Optical system for laser processing equipment, and laser processing equipment

Abstract

The objective is to provide an optical system for a laser processing apparatus equipped with at least one protective glass that can compensate for and correct the shift in focal length caused by changes in the refractive index and radius of curvature of the lens or protective glass due to the heat of the laser beam, thereby preventing the optical system from shifting focus and enabling proper laser processing. [Solution] To achieve this objective, an optical system for a laser processing apparatus is employed for laser processing by irradiating a workpiece with a laser beam emitted from a laser oscillator to form a spot, comprising a collimating lens for making the laser beam into parallel light, a focusing lens for focusing the parallel light, and at least one protective glass, wherein the dn1 / dT of the collimating lens is a negative value, the dn2 / dT of the focusing lens is a negative value, and the dn3 / dT of the protective glass is a positive value.

Description

[Technical Field]

[0001] The present invention relates to an optical system for a laser processing apparatus that irradiates a laser beam emitted from a laser oscillator onto a workpiece to form a spot and perform laser processing, and to a laser processing apparatus equipped with the optical system of the laser processing apparatus. [Background technology]

[0002] In recent years, laser beams have been widely used in the processing of various products. A laser beam is focused to a single point to form a spot and irradiates the workpiece, rapidly increasing the surface temperature of the workpiece and melting or vaporizing the irradiated surface. Laser processing equipment that uses this laser beam is a device that performs processing such as cutting, drilling, and welding on workpieces in this manner. Furthermore, because the laser beam is focused to a single point, pinpoint, precise, and micro-processing is possible. In addition, by using a higher energy laser beam, processing time can be shortened, and it is also possible to process highly hard workpieces that are difficult to process with cutting tools.

[0003] Here, the laser processing apparatus is equipped with an optical system. This optical system includes, for example, optical elements for converting the laser beam emitted radially from the laser oscillator into parallel light, optical elements for focusing the laser beam to a single spot, and optical elements for shaping the laser beam image at the spot into a circular shape with a Gaussian or top-hat energy intensity distribution, or an annular shape.

[0004] Quartz is often used as the optical material for the optical elements in the optical systems of such laser processing devices. Quartz has an average coefficient of linear thermal expansion of 5.9 × 10⁻⁶ for fused silica. -7 / ℃, 4.7 × 10⁻⁶ in synthetic quartz -7This is because the coefficient of thermal expansion is small ( / °C) and the heat resistance temperature is high (approximately 1000°C). However, as mentioned above, the average coefficient of linear expansion of quartz is not zero, so when the energy of the laser beam incident on an optical element using quartz is high, the incident portion of the laser beam in the optical element is heated and expands. Due to this expansion, the incident portion of the laser beam in the optical element becomes partially convex, and the radius of curvature of the optical element changes to a small value. Also, the rate of change of refractive index per unit temperature change of fused silica, dn / dT, is 10 × 10 -6 The temperature is approximately / °C. When a laser beam is incident on an optical element made of quartz and the temperature rises, the refractive index of the optical material of the optical element changes to a large value. This change in the state of the optical element is called the thermal lensing effect.

[0005] Here, the focal length f of the optical element is given by 1 / f = (n-1)(1 / r1-1 / r2)+(n-1), where n is the refractive index of the optical material of the optical element, r1 is the radius of curvature of the first surface, r2 is the radius of curvature of the second surface, and d is the thickness of the center. 2 It is defined as d / (nr1r2). When the thermal lensing effect described above occurs, the values ​​of the radii of curvature r1 and r2 decrease due to expansion, and the value of the refractive index n increases, so the focal length f of the optical element changes to a small value. When such an optical element is used in the optical system of a laser processing device, if the thermal lensing effect occurs, the focus of the optical system of the laser processing device shifts to the under-focus side, causing problems such as deformation of the image shape of the laser beam at the spot and a decrease in the energy density per unit area of ​​the laser beam, which prevents proper laser processing.

[0006] Therefore, Patent Document 1 proposes an optical system for a laser processing apparatus that compensates for changes in the refractive index of a lens due to the heat of the laser beam by comprising a collimating lens using an optical material having positive dn / dT characteristics and a focusing lens using an optical material having negative dn / dT characteristics. Furthermore, Patent Document 2 proposes reducing the amount of focus shift with the lens alone by employing a lens having negative dn / dT characteristics and having a thickness and diameter selected such that the magnitude of the focus shift due to the change in refractive index is less than twice the magnitude of the focus shift due to thermal expansion. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Special table number 2013-524539 [Patent Document 2] Japanese Patent Publication No. 2018-081232 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, the optical system of a laser processing device is exposed to spatter and fumes that molten and scatter from the workpiece during laser processing. When spatter and fumes adhere to the lenses of the optical system of a laser processing device, problems can arise such as the spatter and fumes on the lens surface masking the laser beam, reducing the energy density of the laser beam at the spot; the focal length changing due to changes in the refractive index and curvature of the lens caused by the heat of the attached spatter; and the lens being damaged due to the attached spatter being heated by the laser beam and becoming locally hot. For this reason, protective glass may be provided at least on the spot side of the optical system of a laser processing device to prevent spatter and fumes from entering the optical system of the laser processing device.

[0009] When this protective glass is used, the laser beam incident on the protective glass causes a thermal lensing effect on the protective glass itself. Furthermore, if quartz, which has low thermal expansion and high heat resistance, is used as the optical material for the protective glass, it will have a positive dn / dT characteristic. However, this protective glass is not considered in Patent Documents 1 and 2. If protective glass were to be included in Patent Documents 1 and 2, the positive dn / dT characteristic of the protective glass would be added, making it impossible to adequately compensate for the shift in focal length caused by changes in the refractive index and radius of curvature of the lens and protective glass due to the heat of the laser beam. This would result in a focus shift in the optical system of the laser processing device, preventing proper laser processing.

[0010] The present invention has been made in view of these circumstances. The present invention aims to provide an optical system for a laser processing apparatus equipped with at least one protective glass, which can compensate for the shift in focal length caused by changes in the refractive index and radius of curvature of the lens or protective glass due to the heat of the laser beam, thereby preventing the optical system of the laser processing apparatus from shifting focus and enabling appropriate laser processing, and a laser processing apparatus equipped with said optical system. [Means for solving the problem]

[0011] In order to solve the aforementioned problems, we conducted intensive research and arrived at the following optical system for a laser processing device.

[0012] The optical system of the laser processing apparatus according to the present invention is an optical system for a laser processing apparatus that irradiates a workpiece with a laser beam emitted from a laser oscillator to form a spot and perform laser processing, and comprises a collimating lens for making the laser beam into parallel light, a focusing lens for focusing the parallel light, and at least one protective glass, wherein the dn1 / dT of the collimating lens is a negative value, the dn2 / dT of the focusing lens is a negative value, and the dn3 / dT of the protective glass is a positive value. however, n1: Refractive index of the optical material of the collimating lens n2: Refractive index of the optical material of the condenser lens n3: Refractive index of the optical material of the protective glass T: Temperature

[0013] The laser processing apparatus according to the present invention employs a laser processing apparatus characterized by including the optical system of the above-described laser processing apparatus.

Effect of the Invention

[0014] The optical system of the laser processing apparatus according to the present invention can offset and correct the influence caused by changes in the refractive index and radius of curvature of the lens and the protective glass due to the heat of the laser beam, even when the optical system of the laser processing apparatus includes a protective glass. As a result, the focus of the optical system of the laser processing apparatus does not shift, and appropriate laser processing can be performed.

Brief Description of the Drawings

[0015] [Figure 1] It is a schematic diagram of the optical system of the laser processing apparatus according to the present invention.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, the optical system of the laser processing apparatus and embodiments of the laser processing apparatus according to the present invention will be described. Note that what is described below merely shows one aspect and is not to be construed as being limited to the following description.

[0017] 1. Embodiment of the optical system of the laser processing apparatus The optical system of the laser processing apparatus according to the present invention is an optical system for a laser processing apparatus that irradiates a workpiece with a laser beam emitted from a laser oscillator to form a spot and perform laser processing. The optical system of the laser processing apparatus is an optical system necessary for laser processing, and is an optical system that irradiates the laser beam to focus on the spot by forming the desired image shape of the laser beam and the energy intensity distribution of the laser beam at the spot. The configuration of the optical system of the laser processing apparatus according to the present invention comprises a collimating lens for making the incident laser beam into parallel light, a focusing lens for focusing the parallel light, and at least one protective glass, wherein the dn1 / dT of the collimating lens is a negative value, the dn2 / dT of the focusing lens is a negative value, and the dn3 / dT of the protective glass is a positive value. however, n1: Refractive index of the optical material of the collimating lens n2: Refractive index of the optical material of the focusing lens n3: Refractive index of the optical material of the protective glass T: Temperature

[0018] In this invention, the protective glass is a flat glass plate placed on the spot side or laser oscillator side of the optical system of a laser processing device to prevent sputter and fumes from entering the optical system of the laser processing device during laser processing.

[0019] Figure 1 shows the optical system 1 of the laser processing apparatus according to the present invention. The optical system 1 of the laser processing apparatus has a configuration in which a collimating lens 21 for making the laser beam incident through the optical fiber 30 into parallel light, a focusing lens 22 for focusing the aforementioned parallel light, and a protective glass 23 on the spot side of the focusing lens 22 are arranged along the optical axis 10. By adopting this configuration, the laser beam incident from the optical fiber 30 is focused on the surface of the workpiece 50 as shown by the irradiation trajectory 11 to form a spot.

[0020] In the optical system 1 of the laser processing apparatus, the dn1 / dT of the collimating lens 21 is a negative value, the dn2 / dT of the focusing lens 22 is a negative value, and the dn3 / dT of the protective glass 23 is a positive value. Here, dn / dT is the rate of change of refractive index n per unit temperature change, and is the so-called temperature coefficient of refractive index n.

[0021] Here, the focal length of the optical element is expressed by the following equation (5). 1 / f = (n-1)(1 / r1 - 1 / r2) + (n-1) 2 d / (nr1r2) ···(5) however, f: focal length of the optical element n: Refractive index of the optical material of the optical element r1: This is the radius of curvature of the first surface of the optical element. When the direction of the optical axis (rightward) is considered positive, the value is positive when the center of curvature is to the right of the surface vertex, and negative when it is to the left. r2: This is the radius of curvature of the second surface of the optical element. When the direction of the optical axis (rightward) is considered positive, the value is positive when the center of curvature is to the right of the surface vertex, and negative when it is to the left. d: Thickness of the central part of the optical element

[0022] This section describes the changes in the optical properties of the collimating lens 21, the focusing lens 22, and the protective glass 23 when a laser beam is incident on them. Since the collimating lens 21 has a negative dn1 / dT, the refractive index n1 decreases due to the heat generated by absorbing the laser beam. Furthermore, the radius of curvature of the collimating lens 21 in the area where the laser beam is incident decreases due to thermal expansion. As a result, the focal length of the collimating lens 21 changes according to the magnitude of the changes in the refractive index n1 and the radius of curvature, as expressed in the focal length equation (5) above.

[0023] Since the focusing lens 22 has a negative dn2 / dT, the refractive index n2 decreases due to the heat generated by absorbing the laser beam. Consequently, the radius of curvature of the focusing lens 22 in the area where the laser beam is incident decreases due to thermal expansion. As a result, the focal length of the focusing lens 22 changes according to the magnitude of the changes in the refractive index n2 and the radius of curvature, as expressed in the focal length equation (5).

[0024] Since the protective glass 23 has a positive dn3 / dT, the refractive index n3 increases due to the heat generated by absorbing the laser beam. Furthermore, because the surface of the protective glass 23 in the area where the laser beam is incident is plate-shaped, its radius of curvature, which is originally infinite, becomes a finite value due to thermal expansion. As a result, the focal length of the protective glass 23 becomes a finite value expressed in the focal length equation (5).

[0025] In general terms, when a laser beam is incident on the optical system 1 of the laser processing device, the focal length of the protective glass 23 becomes a finite value due to the thermal lensing effect. This is offset by the change in focal length of the collimating lens 21 and the change in focal length of the condensing lens 22. This explanation is merely a general overview to make the effects of each optical element easier to understand, and is not limited to the above explanation as long as the overall change in focal length of the collimating lens 21, condensing lens 22, and protective glass 23 is offset. That is, when a laser beam is incident on the collimating lens 21, condensing lens 22, and protective glass 23, the above changes occur. Therefore, if the dn1 / dT of the collimating lens 21 is a negative value, the dn2 / dT of the condensing lens 22 is a negative value, and the dn3 / dT of the protective glass 23 is a positive value, and by appropriately selecting the respective dn / dT values, it is possible to suppress the overall change (deviation) in focal length of the optical system 1 of the laser processing device.

[0026] Here, the optical system 1 of the laser processing apparatus is not particularly limited as long as it is possible to suppress the variation in focal length as a whole, but the dn1 / dT of the collimating lens 21 is -1.0 × 10⁻¹⁰ -6It is preferably below / ℃. The dn2 / dT of the condenser lens 22 is -1.0×10 -6 / ℃ or less. The dn3 / dT of the protective glass 23 is 5.0×10 -6 / ℃ or more and 15×10 -6 / ℃ or less. The value of the dn / dT of each of these optical elements is the value at the wavelength of the laser beam used. And the preferred wavelength of the laser beam is 1070 nm. By having the dn / dT of each optical element within this range, as described above, it becomes possible to suppress fluctuations in the focal length as a whole of the optical system 1 of the laser processing apparatus.

[0027] Note that the condenser lens 22 may be replaced with a lens group that realizes the condensing function using a plurality of lenses. When using, instead of the condenser lens 22, a lens group that realizes the condensing function using a plurality of lenses, the average value obtained by averaging the values of dn / dT of each lens according to the refractive power of each lens in the plurality of lenses may satisfy the above range of dn2 / dT.

[0028] Here, the "average value obtained by averaging the values of dn / dT of each lens according to the refractive power of each lens in the plurality of lenses" is, for example, in the case of two lenses, since the combined refractive index N is calculated as in the following formula (6), it is obtained by calculating dN / dT from the combined refractive index N. The same concept is used for calculation even when there are three or more lenses.

[0029] N≒(N1Φ1+N2Φ2) / Φ ···(6) However, N: Combined refractive index of two lenses N1: Refractive index of the first lens N2: Refractive index of the second lens Φ: Combined refractive power of two lenses Φ1: Refractive power of the first lens Φ2: Refractive power of the second lens

[0030] In Figure 1, a protective glass 23 is placed on the spot side of the focusing lens 22, but a protective glass may also be placed on the laser oscillator side of the collimating lens 21. This is because it prevents foreign matter such as dust from entering the optical system 1 of the laser processing device from the laser oscillator side. Alternatively, a configuration using a total of two protective glass pieces is also possible, with one placed on the spot side of the focusing lens 22 and another on the laser oscillator side of the collimating lens 21. When using two protective glass pieces, the dn3 / dT of each protective glass piece should be within the range described above. Even when using two protective glass pieces, by using the dn1 / dT of the collimating lens 21 and the dn2 / dT of the focusing lens 22 within the range described above, it is possible to cancel out the effects of the thermal lensing effect of each optical element in the optical system 1 of the laser processing device as a whole, thereby suppressing fluctuations in focal length.

[0031] Furthermore, it is preferable that the optical system 1 of the laser processing apparatus has a lens barrel in which a collimating lens 21, a focusing lens 22, and a protective glass 23 are arranged and fixed inside the lens barrel. This is because it is possible to prevent reflected light from the optical elements used in the optical system 1 of the laser processing apparatus from being irradiated to the outside other than the spot, and also to prevent dust such as sputter from entering the optical system 1 of the laser processing apparatus.

[0032] The laser beam incident on the optical system 1 of the laser processing apparatus via the optical fiber 30 from the laser oscillator can be any laser beam that can be used for laser processing. In particular, it is preferable to use a near-infrared laser beam with an oscillation wavelength of approximately 920 to 1080 nm, such as a YAG laser (wavelength 1064 nm), fiber laser (wavelength 1070 nm), disk laser (wavelength 1030 nm), or semiconductor laser (wavelengths 935 nm, 940 nm, 980 nm, 940-980 nm, 940-1025 nm). Furthermore, any laser beam that can be used for laser processing may be a laser beam in the blue, green, or ultraviolet range. In addition, the energy distribution of the laser beam incident on the optical system 1 of the laser processing apparatus in a plane perpendicular to the optical axis 10 may be Gaussian in shape with strong energy in the center (optical axis portion), or it may be uniform.

[0033] The power of the laser beam incident on the optical system 1 of the laser processing apparatus via the optical fiber 30 from the laser oscillator is not particularly limited, but is preferably between 100W and 20000W. If the laser beam power is less than 100W, the workpiece cannot be processed properly due to insufficient power. Also, if the laser beam power exceeds 20000W, it becomes difficult to suppress the fluctuation in focal length due to the thermal lensing effect.

[0034] Here, the image shape of the laser beam at the spot can be any shape as long as the laser beam can process the workpiece. For example, at least one of the collimating lens 21 and the focusing lens 22 of the optical system 1 of the laser processing apparatus can have a function (hereinafter referred to as the annular conversion function) that converts the image shape of the laser beam at the spot into an annular shape consisting of at least an annular peripheral region. By making the shape of the energy distribution at the spot an annular shape consisting of at least an annular peripheral region, the laser beam energy is irradiated uniformly in all directions from the central region of the spot onto the surface of the workpiece. As a result, in lap welding of molten galvanized steel sheets, zinc gas escapes, and a clean weld can be achieved.

[0035] Furthermore, the shape of the spot produced by the annular transformation function is not particularly limited; for example, it may consist of an annular shape and a point-like shape at the center of the annular shape (the point portion being Gaussian-shaped), or it may be a top-hat shape. In this case, it is preferable that the energy intensity of the point-like spot at the center of the annular shape is higher than the energy intensity of the annular part. This is because, with materials such as aluminum and copper, which have high light reflectivity, the metal can be melted in the annular part with low energy intensity to reduce reflectivity, and the workpiece can be deeply melted in the center with high energy intensity, making laser processing easier.

[0036] To form the aforementioned spot image shape, it is preferable that at least one of the optically effective surfaces of the optical element with annular conversion function be a diffraction lens, an axicon lens, or an aspherical lens. This is because the spot shape of the laser beam can be made to be annular, or to consist of an annular shape and a point shape at the center of the annular shape.

[0037] Furthermore, the optical system 1 of the laser processing apparatus does not necessarily need to have an annular conversion function; a laser beam that emits from the optical fiber 30 and whose image shape is an annular shape consisting of at least an annular peripheral region may be used.

[0038] Furthermore, the optical system 1 of the laser processing apparatus may include a laser beam direction adjustment mechanism comprising a connector section to which the optical fiber 30 is connected, and a connector receiving section that fixes the connector section with respect to the optical axis 10 of the irradiation trajectory. The laser beam direction adjustment mechanism adjusts the direction of incidence of the laser beam to the irradiation trajectory by having at least one of the connector section and the connector receiving section rotate in an arc shape with the center of the core of the optical fiber 30 at the laser beam output end as the center point. The laser beam output from the laser oscillator is guided to the laser processing head of the laser processing apparatus using the optical fiber 30, but the direction of emission of the laser beam output from the output end of the optical fiber 30 has an inclination within a certain range with respect to the optical axis 10. Specifically, for example, in Raykas Fiber's CW fiber laser, the angle of the optical axis of the laser beam output from the output end of the optical fiber with respect to the reference optical axis determined by the structure of the output end of the optical fiber and the structure of the connector is said to be 30 mrad (millirradians) or less. The laser beam direction adjustment mechanism is used when the emission direction of the laser beam output from the output end of the optical fiber 30 has an inclination within a certain range with respect to the optical axis 10, and can adjust the incident direction of the laser beam onto the irradiation trajectory.

[0039] [Conditional expression] The optical system of the laser processing apparatus according to the present invention preferably employs the above-described configuration and satisfies one or more of the following conditions.

[0040] The optical system 1 of the laser processing apparatus preferably satisfies the following condition. By satisfying the following condition, the optical system 1 of the laser processing apparatus as a whole can cancel out the effects of the thermal lensing effect of each element, limit the shift in back focus according to the focal length, and suppress fluctuations in focal length.

[0041] 100mm < f2 < 500mm ···(1) -0.02 < Δf² / f² < 0 ···(2) however, f2: Focal length of the condensing lens 22 Δf2: Amount of shift in the focal length of the condensing lens 22 when the thermal lensing effect occurs.

[0042] The optical system 1 of the laser processing apparatus preferably satisfies the following condition. In condition (4), ΔBF represents the amount of deviation in the back focus (the distance from the vertex of the final surface of the spot-side lens of the focusing lens 22 to the spot position) when the thermal lensing effect occurs. The value of "ΔBF / (αf1)" normalized by the vertical magnification α and f1 satisfies condition (4), which means that the deviation in the back focus is suppressed in the optical system. In other words, by satisfying the following condition, the optical system 1 of the laser processing apparatus can cancel out the effects of the thermal lensing effect of each element as a whole, reduce the deviation in the back focus according to the vertical magnification, and suppress fluctuations in the focal length.

[0043] f1 ≤ 200mm ···(3) -0.0175 < ΔBF / (αf1) ···(4) however, f1: Focal length of collimating lens 21 ΔBF: Amount of shift in back focus (distance from the vertex of the final lens surface on the spot side of the condensing lens 22 to the spot position) when the thermal lensing effect occurs. α: Vertical magnification = (f2 / f1) 2

[0044] [Collimating lenses] The collimating lens 21 is an optical element for converting the laser beam, which is emitted radially from the output end of the optical fiber 30, into parallel light. The surface shape of the collimating lens 21 is not particularly limited and can be either plano-convex or biconvex, as long as it can convert the laser beam emitted radially from the output end of the optical fiber 30 into parallel light. Furthermore, it is preferable that the thickness of the collimating lens 21 in the portion that the laser beam passes through is thin. This is because if the thickness of the collimating lens 21 in the portion that the laser beam passes through is thick, heat accumulates compared to when it is thin, and the rate of change in refractive index and radius of curvature due to the thermal lensing effect becomes larger. Therefore, although the thickness of the collimating lens 21 in the portion that the laser beam passes through is not particularly limited, it is preferably 20 mm or less, and more preferably 10 mm or less.

[0045] The optical material of the collimating lens 21 is not particularly limited as long as it can achieve the preferred range of dn1 / dT described above. The optical material of the collimating lens 21 preferably contains at least one selected from the group consisting of boron oxide, fluoride, and phosphorus oxide. By including at least one of boron oxide and fluoride as the optical material, the preferred range of dn1 / dT can be achieved. Lenses containing boron oxide are particularly preferable because they have a high thermal softening temperature and a low coefficient of linear expansion, making them less prone to cracking when used in the optical system 1 of a laser processing device. Furthermore, the fluoride is preferably one or more selected from the group consisting of aluminum fluoride, magnesium fluoride, calcium fluoride, strontium fluoride, and yttrium fluoride.

[0046] [Concentrating lens] The focusing lens 22 has the function of focusing the laser beam, which has been converted into parallel light by the collimating lens 21, into a spot. The surface shape of the focusing lens 22 is not particularly limited and can be either plano-convex or biconvex, as long as it can focus the parallel light output from the collimating lens 21 into a spot. Furthermore, it is preferable that the thickness of the focusing lens 22 in the part through which the laser beam passes is thin. This is because if the thickness of the focusing lens 22 in the part through which the laser beam passes is thick, heat accumulates compared to when it is thin, and the rate of change in refractive index and radius of curvature due to the thermal lensing effect becomes larger. Therefore, although the thickness of the focusing lens 22 in the part through which the laser beam passes is not particularly limited, it is preferably 20 mm or less, and more preferably 10 mm or less.

[0047] The optical material of the focusing lens 22 is not particularly limited as long as it can achieve the preferred range of dn2 / dT described above. Preferably, the optical material of the focusing lens 22 contains at least one selected from the group consisting of boron oxide, fluoride, and phosphorus oxide. By including at least one of boron oxide and fluoride as the optical material, a preferred range of dn1 / dT can be achieved. Lenses containing boron oxide are particularly preferable because they have a high thermal softening temperature and a low coefficient of linear expansion, making them less prone to cracking when used in the optical system 1 of a laser processing apparatus. Furthermore, it is preferable that the fluoride is one or more selected from the group consisting of aluminum fluoride, magnesium fluoride, calcium fluoride, strontium fluoride, and yttrium fluoride.

[0048] [Protective glass] The protective glass 23 has the function of preventing spatter generated during laser processing from entering the optical system 1 of the laser processing device. The protective glass 23 is not particularly limited as long as it can prevent spatter from entering the optical system 1 of the laser processing device, but a plate type can be used. Furthermore, it is preferable that the thickness of the protective glass 23 in the part that the laser beam passes through is thin. This is because if the thickness of the protective glass 23 in the part that the laser beam passes through is thick, heat will accumulate compared to when it is thin, and the rate of change in refractive index and radius of curvature due to the thermal lens effect will be larger. Therefore, although the thickness of the protective glass 23 in the part that the laser beam passes through is not particularly limited, it is preferably 20 mm or less, and more preferably 10 mm or less.

[0049] The optical material of the protective glass 23 is not particularly limited as long as it can achieve the preferred range of dn3 / dT described above. Quartz is preferred as the optical material of the protective glass 23 because it has excellent light transmittance and high heat resistance. Furthermore, fused silica or synthetic silica can be used as long as dn3 / dT is within the preferred range.

[0050] 2. Embodiment of a laser processing apparatus The laser processing apparatus according to the present invention employs the optical system of the laser processing apparatus described above as the optical system of the laser processing apparatus according to the present invention. Therefore, even if protective glass is provided in the optical system of the laser processing apparatus, the deviation in focal length caused by changes in the refractive index and radius of curvature of the lens and protective glass due to the heat of the laser beam can be offset and corrected, thereby preventing the focus of the optical system of the laser processing apparatus from shifting and enabling proper laser processing.

[0051] The embodiments of the present invention described above are one aspect of the present invention and can be modified as appropriate without departing from the spirit of the present invention. Furthermore, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples. [Examples]

[0052] In Example 1, the optical system 1 of the laser processing apparatus shown in Figure 1 was configured in which protective glass (incident side) was placed on the optical fiber 30 side of the collimating lens 21. The optical materials used for the collimating lens 21 and the focusing lens 22 were phosphate glass containing boron oxide, PCD4 (manufactured by HOYA Corporation, nd=1.61800, νd=63.40). The dn / dt of PCD4 was -2.1 × 10⁻⁶. -6 The measurement wavelength is 1070 nm, and the temperature range is 20-300 °C. Furthermore, F_SILICA fused silica (manufactured by Ohara Quartz Co., Ltd., nd=1.449, νd=67.8) was used as the optical material for the protective glass 23 and the protective glass (incident side). The dn / dt of F_SILICA is 10 × 10⁻¹⁰. -6 The temperature is measured at a wavelength of 1070 nm and a temperature of 20-300°C.

[0053] The collimating lens 21 was a plano-convex lens with a focal length f1 of 200 mm and a central thickness of 10 mm. The protective glass 23 and the protective glass (incident side) were parallel flat plates with a thickness of 10 mm.

[0054] First, for a condensing lens 22 with a central thickness of 10 mm, the amount of displacement Δf2 (mm) of the condensing lens 22 with respect to each focal length f2 (mm) when the thermal lensing effect occurs was confirmed using the thermal modeling function of the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.). The results are shown in Table 1.

[0055] [Table 1]

[0056] Next, in the configuration of Example 1, the amount of back focus shift ΔBF (mm) when the thermal lens effect occurs was confirmed using the thermal modeling function of the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.). The results are shown in Table 2. Note that α (vertical magnification) = (f2 / f1) 2 That is the case.

[0057] [Table 2]

[0058] From Tables 1 and 2, it became clear that under conditions satisfying conditions (1)-(3), the value of "ΔBF / (αf1)" in condition (4) satisfies the range of condition (4). In other words, the configuration of Example 1 satisfies the requirements that the dn1 / dT of the collimating lens 21 is a negative value, the dn2 / dT of the condensing lens 22 is a negative value, and the dn3 / dT of the protective glass 23 and the protective glass (incident side) is a positive value, making it possible to suppress the variation (shift) of the focal length according to the vertical magnification as a whole. [Examples]

[0059] In Example 2, the optical system 1 of the laser processing apparatus shown in Figure 1 was configured in which protective glass (incident side) was also placed on the optical fiber 30 side of the collimating lens 21. Furthermore, FCD1 (manufactured by HOYA Corporation, nd=1.49700, νd=81.61), a phthalic acid glass containing boron oxide, was used as the optical material for the collimating lens 21 and the focusing lens 22. The dn / dt of FCD1 was -7.3 × 10⁻⁶. -6 The measurement wavelength is 1070 nm, and the temperature range is 20-300 °C. Furthermore, F_SILICA fused silica (manufactured by Ohara Quartz Co., Ltd., nd=1.449, νd=67.8) was used as the optical material for the protective glass 23 and the protective glass (incident side). The dn / dt of F_SILICA is 10 × 10⁻¹⁰. -6 The temperature is measured at a wavelength of 1070 nm and a temperature of 20-300°C.

[0060] The collimating lens 21 was a plano-convex lens with a focal length f1 of 200 mm and a central thickness of 10 mm. The protective glass 23 and the protective glass (incident side) were parallel flat plates with a thickness of 10 mm. The condensing lens 22 had a central thickness of 10 mm.

[0061] In the configuration of Example 2, the amount of back focus shift ΔBF (mm) when the thermal lens effect occurs was confirmed using the thermal modeling function of the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.). The results are shown in Table 3.

[0062] [Table 3]

[0063] Table 3 clearly shows that the value of "ΔBF / (αf1)" in conditional equation (4) satisfies the range of conditional equation (4). In other words, the configuration of Example 2 satisfies the requirements that the dn1 / dT of the collimating lens 21 is a negative value, the dn2 / dT of the condensing lens 22 is a negative value, and the dn3 / dT of the protective glass 23 and the protective glass (incident side) is a positive value, thereby making it possible to suppress the variation (shift) of the focal length according to the vertical magnification as a whole configuration of Example 2. Comparative Example

[0064] [Comparative Example 1] In Comparative Example 1, the optical system 1 of the laser processing apparatus shown in Figure 1 was configured in which protective glass (incident side) was also placed on the optical fiber 30 side of the collimating lens 21. F_SILICA (manufactured by Ohara Quartz Co., Ltd., nd=1.449, νd=67.8) of fused silica was used as the optical material for the collimating lens 21, focusing lens 22, protective glass 23, and protective glass (incident side). The dn / dt of F_SILICA is 10 × 10⁻¹⁰. -6 The temperature is measured at a wavelength of 1070 nm and a temperature of 20-300°C.

[0065] The collimating lens 21 was a plano-convex lens with a focal length f1 of 200 mm and a central thickness of 10 mm. The protective glass 23 and the protective glass (incident side) were parallel flat plates with a thickness of 10 mm. The condensing lens 22 had a central thickness of 10 mm.

[0066] In the configuration of Comparative Example 1, the amount of back focus shift ΔBF (mm) when the thermal lens effect occurs was confirmed using the thermal modeling function of the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.). The results are shown in Table 4.

[0067] [Table 4]

[0068] Table 4 clearly shows that the value of "ΔBF / (αf1)" in conditional equation (4) does not satisfy the range of conditional equation (4). In other words, in the configuration of Comparative Example 1, since the dn / dT values ​​of all three components—collimating lens 21, focusing lens 22, and protective glass 23—are positive, it is clear that the configuration of Comparative Example 1 as a whole cannot suppress the variation (shift) in focal length.

[0069] [Comparative Example 2] In Comparative Example 2, the optical system 1 of the laser processing apparatus shown in Figure 1 was configured in which protective glass (incident side) was placed on the optical fiber 30 side of the collimating lens 21. Furthermore, PCD4 (manufactured by HOYA Corporation, nd=1.61800, νd=63.40), a phosphoric acid glass containing boron oxide, was used as the optical material for the focusing lens 22. The dn / dt of PCD4 was -2.1 × 10⁻⁶. -6 The measurement wavelength is 1070 nm, and the temperature range is 20-300 °C. Furthermore, F_SILICA fused silica (manufactured by Ohara Quartz Co., Ltd., nd=1.449, νd=67.8) was used as the optical material for the collimating lens 21, protective glass 23, and protective glass (incident side). The dn / dt of F_SILICA is 10 × 10⁻¹⁰. -6 The temperature is measured at a wavelength of 1070 nm and a temperature of 20-300°C.

[0070] The collimating lens 21 was a plano-convex lens with a focal length f1 of 200 mm and a central thickness of 10 mm. The protective glass 23 and the protective glass (incident side) were parallel flat plates with a thickness of 10 mm. The condensing lens 22 had a central thickness of 10 mm.

[0071] In the configuration of Comparative Example 2, the amount of back focus shift ΔBF (mm) when the thermal lens effect occurs was confirmed using the thermal modeling function of the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.). The results are shown in Table 5.

[0072] [Table 5]

[0073] Table 5 clearly shows that the value of "ΔBF / (αf1)" in conditional equation (4) does not satisfy the range of conditional equation (4). In other words, in the configuration of Comparative Example 2, the dn1 / dT of the collimating lens 21 is a positive value, the dn2 / dT of the condensing lens 22 is a negative value, and the dn3 / dT of the protective glass 23 and the protective glass (incident side) is a positive value. Therefore, it is clear that the configuration of Comparative Example 2 as a whole cannot suppress the variation (shift) in focal length.

[0074] [Comparative Example 3] In Comparative Example 3, the optical system 1 of the laser processing apparatus shown in Figure 1 was configured in which protective glass (incident side) was also placed on the optical fiber 30 side of the collimating lens 21. Furthermore, PCD4 (manufactured by HOYA Corporation, nd=1.61800, νd=63.40), a phosphoric acid glass containing boron oxide, was used as the optical material for the collimating lens 21. The dn / dt of PCD4 was -2.1 × 10⁻⁶. -6 The measurement wavelength is 1070 nm, and the temperature range is 20-300 °C. Furthermore, F_SILICA fused silica (manufactured by Ohara Quartz Co., Ltd., nd=1.449, νd=67.8) was used as the optical material for the focusing lens 22, protective glass 23, and protective glass (incident side). The dn / dt of F_SILICA is 10 × 10⁻¹⁰. -6 The temperature is measured at a wavelength of 1070 nm and a temperature of 20-300°C.

[0075] The collimating lens 21 was a plano-convex lens with a focal length f1 of 200 mm and a central thickness of 10 mm. The protective glass 23 and the protective glass (incident side) were parallel flat plates with a thickness of 10 mm. The condensing lens 22 had a central thickness of 10 mm.

[0076] In the configuration of Comparative Example 3, the amount of back focus shift ΔBF (mm) when the thermal lens effect occurs was confirmed using the thermal modeling function of the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.). The results are shown in Table 6.

[0077] [Table 6]

[0078] Table 6 clearly shows that the value of "ΔBF / (αf1)" in conditional equation (4) does not satisfy the range of conditional equation (4). In other words, in the configuration of Comparative Example 3, the dn1 / dT of the collimating lens 21 is a negative value, the dn2 / dT of the condensing lens 22 is a positive value, and the dn3 / dT of the protective glass 23 and the protective glass (incident side) is a positive value. Therefore, it is clear that the configuration of Comparative Example 3 as a whole cannot suppress the variation (shift) in focal length.

[0079] [Comparative Example 4] In Comparative Example 4, the optical system 1 of the laser processing apparatus shown in Figure 1 was configured in which protective glass (incident side) was placed on the optical fiber 30 side of the collimating lens 21. Furthermore, FCD1 (manufactured by HOYA Corporation, nd=1.49700, νd=81.61), a phthalic acid glass containing boron oxide, was used as the optical material for the focusing lens 22. The dn / dt of FCD1 was -7.3 × 10⁻⁶. -6 The measurement wavelength is 1070 nm, and the temperature range is 20-300 °C. Furthermore, F_SILICA fused silica (manufactured by Ohara Quartz Co., Ltd., nd=1.449, νd=67.8) was used as the optical material for the collimating lens 21, protective glass 23, and protective glass (incident side). The dn / dt of F_SILICA is 10 × 10⁻¹⁰.-6 The temperature is measured at a wavelength of 1070 nm and a temperature of 20-300°C.

[0080] The collimating lens 21 was a plano-convex lens with a focal length f1 of 200 mm and a central thickness of 10 mm. The protective glass 23 and the protective glass (incident side) were parallel flat plates with a thickness of 10 mm. The condensing lens 22 had a central thickness of 10 mm.

[0081] In the configuration of Comparative Example 4, the amount of back focus shift ΔBF (mm) when the thermal lens effect occurs was confirmed using the thermal modeling function of the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.). The results are shown in Table 7.

[0082] [Table 7]

[0083] Table 7 clearly shows that the value of "ΔBF / (αf1)" in conditional equation (4) does not satisfy the range of conditional equation (4). In other words, in the configuration of Comparative Example 4, the dn1 / dT of the collimating lens 21 is a positive value, the dn2 / dT of the condensing lens 22 is a negative value, and the dn3 / dT of the protective glass 23 and the protective glass (incident side) is a positive value. Therefore, it is clear that the configuration of Comparative Example 4 as a whole cannot suppress the variation (shift) in focal length.

[0084] [Comparative Example 5] In Comparative Example 5, the optical system 1 of the laser processing apparatus shown in Figure 1 was configured in which protective glass (incident side) was also placed on the optical fiber 30 side of the collimating lens 21. Furthermore, FCD1 (manufactured by HOYA Corporation, nd=1.49700, νd=81.61), a phthalic acid glass containing boron oxide, was used as the optical material for the collimating lens 21. The dn / dt of FCD1 was -7.3 × 10⁻⁶. -6The measurement wavelength is 1070 nm, and the temperature range is 20-300 °C. Furthermore, F_SILICA fused silica (manufactured by Ohara Quartz Co., Ltd., nd=1.449, νd=67.8) was used as the optical material for the focusing lens 22, protective glass 23, and protective glass (incident side). The dn / dt of F_SILICA is 10 × 10⁻¹⁰. -6 The temperature is measured at a wavelength of 1070 nm and a temperature of 20-300°C.

[0085] The collimating lens 21 was a plano-convex lens with a focal length f1 of 200 mm and a central thickness of 10 mm. The protective glass 23 and the protective glass (incident side) were parallel flat plates with a thickness of 10 mm. The condensing lens 22 had a central thickness of 10 mm.

[0086] In the configuration of Comparative Example 5, the amount of back focus shift ΔBF (mm) when the thermal lens effect occurs was confirmed using the thermal modeling function of the optical design software OpticStudio (manufactured by Zemax Japan Co., Ltd.). The results are shown in Table 8.

[0087] [Table 8]

[0088] Table 8 clearly shows that the value of "ΔBF / (αf1)" in conditional equation (4) does not satisfy the range of conditional equation (4). In other words, in the configuration of Comparative Example 5, the dn1 / dT of the collimating lens 21 is a negative value, the dn2 / dT of the condensing lens 22 is a positive value, and the dn3 / dT of the protective glass 23 and the protective glass (incident side) is a positive value. Therefore, it is clear that the configuration of Comparative Example 5 as a whole cannot suppress the variation (shift) in focal length. [Industrial applicability]

[0089] The optical system of the laser processing apparatus according to the present invention can compensate for the shift in focal length caused by changes in the refractive index and radius of curvature of the lens and protective glass due to the heat of the laser beam, even when protective glass is provided in the optical system of the laser processing apparatus. As a result, the focus of the optical system of the laser processing apparatus does not shift, and appropriate laser processing can be performed. In other words, the optical system of the laser processing apparatus according to the present invention is suitable as an optical system to be applied to a laser processing apparatus that processes a workpiece by irradiating it with a laser beam. [Explanation of symbols]

[0090] 1. Optical system of a laser processing device 10 Optical axis 11 Irradiation trajectory 21 Collimating Lenses 22 Focusing lenses 23 Protective Glass 30 optical fibers 50. Object to be processed

Claims

1. An optical system for a laser processing apparatus that uses a laser beam emitted from a laser oscillator to form a spot on a workpiece and perform laser processing, The system comprises a collimating lens for making the laser beam into parallel light, a focusing lens for focusing the parallel light, and at least one protective glass. The dn of the collimating lens １ / dT is a negative value, and the dn of the condensing lens ２ / dT is a negative value, and the dn of the protective glass ３ An optical system for a laser processing apparatus characterized in that / dT is a positive value. however, n １ : Refractive index of the optical material of the collimating lens n ２ : Refractive index of the optical material of the aforementioned focusing lens n ３ : Refractive index of the optical material of the protective glass T: Temperature.

2. The optical system of the laser processing apparatus according to claim 1, wherein the protective glass is provided on the spot side of the focusing lens.

3. The optical system of a laser processing apparatus according to claim 1, wherein the protective glass is located on the laser oscillator side of the collimating lens.

4. The optical system of the laser processing apparatus according to claim 1, wherein the optical material of the protective glass is quartz.

5. The optical system of a laser processing apparatus according to claim 1, wherein the optical material of the collimating lens and the focusing lens contains at least one selected from the group consisting of boron oxide, fluoride, and phosphorus oxide.

6. The optical system of a laser processing apparatus according to claim 5, wherein the fluoride is one or more selected from the group consisting of aluminum fluoride, magnesium fluoride, calcium fluoride, strontium fluoride, and yttrium fluoride.

7. The optical system of the laser processing apparatus according to claim 1, satisfying the following conditional expression. 100mm < f2 < 500mm...(1) -0.02 < Δf2 / f2 < 0 (2) however, f2: Focal length of the condensing lens Δf2: Amount of shift in the focal length of the condensing lens when the thermal lensing effect occurs.

8. The optical system of the laser processing apparatus according to claim 1, satisfying the following conditional expression. f1 ≦ 200mm...(3) -0.0175 < ΔBF / (αf1) ... (4) however, f1: Focal length of the collimating lens ΔBF: Amount of shift in back focus (distance from the vertex of the final lens surface on the spot side of the condensing lens to the spot position) when the thermal lens effect occurs. α: Vertical magnification = (f2 / f1) ２

9. A laser processing apparatus characterized by comprising the optical system of the laser processing apparatus described in claim 1.

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