Patent Application
20220350060
The present invention relates to a fixing device for an optical diffraction element and particularly to a fixing device for a reflective diffraction element.
Optical diffraction elements, represented by Fresnel lenses, are optical components that utilize the wave motion characteristic of light and convert patterns of light intensity and that are used in various industrial fields. Fresnel lenses utilize periodicity at a pitch of wavelengths for light with a constant wavelength, allowing a typically thick lens to be replaced with a thin lens.
Currently, in addition to Fresnel lenses that focus light, various reflective diffraction elements, such as a diffraction mirror, with a diffraction pattern formed on a light-reflecting mirror surface for reflecting and converting the light into various forms of light beams are being developed and used as optical diffraction elements used in wave optics.
As described in NPL 1, one application of this technology is a high power laser for processing, and a reflective diffraction element is also used in laser resonator optical systems and laser beam transmission optical systems. Typical examples of a continuous output high power laser include a gas dynamic laser or a chemical laser, both of which have an oscillation wavelength of a longer wavelength in the infrared region. Thus, a metal reflective mirror formed of metal is often used as the material of a diffraction mirror for beam shaping developed for heat ray lasers.
A metal reflective mirror is unable to function as a high reflectivity mirror, such as a dielectric multi-layer film, in the infrared region, with there being an approximately 2% light energy absorption in the diffraction mirror. In a case of a megawatt-class laser device, this 2% light energy absorption results in approximately 20 kilowatts of heat input being regularly present in the diffraction mirror, leading to increased risk of thermal deformation and thermal damage of the diffraction mirror.
In order to avoid thermal deformation of the diffraction mirror as much as possible and prevent thermal damage, not only must the material of the optical substrate of the diffraction mirror be considered, but also the cooling mechanism needs to be considered. An example of a cooling mechanism for a diffraction mirror includes impinging the back surface of the mirror with air containing water droplets to cool the mirror via the heat of evaporation of the water droplets. In this method, in a case where the mirror is made of a material that is resistant to high temperatures, the cooling efficiency can be improved by an amount relative to how high the temperature is compared to room temperature operation.
In order to efficiently cool a mirror like the one in the example described above, the cooling medium needs to be directly impinged on the mirror. However, as the flow rate of the refrigerant increases, the cooling capacity increases, causing the pressure of the cooling medium applied to the mirror to increase. This may cause the curvature to be changed due to deformation of the mirror. In particular, with a metal reflective mirror such as a reflective diffraction element constituted by a metal plate having a thickness less than that of a refractive lens, the deformation due to the effect of pressure is large, so the curvature of the reflective diffraction element may have slightly a different value when used compared to when designed. This deviation in curvature changes the focal length of the diffraction light, thereby complicating the design of the optical system.
NPL 1: Kenichi UEDA, High power laser adaptive optical system, Laser Research, Vol. 27-2, pp. 84-88, 1999
As described above, in the application of a high power lasers, large heat generation occurs in the diffraction element, and a large amount of cooling fluid is needed for cooling. However, the pressure from a large amount of cooling fluid may warp the diffraction element, leading to the focal length problematically changing from the designed focal length.
In light of the foregoing, an object of the present invention is to provide a fixing device for implementing the use of a diffraction element with high power light that fixes a diffraction element in a shape that is less susceptible to warping due to pressure of a cooling fluid and is able to resist deformation.
In a fixing device of the present invention, a diffraction element is fixed in a shape, such as one with an arch-like cross-section, that is able to reduce deformation and is fixed with a structure resistant to deformation due to pressure. Thus, the diffraction element does not deform significantly even when subjected to large water pressure or air pressure for cooling, and the focal length according to specifications can be used.
Examples of embodiments of the present invention include the following configurations to achieve the above object.
Configuration 1
A fixing device for a diffraction element includes:
Configuration 2
In the fixing device for a diffraction element according to Configuration 1,
Configuration 3
In the fixing device for a diffraction element according to Configuration 2,
Configuration 4
In the fixing device for a diffraction element according to any one of Configurations 1 to 3, one of the two of the inner wall surfaces of the element installation portion where the element installation surface is not provided is constituted by a length adjustment portion for changing an effective length of the element installation surface; and
Configuration 5
In the fixing device for a diffraction element according to Configuration 4,
Configuration 6
The fixing device for a diffraction element according to any one of Configurations 1 to 5, wherein
Configuration 7
In the fixing device for a diffraction element according to any one of Configurations 1 to 6,
According to a fixing device for a diffraction element as described above, a diffraction element is fixed in a shape, such as one with an arch-like cross-section, that is able to reduce deformation and is fixed with a structure resistant to bending. Thus, the diffraction element does not deform significantly even when subjected to large water pressure or air pressure for cooling, and the focal length substantially according to specifications can be used.
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following embodiments, a fixing device of a laser device using a reflective diffraction element is described. However, the present invention has many varying applications and should not be construed as being limited to the contents described below.
Overall Configuration in In-use State
The diffraction element 1, as illustrated in
The fixing device 100 according to the first embodiment of
In the first embodiment, the diffraction element 1 is cooled from the back surface by applying pressure and making the cooling fluid 4 flow from outside to inside the fixing device. Thus, the diffraction element 1 receives the pressure P from the cooling fluid 4 acting toward the outside of the fixing device.
In
The cooling fluid 4 passes through a circulation path from an external device (not illustrated) and is forced inside the fixing device via a flow inlet 5a on the upper side of
The element installation portion 2 is a piece of hardware used to install the diffraction element 1, and the shape, material, installation angle, size, weight, fixing method, and the like are not limited by this embodiment.
An example of the element installation portion 2 includes a piece of hardware shaped like a substantially rectangular parallelepiped box-like container that is slightly smaller than the external shape of the diffraction element 1 and includes an opened upper surface for installing the rectangular plate-like diffraction element 1. The four-sided peripheral portion (edge portion) of the rectangular plate-like diffraction element 1 that serves as the lid of the upper surface of the box-like container may be fixed between the element fixing portion 3 that serves as the frame of the lid and the upper end of the inner wall surface of the element installation portion 2.
As illustrated in
The element fixing portion 3 is another piece of hardware for fixing the rectangular plate-like diffraction element 1 that is attached to the upper end or the inner wall surface of the element installation portion 2 and constitutes the frame of the diffraction element 1 that serves as the lid of the upper surface of the element installation portion 2. Here, the shape, material, angle, size, weight, fixing method, and the like are not limited by this example. As in the example described above, the element fixing portion 3 is only required to be a piece of hardware that can be attached to the element installation portion 2 sandwiching the edge portion of the diffraction element 1 and can secure the diffraction element 1 in an immovable state. Because the element fixing portion 3 can curve and secure the diffraction element 1, deformation and displacement of the diffraction element 1 due to the pressure P of the cooling fluid 4 can be reduced.
Configuration of Element Installation Portion and Element Fixing Portion
Also,
The cross-sectional view of the element installation portion 2 as seen from the side surface in
In the cross-sectional view of the element fixing portion 3 in
As illustrated in the cross-sectional view in
As illustrated in
As illustrated in the perspective view of the element installation portion 2 in
In order to prevent leakage of the cooling fluid 4, elastic, water resistant cushioning material (packing) made of rubber of a synthetic resin or filler (sealing material, caulking material) may be disposed in a peripheral gap between the inner wall surface of the element installation portion 2 and the diffraction element 1 on the surface of the step on the element installation surface 6 or the element fixing surface 7.
With the fixing device 100 having this structure, the diffraction element 1 can be supported on the surface of the step including the element installation surface 6 of the element installation portion 2 and sandwiched and fixed by element fixing surface 7 of the element fixing portion 3 on the upper surface side in a manner such that, in this fixed state, the cooling fluid 4 can be brought into contact with the rear surface of the diffraction element 1.
The shape, material, angle, and size of the element installation surface 6 are not limited by the drawings. However, as illustrated by the perspective view of
Then, as illustrated in the perspective view in
Evaluation of Amount of Deflection Due to Arch-like Shape
In a case where the surface is formed in this manner, the amount of deflection of the diffraction element 1 when pressure is received is less when the diffraction element 1 is curved in an arch-like shape and fixed beforehand compared to being fixed flat in a flat plate-like manner, even when the pressure P received by the diffraction element 1 from the cooling fluid 4 flowing into the fixing device is the same.
For example, the material of the diffraction element 1 is SiC and the dimensions are 100×50×1 (mm). In a case where the diffraction element 1 is fixed in a flat manner, a deflection δ (mm) at the center portion of the diffraction element 1 obtained via
where a uniformly distributed load applied in the vertical direction from the cooling fluid is q (N/mm), Young's modulus (N/mm2) is E, the length (mm) of the diffraction element 1 is L, and the cross-sectional secondary moment (mm4) is I.
In a case where the element installation surface 6 is formed in a flat manner, I=4.2 (mm4), E=4.3×105 (N/mm2), and L=100 (mm). Thus, when the uniformly distributed load q=1 (N/mm), the amount of deflection is δ=0.73 (mm).
In contrast, in a case where the element installation surface 6 is formed in an arch-like shape and the diffraction element 1 is fixed in an arch-like shape (a semi-circular shape for example), the cross-sectional secondary moment I=48.6 (mm4), L=50 (mm), and the amount of deflection is δ=0.039 (mm), which is smaller than in the case where it is formed flat. Accordingly, by forming the element installation surface 6 in an arch-like shape, the amount of deflection of the diffraction element 1 can be reduced.
Additionally, as illustrated in another example of the fixing device according to the first embodiment of
In a case where the element installation surface 6 has an inward arc-like shape (concave surface) in this manner, the uniformly distributed load q (N/mm) applied to the diffraction element 1 is balanced with the compression force of the diffraction element 1. In other words, a load can be considered to be applied in a direction parallel with the plate surface of the flat plate of the diffraction element 1. Thus, the amount of deformation AL due to the load can be expressed by
where the strain of the diffraction element is ε , the height of the diffraction element is h (mm), and the width of the diffraction element is b (mm).
When L=100 (mm), h=50 (mm), and b=1 (mm), strain ϵ=4.7×10−6 and ΔL=4.7×10−4 (mm). In a case where the diffraction element has an arch-like shape (a semicircular shape for example), the amount of decrease in the height of the rise of the arch when the arc length decreases by ΔL due to the load becomes equal, thus the amount of deflection δ=2.3×10−4 (mm). In other words, the amount of deformation is reduced in a case such as that illustrated in
From the foregoing, it can be seen that the first embodiment and the following embodiments are not limited in terms of the orientation of the arch being in the inward direction (concave surface) or the outward direction (convex surface), and either may be used.
The fixing device of the second embodiment of
The plurality of grooves 8 are formed as sets on two opposing inner wall surfaces where the element installation surface 6 of the element installation portion 2 is not provided, running parallel with the bottom surface of the element installation portion 2 (the surface on the left end of
With the fixing device according to the second embodiment of
Additionally, with the fixing device according to the second embodiment, by disposing the plurality of grooves 8 in sets, the curvature of the diffraction element 1 can be changed by selecting the groove position to insert the diffraction element 1. By changing the curvature of the diffraction element 1, the focal point of the diffraction light can be adjusted.
In a case where the groove 8 position where to diffraction element 1 is to be fixed at is able to be selected allowing for adjustment, preferably the element installation surface 6 stops sufficiently before the grooves 8 and has a length less than that in the first example or the arch of the element installation surface 6 is formed with a large curvature. Alternatively, the element installation surface 6 may have a cylindrical surface with a low height. In
Although not illustrated in
In a case where gaps are created due to the position of the selected grooves such that leakage of the cooling fluid 4 is a concern, cushioning material (packing) or filler (sealing material, caulking material) may be disposed around the periphery of the diffraction element 1.
For example, take a case where 1 mm grooves 8 are formed in a five set parallel to one another in the inner wall on the short side of the element installation portion 2 at 1 mm intervals, and a portion of the element installation surface 6 is fixed and disposed on the inner wall on the long side. In this case, the curvature of the diffraction element 1 can be selected from five patterns according to the position of the grooves on the short side for receiving the diffraction element 1. As the focal length becomes shorter as the curvature increases, the focal length can be adjusted by changing in which grooves the diffraction element 1 is inserted. Of course, the size, arrangement interval, and the number of grooves are not limited by this example, and the shape and arrangement of the element installation surface is not limited by this example.
The fixing device according to the third embodiment of
As illustrated in
The four screws extend through the length adjustment portion 9 and the cushioning portion 10 and are screwed into the wall surface of the element installation portion 2 or the element fixing portion 3, and screw threads that engage with the screws are formed in the inner surface of the screw holes formed corresponding to the four screws in the element installation portion 2 and the element fixing portion 3. The length adjustment portion 9 enables adjustment of the effective length of the element installation surface 6 within a range of the expansion and contraction range of the cushioning portion 10 via the depth at which the four screws are screwed in.
The length adjustment portion 9 of the third embodiment in
The cushioning portion 10 in
The fixing device according to the fourth embodiment of
The installation surface forming portion 11 is constituted by one or more components and forming a plurality of reference surfaces for installing the diffraction element 1 on the wall surfaces inside the element installation portion 2. This allows the element installation surfaces 6 to be formed independently in the wall surfaces with a discretionary shape, incline, and height. The shape of each of the components constituting the installation surface forming portion 11 may vary from one component to another, for example, the short side component may have a rectangular parallelepiped shape and the long side component may have a cylindrical shape. The component may have a curved shape as with the element installation surface 6 in
The arrangement position may also vary from component to component. For example, the installation surface can be given an arch-like shape by disposing the short side at a lower portion (on the bottom surface side) than the long side. Of course, the shape, arrangement, size, material, number, and the like of the components are not limited, and the components may be the same or different from component to component.
The height adjustment portion 12 is a mechanism for installing the installation surface forming portion 11 at a position at a discretionary height of the inner wall surface of the element installation portion 2. The height adjustment portion 12 is constituted by one or more of a mechanism capable of securing the installation surface forming portion 11, such as a clip, a locking catch, a button, or the like; a mechanism for changing the installation position, such as a rail, engagement groove, band, or the like corresponding to the securing mechanism. In this manner, the arrangement (height) of the installation surface forming portion 11 can be changed. Naturally, the method of changing the installation position is not limited by the example described above, it is only required that the method enable the installation surface forming portion 11 to be attached at a discretionary plurality of positions, examples including but not being limited to forming a plurality of grooves for attaching installation surface forming portions 11, using an adhesive material for the installation surface forming portions 11, and the like.
The element fixing portion 3 according to the fourth embodiment of
As described above, according to a fixing device for a diffraction element of the present invention, the diffraction element does not deform significantly even when subjected to large water pressure or air pressure for cooling, and the focal length substantially according to specifications can be used.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/039205 | 10/3/2019 | WO |
