Patent Publication Number: US-2023143460-A1

Title: Laser machining device and laser machining method

Description:
TECHNICAL FIELD 
     The present disclosure relates to a laser processing apparatus and a laser processing method. 
     BACKGROUND ART 
     Patent Document 1 discloses a technique related to a laser processing method by laser ablation. In this laser processing method, a beam shaping device capable of varying a beam profile is used, and a plurality of processing surfaces arranged in a thickness direction of a processing object are irradiated with laser beams having beam profiles of geometric shapes different from each other. 
     Patent Document 2 discloses a technique related to a laser processing apparatus and a laser processing method. In this laser processing method, laser light output from a laser light source is phase-modulated by a spatial phase modulation element and guided to an imaging optical system, and a processing object is irradiated with the laser light by the imaging optical system to process the processing object. As input data to be input to the spatial phase modulation element, composite data including image reconstruction hologram data for reconstructing a processing shape of the processing object and position movement hologram data for performing image reconstruction at a predetermined processing position is used. Further, laser processing is performed on the processing object while sequentially changing the composite data. 
     CITATION LIST 
     Patent Literature 
     Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2015-521108 
     Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2006-119427 
     Non Patent Literature 
     Non Patent Document 1: F. Mezzapesa et al., “High-resolution monitoring of the hole depth during ultrafast laser ablation drilling by diode laser self-mixing interferometry”, Opt. Lett. Vol.36, pp.822-824 (2011) 
     SUMMARY OF INVENTION 
     Technical Problem 
     A processing object can be processed by focusing laser light output from a laser light source by a focusing optical system and irradiating the processing object with the laser light. When a lens is simply used to focus the laser light, the processing object can be processed into a desired shape by scanning a focusing position of the laser light. However, in this case, processing takes a long time. 
     For reducing the processing time, for example, a configuration may be considered in which multipoint simultaneous processing is performed by simultaneously focusing and applying the laser light to a plurality of irradiation points. As a method for the above configuration, there is a method of presenting a hologram on a spatial light modulator of a phase modulation type, phase-modulating laser light output from a single laser light source by the spatial light modulator, and simultaneously focusing and applying the phase-modulated laser light to the plurality of irradiation points by a focusing optical system. In this case, the hologram presented on the spatial light modulator has a phase modulation distribution for focusing the laser light on the plurality of irradiation points by the focusing optical system. 
     In the method described above, it is desired to freely control a position of the irradiation point and perform more complicated processing. 
     An object of the present invention is to perform more complicated processing in a laser processing apparatus and a laser processing method in which focused irradiation is simultaneously performed on a plurality of irradiation points by phase-modulating laser light using a spatial light modulator. 
     Solution to Problem 
     An embodiment of the present invention is a laser processing apparatus. The laser processing apparatus includes a spatial light modulator for inputting laser light output from a laser light source, presenting a hologram for modulating a phase of the laser light in each of a plurality of pixels arranged two-dimensionally, and outputting laser light after phase modulation by the hologram; a focusing optical system provided at a subsequent stage of the spatial light modulator; and a control unit for presenting, on the spatial light modulator, the hologram for focusing the laser light after the phase modulation output from the spatial light modulator on a plurality of irradiation points in a processing object by the focusing optical system, and the control unit controls light intensities of at least two irradiation points included in the plurality of irradiation points independently of each other. 
     An embodiment of the present invention is a laser processing method. The laser processing method repeatedly performs a control step of presenting, on a spatial light modulator, a hologram for modulating a phase of light in each of a plurality of pixels arranged two-dimensionally; a light modulation step of inputting laser light output from a laser light source to the spatial light modulator, and performing phase modulation of the laser light by the hologram; and a focusing step of focusing the laser light after the phase modulation, and in the control step, the spatial light modulator presents the hologram for focusing the laser light after the phase modulation output from the spatial light modulator on a plurality of irradiation points in a processing object by the focusing step, and light intensities of at least two irradiation points included in the plurality of irradiation points are controlled independently of each other. 
     In the above laser processing apparatus and laser processing method, the control unit (in the control step) controls the light intensities of the at least two irradiation points included in the plurality of irradiation points independently of each other. In this case, when there is a difference in material according to a portion of the processing object, that is, a difference in processing speed for the laser light having the same intensity, each irradiation point corresponding to each portion can be irradiated with the laser light with the appropriate light intensity. Therefore, according to the above configuration, it is possible to easily process the processing object including two or more types of materials into a complicated shape. 
     Further, according to the above configuration, even in the case where a processing region is made of a single material, a removal rate (removal amount) of the processing object can be independently controlled for each portion of the processing region by independently controlling the light intensity for each irradiation point, and thus, a more complicated shape can be realized. 
     Advantageous Effects of Invention 
     According to the embodiments of the present invention, it is possible to perform more complicated processing in a laser processing apparatus and a laser processing method for simultaneously performing focused irradiation on a plurality of irradiation points by phase-modulating laser light using a spatial light modulator. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a block diagram illustrating a configuration of a laser processing apparatus  10  according to an embodiment. 
         FIG.  2    includes (a) a plan view illustrating laser light La 2  after phase modulation with which a processing object W is irradiated through a focusing optical system  14 , and (b) an enlarged view of a part of (a). 
         FIG.  3    includes (a)-(e) diagrams illustrating examples of a planar shape of a processing region A. 
         FIG.  4    is a block diagram illustrating a hardware configuration example of a control unit  18 . 
         FIG.  5    includes (a) a cross-sectional view illustrating a state in which the processing object W including a plurality of regions Wa, Wb, and Wc with different materials is irradiated with the laser light La 2 , and (b) a plan view illustrating a light irradiation surface of the processing object W. 
         FIG.  6    includes (a) a cross-sectional view illustrating a state in which the processing object W including the plurality of regions Wa, Wb, and Wc with different materials is irradiated with the laser light La 2 , and (b) a plan view illustrating the light irradiation surface of the processing object W. 
         FIG.  7    includes (a) a cross-sectional view illustrating a state in which the processing object W including a plurality of regions Wd and We with different materials is irradiated with the laser light La 2 , and (b)-(d) cross-sectional views taken along a line VIIb-VIIb, a line VIIc-VIIc, and a line VIId-VIId in (a). 
         FIG.  8    includes (a) a cross-sectional view illustrating a state in which the processing object W is irradiated with the laser light La 2 , and (b) a cross-sectional view illustrating a hole Ha formed in the processing object W. 
         FIG.  9    includes (a)-(c) diagrams schematically illustrating an arrangement example of irradiation points SP in cross-sections taken along a line IXa-IXa, a line IXb-IXb, and a line IXc-IXc illustrated in (a) in  FIG.  8   . 
         FIG.  10    includes (a)-(c) diagrams schematically illustrating another arrangement example of the irradiation points SP in the cross-sections. 
         FIG.  11    includes (a) a cross-sectional view illustrating a state in which the processing object W is irradiated with the laser light La 2 , and (b) a cross-sectional view illustrating a hole Hb formed in the processing object W. 
         FIG.  12    includes (a) a cross-sectional view illustrating a state in which the processing object W is irradiated with the laser light La 2 , and (b) a cross-sectional view illustrating a hole Hc formed in the processing object W. 
         FIG.  13    includes (a) a cross-sectional view illustrating a state in which the processing object W is irradiated with the laser light La 2 , and (b) a cross-sectional view illustrating holes Hc and Hd formed in the processing object W. 
         FIG.  14    includes (a) a cross-sectional view illustrating a state in which the processing object W is irradiated with the laser light La 2 , and (b) a cross-sectional view illustrating holes Hc, Hd, and He formed in the processing object W. 
         FIG.  15    includes (a) a diagram illustrating a cross-sectional shape of a through hole Hf formed when contours of two processing regions A have curvatures, and (b) a diagram illustrating a cross-sectional shape of a through hole Hg formed when a contour of one processing region A has a curvature. 
         FIG.  16    includes (a) a cross-sectional view illustrating a hole Hh formed by irradiation of the laser light La 2 , (b) a plan view illustrating a shape of the hole Hh on one surface W 1  of the processing object W, and (c) a plan view illustrating a shape of the hole Hh on the other surface W 2  of the processing object W. 
         FIG.  17    includes diagrams conceptually illustrating a change of a shape of the processing region A in an optical axis direction of the laser light La 2  for forming the hole Hh, and illustrates (a) an outline of a configuration for irradiating the processing object W with the laser light La 2  and a cross-section of the processing object W in the optical axis direction of the laser light La 2 , and illustrates (b)-(e) the shape of the processing region A in each plane located at different depths in the processing object W and a plurality of irradiation points SP in each plane. 
         FIG.  18    includes diagrams illustrating an example of a hologram corresponding to the plane illustrated in (b) in  FIG.  17   , and illustrates (a) the plurality of irradiation points SP illustrated in (b) in  FIG.  17   , and illustrates (b)-(d) examples of holograms for realizing the plurality of irradiation points SP illustrated in (a). 
         FIG.  19    includes diagrams illustrating an example of a hologram corresponding to the plane illustrated in (c) in  FIG.  17   , and illustrates (a) the plurality of irradiation points SP illustrated in (c) in  FIG.  17   , and illustrates (b)-(d) examples of holograms for realizing the plurality of irradiation points SP illustrated in (a). 
         FIG.  20    includes diagrams illustrating an example of a hologram corresponding to the plane illustrated in (d) in  FIG.  17   , and illustrates (a) the plurality of irradiation points SP illustrated in (d) in  FIG.  17   , and illustrates (b)-(d) examples of holograms for realizing the plurality of irradiation points SP illustrated in (a). 
         FIG.  21    includes diagrams illustrating an example of a hologram corresponding to the plane illustrated in (e) in  FIG.  17   , and illustrates (a) the plurality of irradiation points SP illustrated in (e) in  FIG.  17   , and illustrates (b)-(d) examples of holograms for realizing the plurality of irradiation points SP illustrated in (a). 
         FIG.  22    is a diagram illustrating a state in which the irradiation point SP of the laser light La 2  is formed farther than the processing object W. 
         FIG.  23    is a flowchart illustrating a laser processing method according to an embodiment. 
         FIG.  24    is a flowchart illustrating a case where a storage step S 0  is performed before a control step S 1 . 
         FIG.  25    is a diagram for describing a laser processing method described in Patent Document 1. 
         FIG.  26    includes (a)-(e) diagrams for describing a laser processing method described in Patent Document 2. 
         FIG.  27    is a diagram for describing the laser processing method described in Patent Document 2. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of a laser processing apparatus and a laser processing method will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference signs, and redundant description will be omitted. Further, the present invention is not limited to these examples. 
       FIG.  1    is a block diagram illustrating a configuration of a laser processing apparatus  10  according to an embodiment. As illustrated in  FIG.  1   , the laser processing apparatus  10  according to the present embodiment includes a laser light source  11 , a spatial light modulator  12 , a dichroic mirror  13 , a focusing optical system  14 , a drive unit  15 , an observation light source  16 , a photodetector  17 , and a control unit (PC or the like)  18 . 
     The laser light source  11  outputs pulse-shaped laser light La 1  having a time width of 1 picosecond or less (for example, several femtoseconds). A wavelength of the laser light La 1  output from the laser light source  11  is, for example, 250 nm or more and 2500 nm or less, and is 1030 nm in one example. Further, a power of the laser light La 1  output from the laser light source  11  is, for example, 0.01 W or more and 1000 W or less, and is 1 W in one example. The laser light source  11  is, for example, a solid-state laser including a Yb:YAG crystal or a Yb:KGW crystal as a laser medium, or a Yb-doped optical fiber laser excited by a semiconductor laser. 
     The spatial light modulator  12  is optically coupled to the laser light source  11 , and inputs the laser light La 1  output from the laser light source  11 . The optical coupling between the spatial light modulator  12  and the laser light source  11  is, for example, spatial coupling. The spatial light modulator  12  includes a plurality of pixels arranged two-dimensionally, and modulates a phase of the laser light La 1  independently in each pixel by presenting a hologram on the plurality of pixels. 
     The spatial light modulator  12  has, for example, a liquid crystal type configuration. When the spatial light modulator  12  is the liquid crystal type, individual voltages constituting the hologram are applied to a plurality of pixel electrodes arranged two-dimensionally. Thus, a magnitude of an electric field applied to a liquid crystal layer is controlled for each pixel electrode. An optical path length in the liquid crystal layer of each pixel changes according to the magnitude of the electric field. Therefore, the phase of the laser light La 1  can be modulated independently in each pixel. 
     The spatial light modulator  12  may be a transmission type or may be a reflection type. Further, the configuration of the spatial light modulator  12  is not limited to the liquid crystal type, and spatial light modulators of various configurations may be used. The spatial light modulator  12  outputs laser light La 2  after phase modulation performed by the hologram. 
     The dichroic mirror  13  is an optical element which transmits light included in a certain wavelength range and reflects light included in another wavelength range. One surface of the dichroic mirror  13  is optically coupled to the spatial light modulator  12 . The laser light La 2  after the modulation reaching the dichroic mirror  13  from the spatial light modulator  12  is reflected (or transmitted) by the dichroic mirror  13  and travels toward a processing object W. The dichroic mirror  13  is, for example, a short-pass dichroic mirror. 
     The laser light La 2  passes through the focusing optical system  14  provided at a subsequent stage of the spatial light modulator  12  (more precisely, at a subsequent stage of the dichroic mirror  13 ), and reaches the processing object W. The focusing optical system  14  is, for example, a lens made of glass, and is optically coupled to the spatial light modulator  12  via the dichroic mirror  13 . The optical coupling of the spatial light modulator  12 , the dichroic mirror  13  and the focusing optical system  14  is, for example, spatial coupling. The focusing optical system  14  is disposed on an optical path between the dichroic mirror  13  and the processing object W. 
     The drive unit  15  is electrically connected to each pixel electrode of the spatial light modulator  12 , and provides, to each pixel electrode, a drive voltage Vd for presenting the hologram on the spatial light modulator  12 . The drive unit  15  includes a plurality of voltage generation circuits electrically connected to the respective pixel electrodes. Each voltage generation circuit includes an amplifier circuit including a transistor. 
     The control unit  18  is electrically connected to the drive unit  15 . The control unit  18  creates the hologram or reads out the hologram from the storage unit, and provides two-dimensional data of the hologram to the drive unit  15 . The drive unit  15  generates a drive signal, being an analog signal based on the hologram, for each pixel. Each amplifier circuit of the drive unit  15  generates the drive voltage Vd by amplifying the drive signal. 
     (a) in  FIG.  2    is a plan view illustrating the laser light La 2  after the phase modulation with which the processing object W is irradiated through the focusing optical system  14 . Further, (b) in  FIG.  2    is an enlarged view of a part of (a) in  FIG.  2   . As illustrated in (a) in  FIG.  2   , the control unit  18  generates the hologram for focusing the laser light La 2  after the phase modulation output from the spatial light modulator  12  on a plurality of irradiation points SP of the processing object W by the focusing optical system  14 , and presents the hologram on the spatial light modulator  12 . 
     The plurality of irradiation points SP define a processing region A in the processing object W. That is, the plurality of irradiation points SP are arranged at intervals on a closed virtual line B, and the processing region A is determined by the virtual line B. Further, the control unit  18  sequentially presents, on the spatial light modulator  12 , a plurality of holograms for changing the position of each irradiation point SP along the virtual line B. Thus, as illustrated in (b) in  FIG.  2   , each irradiation point SP discretely moves on the virtual line B. 
     A planar shape (shape in a plane perpendicular to an optical axis of the laser light La 2 ) of the processing region A defined by the plurality of irradiation points SP is variously set according to the purpose of processing or the like.  FIG.  3    includes diagrams illustrating examples of the planar shape of the processing region A. The processing region A may have a circular shape as illustrated in (a) in  FIG.  3   , or may have an elliptical shape as illustrated in (b) in  FIG.  3   . Further, the processing region A may have a triangular shape as illustrated in (c) in  FIG.  3   , may have a quadrangular shape as illustrated in (d) in  FIG.  3   , or may have an arbitrary polygonal shape as illustrated in (e) in  FIG.  3   . 
     The control unit  18  controls the light intensities (unit: W/cm 2 , which may be restated as an energy density (unit: J/cm 2 )) of at least two irradiation points SP included in the plurality of irradiation points SP independently of each other. In one example, the control unit  18  independently controls the light intensities of all the irradiation points SP. The light intensity of each irradiation point SP is determined, for example, by a processing speed of a material of the processing object W at each irradiation point SP and/or other factors. 
     For example, in the case of a material whose processing speed is fast (that is, processing is easy) with respect to the laser light La 2 , the light intensity is decreased to slow down the processing speed. Further, in the case of a material whose processing speed is slow (that is, processing is difficult) with respect to the laser light La 2 , the light intensity is increased to speed up the processing speed. In this way, even in a case where materials having different processing speeds are mixed in a light irradiation surface or a cross-section of the processing object W, the processing speeds can be made uniform in the plurality of irradiation points SP. Further, for a material being greatly affected by heat, the light intensity may be decreased to minimize a region which is affected by heat. 
     Further, the control unit  18  controls at least one of the light intensity and an irradiation time (in other words, a hologram presenting time) for each of the plurality of irradiation points SP according to a depth position of each of the plurality of irradiation points SP in the processing object W. 
     For example, when processing a deeper portion than when processing the light irradiation surface of the processing object W, debris and the like remaining at the time of immediately preceding irradiation of the laser light La 2  interferes with irradiation of the laser light La 2 , and thus, the processing speed decreases. Therefore, the processing speed and the processing quality are improved by increasing the light intensity of the plurality of irradiation points SP and/or increasing the irradiation time as the depth in the processing object W increases. Further, in the case where the processing object W includes a plurality of layers with different materials (for example, a semiconductor, a printed circuit board, or the like), it is possible to perform laser processing under a condition suitable for each layer by controlling a change period or a presenting time of the hologram. 
     In addition, the processing object W serving as a processing target in the present embodiment can be formed of various substances such as glass, semiconductor, metal (steel material, non-ferrous metal, alloy, or the like), and composite material (carbon fiber reinforced plastic (CFRP) or the like). 
       FIG.  1    is referred again. The observation light source  16  is a laser light source for irradiating the processing object W with observation light Lb. A wavelength of the observation light Lb output from the observation light source  16  is different from the wavelengths of the laser light La 1  and the laser light La 2 . The wavelength of the observation light Lb is, for example, 800 nm or more and 980 nm or less, and is 808 nm in one example. The observation light source  16  is, for example, an Al(In)GaAs-based or InGaAsP-based semiconductor laser. 
     The observation light source  16  is optically coupled to the other surface of the dichroic mirror  13 . The observation light Lb reaching the dichroic mirror  13  from the observation light source  16  is transmitted (or reflected) through the dichroic mirror  13 , travels toward the processing object W along an optical path parallel to the laser light La 2 , and is applied to the processing object W. 
     In addition, the optical axis of the observation light Lb and the optical axis of the laser light La 2  are illustrated side by side in the diagram, and the optical axis of the observation light Lb and the optical axis of the laser light La 2  may coincide with each other. An irradiation region of the observation light Lb on the processing object W includes, for example, the processing region A illustrated in (a) in  FIG.  2   . 
     A part of the observation light Lb reaches the processing object W and becomes reflected light Lc, and is output from the processing object W. Since the wavelength of the reflected light Lc is the same as the wavelength of the observation light Lb, the reflected light Lc is transmitted through the dichroic mirror  13 . The photodetector  17  is optically coupled to the other surface of the dichroic mirror  13 , and detects the reflected light Lc via the dichroic mirror  13 . 
     The photodetector  17  is a two-dimensional image detector or a detector for acquiring three-dimensional information. In the latter case, the photodetector  17  includes, for example, an interference measurement optical system. In this case, the photodetector  17  branches and acquires a part of the observation light Lb output from the observation light source  16  (or acquires back light of a semiconductor laser as the observation light source  16 ), and detects an interference light image by causing the part (or back light) of the observation light Lb and the reflected light Lc to interfere with each other. 
     The photodetector  17  is electrically connected to the control unit  18 , and provides an electrical signal Sa related to the detection result to the control unit  18 . Further, an example of interference measurement used in the present embodiment is described in Non Patent Document 1 (F. Mezzapesa et al., Opt. Lett. Vol.36, pp.822-824 (2011)). 
     The control unit  18  determines the processing state at each irradiation point SP based on the detection result from the photodetector  17 . Further, the control unit  18  controls the hologram presented on the spatial light modulator  12  according to the processing state. The control of the hologram includes, for example, control of the presenting time of the hologram, change to an appropriate hologram, and the like. 
       FIG.  4    is a block diagram illustrating a hardware configuration example of the control unit  18 . As illustrated in  FIG.  4   , the control unit  18  is configured to include a computer including hardware such as a CPU  181 , a RAM  182 , a ROM  183 , an input device  184 , a digital/analog converter  185 , an auxiliary storage device  186 , and a display output device  187 . The control unit  18  implements the above-described functions by operating these components by a program and the like stored in advance in the auxiliary storage device  186 . 
     Hereinafter, examples of the processing by the laser processing apparatus  10  of the present embodiment will be described. each of (a) in  FIG.  5    and (a) in  FIG.  6    is a cross-sectional view illustrating a state in which the processing object W including a plurality of regions Wa, Wb, and Wc with different materials is irradiated with the laser light La 2 , and illustrates a cross-section along the optical axis of the laser light La 2  (in other words, along the thickness direction of the processing object W). each of (b) in  FIG.  5    and (b) in  FIG.  6    is a plan view illustrating the light irradiation surface of the processing object W. 
     In these examples, the regions Wa, Wb, and Wc are arranged in a direction intersecting the optical axis direction of the laser light La 2  (thickness direction of the processing object W), and boundary lines of the regions Wa, Wb, and Wc are exposed on the light irradiation surface. The processing speeds for the materials of the regions Wa, Wb, and Wc with respect to the laser light La 2  having the same light intensity are different from each other. Specifically, for the laser light La 2  having the same light intensity, the processing speed for the region Wa is the slowest, and the processing speed for the region Wc is the fastest. 
     In the example illustrated in  FIG.  5   , three processing regions A independent of each other are set respectively for the regions Wa, Wb, and Wc. Further, a plurality of irradiation points SP for determining one processing region A are formed in the region Wa, a plurality of irradiation points SP for determining another processing region A are formed in the region Wb, and a plurality of irradiation points SP for determining still another processing region A are formed in the region Wc. 
     In the example illustrated in  FIG.  6   , a processing region A provided on the regions Wa and Wb and another processing region A provided on the regions Wb and Wc are set. Further, a plurality of irradiation points SP for determining a part of the one processing region A are formed in the region Wa, a plurality of irradiation points SP for determining the remaining part of the one processing region A and a plurality of irradiation points SP for determining a part of the other processing region A are formed in the region Wb, and a plurality of irradiation points SP for determining the remaining part of the other processing region A are formed in the region Wc. 
     In this case, as illustrated in (b) in  FIG.  5    and (b) in  FIG.  6   , the control unit  18  controls the hologram to be presented on the spatial light modulator  12  such that the light intensity of the irradiation points SP formed in the region Wa is largest and the light intensity of the irradiation points SP formed in the region Wc is smallest. In addition, in (b) in  FIG.  5    and (b) in  FIG.  6   , the light intensity of each irradiation point SP is represented by light and shade of color. The darker the color, the higher the light intensity, and the lighter the color, the lower the light intensity. 
     Thus, the processing speeds for the irradiation points SP in the regions Wa, Wb, and Wc can be brought close to each other, and the processing depths can be made uniform. Ideally, relative relationship between the light intensities of the respective irradiation points SP is adjusted such that the processing speeds at the irradiation points SP are equal to each other. 
     In the examples illustrated in  FIG.  5    and  FIG.  6   , the control unit  18  may detect the material at each irradiation point SP based on the detection result by the photodetector  17  illustrated in  FIG.  1   . The reflectance for the observation light Lb depends on the material, and thus, the material at each irradiation point SP can be known based on the intensity ratio between the observation light Lb and the reflected light Lc. Therefore, the boundaries of the regions Wa, Wb, and Wc can be detected. 
     Further, the spatial light modulator  12  may present the hologram for realizing the light intensities of the irradiation points SP respectively corresponding to the regions Wa, Wb, and Wc. In other words, in this example, the control unit  18  may generate the hologram for setting the light intensities of the irradiation points SP independently of each other based on the detection result by the photodetector  17 . 
     Further, data related to the light intensity of each irradiation point SP according to the distribution of the regions Wa, Wb, and Wc may be stored in advance in the storage unit (for example, the ROM  183  or the auxiliary storage device  186  illustrated in  FIG.  4   ). In this case, the control unit  18  can control the light intensity of each irradiation point SP based on the data. 
     (a) in  FIG.  7    is a cross-sectional view illustrating a state in which the processing object W including a plurality of regions Wd and We with different materials is irradiated with the laser light La 2 , and illustrates a cross-section along the optical axis of the laser light La 2  (in other words, along the thickness direction of the processing object W). (b), (c), and (d) in  FIG.  7    are cross-sectional views taken along a line VIIb-VIIb, a line VIIc-VIIc, and a line VIId-VIId in (a) in  FIG.  7   , respectively, and illustrates cross-sections perpendicular to the optical axis of the laser light La 2 . 
     In this example, the regions Wd and We are arranged in the optical axis direction of the laser light La 2 , and a boundary surface of the regions Wd and We is inclined with respect to a virtual plane perpendicular to the optical axis direction of the laser light La 2 . The processing speeds for the materials of the regions Wd and We with respect to the laser light La 2  having the same light intensity are different from each other. Specifically, for the laser light La 2  having the same light intensity, the processing speed for the region Wd is slower than the processing speed for the region We. 
     In this example, a processing region A is set for the processing object W, and a plurality of irradiation points SP for determining the processing region A are formed in the processing object W. In addition, also in (b), (c), and (d) in  FIG.  7   , the light intensity of each irradiation point SP is represented by light and shade of color. The darker the color, the higher the light intensity, and the lighter the color, the lower the light intensity. 
     First, at the timing illustrated in (b) in  FIG.  7   , the control unit  18  controls the hologram presented on the spatial light modulator  12  such that the processing speed of each irradiation point SP in the region Wd becomes an arbitrary speed. When the processing proceeds to a certain depth, as illustrated in (c) in  FIG.  7   , the processing region A is provided on the region Wd and the region We. In this case, the control unit  18  controls the hologram presented on the spatial light modulator  12  such that the light intensity of the irradiation point SP located in the region We becomes smaller than the light intensity of the irradiation point SP located in the region Wd. 
     When the processing further proceeds, a ratio of the region We in the processing region A gradually increases, and finally, as illustrated in (d) in  FIG.  7   , only the region We is included in the processing region A. In this case, the control unit  18  controls the hologram presented on the spatial light modulator  12  such that the processing speed of each irradiation point SP in the region We becomes an arbitrary speed. 
     In this example, the control unit  18  controls the hologram such that the light intensity of the irradiation point SP formed in the region Wd is larger than the light intensity of the irradiation point SP formed in the region We. Thus, at the timing ((c) in  FIG.  7   ) at which the regions Wd and We are mixed in the processing region A, the processing speeds for the irradiation points SP in the regions Wd and We can be brought close to each other, and the processing depths can be made uniform. Ideally, the light intensities of the respective irradiation points SP are adjusted such that the processing speeds at the irradiation points SP become equal in the depth direction. 
     In the example illustrated in  FIG.  7   , the control unit  18  may detect a material change at each irradiation point SP based on the detection result by the photodetector  17  illustrated in  FIG.  1   . The reflectance for the observation light Lb depends on the material, and thus, when the material at each irradiation point SP changes, an intensity ratio between the observation light Lb and the reflected light Lc changes. Therefore, the material change from the region Wd to the region We can be detected. 
     Further, at the timing of the above change, the spatial light modulator  12  may present the hologram for changing the light intensity for the irradiation point SP changed from the region Wd to the region We. In other words, in this example, a change timing of the hologram for changing the light intensity of each irradiation point SP may be determined based on the detection result by the photodetector  17 . 
     Further, data related to the light intensity of each irradiation point SP according to a material distribution in the processing object W may be stored in advance in the storage unit (for example, the ROM  183  or the auxiliary storage device  186  illustrated in  FIG.  4   ). In this case, the control unit  18  can control the light intensity of each irradiation point SP based on the data. 
     (a) in  FIG.  8    is a cross-sectional view illustrating a state in which the processing object W is irradiated with the laser light La 2 , and illustrates a cross-section along the optical axis of the laser light La 2 . (b) in  FIG.  8    is a cross-sectional view illustrating a hole Ha formed in the processing object W. In the example illustrated in  FIG.  8   , a size of the processing region A continuously changes in the optical axis direction of the laser light La 2  from a light irradiation surface W 1  of the processing object W to an opposite surface W 2 . Continuous change of the size of the processing region A means that there is no step in the contour of the processing region A in a cross-section along the optical axis direction of the laser light La 2 . 
     In this example, the hologram is sequentially switched as the processing proceeds in the optical axis direction of the laser light La 2  (depth direction of the processing object W). Each hologram is configured by superimposing a hologram for realizing the size and the shape of the processing region A in a plane intersecting the optical axis of the laser light La 2  and a hologram for the position in the optical axis direction of the plane. 
     (a), (b), and (c) in  FIG.  9    schematically illustrate arrangement examples of the irradiation points SP in cross-sections along a line IXa-IXa, a line IXb-IXb, and a line IXc-IXc illustrated in (a) in  FIG.  8   . In this example, the shape of the processing region A in the cross-section perpendicular to the optical axis direction of the laser light La 2  is a circular shape. 
     Further, (a), (b), and (c) in  FIG.  10    schematically illustrate other arrangement examples of the irradiation points SP in the respective cross-sections. In this example, the shape of the processing region A in the cross-section perpendicular to the optical axis direction of the laser light La 2  is an arbitrary complicated polygonal shape. 
     The irradiation points SP illustrated in  FIG.  9    and  FIG.  10    determine the processing region A illustrated in (a) in  FIG.  8   . In addition, the shape of the processing region A in the cross-section perpendicular to the optical axis direction of the laser light La 2  is not limited to the examples of  FIG.  9    and  FIG.  10   , and various other shapes are possible. 
     In the example illustrated in  FIG.  8   , from another viewpoint, the control unit  18  sets the sizes of the processing region A to be different from each other in the IXa-IXa cross-section and the IXb-IXb cross-section which are separated from each other in the optical axis direction. In this case, one of the IXa-IXa cross-section and the IXb-IXb cross-section corresponds to a first plane in the present embodiment, and the other corresponds to a second plane in the present embodiment. 
     Further, from still another viewpoint, the control unit  18  sets the sizes of the processing region A to be different from each other in the IXb-IXb cross-section and the IXc-IXc cross-section which are separated from each other in the optical axis direction. In this case, one of the IXb-IXb cross-section and the IXc-IXc cross-section corresponds to the first plane in the present embodiment, and the other corresponds to the second plane in the present embodiment. 
     In addition, also in this example, the control unit  18  sequentially presents, on the spatial light modulator  12 , a plurality of holograms for changing the position of each irradiation point SP along the virtual line B (see (b) in  FIG.  2   ) which determines the processing region A in each cross-section. Thus, each irradiation point SP discretely moves on the contour line of the processing region A. 
     The control unit  18  may determine the processing state at each irradiation point SP based on the detection result by the photodetector  17 , and control the presenting time of the hologram in each cross-section according to the processing state. The processing state is, for example, the processing speed (in other words, progress of the processing) or the like at each irradiation point SP. 
     When the processing object W has a light transmitting property for the laser light La 2 , as illustrated in  FIG.  8   , the inversely tapered processing region A for the light irradiation surface W 1  of the processing object W (tapered for the surface W 2 ) may be set. In other words, an area of the processing region A in one cross-section distant from the light irradiation surface W 1  of the processing object W out of the IXa-IXa cross-section and the IXb-IXb cross-section (or the IXb-IXb cross-section and the IXc-IXc cross-section) may be larger than an area of the processing region A in the other cross-section. 
     In this case, the control unit  18  presents, on the spatial light modulator  12 , a program for focusing the laser light La 2  on each irradiation point SP, so that a contour portion of the processing region A is cut off, and the processing region A falls down from the processing object W. As a result, as illustrated in (b) in  FIG.  8   , the hole Ha, which is an inversely tapered through hole with respect to the light irradiation surface W 1 , is formed in the processing object W. 
     When the processing object W is made of a material such as glass having a light transmitting property for the laser light La 2 , the processing may be sequentially performed from the side of the surface W 2  opposite to the light irradiation surface W 1  of the processing object W toward the light irradiation surface W 1 . The above processing is possible by setting the light intensity larger than the processing threshold value only in the focusing point of the laser light La 2 , and setting the light intensity smaller than the processing threshold value in the other region (region between the light irradiation surface W 1  and the focusing point) in the processing object W. 
     In this case, the laser processing can be performed while causing remainders (debris and fragments) generated by the laser processing to fall downward, and thus, the degree in which the remainders interfere with irradiation of the laser light La 2  is reduced. 
     (a) in  FIG.  11    is a cross-sectional view illustrating a state in which the processing object W is irradiated with the laser light La 2 , and illustrates a cross-section along the optical axis of the laser light La 2 . (b) in  FIG.  11    is a cross-sectional view illustrating a hole Hb formed in the processing object W. In the example illustrated in  FIG.  11   , as in the example illustrated in  FIG.  8   , a size of the processing region A in the cross-section perpendicular to the optical axis of the laser light La 2  continuously changes in the optical axis direction of the laser light La 2  from the light irradiation surface W 1  of the processing object W to the opposite surface W 2 . 
     Specifically, the size of the processing region A in the cross-section gradually increases as a distance from the light irradiation surface W 1  increases. In addition, in the example illustrated in  FIG.  11   , the contour of the processing region A in the cross-section along the optical axis of the laser light La 2  is not linear as illustrated in  FIG.  8   , but has a shape (for example, an arc shape) having a inwardly convex curvature. 
     In this case also, the control unit  18  presents, on the spatial light modulator  12 , a program for focusing the laser light La 2  on each irradiation point SP, so that a contour portion of the processing region A is cut off, and the processing region A falls down from the processing object W. As a result, as illustrated in (b) in  FIG.  11   , the hole Hb, which is an inversely tapered through hole with respect to the light irradiation surface W 1 , is formed in the processing object W. 
     (a) in each of  FIG.  12    to  FIG.  14    is a cross-sectional view illustrating a state in which the processing object W is irradiated with the laser light La 2 , and illustrates a cross-section along the optical axis of the laser light La 2 . (b) in each of  FIG.  12    to  FIG.  14    is a cross-sectional view illustrating holes Hc, Hd, and He formed in the processing object W. 
     In this example, first, as illustrated in (a) in  FIG.  12   , a tapered processing region A reaching one surface W 3  from a substantially central portion of the processing object W in the optical axis direction of the laser light La 2  is set. Further, the laser light La 2  is applied from the other surface W 4  on the side opposite to the surface W 3 , and a contour portion of the processing region A is cut off in the same manner as the example illustrated in  FIG.  8   , thereby forming a hole Hc illustrated in (b) in  FIG.  12   . The hole Hc is a tapered (mortar-shaped) depressed portion extending from the substantially central portion of the processing object W to the one surface W 3 . 
     Next, as illustrated in (a) in  FIG.  13   , the processing object W is turned upside down, and a tapered another processing region A reaching the other surface W 4  from a substantially central portion of the processing object W in the optical axis direction of the laser light La 2  is set. Further, the laser light La 2  is applied from the one surface W 3 , and a contour portion of the processing region A is cut off in the same manner as the example illustrated in  FIG.  8   , thereby forming a hole Hd illustrated in (b) in  FIG.  13   . The hole Hd is a tapered (mortar-shaped) depressed portion extending from the substantially central portion of the processing object W to the other surface W 4 . 
     Finally, as illustrated in (a) in  FIG.  14   , still another processing region A connecting the hole Hc and the hole Hd is set. Further, the laser light La 2  is applied from the surface W 3  or W 4 , and a contour portion of the processing region A is cut off in the same manner as the example illustrated in  FIG.  8   , thereby forming a hole He illustrated in (b) in  FIG.  14   . In this way, a through hole between the one surface W 3  and the other surface W 4  of the processing object W is formed. 
     In addition, in the above example, the contour of each processing region A in the cross-section along the optical axis of the laser light La 2  is linear, but at least one of them may have a curvature. (a) in  FIG.  15    illustrates a cross-sectional shape of a through hole Hf formed when two processing regions A have curvatures. The through hole Hf is formed by communicating a hole Hfa reaching the surface W 3  from a substantially central portion of the processing object W and a hole Hfb reaching the surface W 4  from the substantially central portion of the processing object W. 
     A size of the hole Hfa in a cross-section perpendicular to the optical axis of the laser light La 2  gradually increases from the substantially central portion of the processing object W toward the surface W 3 . A size of the hole Hfb in a cross-section perpendicular to the optical axis of the laser light La 2  gradually increases from the substantially central portion of the processing object W toward the surface W 4 . Further, side surfaces of the holes Hfa and Hfb have inwardly convex curvatures in a cross-section along the thickness direction of the processing object W. 
     Further, (b) in  FIG.  15    illustrates a cross-sectional shape of a through hole Hg formed when a contour of one processing region A has a curvature. The through hole Hg is formed by communicating a hole Hga reaching the surface W 3  from a substantially central portion of the processing object W and a hole Hgb reaching the surface W 4  from the substantially central portion of the processing object W. 
     A size of the hole Hga in a cross-section perpendicular to the optical axis of the laser light La 2  gradually increases from the substantially central portion of the processing object W toward the surface W 3 . Further, a side surface of the hole Hga has an inwardly convex curvature in a cross-section along the thickness direction of the processing object W. The hole Hgb has a tapered shape (mortar shape) when viewed from the surface W 4 , as in the hole Hc illustrated in  FIG.  12    and the hole Hd illustrated in  FIG.  13   . 
     (a) in  FIG.  16    is a cross-sectional view illustrating a hole Hh formed by irradiation of the laser light La 2 , and illustrates a cross-section along the thickness direction of the processing object W. (b) in  FIG.  16    is a plan view illustrating a shape of the hole Hh on the light irradiation surface W 1  of the processing object W, and (c) in  FIG.  16    is a plan view illustrating a shape of the hole Hh on the surface W 2  opposite to the light irradiation surface W 1  of the processing object W. 
     In this example, the shape of the hole Hh on the light irradiation surface W 1  (first plane intersecting the optical axis of the laser light La 2 ) and the shape of the hole Hh on the surface W 2  opposite to the light irradiation surface W 1  (second plane separated from the first plane in the optical axis direction) are different from each other. In the illustrated example, the shape of the hole Hh in the light irradiation surface W 1  is a circular shape, and the shape of the hole Hh in the opposite surface W 2  is an equilateral triangular shape. 
     The above hole Hh may be preferably formed by the control unit  18  setting the shapes of the processing region A defined by the plurality of irradiation points in the planes of the light irradiation surface W 1  and the surface W 2  different from each other. In one example, a cross-sectional shape of the hole Hh perpendicular to the thickness direction of the processing object W changes continuously along the thickness direction of the processing object W. 
       FIG.  17    includes diagrams conceptually illustrating a change of the shape of the processing region A in the optical axis direction of the laser light La 2  for forming the hole Hh illustrated in  FIG.  16   . (a) in  FIG.  17    illustrates an outline of a configuration for irradiating the processing object W with the laser light La 2  and a cross-section of the processing object W in the optical axis direction of the laser light La 2 . (b), (c), (d), and (e) in  FIG.  17    illustrate the shape of the processing region A in each plane located at different depths in the processing object W, and the plurality of irradiation points SP in each plane. 
     As illustrated in (b) in  FIG.  17   , the shape of the processing region A on the light irradiation surface W 1  is a circular shape, and as illustrated in (c) to (e) in  FIG.  17   , the shape of the processing region A gradually approaches a triangular shape from a circular shape as the distance from the light irradiation surface W 1  increases in the optical axis direction. Finally, the shape of the processing region A on the surface W 2  becomes a triangular shape. In addition, as described above, when the processing object W has a light transmitting property, the processing may be performed from the surface W 2  side toward the light irradiation surface W 1 . 
       FIG.  18    to  FIG.  21    include diagrams illustrating examples of holograms corresponding to the planes illustrated in (b) to (e) in  FIG.  17   . (a) in each of  FIG.  18    to  FIG.  21    illustrates the plurality of irradiation points SP illustrated in each of (b) to (e) in  FIG.  17   . (b), (c), and (d) in each of  FIG.  18    to  FIG.  21    illustrate examples of the holograms for realizing the plurality of irradiation points SP illustrated in (a). In addition, in (b), (c), and (d) in  FIG.  18    to  FIG.  21   , a magnitude of the phase is represented by light and shade of color, and the darker the color, the smaller the phase (close to 0 radian), and the lighter the color, the larger the phase (close to 2π radian). 
     Further, in each of  FIG.  18    to  FIG.  21   , (b), (c), and (d) illustrate a plurality of holograms for changing the position of each irradiation point SP along the contour line (virtual line B illustrated in  FIG.  2   ) of the processing region A. As indicated by arrows in the diagram, the control unit  18  performs the processing while moving the position of each irradiation point SP along the contour line of the processing region A by periodically and repeatedly presenting the holograms illustrated in (b), (c), and (d) on the spatial light modulator  12 . 
     In each processing example illustrated in  FIG.  7    to  FIG.  17   , it is necessary to change the hologram in the middle of the laser processing. Further, when the hologram is changed, it takes time to call the hologram to be presented next from the storage unit (for example, the ROM  183  or the auxiliary storage device  186  illustrated in  FIG.  4   ) or to generate the hologram to be presented next by calculation based on the detection result by the photodetector  17 . 
     The control unit  18  presents, on the spatial light modulator  12 , a hologram with which the light intensity of the laser light La 2  is less than the processing threshold value at any portion in the processing object W during a period from erasing a certain hologram to presenting another hologram. For example, as illustrated in  FIG.  22   , the control unit  18  may presents, on the spatial light modulator  12 , a hologram for forming the irradiation point SP of the laser light La 2  farther than the processing object W. Thus, it is possible to realize an operation equivalent to that when the laser light source  11  is turned off. 
     Further, in each plane arranged in the optical axis direction of the laser light La 2  in each processing example illustrated in  FIG.  8    to  FIG.  17   , the control unit  18  may independently control the light intensities of the plurality of irradiation points SP for each irradiation point SP, as in each processing example illustrated in  FIG.  5    to  FIG.  7   . Further, the control unit  18  may independently control the light intensities of the irradiation points SP in each plane arranged in the optical axis direction for each plane. 
     For example, in the example illustrated in  FIG.  8    to  FIG.  10   , the light intensities of the irradiation points SP in the IXa-IXa cross-section, the IXb-IXb cross-section, and the IXc-IXc cross-section may be independently set for each cross-section according to the material (or the processing speed) in each cross-section. Further, the irradiation time for each cross-section may also be set independently. 
       FIG.  23    is a flowchart illustrating a laser processing method according to the present embodiment. The laser processing method can be performed using the laser processing apparatus  10  described above. As illustrated in  FIG.  23   , first, as a control step S 1 , the hologram for modulating the phase of the light in each of the plurality of pixels arranged two-dimensionally is presented on the spatial light modulator  12 . Next, as a light modulation step S 2 , the laser light La 1  output from the laser light source  11  is input to the spatial light modulator  12 , and the phase modulation of the laser light La 1  is performed by the hologram. Further, as a focusing step S 3 , the laser light La 2  after the phase modulation is focused using the focusing optical system  14 . 
     In the previous control step S 1 , the spatial light modulator  12  presents the hologram for focusing the laser light La 2  after the phase modulation on the plurality of irradiation points SP in the processing object W by the focusing step S 3 . Thus, the plurality of irradiation points SP are formed for the processing object W, and the processing (melting, crack generation, cutting, and the like) of the processing object W proceeds at each irradiation point SP. Further, as a photodetection step S 4 , the processing object W is irradiated with the observation light Lb having the wavelength different from the wavelength of the laser light La 2 , and the observation light (reflected light Lc) reflected from the processing object W is detected. 
     Thereafter, the steps S 1  to S 4  are repeatedly performed while changing the hologram. In the control step S 1 , as illustrated in  FIG.  2   , the plurality of holograms for changing the position of each irradiation point SP along the virtual line B which determines the processing region A are sequentially presented on the spatial light modulator  12 . Further, when a difference between a set target value of the light intensity of the irradiation point SP and the detection result of the observation light is larger than a target error (step S 5 : NO), the hologram may be corrected (step S 6 ). 
     As illustrated in  FIG.  5    to  FIG.  7   , in the control step S 1 , the light intensities of the plurality of irradiation points SP are independently controlled for each irradiation point SP. Further, as illustrated in  FIG.  8    to  FIG.  17   , in the control step S 1 , the shape of the processing region A defined by the plurality of irradiation points SP is set different for each of the plurality of planes intersecting the optical axis of the laser light La 2 . Further, in the control step S 1 , the light intensities of the plurality of irradiation points SP are independently controlled for each irradiation point SP, and further, the shape of the processing region A defined by the plurality of irradiation points SP is set different for the plurality of planes intersecting the optical axis of the laser light La 2 . 
     When the light intensity is independently controlled for each irradiation point SP, in the control step S 1 , the material change at each irradiation point SP is detected based on the detection result by the previous photodetection step S 4 , and the light intensity of each irradiation point SP is changed according to the material change. 
     Further, as illustrated in  FIG.  24   , a storage step S 0  is performed before the control step S 1 , and in the storage step S 0 , data related to the light intensity of each irradiation point SP according to the material distribution in the processing object W is stored in advance in the storage unit (for example, the ROM  183  or the auxiliary storage device  186  illustrated in  FIG.  4   ). Further, in the control step S 1 , the light intensity of each irradiation point SP is controlled based on the data. Further, when the difference between the set target value of the light intensity of the irradiation point SP and the detection result of the observation light is larger than the target error (step S 5 : NO), the hologram may be corrected (step S 6 ). 
     Further, in the case where the shape of the processing region A is set different for each of the plurality of planes intersecting the optical axis of the laser light La 2 , as illustrated in  FIG.  8    to  FIG.  15   , it is also possible to continuously change the shape of the processing region A in the optical axis direction of the laser light La 2 . In the case where the processing object W has a light transmitting property for the laser light La 2 , as illustrated in  FIG.  8    to  FIG.  15   , it is also possible to set the area of the processing region A in a plane distant from the light irradiation surface W 1  of the processing object W larger than the area of the processing region A in a plane close to the light irradiation surface W 1 . 
     It is also possible to determine the processing state at each irradiation point SP based on the detection result in the photodetection step S 4 , and control the presenting time of the hologram for each plane according to the processing state. It is also possible to independently control the light intensities of the plurality of irradiation points SP for each plane. 
     Further, when the hologram is changed in the control step S 1 , the spatial light modulator  12  presents the hologram with which the light intensity of the laser light La 2  is less than the processing threshold value in any portion of the processing object W during a period from erasing a certain hologram to presenting another hologram. 
     Effects obtained by the laser processing apparatus  10  and the laser processing method according to the present embodiment described above will be described. 
     In the laser processing apparatus  10  and the laser processing method of the present embodiment, the control unit  18  (or in the control step S 1 ) controls the light intensities of the at least two irradiation points SP included in the plurality of irradiation points SP independently of each other. In this case, when there is a difference in material depending on a portion in the processing object W, that is, a difference in processing speed for the laser light La 2  having the same intensity, the laser light La 2  can be applied to each irradiation point SP corresponding to each portion with an appropriate light intensity. Therefore, it is possible to easily process the processing object W containing two or more types of materials into a complicated shape. 
     Further, according to the present embodiment, adjustment of the light intensity for each irradiation point SP, on/off of each irradiation point SP, and movement of each irradiation point SP along the virtual line B can be realized without using any mechanical unit. Therefore, an apparatus configuration of the laser processing apparatus  10  can be greatly simplified, and the processing processes can be performed at high speed and with high accuracy. 
     As in the present embodiment, the laser processing apparatus  10  may include the observation light source  16  for irradiating the processing object W with the observation light Lb, and the photodetector  17  for detecting the reflected light Lc being the observation light reflected from the processing object W. Further, the laser processing method may further include the photodetection step S 4  of irradiating the processing object W with the observation light Lb, and detecting the reflected light Lc from the processing object W. 
     Further, the control unit  18  (in the control step S 1 ) may determine the processing state at each irradiation point SP based on the detection result by the photodetector  17 , and control the presenting time of the hologram for each plane according to the processing state. Further, the control unit  18  (in the control step S 1 ) may detect the material change at each irradiation point SP based on the detection result by the photodetector  17  (photodetection step S 4 ), and change the light intensities of the at least two irradiation points SP according to the material change. In these cases, processing accuracy can be further improved. 
     As in the present embodiment, the laser processing apparatus  10  may include the storage unit for storing in advance the data related to the light intensity of each irradiation point SP according to the material distribution in the processing object W, and the control unit  18  may control the light intensity of each irradiation point SP based on the data. Further, the laser processing method may include, before the control step S 1 , the storage step S 0  of storing in advance the data related to the light intensity of each irradiation point SP according to the material distribution in the processing object W, and in the control step S 1 , the light intensity of each irradiation point SP may be controlled based on the data. In these cases, the light intensity required for each irradiation point SP can be quickly obtained, and thus, a change time of the hologram can be reduced. 
     As in the present embodiment, the control unit  18  (in the control step S 1 ) may set at least one of the shape and the size of the processing region A to be different from each other in the plurality of planes arranged in the optical axis direction of the laser light La 2 . In this way, by changing the shape and/or the size of the processing region A for each of the plurality of planes separated in the optical axis direction, it is possible to perform the processing that is more complicated than in the past, such as freely setting the shape of the cross-section perpendicular to the optical axis direction. 
     As in the present embodiment, the control unit  18  (in the control step S 1 ) may sequentially present, on the spatial light modulator  12 , the plurality of holograms for changing the position of each irradiation point SP along the virtual line B which determines the processing region A in each of the plurality of planes arranged in the optical axis direction. In this case, it is possible to reduce the output power required for the laser light source  11  compared to the case where the laser light La 2  is applied at one time by a single hologram while providing sufficient light intensity to each irradiation point SP, and it is possible to contribute to downsizing of the laser light source  11 . 
     As in the present embodiment, when the hologram is changed, the control unit  18  (in the control step S 1 ) may present, on the spatial light modulator  12 , the hologram with which the light intensity of the laser light La 2  is less than the processing threshold value at any portion in the processing object W during a period from erasing one hologram to presenting another hologram. In this case, compared to the case where the laser light La 2  is blocked by mechanical means such as a shutter, a mechanical shutter itself, a high-voltage device necessary for operating the mechanical shutter, and the like become unnecessary, and thus, it is possible to simplify the configuration of the laser processing apparatus  10  and contribute to reduction in size and cost of the laser processing apparatus  10 . 
     As in the present embodiment, the processing object W may have the light transmitting property for the laser light La 2  after the phase modulation, and the area of the processing region A in a plane distant from the light irradiation surface W 1  of the processing object W may be larger than the area of the processing region A in a plane close to the surface. In this case, for example, it is possible to easily perform complicated processing such as formation of a hole having an inversely tapered shape in which a hole diameter increases as the distance from the light irradiation surface W 1  of the processing object W increases. 
     As in the present embodiment, the control unit  18  (in the control step S 1 ) may continuously change at least one of the shape and the size of the processing region A in the optical axis direction of the laser light La 2 . In this case, it is possible to easily perform processing of, for example, a hole in which a shape in a cross-section perpendicular to the optical axis direction is smoothly changed in the optical axis direction. 
     As in the present embodiment, the control unit  18  (in the control step S 1 ) may control the light intensities of the irradiation points SP in at least two planes independently for each plane. In this case, when there is a difference in material constituting each plane, that is, a difference in processing speed for the laser light La 2  having the same intensity, the laser light La 2  can be applied with an appropriate light intensity according to the material of each plane. 
     An example of a conventional laser processing method will be described.  FIG.  25    is a diagram illustrating a laser processing method described in Patent Document 1. The laser processing method is a method of processing a workpiece (processing object)  110  having a processing surface  112  by laser ablation, and forms a three-dimensional geometric structure  114  in the workpiece  110 . 
     Three different beam profiles  116 ,  118  and  120  are illustrated in  FIG.  25   . In each of the beam profiles  116 ,  118 , and  120 , the vertical axis indicates the light intensity, and the horizontal axis indicates the position. In each of the beam profiles  116 ,  118 , and  120 , a laser beam has a pattern with an irradiation region  122  and a non-irradiation region  124  at the processing surface  112 . In the irradiation region  122 , the light intensity is larger than the ablation threshold value. In the non-irradiation region  124 , the light intensity is lower than the melting threshold value of the material of the workpiece  110 . 
     The beam profiles  116 ,  118 , and  120  are different from each other in the diameter, equivalent diameter, and/or geometric shape. That is, the beam profiles  116 ,  118 , and  120  have diameters or equivalent diameters decreasing in this order. In addition, a partially-cutout cross-sectional view of the workpiece  110  illustrates that these beam profiles  116 ,  118 , and  120  can have different geometric shapes. Thus, the workpiece  110  has a step-shaped geometric structure. 
     However, in the method described in Patent Document 1, the region irradiated with the laser light at one time is large, and thus, a laser light source having an extremely large output power is required in order to exceed the ablation threshold value over the entire region. Therefore, the size of the laser light source increases. Further, since the diameter of the beam profile basically decreases as the processing proceeds, there is a limitation on the shape that can be formed. In addition, when a plurality of materials having different processing speeds are mixed in the workpiece  110 , it is difficult to set the light intensity and the irradiation time in accordance with the properties of the materials. 
     For the above problems, according to the laser processing apparatus  10  and the laser processing method of the present embodiment, the processing is performed by focusing the laser light La 2  on the plurality of irradiation points SP, and thus, the output power of the laser light source  11  may be relatively small, and it is possible to contribute to downsizing of the laser light source  11 . Further, it is also easy to process complicated shapes such as the hole Ha having an inversely tapered shape as illustrated in  FIG.  8    and the hole Hh as illustrated in  FIG.  16   . 
     In addition, the light intensity and the irradiation time are independently controlled for each irradiation point SP, and thus, even when a plurality of materials are mixed in the processing region, the light intensity and the irradiation time can be easily set according to the property of each material. Further, optical components such as a λ/2 plate and a polarization beam splitter for adjusting the light intensity become unnecessary, and the configuration of the laser processing apparatus can be further simplified. 
       FIG.  26    and  FIG.  27    include diagrams illustrating a laser processing method described in Patent Document 2. In the laser processing method, a plurality of image reconstruction hologram data are prepared to perform laser processing. Specifically, as illustrated in (a) in  FIG.  26   , a processing surface  200  is divided into a plurality of cells  201 , one irradiation point  202  corresponds to one cell  201 , and it is freely selected whether or not to form the irradiation point  202  for each cell  201 . 
     Position movement hologram data is superimposed on the image reconstruction hologram data. Further, by processing and forming discrete point images illustrated in (b) to (e) in  FIG.  26    on the processing surface  200  while changing the position movement hologram data, a processing shape  203  of a complicated shape illustrated in  FIG.  27    is obtained. 
     However, in the method described in Patent Document 2, since the light intensity of each irradiation point  202  is not individually controlled, when a plurality of materials having different processing speeds are mixed in the processing surface  200 , it is difficult to set the light intensity and the irradiation time in accordance with the properties of the materials. 
     On the other hand, according to the laser processing apparatus  10  and the laser processing method of the present embodiment, the light intensity and the irradiation time are independently controlled for each irradiation point SP, and thus, even when a plurality of materials are mixed in the processing region, the light intensity and the irradiation time can be easily set according to the properties of the materials. 
     The laser processing apparatus and the laser processing method are not limited to the embodiments and configuration examples described above, and may be modified in various ways. For example, in the above embodiment, it is described that, when a plurality of materials are included in the processing region A, the light intensity is independently controlled for each irradiation point SP, and thus, it is possible to perform the processing with the light intensities according to the properties of the materials. Without being limited to the above example, for example, even in the case where the processing region A is formed of a single material, a removal rate (removal amount) of the processing object W can be independently controlled for each portion of the processing region A by independently controlling the light intensity for each irradiation point SP, and a more complicated shape can be realized. 
     Further, in the above embodiment, the case where the light intensity of each of the plurality of irradiation points SP is independently controlled has been exemplified, however, when it is not necessary to independently control all the irradiation points SP, the light intensities of at least two irradiation points SP out of the plurality of irradiation points SP may be independently controlled. Even in this case, the effects of the above embodiment can be achieved. 
     The laser processing apparatus of the above embodiment includes a spatial light modulator for inputting laser light output from a laser light source, presenting a hologram for modulating a phase of the laser light in each of a plurality of pixels arranged two-dimensionally, and outputting laser light after phase modulation by the hologram; a focusing optical system provided at a subsequent stage of the spatial light modulator; and a control unit for presenting, on the spatial light modulator, the hologram for focusing the laser light after the phase modulation output from the spatial light modulator on a plurality of irradiation points in a processing object by the focusing optical system, and the control unit controls light intensities of at least two irradiation points included in the plurality of irradiation points independently of each other. 
     The laser processing method of the above embodiment repeatedly performs a control step of presenting, on a spatial light modulator, a hologram for modulating a phase of light in each of a plurality of pixels arranged two-dimensionally; a light modulation step of inputting laser light output from a laser light source to the spatial light modulator, and performing phase modulation of the laser light by the hologram; and a focusing step of focusing the laser light after the phase modulation, and in the control step, the spatial light modulator presents the hologram for focusing the laser light after the phase modulation output from the spatial light modulator on a plurality of irradiation points in a processing object by the focusing step, and light intensities of at least two irradiation points included in the plurality of irradiation points are controlled independently of each other. 
     The above laser processing apparatus may further include an observation light source for irradiating the processing object with observation light; and a photodetector for detecting the observation light reflected from the processing object, and the control unit may detect a material change at each irradiation point based on a detection result by the photodetector, and change the light intensity of each irradiation point according to the material change. 
     The above laser processing method may further include a photodetection step of irradiating the processing object with observation light, and detecting the observation light reflected from the processing object, and in the control step, a material change at each irradiation point may be detected based on a detection result by the photodetection step, and the light intensity of each irradiation point may be changed according to the material change. 
     According to the above configuration, processing accuracy can be further improved. 
     The above laser processing apparatus may further include a storage unit for storing in advance data related to the light intensity of each irradiation point according to a material distribution in the processing object, and the control unit may control the light intensity of each irradiation point based on the data. 
     The above laser processing method may further include, before the control step, a storage step of storing in advance data related to the light intensity of each irradiation point according to a material distribution in the processing object, and in the control step, the light intensity of each irradiation point may be controlled based on the data. 
     According to the above configuration, the light intensity required for each irradiation point can be quickly obtained, and thus, a change time of the hologram can be reduced. 
     In the above laser processing apparatus, the control unit may set at least one of a shape and a size of a processing region defined by the plurality of irradiation points in a first plane intersecting an optical axis of the laser light after the phase modulation with which the processing object is irradiated and a processing region defined by the plurality of irradiation points in a second plane intersecting the optical axis and separated from the first plane in a direction of the optical axis to be different from each other. 
     In the above laser processing method, in the control step, at least one of a shape and a size of a processing region defined by the plurality of irradiation points in a first plane intersecting an optical axis of the laser light after the phase modulation with which the processing object is irradiated and a processing region defined by the plurality of irradiation points in a second plane intersecting the optical axis and separated from the first plane in a direction of the optical axis may be set different from each other. 
     As described above, by changing the shape and/or the size of the processing region for each of the plurality of planes separated in the optical axis direction, it is possible to perform processing that is more complicated than in the past, such as freely setting the shape of the cross-section perpendicular to the optical axis direction. 
     In the above laser processing apparatus, the control unit may sequentially present, on the spatial light modulator, a plurality of holograms for changing a position of each irradiation point along a virtual line which determines a processing region defined by the plurality of irradiation points. 
     In the above laser processing method, in the control step, the spatial light modulator may sequentially present a plurality of holograms for changing a position of each irradiation point along a virtual line which determines a processing region defined by the plurality of irradiation points. 
     According to the above configuration, it is possible to reduce an output power required for the laser light source compared to the case where the laser light is applied at one time by a single hologram while providing sufficient light intensity to each irradiation point, and to contribute to downsizing of the laser light source. 
     In the above laser processing apparatus, when the hologram is changed, the control unit may present, on the spatial light modulator, a hologram with which the light intensity of the laser light is less than a processing threshold value at any portion in the processing object during a period from erasing a certain hologram to presenting another hologram. 
     In the above laser processing method, in the control step, when the hologram is changed, the spatial light modulator may present a hologram with which the light intensity of the laser light is less than a processing threshold value at any portion in the processing object during a period from erasing a certain hologram to presenting another hologram. 
     According to the above configuration, it is possible to simplify the configuration of the laser processing apparatus compared to the case where the laser light is blocked by mechanical means such as a shutter. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be used as a laser processing apparatus and a laser processing method capable of performing more complicated processing in a configuration in which focused irradiation is simultaneously performed on a plurality of irradiation points by phase-modulating laser light using a spatial light modulator. 
     REFERENCE SIGNS LIST 
       10 —laser processing apparatus,  11 —laser light source,  12 —spatial light modulator,  13 —dichroic mirror,  14 —focusing optical system,  15 —drive unit,  16 —observation light source,  17 —photodetector,  18 —control unit,  110 —workpiece,  112 —processing surface,  114 —geometric structure,  116 ,  118 ,  120 —beam profile,  122 —irradiation region,  124 —non-irradiation region,  181 —CPU,  182 —RAM,  183 —ROM,  184 —input device,  185 —digital/analog converter,  186 —auxiliary storage device,  200 —processing surface,  201 —cell,  202 —irradiation point,  203 —processing shape, A—processing region, B—virtual line, Ha, Hb, Hc, Hd, He, Hh—hole, Hf, Hg—through hole, Hfa, Hfb, Hga, Hgb—hole, La 1 , La 2 —laser light, Lb—observation light, Lc—reflected light, Sa—signal, SP—irradiation point, Vd—drive voltage, W—processing object, W 1 —light irradiation surface, W 2 , W 3 , W 4 —surface, Wa, Wb, Wc, Wd, We—region.