JPH11221684A - Pulse laser beam machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pulse laser beam machine which improves machining efficiency by utilizing an ordinary ultrashort pulse light source. SOLUTION: The device is equipped with a laser light source 2 emitting an ultrashort pulse light, with a pulse luminous lines generating part 3 which generates ultreshort pulse luminous lines comprising a plurality of pulse light beams based on one pulse out of ultrashort pulse light beams emitted from the laser light source 2, and with a machining controlling part 4 consisting of an emitting optical system and a machining position controlling part 42, which introduces the generated ultrashort pulse light beam lines to a presctibed location of machining object of a machined work 5 and at the same time controls the emission. The pulse luminous lines generating part 3 is preferably to generate pulse luminous lines composed of a plurality of pulse beams by making inputted light beams branch into a plurality of optical path having different optical path length difference with one another.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser processing apparatus for processing a workpiece using a laser, and more particularly to a laser processing apparatus using ultrashort pulse light.

[0002]

2. Description of the Related Art Laser processing apparatuses for processing a workpiece using a laser are widely used in various fields.

In a usual laser processing apparatus, thermal processing is performed by using a laser having an absorption wavelength of a substance. On the other hand, it is known that if a high-power ultrashort pulse laser is used, ablation can be caused by a multiphoton process, and non-thermal processing can be performed. Regarding this, Takuya Okamoto et al., “Ablation of polytetrafluoroethylene with a high-power ultrashort pulse Ti: Al ₂ O ₃ laser” (Laser Science Research No. 1).
5, 1993, p. 55-57).

[0004]

When an ultra-short pulse laser is applied to a laser processing apparatus, the energy per light pulse is increased in order to improve the processing efficiency, but the laser light source is complicated and large. As the light source of the laser processing apparatus is approaching its limit, it is becoming difficult to configure it as a processing apparatus.

[0005] In view of the above problems, an object of the present invention is to provide a pulse laser processing apparatus that uses a normal ultrashort pulse light source to improve processing efficiency.

[0006]

In order to solve the above-mentioned problems, a laser processing apparatus according to the present invention comprises a laser light source for emitting ultra-short pulse light, and one pulse of the ultra-short pulse light emitted from the laser light source. A pulse light train generation unit that generates an ultrashort pulse light train composed of multiple pulse lights based on the laser beam, and guides the generated ultrashort pulse light train to a predetermined processing target position on the workpiece and controls its irradiation And a processing control unit that performs the processing.

According to this, the pulse light train generation unit generates an ultrashort pulse light train composed of a plurality of pulse lights based on one pulse of the pulse light emitted from the laser light source. This ultrashort pulse light train is guided to a predetermined processing target position on the workpiece and irradiated. On the surface of the workpiece irradiated with the pulse light train, non-thermal processing such as ablation is performed by multiphoton absorption or the like.

[0008] The pulse width of the ultrashort pulse light is preferably 100 nanoseconds or less. This is because a multi-photon reaction is caused by a physical phenomenon different from a normal one-photon absorption process by irradiation with a pulse light having a short pulse width.

The pulse light train generating section includes a plurality of optical paths capable of changing the optical path length difference between each other, an optical branching section for branching and guiding input pulse light to each of these optical paths, and a pulse emitted from each of the optical paths. And a combining output unit that combines and outputs light.

[0010] According to this, the pulse light emitted from the light source is branched into respective optical paths at the light branching section and is guided. If the respective optical path lengths are different, the incident pulse light is output from each optical path with a time difference. A pulse light train composed of a plurality of pulse lights is emitted by combining and outputting these lights at the combining output unit.

The ultrashort pulse light train may be a double pulse composed of two ultrashort pulse lights having a pulse interval of pulse width to 1 millisecond. The present inventor has clarified that laser-induced plasma is effectively generated by double-pulse irradiation with a short pulse interval.

It is preferable that the light splitting section and the combining output section are polarizing beam splitters. According to this, loss of light energy due to branching, transmission and reflection at the time of synthesis is small.

Further, the light branching section may include a polarization control means for changing a polarization state of the ultrashort pulse light emitted from the laser light source. According to this, it is possible to control the polarization state of the ultrashort pulse light emitted from the laser light source to an arbitrary state. When the ultrashort pulse light whose polarization state is adjusted is guided to the polarization beam splitter, the pulse light is separated at a ratio corresponding to the polarization state.

It is preferable that the pulse light train generation unit further includes a beam correction unit that matches at least one of the spatial mode of the branched pulse light and the beam divergence angle.
If the optical path length difference between the branched lights is large, the spatial mode and the beam divergence angle of the pulsed light guided in each optical path are different. By making at least one of the spatial mode and the beam divergence angle coincide with each other in the beam correction unit, the influence caused by the optical path length difference is reduced.

The pulse light train generating section has a plurality of optical paths capable of changing the optical path length difference therebetween, and an optical branching section for branching and guiding the input pulse light to each of the optical paths. Alternatively, the pulse light output from the optical path may be applied to a predetermined processing target position of the workpiece from a plurality of different directions.

According to this, the single ultrashort pulsed light is guided to a plurality of optical paths by the optical branching unit, and by controlling the optical path lengths of the plurality of optical paths, the pulsed light is output from each optical path. Stagger the timing. The pulse light train shifted in time irradiates a predetermined processing target position of the workpiece from different directions. Thus, non-thermal processing such as ablation is performed on the surface of the workpiece irradiated with the pulse light train by multiphoton absorption or the like.

It is preferable that the pulse light train generation unit includes an optical modulator that modulates at least one of the intensity and the phase of the input pulse light. Thus, the workpiece can be irradiated with a light pulse having a desired waveform, and the processing efficiency can be improved.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. To make the explanation easier to understand,
In each of the drawings, the same components are denoted by the same reference numerals as much as possible, and redundant description is omitted. In addition,
The drawings are simplified for explanation, and dimensions, shapes, and the like do not always match actual ones.

FIG. 1 is a block diagram showing a basic configuration of a laser processing apparatus according to the present invention. As shown in FIG. 1, a laser processing apparatus 1 of the present invention generates a laser light source 2 that emits ultrashort pulse light and a pulse light train composed of a plurality of pulse lights based on the emitted ultrashort pulse light. A pulse light train generating unit 3 and a processing control unit 4 that guides the pulse light train to a predetermined processing target position of the workpiece 5 and controls the irradiation thereof.

The laser light source 1 has a pulse width of 1
A light source that emits ultrashort pulse light of milliseconds or less, for example, a titanium-sapphire laser, a Nd: YAG laser, a Nd: Glass laser, or the like, which is combined with an optical amplifier that amplifies the laser. Is also good.

The processing control section 4 comprises an irradiation optical system 41 for guiding laser light to a predetermined processing position, and a processing position control section 42 for controlling the relative positional relationship between the workpiece 5 and the laser light irradiation position. The irradiation optical system 41 is configured by combining a shutter for switching irradiation and non-irradiation of laser light, a lens and a mirror for condensing laser light on a position to be measured. Among them, a mechanical shutter, an acousto-optic modulator, an electro-optic modulator, or the like can be used as the shutter. It is preferable to use a reflective objective lens capable of condensing the laser light without deforming the pulse waveform. The processing position control unit 42 controls the irradiation optical system 41 to drive a table on which the workpiece 5 is mounted or fixed, by irradiating a predetermined processing target position of the workpiece 5 with pulsed light. Any of the types in which the relative position with respect to the fixed irradiation optical system 41 is changed by moving the workpiece 5 to irradiate a desired processing target position with pulsed light may be used, or both may be combined. Although not shown, an observation system for observing the processing target position may be separately provided.

Next, some specific embodiments of the pulse light train generator 3 will be described.

FIG. 2 is a schematic configuration diagram showing the pulse light train generation unit 3a according to the first embodiment. The pulse light train generating unit 3a changes the polarization state of the input pulse light by a quarter.
Wave plate 31, polarization beam splitter 32 for splitting input pulse light, and mirror group M for forming one split optical path A
11, M12 and a mirror group M forming the other branch optical path B
21 to M24, a beam correction unit 34 arranged on the branch optical path A, and a polarization beam splitter 33 that combines the light emitted from the branch optical paths A and B.
Among them, the beam correction unit 34 is configured by combining a convex lens, a concave lens, a reflecting mirror, and the like. Then, the mirrors M22 and M23 of the branch optical path B are connected to the mirror M2.
1. By moving with respect to M24, the length of the branch optical path B, that is, the optical path length can be changed. On the other hand, since the mirror groups M11 and M12 of the branch optical path A are fixed, their optical path lengths are constant. Therefore, mirror M2
2. The difference between the optical path lengths of the branch optical path A and the branch optical path B changes due to the movement of M23.

Next, the operation of the laser processing apparatus 1 using the pulsed light train generator 3a will be described with reference to FIGS.

The ultrashort pulse light emitted from the laser light source shown in FIG. 1 is guided to the pulse light train generation unit 3a. Ultrashort pulse light emitted from a laser light source is generally linearly polarized light. In the pulse light train generation unit 3a, the ultrashort pulse light is firstly transmitted to the quarter wave plate 31 as shown in FIG.
And circularly polarized here. Then, one of the P-polarized light and the S-polarized light is reflected by the polarization beam splitter 32, and the other is transmitted, whereby the light is branched into two branched light paths A and B.

One of the split lights is reflected by a mirror M11.
Are reflected by M12, pass through the branch optical path A passing through the beam correction unit 34, and enter the polarization beam splitter 33. The other of the split lights is reflected by mirrors M21 to M24 and similarly enters polarizing beam splitter 33.
The polarization beam splitter 33 reflects the light from the branch light path A and transmits the light from the branch light path B to combine both lights.

At this time, by changing the positions of the mirrors M22 and M23 of the branch optical path B as described above, the length (optical path length) of the branch optical path B can be made longer (or shorter) than the branch optical path A. When the optical path length of the branch optical path B is longer than that of the branch optical path A, the pulse light traveling through the branch optical path A arrives at the polarization beam splitter 33 earlier than the pulse light traveling through the branch optical path B, and the polarization beam splitter 33
Is a pulsed light train composed of two pulsed lights having a pulse interval corresponding to the difference between the respective optical path lengths. That is, by controlling the optical path length, pulse light trains having different pulse intervals can be generated.

At this time, the beam correction unit 34 matches the spatial mode and the beam divergence angle of the light transmitted through the branch optical path A with the spatial mode and the beam divergence angle of the light transmitted through the branch optical path B. Thereby, the spatial characteristics of the emitted pulse light train can be made uniform.

Various beam splitters other than the polarizing beam splitter can be used for splitting and synthesizing light. However, the polarizing beam splitter is particularly preferable because loss due to transmission and reflection during splitting and synthesizing is small.

The generated pulse light train is guided to the processing target position of the workpiece 5 through the irradiation optical system 41 shown in FIG. The irradiation of the processing target position is controlled by the processing position control unit 42 moving both or one of the workpiece 5 and the laser irradiation position.

By irradiating with ultra-short pulse light at short time intervals, the workpiece 5 can be non-thermally processed by multiphoton absorption or the like. It is considered that laser-induced plasma is involved in the processing using the ultrashort pulse light. Then, the inventor of the present application examined the plasma generation process using ultrashort pulse light by experiments.

First, when water is irradiated with a double pulse of a fundamental wave (wavelength: 1.06 μm) of an Nd: YAG laser pulse having a millijoule order and a pulse width of about 30 picoseconds,
As shown in FIG. 3, it has been found that the relaxation time of light emission at the time of post-pulse irradiation becomes longer depending on the interval between double pulses. It was also found that even when the total energy of the pulsed light was the same, the total energy of light emission was larger in the double pulse than in the single pulse.

In the case of laser-induced light emission using air or nitrogen gas, the use of a double pulse has a longer relaxation time than the case of using a single pulse, and the light emission intensity also increases. FIG. 4 shows the relationship between the time interval of the double pulse and the emission intensity when air is emitted by the double pulse. When a double pulse having a pulse time interval of 200 picoseconds is irradiated, the pulse time interval is reduced. It can be seen that a luminous intensity about 70 times that of the case where is zero is obtained.

FIG. 5 shows the spectral characteristics of breakdown light emission induced by an ultrashort pulse laser of air or nitrogen gas in comparison with the spectral characteristics of light emission of an air-filled discharge tube. Here, the spectrum of the breakdown emission of air is shown by a thick solid line, the spectrum of the breakdown emission of nitrogen is shown by a thin solid line, and the emission spectrum of the discharge tube is shown by a broken line. In this figure, the data of nitrogen breakdown is
The data of 0.25 and the data of the discharge tube are respectively shifted by -0.5 with respect to the vertical axis. The respective spectral characteristics are in good agreement. Light emission of the discharge tube is due to plasma light emission, and breakdown light emission is also considered to be plasma light emission.

Since the laser processing apparatus 1 of the present invention may be considered to utilize laser-induced plasma, the processing efficiency can be improved by increasing the generation efficiency of laser-induced plasma. As described above, it is considered that the emission intensity of the laser-induced plasma is higher in the double pulse irradiation than in the single pulse irradiation, and the generation efficiency is improved. Therefore, by irradiating a double pulse as in the present invention, the generation efficiency of laser-induced plasma can be improved and the processing efficiency can be improved.

By changing the inclination and rotation of the quarter-wave plate 31 with respect to the input light, the input pulse light can be made elliptically polarized light, and the ratio between the P-polarized light component and the S-polarized light component can be changed. . Thereby, the ratio of the light branched to the respective branch optical paths A and B by the polarization beam splitter 32 changes. By utilizing this, it is possible to change the intensity ratio between the preceding pulse and the succeeding pulse of the pulse light train.

Further, the double pulse output from the polarization beam splitter 33 becomes linearly polarized light orthogonal to each other, but by inserting a quarter-wave plate on the output optical path,
Both can be converted to circularly polarized light. Further, by further passing through a polarizer, it is possible to obtain linearly polarized lights equal to each other. In this case, by controlling the tilt and rotation of the quarter-wave plate of the output unit, the output light of the quarter-wave plate is converted into elliptically polarized light, so that the branch ratio can be variably controlled at the output unit. it can. It is preferable to use a Soleil-Babinet compensator for these quarter-wave plates because more precise control of the intensity ratio can be performed.

Next, referring to FIG.
2 shows a second embodiment. Here, the condensing section 41a functioning as the irradiation optical system 41 is also shown.

The pulse light train generator 3 of the second embodiment
b branches an optical pulse to form a branched optical path A having a different optical path length.
The parts leading to and B are the same as those of the pulse light train generation unit 3a of the first embodiment. However, instead of synthesizing the pulsed light transmitted through each of the branch optical paths A and B, a separate condenser lens L is provided via mirrors M12 and M25, respectively.
1 and 2 in that the light is condensed by L2 and guided to the processing target position of the workpiece 5.

Here, an example is shown in which the condensing of the pulse light output from each optical path is condensed by a single condensing lens L1, L2, but the configuration of the condensing section 41a is limited to this. Instead, one or a plurality of lenses and / or mirrors may be combined.

With such a configuration, the pulse light outputted from the branch light path A and the branch light path B with a time difference is applied to the processing target position from different directions. For this reason, the seed of the plasma is generated by the preceding pulse, and the plasma is generated by the subsequent pulse to perform processing. At this time, processing can be performed only on a region of the workpiece 5 where the two laser beams intersect, and three-dimensional fine processing can be performed.

Next, a pulse light train generator 3c according to a third embodiment will be described with reference to FIG. The pulse light train generation unit 3c includes a polarizer 31a that converts the input pulse light into a predetermined polarization state, a diffraction grating 32a that spatially resolves the output light of the polarizer 31a, and intensity-modulates the wavelength-resolved light. An intensity modulator 6, an analyzer 31b that transmits only a predetermined polarized portion of the intensity modulated light, a phase modulator 7 that modulates the phase of the light, and a diffraction grating that combines spatially wavelength-resolved light. 33a. Among them, the intensity modulator 6
And the phase modulation unit 7 have substantially the same configuration, and each of them has a spatial light modulator 61, 71 and the spatial light modulator 61,
It comprises CRTs 63 and 73 for writing modulation information to 71, mirror groups M41 and M42 and M43 and M44 for inputting and outputting pulsed light to and from the projection lenses 62 and 72 and the spatial light modulators 61 and 71.

According to this configuration, the input pulse light is spatially spectrally resolved by the diffraction grating 32a, and then guided to the spatial light modulator 61 by the mirror M41. A modulation pattern is projected onto the spatial light modulator 61 via the lens 62 by the CRT 63, and the polarization state of light of each wavelength component of the input light pulse is independently changed according to the modulation pattern. The light whose polarization state has been changed in this way is collected by the mirror M42 and guided to the analyzer 31b. Since the analyzer 31b allows only light in a predetermined polarization state to pass, it is possible to perform intensity modulation for each wavelength component of the input pulse light. This light is further guided to the phase modulation unit 7, and is similarly subjected to phase modulation for each wavelength component by the spatial light modulator 71 via the mirror M 43. The light after the phase modulation is condensed by the mirror M44 and condensed into one beam by the diffraction grating 33a. Since the spectral characteristics are changed by the intensity modulation and the phase modulation, the pulse waveform of the output light changes. By controlling this modulation, it is possible to generate a desired light pulse such as a pulse light train having a different wavelength.

Next, a pulse light train generator 3d according to the fourth embodiment will be described with reference to FIG. The pulse light train generation unit 3d basically includes dichroic mirrors 32b, 32c, 33b, and 33c instead of the polarization beam splitters 32 and 33 of the pulse light train generation unit 3a of the first embodiment.
, And the light is further branched into three light paths A, B, and C by branching twice. Then, the optical path lengths of the branch optical path B and the branch optical path C are set to the mirror group M22.
And M23 or M32 and M33 are moved to change the time until the pulse light is output from each optical path to generate a pulse light train composed of a plurality of pulses. In this embodiment, a pulse light train composed of three pulse lights having different wavelengths can be generated.

In addition to using the pulse light train generation units of the first to fourth embodiments alone, some of them may be used in combination in series or in parallel. Thereby, a plurality of pulsed lights can be generated with low loss.

In the above-described embodiment, the portion of the branch optical path that changes the optical path length is determined by the mirror groups M22, M23, M23.
Although an example of forming with 32, M33, etc. has been shown, it can also be formed with a right-angle prism or a corner cube reflector. In this case, the number of parts is reduced and the adjustment is simplified. However, since the right-angle prism is a dispersion medium, its waveform is deformed by an ultrashort pulse of picosecond or less, so that it is not preferable to use it. Also, since the corner cube reflector involves rotation of polarized light, care must be taken when using it.

[0047]

As described above, according to the present invention,
Since a pulsed light train composed of a plurality of pulses is generated based on the pulses emitted from the laser light source, and this is irradiated on the workpiece, laser-induced plasma can be generated and laser processing can be performed. The generation efficiency of the laser-induced plasma is improved as compared with the case of one pulse, and the processing efficiency can be improved.

In particular, if the pulse light is branched into a plurality of optical paths and the optical path length differences are made different, a pulse light train composed of a plurality of pulses can be easily generated.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a laser processing apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram of a first embodiment of a pulse light train generation unit of the laser processing apparatus of the present invention.

FIG. 3 is a diagram showing a relationship between a double pulse time interval of breakdown emission of water by a double pulse and a light emission relaxation time.

FIG. 4 is a diagram showing a relationship between a double pulse time interval of air breakdown emission by a double pulse and emission intensity.

FIG. 5 is a diagram comparing emission spectra of breakdown emission of air and nitrogen and emission of an air discharge tube.

FIG. 6 is a schematic configuration diagram of a second embodiment of the pulse light train generation unit of the laser processing apparatus of the present invention.

FIG. 7 is a schematic configuration diagram of a third embodiment of a pulse light train generation unit of the laser processing apparatus of the present invention.

FIG. 8 is a schematic configuration diagram of a fourth embodiment of the pulse light train generation unit of the laser processing apparatus of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser processing apparatus, 2 ... Laser light source, 3 ... Pulse light train generation part, 4 ... Processing control part, 5 ... Workpiece, 41 ... Irradiation optical system, 42 ... Processing position control part.

Claims (9)

[Claims] 1. A laser light source that emits an ultrashort pulse light, and a pulse light that generates an ultrashort pulse light train composed of a plurality of pulse lights based on one pulse of the ultrashort pulse light emitted from the laser light source A pulse laser processing apparatus, comprising: a row generation unit; and a processing control unit that guides the generated ultrashort pulse light sequence to a predetermined processing target position on a workpiece and controls irradiation of the processing. 2. The pulse laser processing apparatus according to claim 1, wherein the pulse width of the ultrashort pulse light is 100 nanoseconds or less. 3. The optical system according to claim 1, wherein the pulse light train generating unit includes: a plurality of optical paths capable of changing a difference in optical path length between each other; an optical branching unit branching and guiding input pulse light to each of the optical paths; A combined output unit that combines and outputs the emitted pulse light;
The pulse laser processing apparatus according to claim 1, further comprising: 4. The pulse laser processing apparatus according to claim 3, wherein the ultrashort pulse light train is a double pulse composed of two ultrashort pulse lights having a pulse interval of pulse width to 1 millisecond. . 5. The optical branching unit and the combining output unit,
The pulse laser processing apparatus according to claim 3, wherein the pulse laser processing apparatus is a polarization beam splitter. 6. The pulse laser processing apparatus according to claim 5, wherein the light branching unit includes a polarization control unit that changes a polarization state of the ultrashort pulse light emitted from the laser light source. 7. The pulse light train generation unit according to claim 3, further comprising a beam correction unit for matching at least one of a spatial mode of the branched pulse light and a beam divergence angle. A pulse laser processing apparatus according to any one of the above. 8. The pulse light train generation unit includes: a plurality of light paths capable of changing a difference in optical path length between each other; and a light branching unit that branches and guides input pulse light to each of the light paths. The pulse laser processing apparatus according to claim 1, wherein the control unit irradiates the pulse light output from the plurality of optical paths to a predetermined processing target position of the workpiece from a plurality of different directions. 9. The pulse laser processing apparatus according to claim 1, wherein the pulse light train generation unit includes an optical modulator that modulates at least one of intensity and phase of the input pulse light. .