Hood for laser device, laser processing device, and laser processing method

Abstract

A hood 30 for a laser processing device 1 comprises: a cylindrical part 31 stretching along the axial direction; a protective glass 31a which is provided at one end of the cylindrical part 31 in the axial direction and transmits a laser; an opening 31b provided at the other end of the cylindrical part 31 in the axial direction; and nozzles 34 which are disposed on the cylindrical part 31 and supply gas to the interior. The nozzles 34 are disposed at the central section of the cylindrical part 31 in the axial direction and at portions thereof in the circumferential direction.

Description

Hood for laser device, laser processing device, and laser processing method

[0001] The present invention relates to a hood for a laser device, a laser processing device, and a laser processing method.

[0002] Conventionally, laser processing devices are known that irradiate a workpiece (object to be processed) with a laser to perform laser processing such as annealing (see, for example, Patent Document 1). In this type of laser processing device, the workpiece may be subjected to laser processing by being exposed to a gas such as an inert gas. In such cases, for example, the workpiece is covered with a hood having a nozzle at the top for supplying gas, and the inside of the hood is purged with the gas supplied from the nozzle. Then, a laser is irradiated into the hood through a protective glass on the top surface of the hood to perform laser processing on the workpiece.

[0003] Japanese Patent Application Laid-Open No. 2022-1372

[0004] However, in the conventional configuration, the nozzle is located at the top of the hood (at the end in the direction of laser irradiation), which creates a single gas flow in the direction of laser irradiation within the hood. This gas flow can stir up and stir up dust particles, such as fine particles, generated from the workpiece during laser processing, which can then adhere to the protective glass on the top of the hood. If dust adheres to the protective glass, the laser light passing through the protective glass will be attenuated.

[0005] The present invention has been made in view of the above circumstances, and has as its object to suppress laser attenuation.

[0006] The present invention is a hood for a laser device, comprising: a cylindrical portion extending along an axial direction; a transparent portion provided at one axial end of the cylindrical portion and allowing laser light to pass through; an opening provided at the other axial end of the cylindrical portion; and a nozzle for supplying gas into the interior of the cylindrical portion, wherein the nozzle is located in the center of the cylindrical portion in the axial direction and at a portion of the circumferential direction.

[0007] According to the present invention, laser attenuation can be suppressed.

[0008] 1 is a schematic diagram of a laser processing device according to an embodiment; FIG. 1 is a cross-sectional view of a hood according to a modified embodiment; FIG. 2 is a perspective view of a hood according to a modified embodiment; FIG. 3 is a perspective view of a hood according to a modified embodiment; FIG. 4 is a diagram showing a gas flow in a hood according to an embodiment; FIG. 5 is a diagram showing a gas flow in a conventional hood; FIG. 6 is a diagram showing a gas flow in a hood according to an embodiment; FIG. 7 is a diagram showing a gas flow in a hood according to a modified embodiment; FIG. 8 is a diagram showing a gas flow in a hood according to a modified embodiment; FIG. 9 is a diagram showing an analysis result; FIG. 10 is a diagram showing an analysis result; FIG. 11 is a diagram showing an analysis result; FIG. 12 is a diagram showing an analysis result; FIG. 13 is a cross-sectional view of a hood according to a modified embodiment; FIG. 14 is a diagram showing a laser processing device according to a modified embodiment;

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0010] [Overall Configuration of Laser Processing Apparatus] Fig. 1 is a schematic diagram of a laser processing apparatus 1 according to this embodiment. As shown in Fig. 1, the laser processing apparatus 1 according to this embodiment irradiates a workpiece WP, which is an object to be processed, with a laser to perform processing such as annealing or welding. The material of the workpiece WP is not particularly limited, but may be, for example, silicon or silicon carbide. Specifically, the laser processing apparatus 1 includes a laser irradiation unit 10, a support table (stage) 20, a hood 30, a gas supply unit 40, and a control unit 50.

[0011] The laser irradiation unit 10 has a laser oscillator and an optical system (not shown). The laser irradiation unit 10 irradiates a predetermined laser beam downward according to the type of processing. The support table 20 is disposed below the laser irradiation unit 10 and supports the workpiece WP on its upper surface. At least one of the laser irradiation unit 10 and the support table 20 may have a movable part so that the laser irradiation position on the workpiece WP can be adjusted.

[0012] The hood 30 is disposed below the laser irradiation unit 10 and above the support table 20, and covers the workpiece WP placed on the support table 20. A predetermined gas is supplied into the hood 30 from a gas supply unit 40. The hood 30 exposes the workpiece WP to a predetermined gas atmosphere while allowing the laser from the laser irradiation unit 10 above to pass through. The specific configuration of the hood 30 will be described later.

[0013] The gas supply unit 40 supplies (applies) a predetermined gas into the hood 30. The supplied gas may be, for example, an inert gas such as nitrogen, or oxygen. The gas supply unit 40 has a gas source 41, which is a gas pump or a gas cylinder, a valve 42, and a pipe 43 that connects the gas source 41 to the hood 30 (each nozzle 34) via the valve 42.

[0014] The control unit 50 is configured by, for example, a CPU (Central Processing Unit) and controls each part of the laser processing apparatus 1. Specifically, the control unit 50 controls the operation of the laser irradiation unit 10 to irradiate the laser, and controls the operation of the valve 42 and gas source 41 of the gas supply unit 40 to supply a predetermined gas to the hood 30. Note that each part of the gas supply unit 40 may be manually controlled.

[0015] [Specific Configuration of Hood] As shown in Fig. 1, the hood 30 includes a tubular portion 31 and a nozzle 34. The tubular portion 31 is formed in a cylindrical shape having a central axis Ax along the up-down direction. However, the shape of the tubular portion 31 is not limited to a cylindrical shape as long as it is cylindrical. Hereinafter, the direction along the central axis Ax may be referred to as the "axial direction," and the direction perpendicular to the axial direction may be referred to as the "radial direction." Furthermore, the erected direction of the nozzle 34 in the hood 30 (the left-right direction on the paper surface of Fig. 1, etc.) may be referred to as the "left-right (direction)."

[0016] The upper end (one end) of the cylindrical portion 31 is closed and has a protective glass 31a (transmitting portion) that transmits the laser. The protective glass 31a is provided over substantially the entire upper end surface of the cylindrical portion 31. The protective glass 31a transmits most of the laser irradiated from the laser irradiation unit 10 above into the hood 30 (cylindrical portion 31). The protective glass 31a also prevents dust PA (see FIGS. 4A, 4B, etc.) such as fine particles generated from the workpiece WP during laser processing from adhering to the optical system of the laser irradiation unit 10.

[0017] The lower end (other end) of the cylindrical portion 31 is an opening 31b that is open on the entire surface. The opening 31b faces the upper surface of the support base 20 in the vertical direction, with a predetermined gap between the opening 31b and the upper surface of the support base 20.

[0018] The nozzles 34 are erected on the outer peripheral surface of the cylindrical portion 31 and blow gas into the interior of the cylindrical portion 31. In this embodiment, the nozzles 34 are arranged in pairs on the left and right sides of the cylindrical portion 31 in the radial direction, and two (two pairs) of nozzles 34 are arranged side by side in the axial direction, for a total of four nozzles. That is, one pair (two nozzles 34a) is provided on the upper side, and one pair (two nozzles 34b) is provided on the lower side. The nozzles 34 are arranged parallel to each other in the radial direction. However, the number and basic arrangement of the nozzles 34 are not particularly limited as long as they include one nozzle 34 arranged in the central portion in the axial direction, as described below. For example, the nozzles 34 may be arranged only on one side without forming a pair in the radial direction (i.e., an odd number), or one pair or three or more pairs may be provided. The two nozzles located on opposite radial sides may not be opposed to each other (their axial positions may be different). The two nozzles 34 facing each other on the left and right sides do not have to be bilaterally symmetrical or axially symmetrical to each other. As will be described later, each nozzle 34 may be divided into a plurality of nozzles in the width direction (see FIG. 3B ). When two nozzles 34 face each other laterally, the two nozzles 34 only need to face each other in a plane perpendicular to the axial direction of the cylindrical portion 31, and do not have to face each other in the radial direction.

[0019] As shown in FIG. 2 , the axial position of each nozzle 34 is the center of the cylindrical portion 31. The "center" in the axial direction refers to the portion of the cylindrical portion 31 excluding the upper and lower ends. In other words, each nozzle 34 only needs to be spaced apart from the upper and lower ends of the cylindrical portion 31. In other words, each nozzle 34 is disposed at an axial position defined by the following first length L1 and second length L2. The first length L1 is the axial length from the upper end (one end) of the cylindrical portion 31 to the nozzle 34, and the second length L2 is the axial length from the lower end (the other end) of the cylindrical portion 31 to the nozzle 34. The first length L1 and the second length L2 need only be non-zero. Note that, for ease of understanding, FIG. 2 illustrates an example of a hood 30 in which only one set of nozzles 34 is provided in the axial direction. Here, the "axial position of the nozzle 34" refers to the center position of the portion of the nozzle 34 that opens to the inner diameter of the cylindrical portion 31. However, the first length L1 may be the distance from the upper end of the inner diameter (hole) of the nozzle 34, and the second length L2 may be the distance from the lower end of the inner diameter of the nozzle 34.

[0020] The first axial length L1 from the upper end of the cylindrical portion 31 to each nozzle 34 preferably satisfies the following formula (3): L1≧0.3D (3) More preferably, the first length L1 satisfies the following formula (6): L1≧0.5D (6) where D is the inner diameter of the cylindrical portion 31. When the cylindrical portion 31 is a rectangular tube, D may be, for example, the equivalent diameter (the diameter of a cylindrical cylindrical portion 31 with the same cross-sectional area), or the minimum or maximum width of a cross section perpendicular to the axial direction. Alternatively, the first length L1 is preferably 50 mm or greater.

[0021] The second axial length L2 from the lower end of the cylindrical portion 31 to each nozzle 34 preferably satisfies the following formula (4): L2≧0.3D (4) Alternatively, the second length L2 is preferably 50 mm or greater. More preferably, the second length L2 satisfies the following formula (7): L2≧0.5D (7)

[0022] As shown in FIG. 3A , the width W of each nozzle 34 preferably satisfies the following formula (5) relative to the inner diameter D of the cylindrical portion 31: W≧0.3D (5) For ease of understanding, FIGS. 3A and 3B illustrate a hood 30 in which only one set of nozzles 34 is provided in the axial direction. Here, the "width W of the nozzle 34" refers to the length of the portion of the nozzle 34 that opens into the inner diameter (hole) of the cylindrical portion 31, along a direction perpendicular to the axial direction. Note that the center of the nozzle 34 in the width direction (direction along the width W) does not have to coincide with the center of the cylindrical portion 31 in that direction (i.e., the central axis Ax).

[0023] As shown in FIG. 3B , the nozzle 34 may be composed of multiple partial nozzles 34c arranged side by side in the width direction. The nozzles 34 may include nozzles 34 that are not radially arranged relative to the central axis Ax of the cylindrical portion 31 when viewed in the axial direction. As shown in FIGS. 11A and 11B , the nozzles 34 may be inclined obliquely with respect to the axial direction. In this case, the pair of left and right nozzles 34 may face in different oblique directions (e.g., diagonally upward and diagonally downward). The axial length (thickness) of the inner diameter (hole) of the nozzle 34 is not particularly limited, but is preferably sufficiently small relative to the axial height of the cylindrical portion 31. The length of the inner diameter (hole) of the nozzle 34 along the gas flow perpendicular to the width direction (the length along the radial direction in this embodiment) is not particularly limited, but preferably has a predetermined run-up length so that a uniform flow is formed in the width direction within the nozzle 34.

[0024] 1 , when laser processing a workpiece WP using the laser processing apparatus 1, first, the workpiece WP is placed on the upper surface of the support table 20 so that the portion to be processed of the workpiece WP is located inside the hood 30 (opening 31 b) in a plan view. Then, a predetermined gas such as an inert gas is supplied to the hood 30 by the gas supply unit 40 to purge the inside of the hood 30. This gas is supplied from each nozzle 34 into the cylindrical portion 31 of the hood 30 at a predetermined flow rate (e.g., approximately 10 L / min), forming a gas flow inside the cylindrical portion 31 of the hood 30.

[0025] At this time, each nozzle 34 of the hood 30 is disposed in the axial center of the cylindrical portion 31. Therefore, as shown in Fig. 4A, multiple layers of vortex gas flows are formed in the axial direction within the cylindrical portion 31.

[0026] In this state, the control unit 50 drives the laser irradiation unit 10, causing the laser to irradiate downward from the laser irradiation unit 10. This laser passes through the protective glass 31a of the hood 30 and is irradiated into the cylindrical unit 31, and performs predetermined laser processing on the workpiece WP placed in the opening 31b. At least the hood 30 and the support base 20 are housed in a chamber (not shown), and gas leaking from the opening 31b of the hood 30 is sealed in the chamber. The gas in the chamber is exhausted to the outside through an exhaust line connected to the chamber.

[0027] In this manner, in the laser processing apparatus 1, the workpiece WP is machined with a laser while multiple layers of gas flow are formed in the hood 30 (cylindrical portion 31) in the axial direction. This prevents dust PA generated from the workpiece WP by laser irradiation from being stirred up and prevents the dust PA from adhering to the protective glass 31a. That is, as shown in FIG. 4B , in the conventional hood 80, the nozzle 84 was positioned approximately at the top of the cylindrical portion 81, so only a single axial gas flow was formed within the cylindrical portion 81. Therefore, dust PA generated from the workpiece WP was sometimes stirred up by the gas flow and adhered to the protective glass 81a at the top of the hood 80. The dust PA adhering to the protective glass 81a attenuates the laser light passing through the protective glass 81a. In this regard, in the present embodiment, multiple layers of gas flow are formed in the axial direction within the hood 30. Even if dust PA is stirred up by the lower gas flow, the upper gas flow prevents the dust PA from approaching the protective glass 31a. This makes it possible to prevent the dust PA from adhering to the protective glass 31a, and thus to prevent the attenuation of the laser.

[0028] The gas flow within the cylindrical portion 31 need only form at least two layers in the axial direction. Here, a single gas flow refers to a gas flow in approximately the same direction, and a two-layer gas flow refers to a gas flow with different flow directions (including a vortex flow with different rotational directions). Therefore, for example, as shown in FIG. 5A , the gas supply amounts may be different between the opposing left and right nozzles 34. Even in this case, even if the left and right gas flows are unbalanced, at least two layers of gas flow can be formed in the axial direction. Alternatively, as shown in FIG. 5B , only one set of nozzles 34 may be provided. In this case, the downward gas flow does not need to be vortex-shaped, as shown in FIG. 6A . Furthermore, even when there is only one set of nozzles 34, the gas supply amounts may be different between the left and right nozzles 34, as shown in FIG. 6B .

[0029] [Technical Effects of the Embodiment] As described above, according to this embodiment, the nozzle 34 of the hood 30 is disposed in the axial center of the cylindrical portion 31. That is, the nozzle 34 is disposed in an axial position spaced apart from the upper and lower ends of the cylindrical portion 31. Therefore, the gas supplied from the nozzle 34 forms at least two layers of gas flow in the axial direction within the cylindrical portion 31. This prevents the dust PA from adhering to the protective glass 31a, thereby suppressing laser attenuation. Furthermore, the nozzle 34 is disposed in a portion of the cylindrical portion 31 in the circumferential direction. That is, the nozzle 34 is not formed around the entire circumference of the cylindrical portion 31. Therefore, gas can easily escape vertically in the inner portion of the cylindrical portion 31 where the nozzle 34 is not formed. This allows for the formation of a vertically swirling vertical vortex.

[0030] Furthermore, according to this embodiment, the first axial length L1 from the upper end of the cylindrical portion 31 to the nozzle 34 satisfies the above-mentioned formula (3), so that a gas flow can be more reliably formed above the nozzle 34. Therefore, adhesion of dust PA to the protective glass 31 a can be more reliably suppressed.

[0031] Furthermore, according to this embodiment, the second axial length L2 from the lower end of the cylindrical portion 31 to the nozzle 34 satisfies the above-mentioned formula (4), so that a gas flow can be more reliably formed below the nozzle 34. Therefore, adhesion of dust PA to the protective glass 31 a can be more reliably suppressed.

[0032] Furthermore, according to this embodiment, the width W of the nozzle along the direction perpendicular to the axial direction satisfies the above-mentioned formula (5), so that at least two layers of gas flow can be suitably formed in the axial direction in the width direction within the cylindrical portion 31. Therefore, adhesion of dust PA to the protective glass 31 a can be more reliably suppressed.

[0033] Furthermore, according to the present embodiment, the nozzles 34 include a pair of nozzles facing each other in a plane perpendicular to the axial direction, which allows the gas flows to collide in the plane perpendicular to the axial direction, thereby favorably forming vertical vortices that swirl in the vertical direction.

[0034] Furthermore, according to this embodiment, the nozzles 34 do not have to be arranged radially with respect to the central axis Ax of the cylindrical portion 31 when viewed in the axial direction. Even if the nozzles 34 are not arranged radially, vertical vortices swirling in the up-down direction can be formed.

[0035] [Analysis Example 1] Next, the effect of preventing the adhesion of dust PA by forming a gas flow inside the hood 30 will be described using an analysis example. In this analysis example 1, the gas flow inside the cylindrical portion 31 was obtained by fluid analysis when the shape of the hood 30 and the gas flow rate conditions were changed. Specifically, based on the shape of the hood 30 of the above embodiment, analysis was performed on a model in which the lower nozzle set was eliminated (Model 1), a model in which the gas volume balance between the left and right sides was equalized (Model 2), and a model in which the gas volume balance between the left and right sides was biased (Model 3). In addition, an analysis was also performed on the gas flow in a conventional hood 80 (see FIG. 4B) as a comparative example.

[0036] The dimensions of each part of the analytical model are as follows: Hood shape Overall height: 258 mm Inner diameter D: 160 mm First length L1: 103 mm Axial distance between upper and lower nozzles: 54 mm Axial height of blowing opening of each nozzle: 2 mm Width W of each nozzle: 136 mm Left-right distance L3 between the ends of the two left and right nozzles (see Figure 2): 300 mm Axial gap between hood and support base: 5 mm Axial range under atmospheric pressure conditions: up to a height of 100 mm from the top surface of the support base Radial range under atmospheric pressure conditions: within a diameter of 400 mm However, first length L1 and the axial distance between the upper and lower nozzles are the lengths to the blowing opening (hole) of each nozzle.

[0037] The gas flow rate conditions for Models 1 to 3 are shown in the upper column of Table 1 below. In this column, the gas flow rates on the left and right are expressed as "(left flow rate), (right flow rate)."

[0038]

[0039] Contour diagrams of the analysis results are shown in Figures 7A to 10C. Figures 7A to 7C show the analysis results for Model 1, Figures 8A to 8C show the analysis results for Model 2, Figures 9A to 9C show the analysis results for Model 3, and Figures 10A to 10C show the analysis results for conventional hood 80. In each diagram, (a) shows the path line from the bottom of the hood (for example, at a height of 50 mm), (b) shows the gas (for example, nitrogen) concentration distribution, and (c) shows a velocity vector diagram. In all of Figures (a) to (c), the top and bottom and left and right of the paper correspond to the top and bottom and left and right of the hood.

[0040] 7A to 7C, the following can be said about Model 1 (hood 30 without a lower nozzle set): The gas flow forms a vortex below the nozzle 34, making it difficult for the dust PA at the bottom of the hood 30 to reach the protective glass 31a. The gas concentration inside the hood 30 is generally high. Two layers of vortex gas flow are formed above and below the nozzle 34.

[0041] 8A to 8C, the following can be said about Model 2 (equal balance of gas volume on the left and right): The gas flow forms a vortex below the lower nozzle 34b, making it difficult for the dust PA at the bottom of the hood 30 to reach the protective glass 31a or the upper nozzle 34a. The gas concentration inside the hood 30 is generally high. Three layers of vortex gas flow are formed above and below the upper nozzle 34a, below the lower nozzle 34b, and between the two upper and lower sets of nozzles 34.

[0042] 9A to 9C, the following can be said about Model 3 (uneven gas volume balance between the left and right): The gas flow forms a vortex below the lower nozzle 34b, making it difficult for the dust PA at the bottom of the hood 30 to reach the protective glass 31a or the upper nozzle 34a. The gas inside the hood 30 exits from the side where the lower nozzle 34b is blowing in stronger. Three layers of vortex gas flow are formed above and below.

[0043] 10A to 10C, the following can be said about the conventional hood 80: The gas flow is a vortex flow with only one layer above and below, and there is a risk that the dust PA at the bottom of the hood 30 will be sucked up onto the protective glass 31a. The gas concentration inside the hood 30 is generally high.

[0044] The results of the above comparison for models 1 to 3 are shown in the lower column of Table 1 (excluding conventional hoods). The results of this comparison are listed below. All of models 1 to 3 can be expected to be effective in preventing dust PA from adhering to the protective glass 31a. Models 2 and 3, which have three upper and lower gas flows, are expected to be more effective in preventing dust PA from adhering than model 1, which has two upper and lower gas flows. Unlike models 2 and 3, model 1 may not be able to properly discharge dust PA. All of models 1 to 3 properly purge gas inside the hood 30.

[0045] [Analysis Example 2] In Analysis Example 2, the dust PA adhesion prevention effect was evaluated by fluid analysis for the hood 30 of the embodiment when the gas application at each nozzle 34 was changed. Gas application refers to the relative flow rate of gas with respect to the size of the hood 30 (the capacity of the cylindrical portion 31), and was evaluated using three levels: "strong," "weak," and "none." The dust PA adhesion prevention effect was evaluated in the same manner as in Analysis Example 1 above.

[0046] Table 2 below shows the main gas application combinations that can be expected to be effective in preventing the adhesion of dust PA. As shown in Table 2, it is preferable that at least one of the upper nozzles 34a has a "strong" gas application. Among the combinations in Table 2, No. 1 and No. 2 produced the most desirable results. It is also believed that the same effect can be obtained even if the difference in gas application between the left and right sides of each nozzle set is reversed. Furthermore, when three or more nozzle sets are provided, the pattern of the third and subsequent sets will affect the magnitude of the dust PA adhesion prevention effect, but will not affect whether or not the effect is achieved.

[0047]

[0048] [Others] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. For example, in the above-described embodiments, the laser is irradiated along the axial direction of the hood 30, but the laser may be inclined with respect to the axial direction.

[0049] The configuration of the laser processing apparatus is not limited to that shown in FIG. 1 . For example, a laser processing apparatus 1A shown in FIG. 12 includes a regulator 44, an on-off valve 45, and a flow control valve 46 as devices for adjusting the gas injection conditions from the nozzle 34. The regulator 44 adjusts the injection pressure from a gas source 41, such as a cylinder. The on-off valve 45 switches the injection ON / OFF. The flow control valves 46 are located on the upper and lower stages and individually adjust the flow rates of the injected gas for the upper and lower stages. In the laser processing apparatus 1A, the laser emitted from the laser oscillator 11 has its shape and output adjusted through the optical system 12, and the laser irradiation position is controlled by the galvanometer scanner 13. The hood 30 is fixed to the chamber 21 arranged within the enclosure 22. The support stage 20 on which the workpiece WP is placed is position-controlled and positioned relative to the hood 30 during processing. At this time, the axial gap between the lower end of the hood 30 and the upper surface of the support base 20 is set to a very short distance (about 2 mm in the actual machine). This allows the inside of the hood 30 to be suitably purged with an inert gas such as nitrogen, and the vicinity of the workpiece WP to be maintained at a low oxygen concentration (for example, on the order of several tens of ppm). This in turn allows the workpiece WP to be suitably laser-machined. Furthermore, each of the above components is controlled by a control unit 50 (see FIG. 1).

[0050] Furthermore, the laser processing device according to the present invention can be widely applied to laser processing of workpieces in a gas atmosphere, regardless of the type of processing or the material of the workpiece, etc. In addition, the details shown in the above embodiment can be modified as appropriate without departing from the spirit of the invention.

[0051] As described above, the present invention is useful for suppressing laser attenuation.

[0052] DESCRIPTION OF SYMBOLS 1 Laser processing device 10 Laser irradiation section (laser irradiation means) 20 Support stand 30 Hood (hood for laser device) 31 Cylindrical section 31a Protective glass (transmitting section) 31b Opening 34 Nozzle 34a Upper nozzle 34b Lower nozzle 34c Partial nozzle 40 Gas supply section (gas supply means) 41 Gas source 42 Valve 43 Piping 50 Control section 80 Conventional hood 81 Conventional cylindrical section 81a Conventional protective glass 84 Conventional nozzle Ax Central axis D Inner diameter PA Particle W Width WP Workpiece

Claims

1. A hood for a laser device comprising: a cylindrical portion extending along an axial direction; a transparent portion provided at one axial end of the cylindrical portion and allowing a laser to pass therethrough; an opening provided at the other axial end of the cylindrical portion; and a nozzle for supplying gas into the interior of the cylindrical portion, the nozzle being located in the center of the cylindrical portion in the axial direction and at a portion of the circumference of the cylindrical portion.

2. The laser apparatus hood according to claim 1, wherein a first axial length L1 from the one end of the cylindrical portion to the nozzle satisfies the following formula (3), where D is an inner diameter of the cylindrical portion. L1≧0.3D (3) 3. The hood for a laser apparatus according to claim 1, wherein a second length L2 in the axial direction from the other end of the cylindrical portion to the nozzle satisfies the following formula (4), where D is an inner diameter of the cylindrical portion. L2≧0.3D (4) 4. The hood for a laser apparatus according to claim 1, wherein a width W of the nozzle along a direction perpendicular to the axial direction satisfies the following formula (5), where D is an inner diameter of the cylindrical portion. W≧0.3D (5) 5. The hood for a laser apparatus according to claim 1, wherein the nozzle includes a pair opposed to each other in a plane perpendicular to the axial direction.

6. The hood for a laser apparatus according to claim 5, wherein the nozzle includes a plurality of sets arranged side by side in the axial direction.

7. The hood for a laser apparatus according to claim 1, wherein the nozzle is inclined with respect to the axial direction.

8. The hood for a laser apparatus according to claim 1, wherein the nozzles are not arranged radially with respect to the central axis of the cylindrical portion when viewed in the axial direction.

9. A laser processing apparatus comprising: a hood for a laser apparatus according to any one of claims 1 to 8; a support table arranged on the opening side of the cylindrical portion and supporting a workpiece; a laser irradiation means for irradiating a laser into the cylindrical portion through the transmission portion; and a gas supply means for supplying gas into the cylindrical portion through the nozzle.

10. A laser processing method for processing a workpiece covered by a hood by irradiating it with a laser, comprising: a hood having a cylindrical portion along an axial direction, a transparent portion provided at one axial end of the cylindrical portion to transmit the laser, an opening provided at the other axial end of the cylindrical portion, and a nozzle located in the center of the cylindrical portion in the axial direction and in a part of the circumferential direction, for supplying gas to the inside; and a laser is irradiated into the cylindrical portion through the transparent portion while gas is supplied from the nozzle into the cylindrical portion to form at least two layers of gas flow in the axial direction, thereby processing a workpiece placed in the opening.