arm drives the entire system to scan, changing the measured position of the optical glass to be tested, sampling and measuring in real time during the scanning process, and repeating steps 2 and 3 until the entire measurement is completed, thus obtaining all measured parallel flat glass The deviation of the refractive index of the point, so as to obtain the information of the glass uniformity.

In summary, the present invention is based on white light interference optical glass uniformity detection method and device, in which the interferometer uses short-coherent white light as the light source, which can effectively reduce the interference of reflected light from other surfaces in the optical system; and does not require high-precision manufacturing The mounting board or the large-diameter high-precision reference mirror reduces the test requirements and test costs; the test process is simple, the adjustment is convenient, and the requirements for the environment are low, making the test easier to implement.

Claims (6)

1. the optical glass homogeneity detection method based on white light interference, it is characterized in that: use white light interferometer to measure the optical path difference variable quantity of optical glass to be measured introducing, and adopt double-frequency laser displacement measuring system to measure the thickness deviation of optical glass to be measured, in conjunction with the homogeneity of these two measurement test optical glass to be measured, concrete steps are as follows:

Step 1, demarcation white light interferometer: use the monochromatic LED compensating glass identical with two panels to demarcate white light interferometer, obtain the scale-up factor C of optical path difference and fringes shift amount, change monochromatic LED into white light source, center striped is adjusted to scale zero-bit x ₀;

Step 2, obtain optical glass to be measured introduce optical path difference variable quantity: after the compensating glass in white light interferometer optical system for testing is replaced with optical glass to be measured, obtain the optical path difference Λ introduced optical glass measured position to be measured according to the offset Δ x of white light interferometer center striped, and use double-frequency laser displacement measuring system to record the thickness deviation Δ d of the same measured position of optical glass to be measured;

Step 3, determine the refractive index deviation of optical glass measured position to be measured: the thickness deviation Δ d that the optical path difference Λ obtained by same measured position white light interferometer and displacement measurement system are obtained, determine the refractive index deviation delta n of this measured position of optical glass to be measured _e;

Step 4, change the measured position of optical glass to be measured, repeat step 2 ~ 3, until scan whole optical glass to be measured, the homogeneity completing optical glass to be measured detects.

2. the optical glass homogeneity detection method based on white light interference according to claim 1, it is characterized in that: obtain the optical path difference Λ introduced optical glass measured position to be measured described in step 2 according to the side-play amount of white light interferometer center striped, concrete formula is as follows:

Λ＝Δx·C

Wherein, C is the scale-up factor that step 1 demarcates optical path difference and the fringes shift amount obtained, and Δ x is step 2 white light interferometer center fringe position x ₁relative to scale zero-bit x ₀side-play amount, i.e. Δ x=x ₁-x ₀.

3. the optical glass homogeneity detection method based on white light interference according to claim 1, is characterized in that: the refractive index deviation delta n determining this measured position of optical glass to be measured described in step 3 _e, formula is as follows:

${\mathrm{\&Delta;n}}_e=\frac{\mathrm{\&Lambda;}}{d+\mathrm{\&Delta;d}}-n_e$

Wherein, d is the reference thickness of optical glass to be measured, n _efor white light source is by the refractive index of optical glass to be measured.

4. based on an optical glass homogeneity pick-up unit for white light interference, it is characterized in that: comprise white light interferometer and two double-frequency laser displacement measuring systems, described white light interferometer adopts Michelson interferometer structure, comprise light source (1), collimator objective (2), spectroscope (3), first compensating glass (4), first catoptron (5), optical glass to be measured (6), second catoptron (7), image-forming objective lens (8), CCD (9), signal processing system (10), wherein light source (1) is positioned at the focal position of collimator objective (2), first compensating glass (4), first catoptron (5), optical glass to be measured (6), second catoptron (7) optical axis respectively with respective is orthogonal, signal processing system (10) is connected with CCD (9), all optical elements are coaxially contour relative to substrate, namely relative to optical table or instrument base coaxially contour, described two double-frequency laser displacement measuring systems are coaxially arranged at the both sides of optical glass to be measured (6) in opposite directions, and the utilizing emitted light of two double-frequency laser displacement measuring systems is all normally incident in optical glass to be measured (6) surface.

5. the optical glass homogeneity pick-up unit based on white light interference according to claim 4, it is characterized in that: the light path of described white light interferometer trend is: from the white light of light source (1) outgoing through collimator objective (2), incide spectroscope (3) with the form of directional light; Spectroscope (3) is divided into mutually perpendicular two-beam road light path: incide the road light that the first compensating glass (4) reflects back into spectroscope (3) by the first catoptron (5) and call reference path, incides the road light that optical glass to be measured (6) reflects back into spectroscope (3) by the second catoptron (7) and is called optical system for testing; The test light reflected by spectroscope (3) and the target surface being converged in CCD (9) by the reference light of spectroscope (3) transmission through image-forming objective lens (8) interfere.

6. the optical glass homogeneity pick-up unit based on white light interference according to claim 4, it is characterized in that: two described double-frequency laser displacement measuring systems and white light interferometer are serial verb construction, the formula structure that two double-frequency laser displacement measuring systems and white light interferometer is combined as a whole carries out motion scan.