JP2008049393A - Laser beam machining apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining apparatus or the like capable of greatly increasing accuracy of output light while making it precisely controllable. <P>SOLUTION: The laser beam machining apparatus irradiates a target machining substance with an ultra-short pulsed laser beam and machines the substance with the energy of the ultra-short pulsed laser beam. The apparatus includes a laser light source for outputting the ultra-short pulsed laser beam, a spacial light modulation element that modulates the ultra-short pulsed laser beam radiated from the laser light source into a spacial arbitrary shape, and a multiple photon absorption detector having sensitivity in the wavelength of optical energy that is generated by multiple photon absorption produced at each point of the modulated ultra-short pulsed laser beam, wherein the spacial light modulation element makes modulation possible of the ultra-short pulsed laser beam on the basis of the detection by the multiple photon absorption detector. Accordingly, the output light presently obtained in the laser beam machining apparatus is detected by the multiple photon absorption detector, on which the spacial light modulation element can be controlled; therefore, machining with an extremely high accuracy is made possible in which design-oriented errors are adjusted. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a laser processing apparatus and a laser processing method, and more particularly to a laser processing apparatus and a laser processing method capable of precisely processing a material to be processed using an ultra-short pulse laser beam.

  A femtosecond pulse laser, which is an ultra-short pulse laser, enables submicron-size microfabrication inside a transparent material through a multiphoton absorption process. Further, since the pulse width of the laser beam is very short compared to the time required for thermal diffusion at the time of energy injection, there is little thermal damage to the periphery of the processed part. Therefore, the femtosecond pulse laser processing is used for manufacturing a new device having a three-dimensional structure. However, in general, manufacturing a three-dimensional device requires an enormous number of processing points, so that it takes time to perform the entire processing. Therefore, the present inventors have developed a parallel processing method in which laser light is divided into a plurality of parts using an optical element such as a hologram and processed in parallel in order to shorten the processing time by the femtosecond pulse laser (patent) Reference 1). Specifically, variable parallel processing was realized by displaying a computer generated hologram on the spatial light modulator, spatially shaping femtosecond laser pulses, and irradiating the object to be processed. Here, the optical element having the function of converting the intensity distribution of light and the function of branching the beam into a plurality of beams displayed on the spatial light modulator is designed in advance by a computer such as a computer.

  By the way, in the design of optical elements such as holograms by computer, the output of the optical element is reproduced in the computer. Based on the reproduction result of the computer, the optical element is redesigned and repeated as desired. The calculation is repeated until the error becomes smaller with respect to the output image, and the optical element is optimized. Therefore, the power distribution of a large number of beams finally obtained has high performance in the computer. This is because, in the design process, the light source, the characteristics of the spatial modulation element, and the characteristics of the optical system are taken into consideration.

  However, the deterioration of the output image produced from the image of the actual optical system is unavoidable compared to the ideal optical system. This is because, in addition to insufficient design of holograms, laser coherence, laser spatial intensity variations, spatial light modulator element spatial variations, spatial light modulator input signals and nonlinearity of phase modulation characteristics This is because the characteristics of the class number of the spatial light modulation element and the deviation from the ideal state of the optical system such as minute scratches and dust on the optical element cannot be fully expressed in the computer. Therefore, when an optical element having high performance designed in the computer is displayed on the spatial light modulation element, an error occurs in the output obtained in the actual optical system with respect to the output calculated in the computer.

  Specifically, errors in a transparent material with little one-photon absorption, such as a material that generates multiphoton absorption such as glass or polymer, are significant. In the reaction caused by the ultrashort pulse laser, the multiphoton absorption that simultaneously absorbs two or more photons becomes dominant, and the error further increases.

  On the other hand, in order to correct a design error, a laser condensing device in which a mechanism for correcting the output of laser light by feeding back data of actual output light has been developed (Patent Document 2). As shown in FIG. 12, the laser condensing device 101 includes a plurality of laser light sources 102 and reflections that modulate each laser light L in order to correct the wavefront of each laser light L output from each laser light source 102. A spatial light modulator (SLM) 111 and a condenser lens 112 that condenses each laser light L output from the reflective spatial light modulator 111 are provided. Between the cylindrical lens arrays 103 and 104 and the SLM 111, a beam splitter 105 inclined by 45 ° with respect to the laser optical axis is disposed, and the light of the branched laser light L bent at a right angle by the beam splitter 105. A Shack-Hartmann sensor 106, which is a wavefront detector, is disposed on the axis. As shown in FIG. 12, the Shack-Hartmann sensor 106 includes a microlens array 107 and a CCD camera 109. Further, the Shack-Hartmann sensor 106 is connected to the SLM controller 110.

FIG. 13A is an explanatory diagram for explaining the relationship between the laser light L output from the LD array 102 and the microlens array 107, and FIG. 13B is an enlarged view of a part of the microlens array 107. . As shown in FIG. 13A, the laser beams L collimated by the cylindrical lens arrays 103 and 104 reach the microlens array 107 in a separated state, and as shown in FIG. The light is incident on each lens element 108 of the array 107 and collected. As can be seen from FIG. 13B, each laser beam L corresponds to each lens element 108 of the microlens array 107. Then, by utilizing the fact that the shift of the focal position of each laser beam L collected by each lens element 108 is proportional to the distortion of the wavefront of each laser beam L, the distortion of the wavefront of each laser beam L is detected. Yes. As described above, since the laser beam having the same wavefront is collected by the condensing lens by the reflective spatial light modulator 111, a laser beam having a small condensing spot and a high energy density can be obtained.
JP 2006-68762 A JP 2001-228449 A

  However, the photodetector used in this apparatus only measures the light intensity with one-photon absorption, and it is difficult to obtain an accurate detection value based on multi-photon absorption with this apparatus. This is because a photodetector that detects one-photon absorption has sensitivity to light of the wavelength of the laser, and the detected value is proportional to the average intensity of the laser light. For this reason, in laser processing, the instantaneous light intensity that depends on the irradiation energy and the pulse shape is related, but the photodetector that detects the one-photon absorption cannot detect the instantaneous light intensity. That is, in the case of one-photon absorption, the detected value is hardly related to the laser pulse width, but in multi-photon absorption, the detection value changes greatly. Thus, since there is a difference between the detection values of the one-photon absorption and the multi-photon absorption, the photodetector that mainly detects the one-photon absorption described in Patent Document 2 has a problem that it is difficult to detect the multi-photon absorption. there were.

  In general, since two-photon absorption is less likely to occur than one-photon absorption, one-photon absorption that is sensitive to the wavelength of the laser as used in the apparatus of Patent Document 2 is the main photodetector. Then, it is difficult to obtain a detection value based on two-photon absorption. Compared with single-photon absorption, the energy amount of laser light in multiphoton absorption varies greatly depending on the position in the optical axis direction. Furthermore, when the laser beam has an instantaneously strong energy such as an ultra-short pulse laser, the position where the laser pulse is focused becomes different from the position where the optical light is focused. Therefore, in order to measure the energy at the condensing position, the installation position of the photo detector such as a camera is extremely important.

  In order to measure the magnitude of multiphoton absorption that occurs in transparent materials with low one-photon absorption, such as glass and polymers, general CCD (charge-coupled device) cameras and CMOS ( complementary metal-oxide semiconductor) There was a problem that the camera could not be used. For this reason, it has been extremely difficult to design accurately in consideration of errors in how to modulate the phase, polarization, and intensity on the spatial light modulation element in laser processing in which multiphoton absorption occurs.

  The present invention has been made to solve the conventional problems. An object of the present invention is to provide a laser processing apparatus and a processing method capable of making output light more accurate by performing control according to output light actually obtained even in laser processing in which multiphoton absorption occurs. is there.

Means for Solving the Problems and Effects of the Invention

  In order to achieve the above object, the first laser processing apparatus of the present invention irradiates a material to be processed with an ultra-short pulse laser beam and processes the material to be processed with the energy of the ultra-short pulse laser beam. A laser processing apparatus, comprising: a laser light source that outputs an ultra-short pulse laser beam; and an ultra-short pulse laser beam emitted from the laser light source into an arbitrary spatial shape at a place where the material to be processed is placed Spatial light modulation element based on the detection result of the multi-photon absorption detector that detects the multi-photon absorption that occurs at each point of the molded ultra-short pulse laser light The element can be controlled to modulate ultra-short pulse laser light. As a result, the output light actually obtained by the laser processing device can be detected by the multiphoton absorption detector, and the spatial light modulation element can be controlled based on the detected output light, enabling extremely high-precision processing with adjustment of design errors. Become.

  In the second laser processing apparatus of the present invention, the multiphoton absorption detector is substantially insensitive to the wavelength of the laser light source and can have sensitivity in a shorter wavelength region than the wavelength of the laser light source. Accordingly, only the light whose wavelength is converted by multiphoton absorption or the like can be efficiently detected by the multiphoton absorption detector regardless of the wavelength of the laser light source.

  Further, according to the third laser processing apparatus of the present invention, the multiphoton absorption detector includes a photocathode that generates an electron image by multiphoton absorption generated at each point of the formed ultrashort pulse laser beam, and a photocathode. And an imaging element on which the emitted electron image is formed. As a result, a multiphoton absorption detector capable of accurately detecting multiphoton absorption with a two-layer structure of a photocathode and a CCD can be realized.

  Further, the fourth laser processing apparatus of the present invention includes a photocathode in which a multiphoton absorption detector generates an electron image by multiphoton absorption generated at each point of the formed ultrashort pulse laser beam, and a photocathode. A phosphor that is irradiated with the emitted electron image, and a fluorescence image detecting unit that detects a fluorescence image generated when the phosphor is excited by the electron image can be provided. As a result, a multiphoton absorption detector capable of detecting multiphoton absorption with higher accuracy can be realized with the three-layer structure of the photocathode, the phosphor, and the fluorescent image detection means.

  In the fifth laser processing apparatus of the present invention, the photocathode is substantially insensitive to the wavelength of the laser light source and has higher sensitivity in a shorter wavelength region than the wavelength of the laser light source. Thereby, the highly accurate multiphoton absorption detector which detects only multiphoton absorption is realizable.

  In the sixth laser processing apparatus of the present invention, the photocathode can be made of GaAsP. Thereby, the laser beam can be selectively incident on the multiphoton absorption detector.

  In the seventh laser processing apparatus of the present invention, the multiphoton absorption detector is substantially insensitive to the wavelength of the laser light source and is high in a wavelength region including approximately half the wavelength of the laser light source. A fluorescent material having sensitivity, a filter that blocks light having a wavelength of the laser light source, and transmits a fluorescent image generated when the fluorescent material is excited by multiphoton absorption; a lens that forms a fluorescent image that has passed through the filter; And a fluorescent image detecting means for detecting a fluorescent image formed by the lens. Thereby, an optical signal can be converted into an electrical signal with high accuracy by a combination of the phosphor, the filter, and the fluorescence image detecting means.

  In the eighth laser processing apparatus of the present invention, the multiphoton absorption detector has a drive system that can move in the optical axis direction, and multiphoton absorption detection is performed according to the detection result of the multiphoton absorption detector. The position in the optical axis direction of the device can be controlled by the drive system. Thereby, it can be adjusted by the drive system so that multiphoton absorption can be detected at an optimum position.

  The ninth laser processing method of the present invention is a laser processing method for irradiating a material to be processed with ultra-short pulse laser light and processing the material to be processed with the energy of ultra-short pulse laser light, A step of forming an ultra-short pulse laser beam output from a laser light source into a spatial arbitrary shape by a spatial light modulator at a place where the material to be processed is placed, and a step of forming the ultra-short pulse laser beam thus formed A step of detecting multiphoton absorption occurring at each point with a multiphoton absorption detector, and a step of modulating the ultrashort pulse laser light by controlling the spatial light modulation element according to the detection result of the multiphoton absorption detector; Can be included. As a result, the output light actually obtained by the laser processing device can be detected by the multiphoton absorption detector, and the spatial light modulation element can be controlled based on the detected output light, enabling extremely high-precision processing with adjustment of design errors. Become.

  The tenth laser processing method of the present invention is a laser processing method for irradiating a material to be processed with ultra-short pulse laser light and processing the material to be processed with the energy of ultra-short pulse laser light, A step of shaping an ultra-short pulse laser beam emitted from a laser light source into a spatial arbitrary shape by a spatial light modulator; a step of cutting out a plurality of shaped ultra-short pulse laser beams by a beam splitter; The spatial light modulator is controlled according to the process of detecting the multiphoton absorption generated at each point of the ultra-short pulse laser beam extracted by the beam splitter with the multiphoton absorption detector and the detection result of the multiphoton absorption detector. And a step of modulating the ultra-short pulse laser beam. Thereby, light in the middle can be detected by the beam splitter, so that a control system for a spatial light modulation element suitable for real-time feedback control or the like can be constructed.

  In the eleventh laser processing method of the present invention, the multiphoton absorption detector comprises a photocathode and a fluorescence image detecting means, and in the step of detecting multiphoton absorption by the multiphoton absorption detector, the photocathode Thus, a step of generating an electron image by multiphoton absorption and a step of driving the electron image emitted from the photocathode into the fluorescence image detecting means can be included. As a result, a multiphoton absorption detector capable of accurately detecting multiphoton absorption with a two-layer structure of the photocathode and the fluorescence image detecting means can be realized.

  In the twelfth laser processing method of the present invention, the multiphoton absorption detector is composed of a photocathode, a phosphor, and a fluorescent image detection means. In the step of detecting multiphoton absorption with the multiphoton absorption detector, A step of generating an electron image by multiphoton absorption on the photocathode, a step of irradiating the phosphor with the electron image emitted from the photocathode and exciting the phosphor, and a fluorescence image detecting means for detecting the excited and emitted fluorescence image The step of detecting can be included. Thereby, a multi-photon absorption detector capable of detecting multi-photon absorption with higher accuracy can be realized with a three-layer structure of a photocathode, a phosphor and an image detector.

  In the thirteenth laser processing method of the present invention, the multiphoton absorption detector is substantially insensitive to the wavelength of the laser light source, and is sensitive to a wavelength region including half the wavelength of the laser light source. A fluorescent material, a filter that blocks light of the wavelength of the laser light source and transmits only the excited fluorescent image, a lens that forms the fluorescent image, and a fluorescent image detection means that detects the fluorescent image. In the step of detecting multiphoton absorption with a multiphoton absorption detector, the step of irradiating the phosphor with the formed ultra-short pulse laser light to excite the phosphor and the filter are not absorbed by the phosphor. The step of blocking the light of the wavelength of the laser light source and transmitting only the excited fluorescence image, the step of forming the excited fluorescence image with the lens, and the fluorescence image formed by the fluorescence image detecting means are detected. Including the process of Can. Thereby, an optical signal can be converted into an electrical signal with high accuracy by a combination of the phosphor, the filter, and the fluorescence image detecting means.

  The fourteenth laser processing method of the present invention is characterized in that the position of the multiphoton absorption detector is controlled based on the detection result of the multiphoton absorption detector. Thereby, it can be adjusted by the drive system so that multiphoton absorption can be detected at an optimum position.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies a laser processing apparatus and a laser processing method for embodying the technical idea of the present invention, and the present invention describes the laser processing apparatus and the laser processing method as follows. Not specific to anything. Further, in this specification, in order to facilitate understanding of the scope of claims, numbers corresponding to the members shown in the embodiments are indicated in the “claims” and “means for solving problems” sections. It is appended to the members shown. However, the members shown in the claims are not limited to the members in the embodiments. In particular, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the embodiments are not intended to limit the scope of the present invention unless otherwise specified, and are merely explanations. It is just an example. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation. Furthermore, in the following description, the same name and symbol indicate the same or the same members, and detailed description thereof will be omitted as appropriate. Furthermore, each element constituting the present invention may be configured such that a plurality of elements are constituted by the same member and the plurality of elements are shared by one member, and conversely, the function of one member is constituted by a plurality of members. It can also be realized by sharing.

  Further, the incident beam angle of laser light in an actual laser processing apparatus is not necessarily the same as the angle represented on the drawing. That is, the incident beam angle may be incident at a specific angle so that the reduction in spatial resolution and diffraction efficiency caused by the thickness of the spatial light modulation element can be ignored. The position is abbreviated and is not a faithful representation of the angle of the incident beam.

  The laser processing apparatus and the laser processing method of the present invention condense an ultra-short pulse laser beam to a plurality of focused spots and irradiate the material to be processed, and specify the target material by the energy of the ultra-short pulse laser beam. Can be processed. Note that the laser processing apparatus and the laser processing method are not intended to limit the application to processing by an ultrashort pulse laser, but are also referred to as processing here including a reaction by laser irradiation and the like.

As the ultra-short pulse laser, a femtosecond pulse laser can be typically used. The femtosecond pulse laser is a laser having a very short pulse width of 1 × 10 ^{−15 to} 1000 × 10 ⁻¹⁵ seconds. However, the present invention can also use an ultra-short pulse laser in which the time width of one pulse is 100 × 10 ⁻¹² sec or less and 30 × 10 ⁻¹⁵ sec or more. As described above, the ultra-short pulse laser with a short pulse width irradiates the energy concentrated in the minimum time, so that the energy per unit time is extremely large. This laser is transmitted from the surface to the inside of the material to be processed up to the focused spot. In this region, the energy density is not high enough for the laser to cause multiphoton absorption. In the focused spot, the laser energy density is extremely high, so that it is efficiently absorbed by the material to be processed by multiphoton absorption.

  By the way, although the absorptivity and refractive index of a substance with respect to light are usually constants, when the light becomes stronger, it changes depending on the light intensity. Specifically, even if it is transparent to weak light, absorption always occurs for strong light. This is explained as multiphoton absorption in which a plurality of photons are absorbed simultaneously when the light is viewed as a collection of photons. At this time, the substance is not only excited to a high energy state but also changes in the substance such as ionization and molecular dissociation. On the other hand, the refractive index generally increases with light intensity. Because of this property, when strong light propagates through the material, a self-action occurs that changes its own properties. For example, there are self-focusing in which the light beam naturally narrows, self-phase modulation in which the spectrum of the light pulse spreads, and a phenomenon that causes polarization rotation.

(wavelength)
Specifically, since the wavelength range of each light energy generated by one-photon absorption and multi-photon absorption is different, it is difficult to obtain a detection value based on two-photon absorption in a photodetector with main one-photon absorption. Therefore, the sensitivity of the wavelength of the laser light source is very small, and the magnitude of multiphoton absorption can be measured by using a photodetector having sensitivity at half or less of the wavelength.

(Detection position)
Also, the higher the photon density in terms of time and space, the higher the probability of multiphoton absorption, so multiphoton absorption is more likely to occur near the focal point when light is collected. Become. Therefore, when the photon density varies depending on the position in the optical axis direction, such as when the light is condensed, the one-photon absorption is the number of photons that reach the light detection region of the photodetector. However, the frequency of multiphoton absorption varies greatly depending on the position in the optical axis direction. For example, in two-photon absorption, the output energy is proportional to the square of the incident energy, so even if the position in the optical axis direction where the two-photon absorption camera is installed is slightly shifted in the order of microns from the focused position of the beam, the output is It changes a lot. In addition, when there is an instantaneously strong energy like a femtosecond laser, the refractive index changes even in air, and in the laser pulse where the intensity at the center of the beam is high and the intensity around the beam is weak, the air itself Acts like a lens, and the position where the laser pulse is focused is different from the position where the geometric optical light is focused. Further, the condensing position changes depending on the intensity of the pulse.

  Therefore, in multiphoton absorption, the detection position must be set accurately. In particular, control in the optical axis direction is important from the above viewpoint. Therefore, a new mechanism is required to adjust the installation position of the multiphoton absorption camera so that high signal intensity can be obtained.

(Multiphoton absorption detector)
The laser processing apparatus of Example 1 is demonstrated based on FIG. In the laser processing apparatus shown in FIG. 1, a pre-adapting optical system 7 is disposed between the laser light source 1 and the spatial light modulator 4. In Example 1, a femtosecond pulse laser was used as the laser light source 1. The pre-adapting optical system 7 equalizes the energy distribution in the cross section of the laser output from the laser light source 1 and inputs it to the spatial light modulator 4. That is, the laser light output from the laser light source 1 is expanded so as to uniformly irradiate the entire surface of the spatial light modulator 4. The pre-adapting optical system 7 in FIG. 1 includes a plurality of lenses 2, and the laser output from the laser light source 1 is enlarged by the lenses 2 and is uniformly input to the spatial light modulator 4.

  Furthermore, the pre-adapting optical system 7 can use a beam shaping element 3 as shown in FIG. The laser beam output from the laser light source 1 usually has a spatial distribution in which the center is strong and gradually becomes weak as it goes to the periphery like a Gaussian distribution. The beam shaping element 3 is an element that makes the laser beam output from the laser light source 1 uniform, and makes the intensity distribution uniform within the effective diameter of the spatial light modulation element 4.

  The spatial light modulator 4 is a device that changes the phase and amplitude of light by a control signal. That is, the laser beam can be formed into an arbitrary shape. Specifically, the spatial light modulation element 4 divides the ultra-short pulse laser light emitted from the laser light source 1 two-dimensionally or three-dimensionally, and a large number of focused spots inside the multiphoton absorption detector 20. To form. The focused spot can be distributed two-dimensionally or three-dimensionally inside the multiphoton absorption detector 20.

  As the spatial light modulation element 4, a transmissive diffractive optical element, a reflective diffractive optical element, a refractive optical element, a reflective optical element, or the like can be used. The spatial light modulation element 4 of the transmission type diffractive optical element or the reflection type diffractive optical element has a spatial light modulation element using liquid crystal, and changes the refractive index for each place in accordance with a signal sent from the control device 11. Thus, a diffractive optical element is formed. The refractive optical element forms a large number of condensing spots at the same time by using a lens array in which a large number of lenses 2 are arranged. When the focal length of each lens 2 is changed, processing is possible with three-dimensional distribution. If a deformable refractive optical element is used, the processing shape can be arbitrarily changed. The reflective optical element uses an element such as a deformable mirror whose shape can be changed to change the phase at each point on the reflective optical element in order to form a two-dimensional or three-dimensional light intensity distribution. .

  As the spatial light modulator 4 of Example 1, PPM (Programmable Phase Modulator) manufactured by Hamamatsu Photonics Co., Ltd. was used. Thereby, the laser output from the laser light source 1 can be divided into a plurality of focused spots inside the multiphoton absorption detector 20.

  On the other hand, in the laser processing apparatus of FIG. 1, the post-adaptive optical system 8 is disposed between the spatial light modulation element 4 and the multiphoton absorption detector 20. The post-adaptive optical system 8 collects the condensing spot collected by the spatial light modulator 4 to be smaller in the multiphoton absorption detector 20. The post-adaptive optical system 8 in FIG. 1 uses a lens 9 having a high aperture ratio such as an objective lens of a microscope to focus the laser small inside the multiphoton absorption detector 20 while maintaining a spatial distribution. .

  In the first embodiment, a two-photon absorption camera 21 that senses two-photon absorption is provided as the multiphoton absorption detector shown in FIG. FIG. 2 is an explanatory diagram of the two-photon absorption camera 21. The bimolecular absorption camera b of the first embodiment includes a photocathode 24 made of GaAsP (gallium arsenide phosphorus). The photocathode 24 has little sensitivity to light having a wavelength of 800 nm, and has sensitivity in a wavelength region of about 280 to 720 nm. In particular, there is a sensitivity peak near 450 to 550 nm, and the maximum quantum efficiency is about 50%. Photons corresponding to the energy in the specific wavelength range incident on the photocathode are converted into electrons.

  In the first embodiment, a CCD camera is used as the imaging element 28 for the two-photon absorption camera 21. A CCD (charge-coupled device) camera 28 is installed on the side facing the photocathode 24. The CCD is a light receiving element made of semiconductor that converts light into an electrical signal. The electronic image emitted from the photocathode 24 is shot into the CCD camera 28 and formed.

  In Example 1, the center wavelength of the laser beam output from the laser light source 1 is 800 nm. Subsequently, two-photon absorption occurs at the focused spot of the ultra-short pulse laser beam divided by the spatial light modulator 4, that is, energy corresponding to a wavelength of 400 nm is detected. The photocathode 24 has little sensitivity to incident 800 nm laser light, but has sensitivity to energy corresponding to a wavelength near 400 nm generated by two-photon absorption. As a result, only photons related to two-photon absorption are converted into an electronic image by the photocathode. Further, the electron image emitted from the photocathode 24 is accelerated by the applied voltage, and is shot into the CCD camera 28 to obtain a multiplication gain.

(Redesign method)
A method for controlling the spatial light modulation element 4 based on the detection result by the two-photon absorption camera 21 so that the ultrashort pulse laser beam can be modulated will be described with reference to FIG. Here, the ultra-short pulse laser beam is modulated by adjusting the focal position of the ultra-short pulse laser beam to the intended processing position. FIG. 3 is a configuration diagram of the multiphoton absorption detector 20 including the two-photon absorption camera 21 according to the first embodiment. The two-photon absorption camera 21 has a drive system 34 that can move in the optical axis direction. With this drive system 34, the two-photon absorption camera 21 has a mechanism that can detect two-photon absorption while moving in the optical axis direction and set it to an appropriate position. Specifically, the image signal obtained by the two-photon absorption camera 21 is transmitted to the controller 35. Based on this image signal, a control signal is transmitted to the drive system 34 provided in the two-photon absorption camera 21. As a result, the two-photon absorption camera 21 moves to an appropriate position. At the same time, the image signal obtained by the two-photon absorption camera 21 is transmitted to the hologram calculation computer 10 connected to the multi-photon absorption detector 20 as shown in FIGS. Is output.

This data is an output result obtained by the multi-photon absorption detector 20 when the optical element displayed on the spatial light modulator 4 is actually reproduced in the processing optical system. By comparing this output result with a desired output result, the spatial distribution of the phase modulation, polarization modulation, and intensity modulation of the optical element displayed on the spatial light modulation element 4 is updated. By repeating this, the light output from the optical system approaches the desired intensity distribution, and the optical element is optimized. Since the output result is a result of the characteristics of the beam and the characteristics of the optical system, the design result of the optical element obtained by this process can be used as it is.
The mechanism of movement in the optical axis direction is also used for detecting a three-dimensional intensity distribution generated by the hologram.

  4 and 5 are process diagrams illustrating a method for optimizing an optical element. FIG. 4 shows a conventional method in which the optical element is reproduced in a computer. On the other hand, FIG. 5 shows a calculation process for optimizing the optical element in the first embodiment, and the optical element is reproduced by the processing optical system. In general, the process using the computer regeneration shown in FIG. 4 is executed in a shorter calculation time than the process using the optical regeneration shown in FIG. However, as described above, when the optical element shown in FIG. 5 is reproduced by the processing optical system, the design result of the optical element according to the actual output result can be used. Therefore, considering the advantages of both, after performing the process using the computer regeneration of FIG. 4 and optimizing the optical element to a state close to the optimum value, the design value by this computer regeneration is used as the initial value, as shown in FIG. It is also effective to perform an optical element optimization finish by a process using optical reproduction.

(Correction of pulse width variation)
In multiphoton absorption, the detection value of multiphoton absorption in the multiphoton absorption detector greatly depends on the pulse width of the laser. In other words, the change in the output image due to the change in the pulse width in the optical system can be reflected in the design of the optical element by the detection value of the multiphoton absorption obtained by the multiphoton absorption detector.

  Moreover, light detection can be performed with energy weaker than the beam energy for actual processing so as not to damage the multiphoton absorption detector. In this case, further optimization of the optical element is required. Using the optical element obtained with the energy at the time of optical system design, calculate the output value when the energy is changed, and adjust the output value at the design stage so that the output value becomes the desired output value Design to do. As a result, a desired light intensity distribution is obtained in the energy during processing.

  Further, another two-photon absorption camera 22 can be used as the multiphoton absorption detector 20. The laser processing apparatus including the two-photon absorption camera 22 illustrated in FIG. 6 has the same mechanism as the laser processing apparatus of the first embodiment except for the two-photon absorption camera 22.

  The two-photon absorption camera 22 in the second embodiment includes the same photocathode 24 as the two-photon absorption camera 21 in the first embodiment. That is, the two-photon absorption corresponding to the energy of the wavelength of 400 nm is generated by condensing the split light of the ultra-short pulse laser beam having the wavelength of 800 nm. When only the photon related to the two-photon absorption is incident on the photocathode 24, the photon is converted into an electronic image.

  The photoelectron image converted by the photocathode 24 is emitted into the photomultiplier tube 29 and multiplied by the secondary electron emission effect. As a result, high sensitivity and high-speed time response are possible. Further, since the mechanism for multiplying photoelectrons by the photomultiplier tube 29 is performed in a vacuum tube, it is possible to measure weak light with little noise.

  The photoelectron image multiplied by the photomultiplier tube 29 is applied to the phosphor 30. The phosphor 30 is excited by the photoelectron image, and this fluorescence emission pattern is detected by the fluorescence image detecting means 39. At this time, it is preferable to use a lens 31 for forming a fluorescent image on the fluorescent image detecting means 39. The method for optimizing the optical element using the detection value obtained by the two-photon absorption camera 22 is the same as in the first embodiment.

  As another multiphoton absorption detector 20, another two-photon absorption camera 23 can be used. The laser processing apparatus including the two-photon absorption camera 23 illustrated in FIG. 7 has the same mechanism as the laser processing apparatus of the first embodiment except for the two-photon absorption camera 23.

  The two-photon absorption camera 23 according to the third embodiment uses a phosphor 32 that is very sensitive to the wavelength of the laser and has sensitivity at half that wavelength. The phosphor 32 is directly excited by the energy of the two-photon absorption reaction generated by condensing the split light of the ultra-short pulse laser beam having a wavelength of 800 nm. A fluorescent image of the phosphor 32 excited by energy corresponding to a wavelength of about 400 nm generated by the two-photon absorption is detected by the fluorescent image detecting means 39. At this time, as in the second embodiment, it is preferable to use a lens 31 for forming a fluorescent image on the fluorescent image detecting means 39. Furthermore, it is preferable to use an incident light cut filter 33 that cuts off the light of the laser light source incident on the phosphor 32 and transmits only the fluorescence image excited by the phosphor 32. By using the lens 31 and the incident light cut filter 33, it is possible to accurately detect data of only a desired fluorescent image, and it is possible to optimize the optical element more precisely. The two-photon absorption camera 23 does not have a function of multiplying photoelectrons. Therefore, when the incident pulse is weak, there is a possibility that the sensitivity becomes small and the fluorescent image cannot be detected, but the cost can be reduced because the structure is simple. Of course, a function of multiplying photoelectrons such as a photomultiplier tube can be added if necessary.

  The method for optimizing the optical element using the detection value obtained by the two-photon absorption camera 23 is the same as in the first embodiment.

  As the multiphoton absorption detector described above, a two-dimensional image sensor in which detectors are arranged two-dimensionally can be suitably used so that a two-dimensional output image can be acquired simultaneously. However, a method of obtaining an output image in a time division manner by scanning one multiphoton absorption detector 20 two-dimensionally as shown in FIG. In this case, since the laser pulse has energy variation for each pulse, a method of measuring the number of times and averaging can be considered.

  In addition, as shown in FIG. 9, when the condensing points of a large number of divided beams are distributed three-dimensionally, the multiphoton absorption detector 20 is operated three-dimensionally with a single detector or two photons. A three-dimensional light intensity is measured by moving the absorption camera.

  FIG. 10 shows the multi-photon absorption generated at each focal point of the ultra-short pulse laser beam cut out by the beam splitter 36 by cutting the ultra-short pulse laser beam formed by the spatial light modulator 4. This is a method of detecting with the detector 20. This is effective when there is a change in the characteristics of the laser, the spatial light modulator, or the optical system due to changes in temperature, etc., or when the multiphoton absorption detector cannot be placed at the position of the sample 37.

  Further, FIG. 11 shows an arrangement of the optical system when the reflective spatial light modulation element 38 is used in the optical system of the first embodiment. The angle between the reflective spatial light modulator 38 and the incident beam is 45 degrees to 90 degrees, and in many cases, a reduction in spatial resolution and diffraction efficiency can be ignored depending on the thickness of the reflective spatial light modulator 38. In addition, the incident beam is incident on the reflective spatial light modulator at an angle close to perpendicular. Similarly to FIG. 10, it is also possible to perform a method in which the formed ultra-short pulse laser light is cut out by a beam splitter, and the light is detected using a multiphoton absorption detector.

  The laser processing apparatus and processing method of the present invention are suitable for applications such as displaying a three-dimensional solid pattern, figure, character, etc. by providing a void inside the transparent body or modifying the refractive index. Available. Furthermore, it is suitable for applications such as optical memory, optical circuit, optical member manufacturing, and microchip reaction container manufacturing in optical information processing.

It is explanatory drawing explaining the laser processing apparatus of Example 1. FIG. FIG. 3 is an explanatory diagram for explaining a two-photon absorption camera of Example 1. It is a block diagram explaining the multiphoton absorption detector of Example 1. FIG. FIG. 6 is a process diagram illustrating a conventional method for optimizing an optical element. FIG. 3 is a process diagram illustrating a method for optimizing the optical element according to the first embodiment. FIG. 6 is an explanatory diagram illustrating a two-photon absorption camera according to a second embodiment. FIG. 6 is an explanatory diagram for explaining a two-photon absorption camera of Example 3. It is explanatory drawing explaining the operation method of a multiphoton absorption detector. It is explanatory drawing explaining another operation method of a multiphoton absorption detector. It is explanatory drawing explaining another laser processing apparatus. It is explanatory drawing explaining another laser processing apparatus. It is explanatory drawing explaining the conventional laser processing apparatus. FIG. 13A is a partially enlarged view of a conventional laser processing apparatus, FIG. 13A is an explanatory diagram for explaining the relationship between laser light and a microlens array, and FIG. It is the enlarged view to which the part was expanded.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser light source 2 ... Lens 3 ... Beam shaping element 4 ... Spatial light modulation element 7 ... Pre-adaptation optical system 8 ... Post-adaptation optical system 9 ... Lens 10 ... Computer for hologram calculation 11 ... Control apparatus 20 ... Multiphoton absorption detector DESCRIPTION OF SYMBOLS 21 ... Two-photon absorption camera 22 ... Two-photon absorption camera 23 ... Two-photon absorption camera 24 ... Photocathode 28 ... Imaging element (CCD camera)
DESCRIPTION OF SYMBOLS 29 ... Photomultiplier tube 30 ... Phosphor 31 ... Lens 32 ... Phosphor 33 ... Incident light cut filter 34 ... Drive system 35 ... Controller 36 ... Beam splitter 37 ... Sample 38 ... Reflection type spatial light modulator 39 ... Fluorescence image detection Means 101 ... Laser condensing device 102 ... Laser light source (laser diode array)
DESCRIPTION OF SYMBOLS 103 ... Cylindrical lens array 104 ... Cylindrical lens array 105 ... Beam splitter 106 ... Shack-Hartmann sensor 107 ... Micro lens array 108 ... Lens element 109 ... CCD camera 110 ... SLM controller 111 ... Reflection type spatial light modulator (SLM)
112 ... Condenser lens L ... Laser light

Claims (14)

A laser processing apparatus that irradiates a material to be processed with an ultra-short pulse laser beam and processes the material to be processed with the energy of the ultra-short pulse laser beam,
A laser light source that outputs an ultra-short pulse laser beam;
A spatial light modulator for shaping an ultra-short pulse laser beam output from the laser light source into an arbitrary spatial shape at a place where the material to be processed is placed;
A multiphoton absorption detector for detecting multiphoton absorption occurring at each point of the shaped ultra-short pulse laser beam;
A laser processing apparatus characterized in that the ultra-short pulse laser beam can be modulated by controlling the spatial light modulation element based on a detection result of the multiphoton absorption detector. The laser processing apparatus according to claim 1,
The laser processing apparatus, wherein the multiphoton absorption detector is substantially insensitive to the wavelength of the laser light source and has sensitivity in a shorter wavelength region than the wavelength of the laser light source. The laser processing apparatus according to claim 1 or 2,
The multiphoton absorption detector is
A photocathode that generates an electron image by multiphoton absorption occurring at each point of the shaped ultra-short pulse laser beam;
An imaging element on which an electron image emitted from the photocathode is formed;
A laser processing apparatus comprising: The laser processing apparatus according to claim 1 or 2,
The multiphoton absorption detector is
A photocathode that generates an electron image by multiphoton absorption occurring at each point of the shaped ultra-short pulse laser beam;
A phosphor irradiated with an electron image emitted from the photocathode;
Fluorescence image detection means for detecting a fluorescence image generated when the phosphor is excited by the electronic image;
A laser processing apparatus comprising: The laser processing apparatus according to claim 3 or 4,
The laser processing apparatus, wherein the photocathode is substantially insensitive to the wavelength of the laser light source and has a higher sensitivity in a shorter wavelength region than the wavelength of the laser light source. A laser processing apparatus according to any one of claims 3 to 5,
A laser processing apparatus, wherein the photocathode is made of GaAsP. The laser processing apparatus according to claim 1 or 2,
The multiphoton absorption detector is substantially insensitive to the wavelength of the laser light source, and has a high sensitivity in a wavelength region including a wavelength approximately half of the wavelength of the laser light source;
A filter that blocks light of the wavelength of the laser light source and transmits a fluorescent image generated by excitation of the phosphor by multiphoton absorption;
A lens for forming a fluorescent image transmitted through the filter;
A fluorescence image detecting means for detecting a fluorescence image formed by the lens;
A laser processing apparatus comprising: It is a laser processing apparatus as described in any one of Claims 1-7,
The multiphoton absorption detector has a drive system movable in the optical axis direction,
A laser processing apparatus, wherein the position of the multiphoton absorption detector in the optical axis direction can be controlled by the drive system in accordance with the detection result of the multiphoton absorption detector. A laser processing method of irradiating a material to be processed with an ultra-short pulse laser beam and processing the material to be processed with energy of the ultra-short pulse laser beam,
Forming the ultra-short pulse laser beam output from a laser light source into a spatial arbitrary shape by a spatial light modulation element at a place where the material to be processed is placed;
Detecting multiphoton absorption occurring at each point of the shaped ultra-short pulse laser beam with a multiphoton absorption detector;
A step of controlling the spatial light modulator and modulating the ultrashort pulse laser beam according to a detection result of the multiphoton absorption detector;
A laser processing method comprising: A laser processing method of irradiating a material to be processed with an ultra-short pulse laser beam and processing the material to be processed with energy of the ultra-short pulse laser beam,
Forming the ultra-short pulse laser light emitted from a laser light source into a spatial arbitrary shape by a spatial light modulator;
A step of cutting the plurality of ultra-short pulse laser lights formed by a beam splitter;
Detecting a multiphoton absorption generated at each point of the ultra-short pulse laser beam cut out by the beam splitter with a multiphoton absorption detector;
A step of controlling the spatial light modulator and modulating the ultrashort pulse laser beam according to a detection result of the multiphoton absorption detector;
A laser processing method comprising: The laser processing method according to claim 9 or 10,
The multiphoton absorption detector is composed of a photocathode and an imaging element,
In the step of detecting the multiphoton absorption with a multiphoton absorption detector,
Generating an electronic image by the multiphoton absorption by the photocathode;
Imaging the electron image emitted from the photocathode onto the imaging element;
A laser processing method comprising: The laser processing method according to claim 9 or 10,
The multiphoton absorption detector is composed of a photocathode, a phosphor, and a fluorescence image detecting means,
In the step of detecting the multiphoton absorption with a multiphoton absorption detector,
Generating an electronic image by the multiphoton absorption on the photocathode;
Irradiating the phosphor with an electron image emitted from the photocathode to excite the phosphor;
Detecting the excited and emitted fluorescent image by the fluorescent image detecting means;
A laser processing method comprising: The laser processing method according to claim 9 or 10,
The multiphoton absorption detector is substantially insensitive to the wavelength of the laser light source, and has a sensitivity in a wavelength region including a half wavelength of the wavelength of the laser light source;
A filter that blocks light of the wavelength of the laser light source and transmits only the excited fluorescence image;
A lens that forms the fluorescent image;
Fluorescence image detecting means for detecting the fluorescence image;
With
In the step of detecting the multiphoton absorption with a multiphoton absorption detector,
Irradiating the phosphor with the ultra-short pulse laser beam thus shaped, and exciting the phosphor;
Blocking the light of the wavelength of the laser light source not absorbed by the phosphor by the filter and transmitting only the excited fluorescence image;
Forming the excited fluorescence image with the lens;
Detecting the imaged fluorescent image by the fluorescent image detecting means;
A laser processing method comprising: It is a laser processing method of Claims 9-13,
Furthermore, the laser processing method characterized by controlling the position of the multiphoton absorption detector according to the detection result of the multiphoton absorption detector.

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