A Lyot filter for wavelength tuning of a solid-state laser

Abstract

The present invention relates to a Lyot filter for wavelength tuning of a solid-state laser, characterized in that: a base, a main mirror ring coaxially nested on the base, and a top block fixedly connected to the main mirror ring, and the base is fixed on a bottom plate; a linear motor is fixed on the bottom plate by a motor base, and the cylindrical top end of a push rod on the linear motor abuts against the inner side of a limit groove of the top block. Three birefringent filters with different thicknesses are placed in parallel at an interval of 0.5 mm within the same frame structure. Each of the birefringent filters can independently achieve the complex functions of 360° coaxial rotation and 45° common rotation of the three lenses. Its mechanical structure is small and compact, with few components and high precision. At the same time, it is driven by a micro linear motor to achieve a programmable control function; it has the advantages of few transmission components and high rotation angle precision.

Description

Technical Field

[0001] The present invention relates to a Lyot filter for wavelength tuning of a solid-state laser, which is a Lyot filter for controllable fully automated adjustment of the wavelength of a titanium sapphire laser based on the tuning principle of a birefringent filter. Background Art

[0002] Since 1986 when Moulton P F. of the MIT Lincoln Laboratory achieved the operation of a titanium-doped sapphire (Ti 3+ :AL2O3, hereinafter referred to as titanium sapphire) laser at room temperature, titanium sapphire lasers have made rapid progress worldwide. The coupling between the electronic energy levels of trivalent titanium ions in the titanium-doped sapphire crystal and the vibration energy levels of the surrounding crystal lattice determines that the most important feature of a titanium sapphire laser is the tunability of the wavelength of the fixed laser, with characteristics such as a wide tunable range and high gain. Therefore, when selecting a wavelength tuning method for a tunable titanium sapphire laser, it is necessary to ensure that the wavelength tuning range is wide enough while minimizing the linewidth as much as possible. The main wavelength tuning methods for lasers include birefringent filter (BF) tuning, grating tuning, prism tuning, etc. Among them, the birefringent filter (BF) tuning method is recognized in the industry as the best tuning method for current titanium sapphire lasers.

[0003] When light propagates in an inhomogeneous medium, its propagation speed and refractive index change with the vibration direction. Therefore, when a light beam is incident on an anisotropic crystal, it will be decomposed into two beams of light and refracted along different directions. This is the phenomenon of double refraction of light.

[0004] Stacking one or more birefringent plates can form the simplest Lyot filter. The thickness of each birefringent plate in a multi-layer Lyot filter is half of the thickness of the previous plate. The ordinary light and extraordinary light of the incident light beam have different phase velocities due to different refractive indices. Therefore, the polarization state of any wavelength of light beam will be changed after passing through the filter, thereby achieving the filtering of light waves of a specific length. We can change the working wavelength of the Lyot filter by rotating the refractive plate.

[0005] The refractive plate with the largest thickness determines the working bandwidth of the Lyot filter, and the refractive plate with the smallest thickness determines the free spectral range of the Lyot filter.

[0006] The Lyot filters currently available on the market are only traditional multi-layer birefringent plate stacking types and all have a manually rotated adjustment structure. At the same time, the Lyot filters used in related tunable titanium sapphire lasers are all laboratory-level devices simply stacked and placed. There is no controllable high-precision tuning mechanism that can be mass-produced and applied inside the laser.

[0007] Currently, a similar implementation method to the present invention is to use the form of stacking multiple birefringent plates to achieve wavelength tuning. First, each birefringent plate is separately placed in an independent support frame, and finally, multiple birefringent plates are placed in parallel at the Brewster angle with respect to the optical path. Then, the wavelength tuning of the laser is achieved by manually rotating each birefringent plate separately. This kind of structure is large in size, clumsy in structure, requires complex devices, can only be manually adjusted, has a large adjustment error, extremely low tuning accuracy, and poor laser stability. Summary of the Invention

[0008] The object of the present invention is to provide a Lyot filter for wavelength tuning of a solid-state laser. By utilizing the special structure and automatic controllability of the filter, the upper computer program controls the motor to drive a three-piece birefringent filter group to rotate coaxially, and finally realizes the overall object that the wavelength of the titanium sapphire laser can be automatically tuned within the range of 770 nm - 840 nm with a tuning accuracy of up to 1 nm; its mechanical structure is small and compact, with few devices and high precision. At the same time, a micro linear motor is used to drive, realizing a programmable control function; three birefringent filters with different thicknesses are placed in parallel at an interval of 0.5 mm in the same frame structure. Each birefringent filter can independently achieve the complex functions of 360° coaxial rotation and the common rotation of the three lenses by 45°. It has the advantages of fewer transmission devices and high rotation angle accuracy.

[0009] The technical solution of the present invention is implemented as follows: A Lyot filter for wavelength tuning of a solid-state laser, comprising a base; a main mirror ring; a top block; a tension spring; a linear motor; a push rod; a motor base; a bottom plate; a mirror ring - III;. mirror ring - II; birefringent filter - III; birefringent filter - II; birefringent filter - I; a PEEK ring; a mirror ring - II rotation angle limiting groove; a mirror ring - III rotation adjustment hole; a mirror ring - II rotation adjustment hole; a main mirror ring top block fixing hole; a pressing piece; a pressing piece fixing hole; a fixing screw I; a fixing screw II; a main mirror ring locking hole; a top block limiting groove; characterized in that: The base is fixed on the bottom plate by screws, the main mirror ring is coaxially nested on the PEEK ring, and the PEEK ring is then sleeved onto the base, and the PEEK ring functions as a lubricating bearing; the front end of the main mirror ring coincides with the front end of the PEEK ring and is limited by a pressing piece, and at the same time the rear end of the main mirror ring is limited by the limiting flange of the base, thus ensuring the coaxiality of the main mirror ring and the base during rotation; the top block is fixedly connected to the front end face of the main mirror ring by double screws, the linear motor is fixed on the bottom plate by a motor base, and the power system and the motion system are connected and the displacement is transmitted by the push rod on the motor, the linear motor push rod performs a linear telescopic motion, the cylindrical top end of the telescopic rod pushes the limiting groove of the top block, and at the same time the top block is connected to the tension spring by a fixing screw I, and the tension spring is fixed on the bottom plate 15 mm away from the center line of the top block by a fixing screw II, so that the tension spring plays a role in pulling the top block in the reverse direction, and finally the linear reciprocating motion of the push rod is converted into the circumferential reciprocating motion of the main mirror ring around the axis. The birefringent filter - I is glued into the groove with a diameter of 25.4 mm at the very front end of the main mirror ring, the birefringent filter - II is glued on the mirror ring - II, and the mirror ring - II is then sleeved into the groove with a diameter of 27 mm at the middle position of the main mirror ring. The internal boss structure of the main mirror ring ensures that the distance between the birefringent filter - I and the birefringent filter - I is 0.5 mm. Similarly, the birefringent filter - III is glued on the mirror ring - III, and the mirror ring - III is installed at the groove position with a diameter of 30 mm at the very end of the main mirror ring. The internal boss structure of the main mirror ring also ensures that the distance between the birefringent filter - III and the birefringent filter - II is 0.5 mm. In this way, the three birefringent filters achieve a spatially arranged state with coaxial and equal spacing. Before the entire set of mirror groups rotates coaxially together, it is necessary to first connect the mirror ring - II with a fine screw through the mirror ring - II rotation adjustment hole on the circumferential surface of the mirror ring - II, and then manually control the screw to achieve the reciprocating rotational motion of the mirror ring - II with a maximum angle of 45° along the rotation angle adjustment groove on the circumferential surface of the mirror ring - II side.Similarly, use fine screws to connect the lens ring-III 9 through the lens ring-III adjustment holes on the rear end face of the lens ring-III, and then manually control the screws to achieve a 360° rotational movement of the lens ring-III. After both lens rings are rotated to specific positions, use set screws to lock and fix the positions of the two lens rings respectively through the locking holes on the circumferential surface of the main lens ring side, so as to ensure that the relative positions of the three groups of lenses remain unchanged and achieve the tuning purpose of the common rotation of the three groups of lenses.

[0010] Each of the birefringent filter-I, birefringent filter-II, and birefringent filter-III can rotate independently 360° coaxially and the three lenses can rotate together by 45°. The thickness of the birefringent filter-I is 4mm, the thickness of the birefringent filter-II is 2mm, and the thickness of the birefringent filter-III is 0.5mm.

[0011] The main lens ring is provided with three boss structures.

[0012] After the lens ring-II rotates 22.5° and the lens ring-III rotates 37.4°, use set screws to lock the two lens rings respectively through the locking holes of the main lens ring, and the relative positions of the three groups of lenses remain unchanged.

[0013] The positive effects of the present invention are: improving the accuracy and tunable range of laser wavelength tuning; having a compact structure and high stability, effectively reducing the space size and the number of parts; realizing controllable automation program, and the laser wavelength control accuracy is as high as 1nm. Brief Description of the Drawings

[0014] Figure 1 is a 3D stereoscopic view of the present invention.

[0015] Figure 2 is a structural schematic diagram of the present invention.

[0016] Figure 3 is a left side sectional view of the base.

[0017] Figure 4 is a top view of the present invention.

[0018] Figure 5 is a rear view of the present invention. Embodiment

[0019] The following further describes the present invention in conjunction with the drawings and embodiments: As Figure 1As shown in the figure, a Lyot filter for wavelength tuning of a solid-state laser includes a base 1; a main mirror ring 2; a top block 3; a tension spring 4; a linear motor 5; a push rod 6; a motor base 7; a bottom plate 8; a mirror ring - III 9; a mirror ring - II 10; a birefringent filter - III 11; a birefringent filter - II 12; a birefringent filter - I 13; a PEEK ring 14; a mirror ring - II rotation angle limiting groove 15; a mirror ring - III rotation adjustment hole 16; a mirror ring - II rotation adjustment hole 17; a main mirror ring top block fixing hole 18; a pressing piece 19; a pressing piece fixing hole 20; a fixing screw I 21; a fixing screw II 22; a main mirror ring locking hole 23;. a top block limiting groove 24; and is characterized in that: the base 1 is fixed on the bottom plate 8 by screws, the main mirror ring 2 is coaxially nested on the PEEK ring 14, and the PEEK ring 14 is then sleeved on the base 1, and the PEEK ring 14 functions as a lubricating bearing. The front end of the main mirror ring 2 coincides with the front end of the PEEK ring 14 and is limited by the pressing piece 19. At the same time, the rear end of the main mirror ring 2 is limited by the limiting flange of the base 1, so as to ensure the coaxiality of the main mirror ring 2 and the base 1 during the rotation process. The top block 3 is fixedly connected to the front end face of the main mirror ring 2 by double screws, the linear motor 5 is fixed on the bottom plate 8 by the motor base 7, and the displacement is connected and transmitted between the power system and the motion system by the push rod 6 on the motor. The linear motor push rod 6 performs a linear telescopic motion, and the cylindrical top end of the telescopic rod pushes the limiting groove 24 of the top block 3. At the same time, the top block 3 is connected to the tension spring 4 by the fixing screw I 21, and the tension spring 4 is fixed on the bottom plate 8 at a distance of 15 mm from the center line of the top block 3 by the fixing screw II 22. In this way, the tension spring 4 plays a role in pulling the top block 3 in the reverse direction, and finally converts the linear reciprocating motion of the push rod 6 into the circumferential reciprocating motion of the main mirror ring 2 around the axis. The birefringent filter - I 13 is glued into the groove with a diameter of 25.4 mm at the front end of the main mirror ring 2, the birefringent filter - II 12 is glued on the mirror ring - II 10, and the mirror ring - II 10 is then sleeved into the groove with a diameter of 27 mm at the middle position of the main mirror ring 2. The distance between the birefringent filter - I 13 and the birefringent filter - I 12 is ensured to be 0.5 mm by the internal boss structure of the main mirror ring 2. Similarly, the birefringent filter - III 11 is glued on the mirror ring - III 9, and the mirror ring - III 9 is installed at the groove position with a diameter of 30 mm at the end of the main mirror ring 2. The distance between the birefringent filter - III 11 and the birefringent filter - II 12 is also ensured to be 0.5 mm by the internal boss structure of the main mirror ring 2. In this way, the three birefringent filters achieve a spatially placed state with coaxial and equal spacing. Before the entire mirror group rotates coaxially together, it is necessary to first connect the mirror ring - II 10 with a thin screw through the mirror ring - II rotation adjustment hole 17 on the circumferential surface of the mirror ring - II 10, and then manually control the screw to realize the reciprocating rotational motion of the mirror ring - II 10 along the rotation angle adjustment groove 15 on the circumferential surface of the mirror ring - II 10 with a maximum angle of 45°.Similarly, use fine screws to connect the lens ring - III9 through the lens ring - III adjustment holes 16 on the rear end face of the lens ring - III9, and then manually control the screws to achieve a 360° rotational movement of the lens ring - III9. After both lens rings are rotated to specific positions, use set screws to lock and fix the positions of the two lens rings respectively through the locking holes 23 on the circumferential surface of the main lens ring 2. In this way, the relative positions of the three groups of lenses are ensured to remain unchanged, and the tuning purpose of the common rotation of the three groups of lenses is achieved.

[0020] Each of the birefringent filter - I13, birefringent filter - II12, and birefringent filter - III11 can independently rotate 360° coaxially and the three lenses can rotate together by 45°. The birefringent filter - I13 has a thickness of 4 mm, the birefringent filter - II12 has a thickness of 2 mm, and the birefringent filter - III11 has a thickness of 0.5 mm.

[0021] The main lens ring 2 is provided with three boss structures.

[0022] As Figure 2 shown, the base 1, the main lens ring 2 coaxially nested on the base 1, and the top block 3 fixedly connected to the main lens ring 2. At the same time, the base 1 is fixed on the bottom plate 8. The linear motor 5 is fixed on the bottom plate 8 by the motor base 7. The cylindrical top end of the push rod 6 on the linear motor 5 abuts against the inner side of the limit groove 24 of the top block 3. As Figure 3 、 4 shown, the birefringent filter - I13 is glued to the front end of the main lens ring 2. The birefringent filter - II12 is glued to the lens ring - II10. The lens ring - II10 is installed in the middle position of the main lens ring 2. The inner boss structure of the main lens ring 2 ensures that the distance between the birefringent filter - I13 and the birefringent filter - I12 is 0.5 mm. Similarly, the birefringent filter - III11 is glued to the lens ring - III9. The lens ring - III9 is sleeved on the outermost end of the main lens ring 2. The inner boss structure of the main lens ring 2 also ensures that the distance between the birefringent filter - III11 and the birefringent filter - II12 is 0.5 mm. The end of the lens ring - III9 coincides with the end of the main lens ring 2 and is stuck inside the limit flange of the base 1 to achieve the effect of axial positioning. In this way, the three birefringent filters are placed coaxially and at the same distance. As Figure 4 shown, before the entire lens group rotates coaxially together, it is necessary to first connect to the lens ring - II rotation adjustment hole 17 with fine screws and manually adjust the screws to achieve the rotational movement of the lens ring - II10 along the lens ring - II rotation adjustment groove 15. As Figure 5As shown, it is connected to the rotation adjustment hole 16 of the lens ring - III with a thin screw. The manual adjustment screw is used to achieve the rotational movement of the lens ring - III 9. When the lens ring - II 10 rotates 22.5°, and the lens ring - III 9 rotates 37.4°, then the two lens rings are respectively locked with set screws through the main lens ring locking holes 23 to ensure that the relative positions of the three groups of lenses remain unchanged.

[0023] When the above - mentioned Leo filter is in use, the linear motor 5 transmits the linear motion to the top block 3 through the push rod 6. The top block 3 drives the main lens ring 2 to make an axial rotational motion around the base 1. The tension spring 4 plays a role in damping and resetting, ensuring that the top block 3 can return to the initial position of the previous time during each reciprocating motion, and finally ensuring the adjustment accuracy of the entire system. In this way, the three groups of birefringent filters in the main lens ring 2 achieve a rotation of 0 - 45°, and finally realize the wavelength tuning of the titanium - sapphire laser.

[0024] The specific steps are as follows: 1. First, place the thickest birefringent filter - I 13 into the innermost partition groove of the main lens ring 2. Then, place the birefringent filter - II 12 with a medium thickness into the lens ring - II 10. At the same time, place the lens ring - II 10 parallel to the birefringent filter - I 13 with a spacing of 0.5 mm into the second - layer partition groove of the main lens ring. Finally, place the thinnest birefringent filter - III 11 into the lens ring - III 9, and then place the lens ring - III 9 parallel to the birefringent filter - II 12 with the same 0.5 - mm spacing into the outermost partition groove of the main lens ring 2. The main lens ring 2 containing the three birefringent filters is then placed in the base. The outer - circular end face of the main lens ring 2 is connected to the inner - circular end face of the base with a lubricating PEEK ring 14. The rear end face of the main lens ring 2 is limited by the flange end face of the base, and the front end face is limited by the pressing piece 19 to prevent it from swinging back and forth relative to the base. The outer - circular end face of the main lens ring 2 is drilled with a slot hole and a threaded hole with a specific length and width at the position of the lens ring - II 10, which respectively play the roles of manually rotating the birefringent filter - II by a certain angle and locking and fixing. Similarly, the outer - circular end face of the main lens ring 2 is also drilled with a locking and positioning threaded hole at the position of the lens ring - III 9 to fix the birefringent filter - III 11. The independent rotational movement of the birefringent filter - III 11 is operated through the adjustment threaded hole and the screw on the rear end face of the lens ring - III 9.

[0025] After the relative positions of the three birefringent filters are adjusted, lock the lens ring II and the lens ring III with set screws to ensure no relative rotation between them. Then, through the top block 3 installed on the front of the main lens ring 2 and transmission mechanisms such as linear motors, convert linear motion into circular motion. When the motor receives a drive signal command, it makes a linear telescopic motion (the motion displacement can be precisely controlled by a pulse signal, with a maximum precision of up to 0.01 mm). A tension spring 4 is connected between the top block 3 and the bottom plate 8 to play a role in reverse reset control. At this time, the top block 3 in contact with it will drive the main lens ring 2 to achieve a reciprocating rotation of 0 - 45°, and when the laser passes through the rotating refractive sheet, the output wavelength of the laser is changed.

Claims

1. A Lyot filter for wavelength tuning of a solid-state laser, comprising a base; a main mirror ring; a top block; a tension spring; a linear motor; a push rod; a motor base; a bottom plate; a mirror ring - III; a mirror ring - II; a birefringent filter - III; a birefringent filter - II; a birefringent filter - I; a PEEK ring; a mirror ring - II rotation angle limit groove; a mirror ring - III rotation adjustment hole; a mirror ring - II rotation adjustment hole; a main mirror ring top block fixing hole; a pressing piece; a pressing piece fixing hole; a fixing screw I; a fixing screw II; a main mirror ring locking hole; a top block limit groove; and characterized in that: The base is fixed on the bottom plate. The main mirror ring is coaxially nested on the PEEK ring, and the PEEK ring is then sleeved onto the base. The front end of the main mirror ring coincides with the front end of the PEEK ring and is limited by a pressing piece. At the same time, the rear end of the main mirror ring is limited by the limiting flange of the base, and the main mirror ring is coaxial with the base. The top block is fixedly connected to the front end face of the main mirror ring by two screws. The linear motor is fixed on the bottom plate through a motor base. The displacement is connected and transmitted between the power system and the motion system by a push rod on the motor. The push rod of the linear motor performs a linear telescopic motion. The cylindrical top end of the push rod abuts against the inner side of the limiting groove of the top block. At the same time, the top block is connected to a tension spring through a fixing screw I, and the tension spring is fixed on the bottom plate 15 mm away from the center line of the top block through a fixing screw II, converting the linear reciprocating motion of the push rod into the circumferential reciprocating motion of the main mirror ring around the axis. The birefringent filter-I is glued into the birefringent filter-I groove with a diameter of 25.4 mm at the very front end of the main mirror ring. The birefringent filter-II is glued on the mirror ring-II, and the mirror ring-II is then sleeved into the mirror ring-II groove with a diameter of 27 mm at the middle position of the main mirror ring. The birefringent filter-III is glued on the mirror ring-III, and the mirror ring-III is installed at the position of the mirror ring-III groove with a diameter of 30 mm at the very end of the main mirror ring. The inside of the main mirror ring is a boss structure. The birefringent filter-I, the birefringent filter-I, and the birefringent filter-III are arranged at intervals of 0.5 mm inside the main mirror ring; that is, the three birefringent filters, namely the birefringent filter-I, the birefringent filter-I, and the birefringent filter-III, are placed coaxially and equidistantly in space. The circumferential surface of the mirror ring-II is provided with a mirror ring-II rotation adjustment hole to connect the mirror ring-II, and the mirror ring-II performs a reciprocating rotation motion with a maximum angle of 45° along the rotation angle adjustment groove on the circumferential surface of the mirror ring-II side. The mirror ring-III adjustment hole on the rear end face of the mirror ring-III connects the mirror ring-III, and the mirror ring-III performs a 360° rotation motion. The two mirror rings, namely the mirror ring-II and the mirror ring-III, are locked and fixed by a set screw respectively through the locking holes on the circumferential surface of the main mirror ring side.

2. The Lyot filter for wavelength tuning of a solid-state laser according to claim 1, wherein Each of the birefringent filter-I, the birefringent filter-II, and the birefringent filter-III can independently rotate 360° coaxially and the three lenses can rotate together by 45°. The thickness of the birefringent filter-I is 4 mm, the thickness of the birefringent filter-II is 2 mm, and the thickness of the birefringent filter-III is 0.5 mm.

3. The Lyot filter for wavelength tuning of a solid-state laser according to claim 1, characterized in that The main mirror ring is provided with three boss structures.

4. The Lyot filter for wavelength tuning of a solid-state laser according to claim 1, characterized in that After the mirror ring-II rotates 22.5° and the mirror ring-III rotates 37.4°, the two mirror rings are locked respectively by a set screw through the locking holes of the main mirror ring, and the relative positions of the three groups of lenses remain unchanged.

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