JP2003255262A - Specialized optical system using femtosecond laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize various machinings such as a forming of a hole with a flat bottom or a polygonal section, a cutting, and a multi-point machining in a laser machining using a femtosecond pulse laser beam. <P>SOLUTION: The optical system is provided with a microlens array 2 composed of a plurality of concave or convex lenses which form a multiple circular form on which the femtosecond pulse laser beam 1, of which the light intensity distribution in the beam radius direction is Gaussian, is made incident, and an objective lens 3 which focuses respective laser beams, which are formed or deformed through respective lenses composing the microlens array 2, on an image plane 4. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a femtosecond pulse laser beam, which converts the light intensity distribution in the beam radial direction and the beam shape to make the femtosecond pulse laser beam a laser beam suitable for laser processing and the like. Special optical system using laser.

[0002]

2. Description of the Related Art Conventionally, a femtosecond (fs: ^10-12 sec) has been used as a laser beam suitable for laser fine processing.
It has been proposed to use a pulsed laser beam.
This femtosecond pulsed laser beam is completely different from the conventional carbon dioxide laser and nanosecond YAG laser when it is used for processing metals and transparent materials.
It is characterized in that it causes almost no thermal or chemical damage (deformation or deterioration) around the laser beam irradiation site.

In conventional laser processing, most of the light energy applied to the material to be processed is converted into heat energy, and the heat causes melting, decomposition, and scattering to proceed, whereas a femtosecond laser is used. When used, energy is concentrated on the material to be processed in a very short time, so nanoplasma, nanoshock, breakdown, lattice distortion, and shock wave are generated at ultra-high speed, and ablation (scattering) occurs before heat is generated. It is considered that, because the processing by the process proceeds, the processing of only the irradiation site is induced and the surrounding is not damaged, and the processing is performed cleanly.

Further, in processing a transparent material using a femtosecond pulse laser beam, since processing by multiphoton absorption progresses, it is possible to perform remote processing only inside the material three-dimensionally without damaging the material surface. is there. Furthermore, since the processing uses a non-linear phenomenon such as multiphoton absorption, processing resolution exceeding the diffraction limit of the wavelength of the irradiation light can be obtained despite using light.

As described above, in the laser processing using the femtosecond pulse laser beam, the processing mechanism is completely different from the conventional laser processing, the resolution is much higher, and the processing area is inside the material to be processed. Therefore, it is possible to realize an ultrafine processing technology of 100 nm or less, which is far beyond the conventional wisdom of laser processing.

[0006]

By the way, the processing using the femtosecond pulsed laser beam as described above is the first time due to the high temporal and spatial high photon density realized by the focused femtosecond pulsed laser beam. It will be possible. That is, in order to perform processing using the femtosecond pulse laser beam, the femtosecond pulse laser beam must be focused on the material to be processed.

When the femtosecond pulse laser beam is focused using a simple convex lens, the light intensity distribution of the femtosecond pulse laser beam incident on the convex lens in the beam radial direction is a Gaussian distribution. In the condensed light spot, the light intensity at the central portion becomes stronger than that at the peripheral portion. The light intensity distribution in the radial direction of this light spot is almost a Gaussian distribution. When processing is performed by irradiating the material to be processed with such a light spot, only the part irradiated with the central part of the light spot is processed as a deep hole, and the part irradiated with the peripheral part of the light spot is not much. It will not be processed. In addition, when processing is performed by moving such a light spot onto the material to be processed while irradiating it, only the portion where the central portion of the light spot passes is processed as a deep groove, and the portion where the peripheral portion passes is not so much. It will not be processed.

Therefore, in the processing using such a light spot, for example, when groove processing is performed, deep V-shaped groove processing is possible, but a flat bottom groove having a flat bottom surface is formed. Processing is extremely difficult. Further, in the processing using such a light spot, it is also difficult to form a hole whose opening has a polygonal shape such as a rectangular shape.

Therefore, the present invention has been proposed in view of the above circumstances, and in laser processing using a femtosecond pulse laser beam, various processing such as forming flat-bottomed grooves or polygonal holes is performed. It is intended to provide a special optical system using a femtosecond laser that enables processing.

[0010]

In order to solve the above problems, a special optical system using a femtosecond laser according to the present invention is a femtosecond pulse laser in which the light intensity distribution in the beam radial direction is a Gaussian distribution. It is provided with a microlens array including a plurality of convex lenses or concave lenses on which beams are incident, and an objective lens that forms an image on the image plane of each laser beam that has passed through each of the convex lenses or the concave lenses forming the microlens array. The special optical system is characterized in that the light intensity distribution of the femtosecond pulse laser beam on the image plane in the beam diameter direction is substantially rectangular.

In the special optical system using the femtosecond laser described above, each convex lens or concave lens in the microlens array has a multi-circular or polygonal shape of the entrance aperture, and a femtosecond image plane is formed. The beam shape of the pulsed laser beam is the shape of the entrance aperture of each convex lens or concave lens in the microlens array.

The special optical system using the femtosecond laser according to the present invention comprises a plurality of convex or concave cylindrical lenses on which the femtosecond pulsed laser beam having a Gaussian distribution in the light intensity distribution in the beam diameter direction is incident. And a objective lens for forming an image on the image plane of each laser beam that has passed through each convex or concave cylindrical lens that constitutes the microlens array. The special optical system is characterized in that the beam shape of the femtosecond pulse laser beam on the image plane is one line.

Further, the special optical system using the femtosecond laser according to the present invention comprises a plurality of convex or concave cylindrical lenses on which the femtosecond pulsed laser beam having a Gaussian distribution in the light intensity distribution in the beam diameter direction is incident. And a plurality of convex or concave cylindrical lenses whose axial direction intersects the plurality of convex or concave cylindrical lenses forming the first microlens array. A second microlens array on which the laser beam that has passed through the microlens array is incident, and each laser beam that has passed through the respective convex or concave cylindrical lenses forming the first and second microlens arrays are formed on the image plane. And an objective lens for The special optical system is characterized in that the beam shape of the femtosecond pulse laser beam on the image plane is a shape in which two lines intersect.

Further, the special optical system using the femtosecond laser according to the present invention comprises a plurality of convex lenses or concave lenses on which the femtosecond pulse laser beam having a Gaussian distribution in the light intensity distribution in the beam diameter direction is incident. A microlens array, a relay lens arranged at a confocal position with respect to each convex lens or concave lens forming this microlens array, and each laser beam passing through this relay lens is condensed on the image plane to form a plurality of lenses. And an objective lens for forming a light spot. In this special optical system, each light spot on the image plane corresponds to each convex lens or concave lens forming the microlens array, and is characterized by performing multipoint processing.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

[1] Configuration of Special Optical System Using Femtosecond Laser According to the Present Invention (1) A special optical system using a femtosecond laser according to the present invention, as shown in FIGS. It has a microlens array 2 on which the second pulse laser beam 1 is incident. The femtosecond pulse laser beam 1 is shown in FIG.
As shown in, the light intensity distribution in the beam diameter direction is a Gaussian distribution. In addition, the microlens array 2 is
A plurality of circular convex lenses or concave lenses are arranged in parallel two-dimensionally on a plane orthogonal to the optical axis to form a multi-circular shape.

The femtosecond pulse laser beam 1 is emitted by a femtosecond titanium sapphire laser (not shown). The femtosecond titanium sapphire laser has an oscillation wavelength of 800 nm,
Frequency 1kHz (or 300kHz), pulse width 15
A device having 0 fs (femtosecond) and an output of about 0.8 mJ / pulse (or 4 μJ / pulse) can be used.

The special optical system is provided with an objective lens 3 for forming an image on the image plane 4 of each laser beam that has passed through each lens of the microlens array 2. As shown in FIG. 1, when the microlens array 2 is composed of a plurality of convex lenses, the objective lens 3 is
Each laser beam that is diffused after being condensed through each convex lens forming the microlens array 2 is imaged on the image plane 4. In addition, as shown in FIG. 2, when the microlens array 2 is composed of a plurality of concave lenses, the objective lens 3 projects each laser beam diffused through each concave lens forming the microlens array 2 on the image plane. Four
Focus on top.

In this special optical system, the incident femtosecond pulse laser beam 1 has a Gaussian light intensity distribution in the beam diameter direction. The intensity distribution has a substantially rectangular shape as shown in FIG. Since the light intensity distribution in the beam diameter direction on the image surface 4 is thus substantially rectangular, if a material to be processed is placed on the image surface 4, processing for forming flat-bottomed grooves or flat-bottomed holes or cutting processing is performed. Can be easily performed, and even if the light intensity of the original femtosecond pulse laser beam 1 fluctuates, the width to be processed is hardly affected.

When the beam diameter on the image plane 4 is a, the aperture diameter of each lens in the microlens array 2 is D,
When the focal length of each lens in the microlens array 2 is F and the focal length of the objective lens 3 is f, the beam diameter a is shown as follows.

A = f × (D / F) In the processing using the femtosecond pulse laser beam, as described above, in addition to opaque materials such as metal and silicon, glass, crystal, sapphire, diamond and the like are used. A transparent material can also be processed as a material to be processed.

[2] Structure of special optical system using femtosecond laser according to the present invention (2) Further, in this special optical system, FIG. 5, FIG. 6 and FIG.
As shown in FIG. 5, the shape of the entrance aperture of each lens in the microlens array 2 is not a circle but a rectangle (FIG. 5),
It can be polygonal, such as rectangular (FIG. 6) or hexagonal (FIG. 7).

In this case, the beam shape of the femtosecond pulse laser beam on the image plane 4 becomes the shape of the entrance aperture of each lens in the microlens array 2 as shown in FIG. Since the beam shape on the image plane 4 becomes the shape of the entrance aperture of each lens of the microlens array 2, if a material to be machined is placed on the image plane 4, the holes are polygonal and flat-bottomed holes are easily drilled. be able to. Also,
In this case, the energy efficiency can be increased as compared with the case where the entrance aperture of each lens in the microlens array 2 is circular. This is because, in this case, there is no laser beam that is blocked by the portion between the lenses in the microlens array 2.

[3] Structure of special optical system using femtosecond laser according to the present invention (3) In this special optical system, as shown in FIG. 9, the light intensity distribution in the beam diameter direction is a Gaussian distribution. The microlens array 2 on which the femtosecond pulsed laser beam 1 is made incident can be constituted by a plurality of convex or concave cylindrical lenses. In the microlens array 2, the plurality of cylindrical lenses are formed in a state where the axes are parallel to each other on a plane orthogonal to the optical axis.

Each laser beam that has passed through each cylindrical lens forming the microlens array 2 is incident on the objective lens 3. When the microlens array 2 is composed of a plurality of convex cylindrical lenses, this objective lens 3 has an image plane of each laser beam that is diffused after being converged through each convex cylindrical lens that constitutes the microlens array 2. Image on 4. When the microlens array 2 is composed of a plurality of concave cylindrical lenses, the objective lens 3
Forms an image on the image plane 4 of each laser beam that diffuses through each concave cylindrical lens that constitutes the microlens array 2. The beam shape of the femtosecond pulse laser beam on the image plane 4 becomes one line shape.

The length of this linear beam is determined by the above equation (a = f × (D / F)). For example, when f is 4.5 mm and (D / F) is 0.1. At
It becomes 450 μm. Also, the width d of this linear beam
Is determined by the following formula based on the wavelength λ of the femtosecond pulse laser beam and the numerical aperture NA of the objective lens 3.

D = 0.63 × λ / NA The wavelength λ is 800 nm (0.8 μm) and the numerical aperture NA is 0.
55, the width d of the linear beam is about 1
μm.

Then, in this line-shaped beam,
The change in the light intensity in the length direction is suppressed to about ± 10% over the entire length.

Further, in this special optical system, as shown in FIG. 10, a microlens array consisting of the above-mentioned plurality of convex or concave cylindrical lenses is used as a first microlens array 2, and further the first in the axial direction. A second microlens, which comprises a plurality of convex or concave cylindrical lenses in a direction intersecting with the plurality of convex or concave cylindrical lenses forming the microlens array, and on which the laser beam that has passed through the first microlens array is incident An array 5 can be provided and configured.

In this case, the objective lens 3 causes an image plane 4
The beam shape of the femtosecond pulse laser beam imaged above is a cross shape in which two lines intersect. The length and width of each line forming this cross shape is 1 as described above.
This is similar to the case of the linear beam shape of a book. Also,
The angle at which these two lines intersect is equal to the angle formed by the axes of the respective convex or concave cylindrical lenses in the first and second microlens arrays.

[4] Structure of special optical system using femtosecond laser according to the present invention (4) Then, as shown in FIG. 11, this special optical system is a micro-beam on which the femtosecond pulse laser beam 1 is incident. The relay lens 6 may be arranged at a position that is confocal with respect to each lens forming the lens array 2, and each laser beam passing through the relay lens 6 may be incident on the objective lens 3.

In this case, the objective lens 3 condenses the plurality of parallel light fluxes emitted from the relay lens 6 onto the image plane 4 to form a plurality of light spots. Each light spot thus formed on the image plane 4 corresponds to each lens forming the microlens array 2.

Therefore, in this special optical system,
On the image plane 4, a plurality of light spots corresponding to the respective lenses forming the microlens array 2 are formed, and if a material to be processed is placed on the image plane 4, multipoint processing can be performed.

Further, in this special optical system, a light-shielding shutter 7 is provided corresponding to each lens constituting the microlens array 2 so that the femtosecond pulse laser beam 1 can be selectively transmitted from each lens. As shown in FIG. 12, a plurality of light spots are selectively formed on the image plane 4 to form a desired pattern.

That is, it is possible to form a pattern such as a character or a figure composed of a plurality of light spots on the image plane 4. If a material to be processed is placed on the image plane 4, it is possible to process a desired pattern such as characters and figures.

A liquid crystal shutter or the like can be used as the light-shielding shutter 7.

[0037]

As described above, in the special optical system using the femtosecond laser according to the present invention, with respect to the incident femtosecond pulse laser beam, the light intensity distribution in the beam radial direction is made substantially rectangular. The beam shape can be a polygonal shape, a line shape, a cross shape, or a predetermined pattern can be projected on the image plane.

That is, the present invention is a special optical system using a femtosecond laser capable of various processing such as forming a flat bottom groove or a polygonal hole in laser processing using a femtosecond pulse laser beam. Can be provided.

[Brief description of drawings]

FIG. 1 is a side view showing a configuration of a special optical system (a microlens array including a plurality of convex lenses) using a femtosecond laser according to the present invention.

FIG. 2 is a side view showing a configuration of a special optical system (a microlens array includes a plurality of concave lenses) using a femtosecond laser according to the present invention.

FIG. 3 is a graph showing a light intensity distribution of a femtosecond pulse laser beam incident on a special optical system using the femtosecond laser in the beam diameter direction.

FIG. 4 is a graph showing a light intensity distribution in a beam radial direction of a beam imaged on an image plane in a special optical system using the femtosecond laser.

FIG. 5 is a front view showing the shape (rectangle) of each lens forming the microlens array in the special optical system using the femtosecond laser.

FIG. 6 is a front view showing a shape (rectangular shape) of each lens forming a microlens array in a special optical system using the femtosecond laser.

FIG. 7 is a front view showing the shape (hexagon) of each lens forming the microlens array in the special optical system using the femtosecond laser.

8 is a front view showing a beam shape formed on an image plane in a special optical system using a femtosecond laser having the microlens array shown in FIGS. 5 to 7. FIG.

FIG. 9 is a perspective view showing a configuration of a special optical system using a femtosecond laser having a microlens array including a plurality of cylindrical lenses.

FIG. 10 is a perspective view showing a configuration of a special optical system using a femtosecond laser having two microlens arrays each including a plurality of cylindrical lenses.

FIG. 11 is a side view showing the configuration of a special optical system using a femtosecond laser for forming a plurality of light spots on the image plane.

12 is a front view showing a pattern composed of a plurality of light spots formed on an image plane in the special optical system using the femtosecond laser shown in FIG.

[Description of Reference Signs] 1 femtosecond pulse laser beam, 2 microlens array, 3 objective lens, 4 image plane, 5 2nd microlens array, 6 relay lens, 7 light-shielding shutter

Continued front page    (71) Applicant 502080508             Nakamura Osamu             10-21-301, Hiyoshidai 4th-cho, Takatsuki City, Osaka Prefecture (72) Inventor Kudryashov Igor             6-18-14, Nishikasai, Edogawa-ku, Tokyo             Ceremony Company Tokyo Instruments (72) Inventor, Shoji Suruga             1-4-1-305 Kiyoshincho, Edogawa-ku, Tokyo (72) Inventor Satoshi Kawada             4-1-1 Minoh, Minoh City, Osaka Prefecture (72) Inventor Osamu Nakamura             10-21-301, Hiyoshidai 4th-cho, Takatsuki City, Osaka Prefecture F term (reference) 5F072 JJ20 KK30 SS08 YY06

Claims (5)

[Claims] 1. A microlens array comprising a plurality of convex lenses or concave lenses to which a femtosecond pulsed laser beam having a Gaussian distribution in the light intensity distribution in the beam diameter direction is incident, and each of the convex lenses constituting the microlens array or An objective lens for forming an image on the image plane of each laser beam that has passed through the concave lens, and the light intensity distribution of the femtosecond pulsed laser beam in the beam diameter direction on the image plane is substantially rectangular. Special optical system using femtosecond laser. 2. A convex lens or a concave lens in the microlens array has an entrance aperture of a multi-circular shape or a polygonal shape, and a beam shape of a femtosecond pulse laser beam on the image plane is the microlens array. The special optical system using a femtosecond laser according to claim 1, wherein the convex lens or the concave lens has a shape of an entrance aperture. 3. A microlens array comprising a plurality of convex or concave cylindrical lenses on which a femtosecond pulsed laser beam having a Gaussian distribution in light intensity distribution in the beam radial direction is incident, and each of the microlens arrays constituting the microlens array. An objective lens for focusing each laser beam passing through a convex or concave cylindrical lens on an image plane, and the beam shape of the femtosecond pulse laser beam on the image plane is one line shape. Special optical system using femtosecond laser. 4. A first microlens array comprising a plurality of convex or concave cylindrical lenses on which a femtosecond pulsed laser beam having a Gaussian distribution in light intensity distribution in the beam radial direction is incident, and the first microlens array in the axial direction is A plurality of convex or concave cylindrical lenses forming a single microlens array, the plurality of convex or concave cylindrical lenses intersecting each other, and the laser beam that has passed through the first microlens array is incident. And an objective lens for forming an image on the image plane of each laser beam that has passed through each of the convex or concave cylindrical lenses forming the first and second microlens arrays. The beam shape of the second pulsed laser beam is such that two lines intersect. A special optical system that uses a femtosecond laser. 5. A microlens array comprising a plurality of convex lenses or concave lenses to which a femtosecond pulsed laser beam having a Gaussian distribution in the light intensity distribution in the beam diameter direction is incident, and each convex lens forming the microlens array, or A relay lens arranged at a position confocal with respect to the concave lens, and an objective lens for converging each laser beam passing through the relay lens on an image surface to form a plurality of light spots, Each light spot in 2 corresponds to each convex lens or concave lens forming the above-mentioned microlens array, and is a special optical system using a femtosecond laser characterized by performing multipoint processing.