CN107450173B - A Mirau-type wide-field interference microscope objective optical system - Google Patents

Abstract

The invention discloses a Mirau type wide-field interference microscope objective optical system. The system comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a reference plate and a light splitting plate which are sequentially arranged along the same optical axis; the illumination light passes through the first lens, the second lens, the third lens, the fourth lens and the fourth lens in sequence, the illumination light is divided into two beams at the light splitting plate, one beam is incident on the surface of the reference flat plate and returns, the other beam is incident on the surface of the piece to be detected and returns, the two beams of emission light are overlapped at the light splitting plate and then interfere, and the microscopic characteristics of the piece to be detected are analyzed according to the generated interference fringes. The system has the magnification of 0.5X, the numerical aperture of 0.015, the diameter of an entrance pupil of 12 mm, the focal length of 400 mm, the parfocal distance of 280 mm and the visual field of 48 mm. The optical system has simple structure and good imaging quality, is suitable for a coherent scanning interferometry, and can be used for measuring the three-dimensional morphology of a rough surface.

Description

A Mirau-type wide-field interference microscope objective optical system

technical field

The invention belongs to the design field of a microscope objective lens optical system, and relates to a Mirau type wide field of view interference microscope objective lens optical system.

Background technique

Interference microscope objectives are mainly used in the measurement of three-dimensional topography of microscopic surfaces. For example, non-contact profilers commonly used in industry and scientific research fields need to be equipped with interference microscope objectives of various magnifications. When the CCD is 2/3" and the tube lens is 1X, the line field of view of 2.5X interference microscope objective is 9.3mm, the line field of 10X interference microscope objective is 0.58mm, and the line field of 20X interference microscope objective is 0.58mm. The field is 0.15mm, the line field of view of the 50X interference microscope objective is 0.023mm, and the line field of view of the 100X interference microscope objective is 0.0009mm. Generally, the lower the magnification, the larger the field of view, so the lower magnification The interference microscope objective usually has a larger field of view. The main structure of the interference microscope objective has three types: Linnik type, Mirau type and Michelson type. The Linnik type occupies a large space and costs due to the need for two completely equal beam splitting prisms. High, generally only used for high-magnification interference microscope objectives.

When the magnification of Mirau is lower than 10X, too much light is blocked due to the existence of central occlusion, which affects the imaging effect. J.F.Biegen gave a speech on "New developments in Mirauinterferometry" at the 1988 Optical Society of America Annual Meeting, and proposed a solution to use polarizing elements to control the amount of light transmitted through the transparent part of the reference plate surface, which is unobstructed Mirau-type objectives. But polarizing elements make the design more complicated, make it more difficult to compensate for dispersion, and also introduce sensitivity issues due to polarization effects.

The low-magnification interference microscope objectives currently produced on the market are mainly Michelson-type interference microscope objectives. However, since the magnification of the microscope objective is smaller and the working distance is larger, when designing an interference microscope objective less than 2X, the Michelson-type structure occupies space due to the orthogonality between the beam splitter prism and the off-axis reference optical path. too large to be practical. In the article "Three-dimensional sensing of roughsurface by coherence radar" published in AO, T. Dresel et al. proposed that when the field of view is larger than 10mm, the mechanical structure of the Michelson-type interference microscope objective lens is too large, so that it can only be used in specific areas. interferometers, and the inflexibility to switch other objectives is not desirable.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a Mirau type wide field of view interference microscope objective lens optical system with simple structure and good imaging quality.

The technical solution to achieve the purpose of the present invention is: a Mirau type wide-field interference microscope objective optical system, comprising a first lens, a second lens, a third lens, and a fourth lens arranged from left to right along the same optical axis , the fifth lens, the sixth lens, the seventh lens, the eighth lens, the reference plate and the beam splitter plate;

The illumination light passes through the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens and the reference plate in sequence, and is divided into two beams at the beam splitter, one is The beam is incident on the surface of the reference plate and returns, and the other beam is incident on the surface of the DUT and returns. The two emitted beams overlap at the beam splitter and interfere, and the microscopic characteristics of the DUT are analyzed according to the generated interference fringes.

Further, the first lens and the second lens are doublet lenses, the third lens and the fourth lens are doublet lenses, and the fifth lens and the sixth lens are doublet lenses.

Further, the diameter of the first lens is 14 mm, the center thickness is 2.5 mm, the left and right surfaces are spherical, the left spherical curvature radius is 27.15 mm, the right spherical curvature radius is -51.30 mm, and the glass grade used is H-BAK2; the diameter of the second lens is 14 mm, the center thickness is 2.0 mm, the left and right surfaces are spherical, the left spherical curvature radius is -51.30 mm, and the right spherical curvature radius is 327.14 mm, the glass used is H -LAK7A; the diameter of the third lens is 12 mm, the center thickness is 2.5 mm, the left and right surfaces are spherical, the left spherical curvature radius is -97.36 mm, and the right spherical curvature radius is -12.30 mm, the glass grade used is H -FK61; the diameter of the fourth lens is 12 mm, the center thickness is 2 mm, the left and right surfaces are spherical, the curvature radius of the left spherical surface is -12.30 mm, and the right spherical curvature radius is -890.55 mm. The glass used is H -ZLAF76; the aperture of the fifth lens is 20 mm, the center thickness is 3 mm, the left and right surfaces are spherical, the left spherical curvature radius is -36.13 mm, the right spherical curvature radius is 21.02 mm, the glass grade used is F6; The diameter of the sixth lens is 20 mm, the center thickness is 4 mm, the left and right surfaces are spherical, the left spherical curvature radius is 21.02 mm, and the right spherical curvature radius is 90.67 mm. The glass used is H-ZBAF4; the seventh lens is H-ZBAF4; The diameter of the lens is 54 mm, the center thickness is 6 mm, the left and right surfaces are spherical, the left spherical curvature radius is -88.51 mm, and the right spherical curvature radius is -44.10 mm. The glass used is H-ZK21; the eighth The diameter of the lens is 58 mm, the center thickness is 6 mm, the left and right surfaces are spherical, the left spherical curvature radius is 232.69 mm, and the right spherical curvature radius is -232.69 mm. The glass used is H-ZF5; the reference plate is A circular optical flat plate with a diameter of 60 mm and a thickness of 8 mm, the glass material used is fused silica; the beam splitter plate is a circular optical flat plate with a diameter of 60 mm and a thickness of 8 mm, and the glass material used is fused silica;

The air space between the second lens and the third lens is 40.2 mm, the air space between the fourth lens and the fifth lens is 31.04 mm, the air space between the sixth lens and the seventh lens is 38.56 mm, and the air space between the seventh lens and the eighth lens is 38.56 mm. The air space between the lenses is 0.2 mm, the air space between the eighth lens and the reference plate is 8 mm, and the air space between the reference plate and the beam splitter is 58 mm.

Further, the inclination angle of the reference plate is 3°.

Further, the surface of the reference plate is coated with a depolarization beam splitting film, and the transmittance and reflectance ratios are 85%:15%.

Further, the surface roughness Ra value of the surface of the reference plate on one side of the eighth lens is better than 0.2 nm, and the surface roughness Ra value of the surface on the side of the beam splitter plate is better than 0.5 nm.

Further, the inclination angle of the beam splitter plate is 1.5°.

Further, the surface of the beam splitter plate is coated with a depolarization beam splitter film, and the transmittance and reflection ratio are 50%:50%.

Further, the surface roughness Ra value of the surface of the beam splitter plate is better than 0.5 nm.

Further, it is characterized in that the numerical aperture of the optical system of the interference microscope objective lens is 0.015, the entrance pupil diameter is 12 mm, the focal length is 400 mm, the parfocal distance is 280 mm, the working distance is 58 mm, and the line field of view is 48 mm. mm, using a partially transparent flat plate to form an unobstructed Mirau structure, through the inclination of the reference plate and the beam splitter plate, the reflected beam that does not participate in the interference is off-axis.

Compared with the prior art, the present invention has the following significant advantages: (1) a partial light-transmitting flat plate is used, and there is no central blocking; at the same time, the inclination of the reference plate and the beam splitter plate makes the reflected beam that does not participate in the interference off-axis, forming a complete dual beam interference, so that high fringe contrast can be obtained; (2) the numerical aperture is 0.015, the entrance pupil diameter is 12 mm, the focal length is 400 mm, the parfocal distance is 280 mm, the working distance is 58 mm, and the line field of view is 48 mm , the imaging quality is excellent, and the imaging quality is close to the diffraction limit; (3) the structure is simple, the use of optical components is low, and the cost is low. It is suitable for coherent scanning interferometry and can be used to measure the three-dimensional topography of rough surfaces.

Description of drawings

FIG. 1 is a schematic structural diagram of the optical system of the Mirau type wide-field interference microscope objective lens according to the present invention.

FIG. 2 is a schematic diagram of the optical path of the optical system of the Mirau type wide-field interference microscope objective lens according to the present invention.

FIG. 3 is a transfer function curve diagram of the Mirau type wide-field interference microscope objective lens optical system of the present invention.

FIG. 4 is a wave aberration curve diagram of the Mirau type wide-field interference microscope objective lens optical system of the present invention.

FIG. 5 is a field curvature/distortion curve diagram of the Mirau type wide-field interference microscope objective lens optical system of the present invention.

FIG. 6 is a vertical axis aberration curve diagram of the Mirau type wide-field interference microscope objective lens optical system of the present invention.

Detailed ways

The optical system of the interference microscope objective lens of the invention has a magnification of 0.5X, a numerical aperture of 0.015, an entrance pupil diameter of 12 mm, a focal length of 400 mm, a parfocal distance of 280 mm, and a field of view of 48 mm. The 0.5 times non-polarized and unobstructed Mirau type wide-field interference microscope objective of the present invention is similar to the Mirau type, the difference lies in that a part of the transparent plate is used, and there is no central obstructing. The reflected beam is off-axis to form complete double-beam interference, so that high fringe contrast can be obtained.

As shown in FIG. 1 , the Mirau type wide-field interference microscope objective optical system of the present invention includes a first lens 1 , a second lens 2 , a third lens 3 , and a fourth lens 4 arranged from left to right along the same optical axis , the fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8, the reference plate 9 and the beam splitter plate 10;

The illumination light passes through the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8 and the reference plate 9 in sequence, The plate 10 is divided into two beams, one beam is incident on the surface of the reference plate and returns, and the other beam is incident on the surface of the DUT and returns. The two beams of emitted light overlap and interfere at the beam splitter plate 10. Microscopic properties of the test piece.

Further, the first lens 1 and the second lens 2 are doublet lenses, the third lens 3 and the fourth lens 4 are doublet lenses, and the fifth lens 5 and the sixth lens 6 are doublet lenses.

Combining with Table 1, the first lens 1 has a diameter of 14 mm, a center thickness of 2.5 mm, both left and right surfaces are spherical, the left spherical curvature radius is 27.15 mm, and the right spherical curvature radius is -51.30 mm. The grade is H-BAK2; the diameter of the second lens 2 is 14 mm, the center thickness is 2.0 mm, the left and right surfaces are spherical, the left spherical curvature radius is -51.30 mm, and the right spherical curvature radius is 327.14 mm. The grade is H-LAK7A; the diameter of the third lens 3 is 12 mm, the center thickness is 2.5 mm, the left and right surfaces are spherical, the left spherical curvature radius is -97.36 mm, and the right spherical curvature radius is -12.30 mm. The glass grade is H-FK61; the diameter of the fourth lens 4 is 12 mm, the center thickness is 2 mm, the left and right surfaces are spherical, the left spherical curvature radius is -12.30 mm, and the right spherical curvature radius is -890.55 mm. The glass grade is H-ZLAF76; the aperture of the fifth lens 5 is 20 mm, the center thickness is 3 mm, the left and right surfaces are spherical, the left spherical curvature radius is -36.13 mm, and the right spherical curvature radius is 21.02 mm. The glass grade is F6; the diameter of the sixth lens 6 is 20 mm, the center thickness is 4 mm, the left and right surfaces are spherical, the left spherical curvature radius is 21.02 mm, and the right spherical curvature radius is 90.67 mm. It is H-ZBAF4; the aperture of the seventh lens 7 is 54 mm, the center thickness is 6 mm, the left and right surfaces are spherical, the left spherical curvature radius is -88.51 mm, and the right spherical curvature radius is -44.10 mm. The grade is H-ZK21; the diameter of the eighth lens 8 is 58 mm, the center thickness is 6 mm, the left and right surfaces are spherical, the left spherical curvature radius is 232.69 mm, and the right spherical curvature radius is -232.69 mm. The grade is H-ZF5; the reference plate 9 is a circular optical flat plate with a diameter of 60 mm and a thickness of 8 mm, and the glass material used is fused silica; the beam splitter plate 10 is a circular optical flat plate with a diameter of 60 mm , the thickness is 8 mm, and the glass material used is fused silica;

The air space between the second lens 2 and the third lens 3 is 40.2 mm, the air space between the fourth lens 4 and the fifth lens 5 is 31.04 mm, and the air space between the sixth lens 6 and the seventh lens 7 is 38.56 mm, The air interval between the seventh lens 7 and the eighth lens 8 is 0.2 mm, the air interval between the eighth lens 8 and the reference plate 9 is 8 mm, and the air interval between the reference plate 9 and the beam splitter plate 10 is 58 mm.

Table 1

As a specific example, the inclination angle of the reference plate 9 is 3°.

As a specific example, the upper surface of the reference plate 9 is coated with a depolarization beam splitter film, and the transmittance to reflectance ratio is 85%:15%.

As a specific example, the surface roughness Ra value of the surface of the reference plate 9 on the side of the eighth lens 8 is better than 0.2 nm, and the surface roughness Ra value of the surface on the side of the beam splitter plate 10 is better than 0.5 nm.

As a specific example, the inclination angle of the beam splitter plate 10 is 1.5°.

As a specific example, the surface of the beam splitter plate 10 is coated with a depolarization beam splitter film, and the transmittance ratio and the reflectance ratio are 50%:50%.

As a specific example, the surface roughness Ra value of the surface of the beam splitter plate 10 is better than 0.5 nm.

As a specific example, the optical system of the interference microscope objective has a numerical aperture of 0.015, an entrance pupil diameter of 12 mm, a focal length of 400 mm, a parfocal distance of 280 mm, a working distance of 58 mm, and a line field of view of 48 mm , a partially transparent flat plate is used to form an unobstructed Mirau structure, and the reflected beam that does not participate in the interference is off-axis through the inclination of the reference plate 9 and the beam splitter plate 10 .

The optical system of the present invention is an optical system with infinite conjugate distance, and parallel light is required for incident illumination during operation.

Combined with Figure 2, the working principle of the 0.5x unpolarized and unobstructed Mirau type wide-field interference microscope objective lens optical system is parallel light illumination, and the illumination light passes through the first lens 1, the second lens 2, the third lens 3, the fourth lens in turn The lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8 and the reference plate 9 are divided into two beams at the beam splitter plate 10, one beam is incident on the surface of the reference plate and returns, the other beam When it is incident on the surface of the DUT and returns, the two beams of light overlap at the beam splitter and interfere, and the microscopic characteristics of the DUT can be analyzed according to the interference fringes generated.

Fig. 3 is the transfer function curve diagram of the 0.5 times non-polarized unobstructed Mirau type wide field of view interference microscope optical system of the present invention. It can be seen from the figure that the transfer function is in 0 field of view, 0.707 field of view and full field of view. The function is greater than 0.4 when the function is 20 line pairs/mm.

Fig. 4 is the wave aberration curve diagram of the optical system of the 0.5 times non-polarized and unobstructed Mirau type wide-field interference microscope objective lens according to the present invention. It can be seen from the figure that the wavelength is in the range of 486nm to 656nm, and the whole field of view is better than Diffraction limit.

5 is a field curvature/distortion curve diagram of the 0.5 times unpolarized unobstructed Mirau type wide-field interference microscope objective lens optical system of the present invention, and it can be seen from the figure that the maximum optical distortion of the entire system is less than 0.05%.

Fig. 6 is the vertical axis aberration curve diagram of the 0.5 times non-polarized and unobstructed Mirau type wide-field interference microscope objective lens optical system of the present invention, the maximum value of the ordinate in the figure is ±50 microns, the wavelength is in the range of 486nm-656nm, each color The shape of the light curve is similar, and the maximum deviation is controlled within 20 microns.

The 0.5 times non-polarized and unobstructed Mirau type wide-field interference microscope objective lens optical system of the invention can work in the visible light band (486nm-656nm), the numerical aperture is 0.015, the entrance pupil diameter is 12 mm, and the focal length is 400 mm. The parfocal distance is 280mm, the working distance is 58mm, the line field of view is 48mm, and the imaging quality is excellent, and the imaging quality is close to the diffraction limit.

Claims (8)

1. The Mirau type wide-field interference microscope objective optical system is characterized by comprising a first lens (1), a second lens (2), a third lens (3), a fourth lens (4), a fifth lens (5), a sixth lens (6), a seventh lens (7), an eighth lens (8), a reference plate (9) and a beam splitter plate (10) which are arranged from left to right along the same optical axis;

the illumination light sequentially passes through a first lens (1), a second lens (2), a third lens (3), a fourth lens (4), a fifth lens (5), a sixth lens (6), a seventh lens (7), an eighth lens (8) and a reference plate (9), the illumination light is divided into two beams at a beam splitter plate (10), one beam is incident on the surface of the reference plate and returns, the other beam is incident on the surface of the piece to be measured and returns, the two beams of emission light are overlapped at the beam splitter plate (10) and then interfere with each other, and the microscopic characteristics of the piece to be measured are analyzed according to the generated interference fringes;

the aperture of the first lens (1) is 14 mm, the center thickness is 2.5 mm, the left surface and the right surface are both spherical surfaces, the curvature radius of the left spherical surface is 27.15 mm, the curvature radius of the right spherical surface is-51.30 mm, and the adopted glass brand is H-BAK 2; the aperture of the second lens (2) is 14 mm, the center thickness is 2.0 mm, the left surface and the right surface are both spherical surfaces, the curvature radius of the left spherical surface is-51.30 mm, the curvature radius of the right spherical surface is 327.14 mm, and the adopted glass brand is H-LAK 7A; the aperture of the third lens (3) is 12 mm, the center thickness is 2.5 mm, the left surface and the right surface are both spherical surfaces, the radius of curvature of the left spherical surface is-97.36 mm, the radius of curvature of the right spherical surface is-12.30 mm, and the adopted glass brand is H-FK 61; the aperture of the fourth lens (4) is 12 mm, the center thickness is 2 mm, the left surface and the right surface are both spherical surfaces, the curvature radius of the left spherical surface is-12.30 mm, the curvature radius of the right spherical surface is-890.55 mm, and the adopted glass brand is H-ZLAF 76; the aperture of the fifth lens (5) is 20 mm, the center thickness is 3mm, the left surface and the right surface are both spherical surfaces, the curvature radius of the left spherical surface is-36.13 mm, the curvature radius of the right spherical surface is 21.02 mm, and the adopted glass brand is F6; the aperture of the sixth lens (6) is 20 mm, the center thickness is 4 mm, the left surface and the right surface are both spherical surfaces, the radius of curvature of the left spherical surface is 21.02 mm, the radius of curvature of the right spherical surface is 90.67 mm, and the adopted glass brand is H-ZBAF 4; the aperture of the seventh lens (7) is 54 mm, the center thickness is 6 mm, the left surface and the right surface are both spherical surfaces, the curvature radius of the left spherical surface is-88.51 mm, the curvature radius of the right spherical surface is-44.10 mm, and the adopted glass brand is H-ZK 21; the caliber of the eighth lens (8) is 58mm, the center thickness is 6 mm, the left surface and the right surface are both spherical surfaces, the curvature radius of the left spherical surface is 232.69 mm, the curvature radius of the right spherical surface is-232.69 mm, and the adopted glass brand is H-ZF 5; the reference plate (9) is a circular optical flat plate, the diameter of the reference plate is 60 mm, the thickness of the reference plate is 8mm, and the adopted glass material is fused quartz; the light splitting plate (10) is a circular optical flat plate, the diameter of the light splitting plate is 60 mm, the thickness of the light splitting plate is 8mm, and the adopted glass material is fused quartz;

the air space between the second lens (2) and the third lens (3) is 40.2 mm, the air space between the fourth lens (4) and the fifth lens (5) is 31.04 mm, the air space between the sixth lens (6) and the seventh lens (7) is 38.56 mm, the air space between the seventh lens (7) and the eighth lens (8) is 0.2 mm, the air space between the eighth lens (8) and the reference plate (9) is 8mm, and the air space between the reference plate (9) and the beam splitter plate (10) is 58 mm;

the first lens (1) and the second lens (2) are double-cemented lenses, the third lens (3) and the fourth lens (4) are double-cemented lenses, and the fifth lens (5) and the sixth lens (6) are double-cemented lenses.

2. Mirau-type wide-field interference microscope objective optical system according to claim 1, characterized in that the reference plate (9) is tilted at an angle of 3 °.

3. The Mirau wide-field interference microscope objective optical system according to claim 1, wherein the reference plate (9) is coated with a depolarizing beam splitting film on the upper surface, and the transmission ratio and the reflection ratio are 85% to 15%.

4. Mirau-type wide-field interference microscope objective optical system according to claim 1, characterized in that the reference plate (9) has a surface roughness Ra value of better than 0.2 nm on the side of the eighth lens (8) and a surface roughness Ra value of better than 0.5 nm on the side of the beam splitter plate (10).

5. Mirau-type wide-field interference microscope objective optical system according to claim 1, characterized in that the inclination angle of the beam splitter plate (10) is 1.5 °.

6. The Mirau wide-field interference microscope objective optical system according to claim 1, wherein the surface of the beam splitter plate (10) is plated with a depolarizing beam splitter film, and the transmission ratio and the reflection ratio are 50% to 50%.

7. Mirau-type wide-field interference microscope objective optical system according to claim 1, characterized in that the surface roughness Ra value of the surface of the beam splitter plate (10) is better than 0.5 nm.

8. Mirau-type wide-field interference microobjective optical system according to any of the preceding claims, characterized in that the interference microobjective optical system has a numerical aperture of 0.015, an entrance pupil diameter of 12 mm, a focal length of 400 mm, a parfocal distance of 280 mm, a working distance of 58mm, and a line field of view of 48 mm, and uses a partially transparent flat plate to form an unblanked Mirau-type structure, and the reflected light beams not participating in interference are off-axis by the inclination of the reference plate (9) and the splitting plate (10).

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