Helium-neon laser discharge tube and laser

Abstract

The invention relates to a helium-neon laser discharge tube and a laser. According to one embodiment, a helium-neon laser discharge tube comprises: a cylindrical tube body having a substantially constant diameter over the entire length; the first end part element comprises a cylindrical first part and an umbrella-shaped second part, and is mounted on the first end surface of the pipe body through the second part; the second end part element comprises a cylindrical third part and an umbrella-shaped fourth part, and is mounted on a second end surface, opposite to the first end surface, of the pipe body through the fourth part; the cathode component is arranged in the tube body and is adjacent to the second part of the first end part element, and the first part of the first end part element comprises two or more annular grooves in the axis direction of the first part.

Description

Technical Field

[0001] The embodiments of the present invention generally relate to a helium-neon laser discharge tube and a helium-neon laser using the discharge tube. Background Technology

[0002] Helium-neon lasers possess excellent monochromaticity, collimation, and frequency stability, making them commonly used as light sources for various optical measuring instruments in industrial and metrology fields, such as single-frequency laser interferometers, dual-frequency laser interferometers, frequency-modulated laser interferometers, vibration meters, and surface topography interferometers. These instruments play an irreplaceable role in areas such as lithography machine tool movement, machine tool calibration, and high-precision surface roughness measurement of parts.

[0003] The main structural component of a helium-neon laser is the laser discharge tube. Figure 1 This is a schematic diagram of a conventional laser discharge tube 30. The tube body of the laser discharge tube 30 is made using glass blowing technology, and there are significant diameter differences between different parts. Specifically, the cylindrical main body 31 has necks 32 and 33 with significantly reduced diameters at both ends. Two glass windows 34 and 35 are fixed to the end faces of the two necks 32 and 33 with epoxy resin or molten glass powder to seal the laser discharge tube 30. The capillary discharge tube and the aluminum cylinder (not shown) serving as the cathode are disposed inside the main body 31. Summary of the Invention

[0004] According to one aspect of the present invention, a helium-neon laser discharge tube includes: a cylindrical tube body having a substantially constant diameter over its entire length; a first end element comprising a cylindrical first portion and an umbrella-shaped second portion, and mounted to a first end face of the tube body via the second portion; a second end element comprising a cylindrical third portion and an umbrella-shaped fourth portion, and mounted to a second end face of the tube body opposite to the first end face via the fourth portion; and a cathode component disposed within the tube body and adjacent to the second portion of the first end element. The first portion of the first end element includes two or more annular grooves along its axial direction.

[0005] According to another aspect of the present invention, a helium-neon laser includes the aforementioned helium-neon laser discharge tube, wherein a second window has a reflective film on the side facing away from the tube body and an antireflective film on the side facing the tube body. Alternatively, the second window has an antireflective film on the side facing away from the tube body and a reflective film on the side facing the tube body.

[0006] According to another aspect of the present invention, a helium-neon laser includes the aforementioned helium-neon laser discharge tube, wherein the second window has an antireflective coating on both the side facing away from the tube body and the side facing the tube body; and the helium-neon laser includes a mirror element located outside the helium-neon laser discharge tube on the axis of the helium-neon laser discharge tube, the mirror element having a reflective coating on the side facing the helium-neon laser discharge tube and an antireflective coating on the side facing away from the helium-neon laser discharge tube. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of a traditional laser discharge tube.

[0008] Figure 2 This is a schematic diagram of a helium-neon laser discharge tube according to an embodiment of the present invention.

[0009] Figure 3 Examples of coating types for windows according to embodiments of the present invention are shown.

[0010] Figure 4 The installation location of the getter is shown according to another embodiment of the invention. Detailed Implementation

[0011] Various embodiments of the invention will now be described with reference to the accompanying drawings. It should be understood that these embodiments are merely illustrative examples that may be used to implement the invention, and are not intended to limit the scope of the invention to these specific examples. In the drawings, the same reference numerals denote the same elements. The drawings are not necessarily drawn to scale.

[0012] Figure 2 This is a schematic cross-sectional view of a helium-neon laser discharge tube 100 according to an embodiment of the present invention. As shown, the laser discharge tube 100 includes a tube body 1. The tube body 1 can be made of a glass material (e.g., DM-305 glass) or other suitable materials known in the art, such as glass materials having a similar coefficient of thermal expansion. Depending on the output power and mode requirements of the laser, the length of the tube body 1 is typically between 60 and 300 mm, for example, 80 to 120 mm; the diameter is typically between 20 and 30 mm. The ends of the tube body 1 can be mechanically polished for assembly with the end components described below. The tube body 1 serves as the mounting base for the helium-neon laser discharge tube, on which other components are mounted directly or indirectly. Unlike conventional laser discharge tubes 30 made using glass blowing technology, according to an embodiment of the present invention, the tube body 1 of the laser discharge tube 100 is cylindrical, has a substantially constant diameter along its entire length, and does not have prominent necks at both ends.

[0013] At both ends of the tube body 1, the laser discharge tube 100 includes a first end element 2 (or cathode sealing joint), a second end element 5 (or anode sealing joint), a cathode component 4 disposed within the tube body 1, and an anode component disposed on the second end element 5. A window 3 and a window 6 are respectively hermetically fixed to one end of the first end element 2 and the second end element 5. A capillary discharge tube 8 is mounted to the second end element 5 and extends within the tube body 1 in a substantially coaxial manner. The laser discharge tube 100 is filled with high-purity helium and neon gas after being evacuated. During operation, a high-voltage direct current is applied by an external power source through the cathode terminal connected to the cathode component 4 and the anode terminal 7 connected to the anode component (e.g., a nickel rod or a tungsten rod), inducing stimulated emission of neon atoms within the capillary discharge tube 8. The operating principle of a helium-neon laser is well known in the art and will not be described further herein. The structure of the laser discharge tube 100 will be described in detail below.

[0014] like Figure 2 As shown, the first end element 2 can be visually divided into two parts: a cylindrical first part 21 and an umbrella-shaped second part 22. The first end element 2 can be made of an alloy material (e.g., the well-known 4J29 alloy), also known as Kovar, whose coefficient of thermal expansion matches that of the tube body 1 material. Therefore, when the laser discharge tube 100 expands due to temperature rise during operation, the difference in the coefficients of thermal expansion between the tube body 1 and the first end element 2 will not cause a breach in airtightness. Figure 2 As shown, the first end element 2 is mounted to the left end face of the tube body 1 via its second part 22. This mounting process can be performed, for example, by using a high-frequency heated glass-gold bonding process (also known as high-frequency sealing) known in the field of vacuum electronic devices.

[0015] The cylindrical first part 21 has multiple annular grooves 11, 12 on its outer periphery. Although Figure 2 The embodiment shows two grooves, but the number can also be three or more. At the grooves, the cylindrical wall thickness of the first portion relatively decreases. The depth and width of each groove can be the same or different. The function of these annular grooves will be explained below.

[0016] The second part 22 includes a through hole at its center, which communicates with the interior space of the first part 21 along its axial direction. In an alternative embodiment, such as Figure 2 As shown, at the junction of the second part 22 and the first part 21, the second part 22 has a shoulder surface about the axial direction. This shoulder surface can be formed by making the inner diameter of the through hole in the second part 22 smaller than the inner diameter of the first part 21, or by creating a slot at the junction of the second part and the first part.

[0017] like Figure 2 As shown, the second part 22 is also provided with a hollow exhaust pipe 23 for connecting the interior of the tube body 1 to the outside. During the manufacturing process of the laser, the air inside the tube body 1 is discharged through the exhaust pipe 23, and helium and neon gas of a predetermined pressure and ratio are filled into the tube body 1 through the exhaust pipe 23, after which the hollow exhaust pipe 23 is sealed. According to an optional embodiment, during operation, the hollow exhaust pipe 23 can serve as a cathode terminal connected to the cathode component 4 for supplying high-voltage direct current from an external power source to the cathode component 4. In other embodiments, a separate cathode terminal can be provided on the second part 22 for connection to the cathode component 4.

[0018] The cathode component 4 can be a cylindrical shape made of a thin aluminum sheet. For example... Figure 2 As shown, the cathode component 4 includes a first part 4a and a second part 4b. The first part 4a is fitted into the tube body 1, and therefore has a diameter substantially the same as the inner diameter of the tube body 1. Its length can occupy 30%-70% of the total length of the tube body 1, for example, 40-60%. The second part 4b is fitted into the second part 22 of the first end element 2. Its diameter is substantially the same as the inner diameter of the through hole of the second part 22 of the second end element 2, and smaller than the diameter of the first part 4a. The first part 4a and the second part 4b of the cathode component 4 are connected by a tapered connecting portion 4c. Figure 2 In the first part, the tapered connecting portion 4c has a conical cross-section, but it can also adopt any cross-sectional shape that facilitates the transition from the larger diameter first portion 4a to the smaller diameter second portion 4b, such as a roughly spherical or parabolic surface. According to an alternative embodiment, one end of the second portion 4b (i.e., the end facing away from the tube body 1) has a flange that extends away from the axial direction in a direction substantially orthogonal to the axial direction of the laser discharge tube 100. Thus, the second portion 4b forms an annular flange through this flange, overlapping the shoulder surface of the first end element 2.

[0019] According to one alternative embodiment, the laser discharge tube 100 may include a spring element 10 for improving the installation stability of the cathode component 4. For example... Figure 2 As shown, the spring element 10 can be a helical spring, with one end abutting against the second part 22 of the first end element 2 and the other end abutting against the tapered connecting part 4c of the cathode component 4. The spring element 10 is not limited to the helical form, and can also adopt other forms that enable the cathode component 4 to be stably installed relative to the tube body 1.

[0020] Similar to the first end element 2, the second end element 5 can also be visually divided into two parts: a cylindrical third part 51 and an umbrella-shaped fourth part 52. Figure 2In this process, the second end element 5 is fixed to the right end face of the tube body 1 via the fourth part 52 using, for example, a high-frequency sealing method. The second end element 5 can be made of the same alloy material as the first end element 2. The fourth part 52 also includes a through hole along its axial direction. This through hole communicates with the internal space of the cylindrical third part 51, and its inner diameter can be the same as or different from the inner diameter of the third part 51.

[0021] The capillary discharge tube 8 is mounted to the fourth part 52 of the second end element 5 through its flared end. This mounting process can be, for example, using a high-frequency sealing method. The material of the capillary discharge tube 8 can be the same as that of the tube body 1, or it can be other materials or quartz glass, etc. The length of the capillary discharge tube 8 is typically 50%-80% of the total length of the tube body 1, for example, 40-80 mm, and can even reach more than 200 mm in the case of long tube bodies used in high-power lasers; its inner diameter can be between 0.5-1.5 mm, for example, 0.8-1.2 mm. The axis of the capillary discharge tube 8 is substantially coincident with the axis of the tube body 1. According to an optional embodiment, an elastic support 15 can be provided inside the tube body 1 to support the slender capillary discharge tube 8, making the selection of the support point more flexible. The elastic support 15 can be made of materials such as metal, plastic or polymer, and is in the shape of a multi-claw spring sheet radiating radially outward from the central hole. The outer ends of each spring sheet contact the inner wall of the tube body 1, and the capillary discharge tube 8 passes through the central hole of the elastic support 15. Along the axial direction of the tube body 1, the position of the elastic support 15 can be set between the cathode component 4 and the second end element 5.

[0022] According to an optional embodiment, the laser discharge tube 100 may further include a getter 9, which may include, for example, barium titanium, barium aluminum nickel, etc., as known in the art. The getter 9 can adsorb residual gas after the laser discharge tube 100 is evacuated and gases released during laser operation, thus extending the lifespan of the laser. Figure 2 As shown, the getter 9 can be fixed to the cathode component 4 by clips. The getter 9 can also be disposed in other locations within the tube body 1, such as on the capillary discharge tube 8 (see [reference]). Figure 4 (Example).

[0023] The first window 3 is fixed to the end of the first portion 21 of the first end element 2, and the second window 6 is fixed to the end of the third portion 51 of the second end element 5. The windows 3 and 6 can be made of optical glass material (e.g., K4 glass), and at least one end face (but typically both end faces) has an optical coating. The surface finish of the windows 3 and 6, as well as the type of coating, can depend on the type of laser. The mounting of the windows 3 and 6 to the first portion 21 and the third portion 51 can, for example, be achieved using a high-frequency sealing method.

[0024] Figure 3(A) and (B) show some examples of the coating categories for windows 3 and 6. For clarity, Figure 3 The tube body 1 and the first and second end elements 2 and 5 are omitted. For example, if the laser discharge tube 100 is used in a fully internal cavity helium-neon laser, then windows 3 and 6 need to have high reflectivity to achieve low resonant cavity loss. In this case, such as Figure 3 As shown in (A), a reflective film (having a reflectivity of, for example, higher than 99.9%) can be deposited on the surface 302 of the first window 3 facing the tube 1, and preferably an anti-reflective film can be deposited on its surface 301 facing away from the tube 1. Simultaneously, a reflective film (having a reflectivity of, for example, about 99.8%, lower than the reflectivity of surface 302 to avoid excessively low power output laser beam) can be deposited on the surface 601 of the second window 6 facing the tube 1, and preferably an anti-reflective film can be deposited on its surface 602 facing away from the tube 1. In this case, surfaces 302 and 601 constitute the resonant cavity of the helium-neon laser.

[0025] In some applications, it is necessary to make Figure 3 (A) The material of the window 6 is located inside the resonant cavity. In these cases, a reflective film (having a reflectivity of, for example, higher than 99.9%) can be deposited on the surface 302 of the first window 3 facing the tube 1, and an anti-reflection film can preferably be deposited on its surface 301 facing away from the tube 1. Simultaneously, an anti-reflection film is deposited on the surface 601 of the second window 6 facing the tube 1, and a reflective film (having a reflectivity of, for example, about 99.8%, lower than the reflectivity of surface 302) can be deposited on its surface 602 facing away from the tube 1. In this case, surfaces 302 and 602 constitute the resonant cavity of the helium-neon laser.

[0026] On the other hand, if the laser discharge tube 100 is used in a semi-external cavity helium-neon laser, then only one of the windows 3 and 6 needs to have high reflectivity, while the other needs to be coated with antireflection films on both sides. In this case, such as Figure 3As shown in (B), for example, a reflective film (e.g., reflectivity higher than 99.9%) can be deposited on the surface 304 of the first window 3 facing the tube 1, and an anti-reflection film can preferably be deposited on its surface 303 facing away from the tube 1. Similarly, anti-reflection films are deposited on both the surface 603 of the second window 6 facing the tube 1 and the surface 604 facing away from the tube 1. Correspondingly, for the mirror element 16 located on the axis of the laser discharge tube 100, a reflective film is deposited on the surface 1601 facing the laser discharge tube 100 as a mirror for the resonant cavity, while an anti-reflection film can preferably be deposited on the surface 1602 facing away from the laser discharge tube 100. In this case, surfaces 302 and 1601 constitute the resonant cavity of the helium-neon laser. Furthermore, according to some embodiments, the surface orientation of the second window 6 may not be orthogonal to the axis of the laser discharge tube 100, but may have an angle, for example, a Brewster angle relative to the axis, to provide a single polarization direction.

[0027] exist Figure 3 In the examples shown, the resonant cavities of the helium-neon lasers all adopt a plano-concave cavity design. Of the two mirrors constituting the resonant cavity, the first window 3 provides a concave mirror, and the second window 6 or external mirror element 16 provides a planar mirror. In other embodiments, the first window 3 may provide a planar mirror, and the second window 6 or external mirror element 16 may provide a concave mirror. Furthermore, in some cases, the resonant cavity may also adopt a double-concave cavity design, where both mirrors are concave mirrors; in this case, in addition to the surface 302 or 304 of the first window 3, the surface 601 of the second window 6 or the surface 1601 of the mirror element 16 is also concave.

[0028] The helium-neon laser according to embodiments of the present invention is particularly suitable for various measurement applications in industrial, metrology, and scientific research fields. Under typical operating conditions, its vacuum wavelength is 633 nm, and its output power is typically 0.5-1.2 mW, which can reach 1.5-2.5 mW or higher for high-power applications.

[0029] The laser discharge tube 100 according to an embodiment of the present invention adopts an assembled structure, wherein its glass element and metal element are assembled into a whole by high-frequency sealing technology, instead of using traditional glass blowing technology. According to an embodiment of the present invention, the laser discharge tube has good overall thermal conductivity, reducing the thermal gradient between different parts of the tube body, which is beneficial for obtaining stable laser output power and stable laser polarization direction.

[0030] For a helium-neon laser, the surfaces of the two mirrors in the resonant cavity need to be perpendicular to the axis of the capillary discharge tube to minimize beam loss as it travels between the two mirrors through the capillary discharge tube. According to an embodiment of the present invention, after the first end element 2 and the second end element 5 are installed into the tube body 1, the thin tip of a dimming tool can be inserted into the annular groove 12 of the first part 21, and the opening of the groove 12 can be pried to fine-tune the axial direction of the first part 21, thereby aligning the mirror normal of the window 3 with the axis of the capillary discharge tube 8. Similarly, the tip of a dimming tool can be inserted into the annular groove 13 of the third part 51, and the opening of the groove 13 can be pried to fine-tune the axial direction of the third part 51, thereby aligning the mirror normal of the window 6 with the axis of the capillary discharge tube 8. The annular groove 12 is one of the plurality of grooves 11 and 12 on the outer periphery of the first part 21 that is closer to the tube body 1, and the annular groove 13 is one of the plurality of grooves 13 and 14 on the outer periphery of the second part 51 that is closer to the tube body 1.

[0031] If used only for the purpose of fine-tuning alignment, one annular groove in each of the first part 21 and the third part 51 is sufficient. However, the inventors have found that when the first end element 2 and the second end element 5 are installed onto the tube body 1 using a high-frequency sealing method, the axial position of the annular groove may affect the sealing process and the quality of the laser discharge tube. Take the first part 21 as an example. With only one annular groove, if the groove is far from the window, the metal portion of the first part 21 is longer, resulting in a larger heat capacity. This causes the heat applied during the high-frequency sealing process to dissipate faster, slowing down the material's melting point and increasing the difficulty of the sealing process. However, if the annular groove is close to the window, using a light-adjusting tool to pry the groove may cause deformation of the window, reducing the output stability of the laser discharge tube. According to an embodiment of the present invention, the outer periphery of the first part 21 has at least two annular grooves 11 and 12. The annular groove 11 is closer to the window 3, resulting in a shorter metal portion, reducing the heat capacity, thereby accelerating the material's heating and making it easier to achieve a good sealing process. The annular groove 12 is closer to the tube body 1 and farther from the window slat 3, so it is less likely to affect the window slat 3 when pried by the dimming tool. The same applies to the third part 51.

[0032] Furthermore, the second portion 22 of the first end element 2 has a shoulder surface adjacent to the first portion 21, and the second portion 4b of the cathode component 4 overlaps on this shoulder surface, simplifying the manufacturing process of the laser discharge tube 100 and maintaining high reliability of the laser operation. The cathode component of a helium-neon laser is typically a long aluminum tube. In conventional helium-neon lasers, connectors or welding processes are required to fix the cathode component relative to the tube body to ensure it remains stationary. According to an embodiment of the invention, during assembly, the second portion 4b of the cathode component 4 is flanged at its end to overlap the shoulder surface, eliminating the need for additional connectors or welding processes. In a further embodiment, a spring element 10 may be included to press the cathode component 4, further improving its installation stability. The spring element 10 is also a separate component and does not need to be fixed integrally with the first end element 2 or the cathode component 4, thus still allowing for a simple manufacturing process and reliable operation of the laser discharge tube 100.

[0033] The foregoing has described exemplary embodiments of the present invention in detail to enable those skilled in the art to implement the technical solutions disclosed herein. Various structural and logical substitutions and changes may be made without departing from the scope of this disclosure. Therefore, the specific description in the specification should not be construed as limiting, and the scope of the invention is defined only by the appended claims.

Claims

1. A helium-neon laser discharge tube (100), comprising: The cylindrical tube (1) has a substantially constant diameter along its entire length; The first end element (2) includes a cylindrical first part (21) and an umbrella-shaped second part (22), and is mounted to the first end face of the tube body (1) through the second part (22); The second end element (5) includes a cylindrical third portion (51) and an umbrella-shaped fourth portion (52), and is mounted to the second end face of the tube body (1) opposite to the first end face via the fourth portion (52); and A cathode component (4) is disposed inside the tube body (1) and adjacent to the second part (22) of the first end element (2). The first portion (21) of the first end element (2) includes two or more annular grooves (11, 12) along its axial direction.

2. The helium-neon laser discharge tube (100) according to claim 1, wherein, The second portion (22) of the first end element (2) includes a through hole along its axial direction and a shoulder surface adjacent to the first portion (21). The cathode component (4) includes a larger diameter portion (4a) fitted into the tube body (1) and a smaller diameter portion (4b) fitted into the through hole, the smaller diameter portion (4b) having a flange at its end facing the first portion (21) that overlaps the shoulder surface.

3. The helium-neon laser discharge tube (100) according to claim 2 further includes a spring element (10). in, The cathode component (4) includes a tapered connecting portion (4c) that connects the larger diameter portion (4a) and the smaller diameter portion (4b). One end of the spring element (10) abuts against the second part (22), and the other end abuts against the tapered connecting part (4c).

4. The helium-neon laser discharge tube (100) according to claim 1, wherein, The third part (51) of the second end element (5) includes two or more annular grooves (13, 14) along its axial direction.

5. The helium-neon laser discharge tube (100) according to claim 1 further includes: A capillary discharge tube (8) coaxial with the tube body (1), the capillary discharge tube (8) being mounted to the fourth portion (52) of the second end element (5); and An elastic support (15) is located between the cathode component (4) and the second end element (5) to support the capillary discharge tube (8).

6. The helium-neon laser discharge tube (100) according to claim 5 further comprises: Anode terminal (7) is disposed at the second end element (5); as well as Getter (9) is disposed at the cathode component (4) or on the capillary discharge tube (8).

7. The helium-neon laser discharge tube (100) according to claim 1, wherein, The tube body (1) is made of glass material, and the first end element (2) and the second end element (5) are made of alloy material with a coefficient of thermal expansion that matches that of the glass material.

8. The helium-neon laser discharge tube (100) according to any one of claims 1-7, further comprising: A first window (3), mounted to a first portion (21) of the first end element (2), the first window (3) having a reflective film on the side (302, 304) facing the tube body (1); and The second window (6) is mounted to the third part (51) of the second end element (5).

9. A helium-neon laser, comprising the helium-neon laser discharge tube (100) according to claim 8, wherein, The second window (6) has a reflective film on the side (602) facing away from the tube body (1) and an anti-reflective film on the side (601) facing the tube body (1), or The second window (6) has a reflective film on the side (601) facing the tube (1).

10. A helium-neon laser, comprising the helium-neon laser discharge tube (100) according to claim 8, wherein, The second window (6) has an anti-reflective film on both the side (603) facing away from the tube body (1) and the side (604) facing the tube body (1); and The helium-neon laser includes a mirror element (16) located outside the helium-neon laser discharge tube (100) on the axis of the helium-neon laser discharge tube (100), the mirror element (16) having a reflective film on the side (1601) facing the helium-neon laser discharge tube (100).

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