CN101369051B - Metallographic microscope with high signal-to-noise ratio - Google Patents

Abstract

A metallographic microscope with a high signal-to-noise ratio comprises a light source, an objective lens group, a subsequent optical path system and an eyepiece group, wherein a corner mirror is arranged in the optical path between the objective lens group and the subsequent optical path system, the corner mirror is composed of a polarization beam splitter and a quarter wave plate, the angle between the polarization beam splitter and the optical path between the objective lens group and the subsequent optical path system is 45° to 55°, the quarter wave plate is perpendicular to the optical path between the objective lens group and the subsequent optical path system, the optical axis direction of the quarter wave plate is at an angle of 45° to the polarization direction of the incident linear polarized light, and the light source is a monochromatic collimated polarized light source. The signal-to-noise ratio of the present invention is more than 10 times better than that of the prior art, thereby significantly improving the imaging quality and contrast of the instrument.

Description

Metallographic microscope with high signal-to-noise ratio

technical field

The invention relates to a microscope, in particular to a metallographic microscope with high signal-to-noise ratio.

Background technique

Metallographic microscope is a basic tool for observing organizational details and defects in material analysis. Metallographic microscopes based on the principles of geometric optics and diffractive optics have an effective magnification of up to 1500-1600 times and can observe structures as small as 200nm. The imaging quality of this type of microscope depends largely on the quality of the objective lens. Because the objective lens must collect as much information from the object as possible, and transmit the signal to the eyepiece without distortion. In order to achieve this goal, people have designed objective lenses with large numerical apertures, apochromatic objectives, flat field objectives, etc. . . . The eyepiece is responsible for transmitting the signal from the objective lens to the human eye with a suitable magnification.

In addition, the illumination system and optical path are also one of the main factors affecting the imaging quality of metallographic microscopes. People have taken various measures to improve the lighting source and design a reasonable optical path system. In order to make the light signal from the object reach the eyepiece as much as possible, the background stray light is eliminated as much as possible, so that it can still be seen under the magnification of 1500 times. Maintain high imaging clarity and contrast.

Whether it is bright field or dark field illumination for commonly used microscopes, the main components of the optical path usually use a flat glass placed at an angle of 45 degrees to the light source as the vertical illuminator. The function is to turn the light from the light source at 90 degrees to reach the sample. , and then make the light from the sample 3 pass through the illuminator and the subsequent optical path system and then reach the eyepiece. The structure diagram of the optical path is shown in Figure 1. It consists of a light source 1, a collimating lens 2, a sample 3, an objective lens group 4, a flat glass 5, a follow-up optical path system 6, and an eyepiece group 7. The advantage of this optical path system is that the imaging is flat and clear, and it is a commonly used optical path system ( See Sun Yeying, "Optical Microanalysis" Tsinghua University Press). However, the disadvantage of this light path system is that the vertical illuminator made of flat glass 5 cannot meet high reflectivity and transmittance at the same time, and the light from light source 1 will lose 50% every time it passes through the flat glass. The light that reaches the eyepiece is at most only 25% of the original, which affects the quality and clarity of the image.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art, to provide a metallographic microscope with a high signal-to-noise ratio, to significantly improve the utilization rate of the light signal of the metallographic microscope, and theoretically to obtain an optical microscope that is more than 10 times better than the prior art. Signal-to-noise ratio, thus significantly improving image quality and contrast.

Technical solution of the present invention is as follows:

A metallurgical microscope with a high signal-to-noise ratio, including a light source, an objective lens group, a follow-up optical path system and an eyepiece set, is characterized in that: a corner mirror is arranged in the light path between the objective lens group and the follow-up light path system, and the corner mirror The mirror is composed of a polarization beam splitter and a quarter wave plate, the angle between the polarization beam splitter and the optical path between the objective lens group and the subsequent optical path system is 45 ° ~ 55 °, the quarter wave One of the wave plates is perpendicular to the optical path between the objective lens group and the subsequent optical path system, the optical axis direction of the quarter wave plate is at an angle of 45° to the polarization direction of the incident linearly polarized light, and the light source It is a monochromatic collimated polarized light source, and the polarized beam emitted by the monochromatic collimated polarized light source is irradiated on the polarized beam splitter, and the polarized beam splitter is used for the polarized beam whose polarization direction is perpendicular to the incident plane from the light source It is reflected with high reflectivity and is incident on the quarter-wave plate. After passing through the quarter-wave plate, it becomes circularly polarized light. The light irradiates the sample through the objective lens group, and the reflection modulated by the sample The circularly polarized light passes through the objective lens group, and then passes through the quarter-wave plate again to convert the polarization direction of the light to be perpendicular to the polarization direction of the original incident light, and transmits through the light with high transmittance. The polarizing beam splitter enters the eyepiece group through the subsequent optical path system.

The monochromatic collimated polarized light source is composed of a monochromatic illuminating light source, a collimating lens and a polarizer in sequence.

Said monochromatic lighting source is a high-brightness monochromatic semiconductor light-emitting diode.

Technical effect of the present invention is as follows:

The polarized beam emitted by the monochromatic collimated polarized light source is irradiated on the polarized beam splitter, and the polarized beam splitter turns the incident polarized light at an angle of 90 degrees or greater than 90 degrees and is incident on the quarter of the A wave plate, the linearly polarized light becomes circularly polarized light after passing through the quarter wave plate, reaches the objective lens group and then reaches the sample. The circularly polarized light reflected back from the sample through the objective lens 4 becomes linearly polarized light again when passing through the quarter-wave plate for the second time, and its polarization direction is perpendicular to the vibration direction of the polarized light that was originally emitted to the sample. Therefore, the light will pass through the corner mirror with a transmittance higher than 90%, pass through the subsequent optical path system, and finally reach the eyepiece.

Compared with the prior art, the present invention avoids the situation in the prior art that half of the energy loss of the light becomes stray light after passing through the refraction of the plane glass in the prior art. The invention greatly reduces the background light, significantly increases the signal light, and has a signal-to-noise ratio more than 10 times better than that of the prior art, thus significantly improving the imaging quality and contrast.

Description of drawings

Fig. 1 is a schematic diagram of the structure of an existing microscope using a flat glass element as a vertical illuminator.

Fig. 2 is a structural schematic diagram of an embodiment of a metallographic microscope with a high signal-to-noise ratio in the present invention.

Fig. 3 is a schematic view of the direction of the optical axis of the quarter-wave plate of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the embodiments and accompanying drawings, but the protection scope of the present invention should not be limited thereby.

Please refer to FIG. 2 first. FIG. 2 is a schematic structural diagram of an embodiment of a metallographic microscope with a high signal-to-noise ratio in the present invention. As can be seen from the figure, the metallographic microscope with high signal-to-noise ratio in the embodiment of the present invention includes a light source, an objective lens group 4, a follow-up optical path system 6 and an eyepiece set 7, and is characterized in that: between the described objective lens group 4 and the follow-up optical path system 6 A corner mirror 11 is provided in the optical path between, and the corner mirror 11 is composed of a polarizing beam splitter 8 and a quarter wave plate 9, between the polarizing beam splitter 8 and the described objective lens group 4 and the subsequent optical path system 6 The included angle of the optical path is 45°～55°, and the optical path between the described quarter-wave plate 9 and the described objective lens group 4 and the subsequent optical path system 6 is vertical, and the light of the quarter-wave plate 9 The axis direction and the polarization direction of the incident linearly polarized light are at an angle of 45 °, and the described light source is a monochromatic collimated polarized light source, and the described monochromatic collimated polarized light source is composed of sequential monochromatic illumination light source 12, collimated The lens 2 and the polarizer 10 are composed. The monochromatic light emitted by the monochromatic illumination source 12 is collimated by the collimator lens 2 and then irradiates on the polarizer 10 to form linearly polarized light, and its polarization direction is perpendicular to the incident surface of the polarizing beam splitter, i.e. in Fig. 2 On paper, the polarized light beam is irradiated on the polarizing beam splitter 8 . The polarizing beam splitter 8 performs beam splitting by totally reflecting the polarized light whose polarization direction is perpendicular to the incident plane and totally transmitting the polarized light whose polarization direction is parallel to the incident plane. The polarization beam splitter 8 reflects the incident polarized light beam whose polarization direction is perpendicular to the plane of incidence and is incident on the quarter-wave plate 9, and becomes circularly polarized light after passing through, and irradiates the sample through the objective lens group 4. 3. The circularly polarized light modulated and reflected by the sample 3, after passing through the objective lens group 4, the circularly polarized light is converted into a polarization direction parallel to the polarized beam splitter by the quarter wave plate 9 8 The polarized light beam on the incident plane passes through the polarization beam splitter 8 with high transmittance, and enters the eyepiece group 7 through the subsequent optical path system 6 .

The monochromatic illumination light source 12 is a high brightness monochromatic semiconductor light emitting diode.

The direction of the optical axis of the quarter-wave plate 9 is placed at an angle of 45 degrees with the polarization direction of the incident polarized light to play a role in changing the polarization state of the incident light, see FIG. 3 for details. In the figure: (a) is the front view, that is, the surface where the light is incident, and the dotted line group AA' represents the orientation of the crystal optical axis in the plane of the paper. (b) is the side view of the quarter-wave plate, and the arrow is the direction of the incident light.

The polarized beam splitter 8 is a specially designed coated lens, and a multilayer composite film with alternating refractive index is coated on a glass substrate to obtain polarization of light in two directions perpendicular to and parallel to the incident surface. beam split. If the design of the refractive index of the composite film matches the wavelength and incident angle of the illumination source, then when there are enough film layers, high polarization splitting efficiency can be obtained. If the wavelength and incident angle do not match the designed film system, then the polarization splitting ratio will not reach the optimal setting value, resulting in a significant decrease in the polarization reflectance or polarization transmittance of the light, that is, the signal intensity decreases.

The present invention can reflect more than 90% of the light from the monochromatic polarized light source through careful adjustment of the corner mirror 11, and emit the light from the sample 3 and the objective lens group 4 with a transmittance higher than 90%, so that the light passes through the corner twice After the mirror, if the absorption is not considered, the total loss is less than 20%, that is, the background light is reduced to less than 20%. The signal-to-noise ratio is improved by an order of magnitude compared to prior art flat glass elements that lose 50% each time.

Described quarter-wave plate 9 refers to the single wafer whose front and rear surfaces are parallel to the optical axis of the crystal made of commonly used uniaxial crystals. The direction is at an angle of 45 degrees, as shown in Figure 3(a), the purpose is to change the line deviation state of the light.

The illumination light source 12 in the present invention is a monochromatic high-brightness InGaAlP semiconductor light-emitting diode light source, which has high brightness, low energy consumption and high collimation, such as InGaAlP orange 620nm light, or 590nm yellow super high-brightness light source. The light emitted by this light source has better monochromaticity and higher collimation than conventional tungsten or xenon lamps.

After the monochromatic illumination source 12 is collimated by the conventional collimator lens 2, it passes through the polarizer 10, and becomes polarized light and enters the corner mirror 11. Polarized light at the incident surface of a polarizing beamsplitter. The incident plane of the so-called polarizing beam splitter refers to the plane formed by the advancing direction vector of the incident light and the normal vector of the optical surface of the polarizing beam splitter. In Figure 2, it is the paper plane, and the polarization direction perpendicular to the incident plane is perpendicular to the paper plane The direction of , is marked with a dot in Figure 2, and the polarization state parallel to the incident plane is marked with a small horizontal line. When the light is obliquely incident on the polarizing beam splitter 8 at an angle of 45 degrees (or close to 45 degrees), it is emitted at an angle of 90 degrees (or close to 90 degrees), and finally reaches the sample 3 . The circularly polarized light reflected back from the sample 3 through the objective lens group 4 becomes linearly polarized light again when it passes through the quarter-wave plate 9 for the second time, and the polarization direction is perpendicular to the polarization direction of the original incident light, that is, on the paper plane Therefore, the polarized light will pass through the polarization beam splitter with a high transmittance, and finally reach the eyepiece group 7 through the subsequent optical path system 6 .

The monochromatic light emitted by the monochromatic illumination source 12 is collimated by the conventional collimating mirror 2, and then exits through the polarizer 10. direction is incident on the polarization beam splitter 8, and then passes through the quarter wave plate 9, because the crystal optical axis direction of the wave plate 9 and the vibration direction of the incident line polarized light have an angle of 45 degrees, as shown in Figure 3 (a), When the light passes through the quarter wave plate 9, it is divided into two parts equal to the o light and the e light, and the thickness d of the wave plate satisfies: (n _e -n _o )d=(2k+1)λ/4, where k is any integer, λ is the wavelength of illumination light, n _e and n _o are the sum of e light. The refractive index of light, in this way, when the linearly polarized light that is normal incident and clamped 45° with the optical axis of the wave plate exits, the optical path difference between o light and e light is ±λ/4, so it is formed as circularly polarized light exiting through the objective lens Group 4 arrives at sample 3.

When the circularly polarized light returned from the sample 3 through the objective lens group 4 passes through the quarter-wave plate 9 again, it changes from circularly polarized light to linearly polarized light, and due to spatial refraction, the circularly polarized light becomes linearly polarized light The original incident linearly polarized light is perpendicular to each other, so it passes through the polarizing beam splitter 8 with a high transmittance, passes through the subsequent optical path system 6, and finally reaches the eyepiece 7 or the recording plane.

The design and manufacture of the polarizing beam splitter 8 is realized by plating a multilayer composite film with alternating refractive index on the glass substrate, and each layer of the multilayer film entering according to the incident light is Bruce Special angle design, the thickness of the film layer meets certain conditions of light interference enhancement, and the thickness of each layer of film can be dozens of atomic layers. When the composite film layer matches the wavelength and incident angle of the designed illumination source, a polarization rate higher than 90% can be obtained. If the two do not match, the optimal design value will not be reached.

Claims (3)

1. a metallurgical microscope with high signal-to-noise ratio, comprising light source, objective lens group (4), follow-up optical path system (6) and eyepiece group (7), it is characterized in that: in described objective lens group (4) and follow-up A corner mirror (11) is provided in the light path between the optical path system (6), and the corner mirror (11) is made of a polarization beam splitter (8) and a quarter wave plate (9), and the polarization beam splitter (8) The angle between the optical path between the objective lens group (4) and the follow-up optical path system (6) is 45°～55°, and the quarter wave plate (9) and the objective lens The optical path between the group (4) and the subsequent optical path system (6) is vertical, the optical axis direction of the quarter wave plate (9) is at an angle of 45° to the polarization direction of the incident linearly polarized light, and the light source It is a monochromatic collimated polarized light source, and the polarized light beam emitted by the monochromatic collimated polarized light source is irradiated on the described polarization beam splitter (8), and the polarized beam splitter (8) is perpendicular to the incident polarization direction The polarized light beam on the incident plane is reflected with high reflectivity and is incident on the quarter-wave plate (9), and becomes circularly polarized light after passing through the quarter-wave plate (9), and the light passes through the described quarter-wave plate (9). The objective lens group (4) irradiates the sample (3), and the reflected circularly polarized light modulated by the sample (3) passes through the described objective lens group (4), and then passes through the described quarter-wave plate (9) again , convert the polarization direction of the light to be perpendicular to the polarization direction of the original incident light, pass through the polarization beam splitter (8) with high transmittance and enter the eyepiece group through the subsequent optical path system (6) (7). 2. the metallographic microscope of high signal-to-noise ratio according to claim 1, is characterized in that described monochromatic collimated polarized light source is by successive monochromatic illumination light source (12), collimating lens (2) and polarizer (10) Composition. 3. The metallographic microscope with high signal-to-noise ratio according to claim 2, characterized in that said monochrome illumination source (12) is a high-brightness monochrome semiconductor light-emitting diode.

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