JP2001276985A - Marking method and equipment, and marked optical member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a marking method capable of easily recognizing an existence of a marking without using a special reading equipment and also capable of avoiding a destruction of material and a deterioration of material strength. SOLUTION: A transparent glass substrate 1 is provided for a marking object. A laser beam with a wavelength capable of permeating a material forming the transparent glass substrate 1 is focused inside the transparent glass substrate 1 so as to cause a multiphoton absorption. A focusing position of the laser beam is moved so that a range of a changed refractive index caused by the multiphoton absorption can provide for a diffraction pattern causing a visible light to diffract.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for converging a laser beam inside a transparent material, changing the optical properties of the converged portion, and forming a mark.

[0002]

2. Description of the Related Art Conventionally, as a method of marking inside a transparent material, Japanese Patent Application Laid-Open No. Hei 6-500275 and Japanese Patent Application Laid-Open No.
The methods disclosed in, for example, Japanese Patent Publication No. -136782 and Japanese Patent No. 2810151 are known. Each of these methods is a method of condensing a laser beam inside a transparent material and generating a crack inside by a nonlinear absorption effect. The opaque part due to the crack constitutes a mark. In order to obtain a clear mark using such a marking method, it is necessary to increase cracks. However, if the cracks are increased, the strength of the material may be reduced, or the cracks may reach the surface and may be broken.

As disclosed in Japanese Patent Application Laid-Open No. 11-13896, the inventor of the present application has already attempted a laser beam irradiation method for performing special control to form a crack only inside a thin glass substrate.

Further, the inventor of the present application disclosed in Japanese Patent Laid-Open No. 11-267.
As disclosed in Japanese Patent No. 861, regardless of crack generation,
A method of causing a change in the refractive index and using the mark as a mark was also developed. In this method, cracks are not generated, so that the possibility of breakage can be further reduced as compared with the method disclosed in JP-A-11-13896.

[0005]

In the above method using the change in the refractive index, the size of the mark becomes extremely small. Therefore, it is necessary to use a special reading device to detect the presence of the mark. In other words, the above method is suitable for forming “hidden marks”, but is not very suitable for general marking.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a marking method and apparatus which can relatively easily confirm the presence of a mark without using a special reading device and which can avoid destruction of a material and a decrease in strength. Display device.

[0007]

According to one aspect of the present invention, there is provided a step of preparing a marking object, and applying a laser beam in a wavelength range that transmits a material forming the marking object to the inside of the marking object. The marking method includes a step of converging and multi-photon absorption, and a step of moving the convergence position of the laser light so that a region having a changed refractive index due to multi-photon absorption forms a diffraction pattern for diffracting visible light. Provided.

According to another aspect of the present invention, a stage on which a marking object is placed, a light source for generating laser light in a wavelength range that transmits a material forming the marking object, and the laser from the light source An optical system that causes light to converge inside the marking object and absorbs multiphotons, and an altered region formed by multiphoton absorption at the convergence position of the laser light forms a diffraction grating that diffracts visible light. Thus, there is provided a marking device having moving means for moving the convergence position.

In the above method and apparatus, the laser beam having a relatively low photon energy is used because the laser light in the wavelength range that passes through the material forming the marking object is converged into the inside of the marking object and multiphoton absorbed. However, by using this, a relatively large change in the optical characteristics (for example, the refractive index) can be caused by limiting the focus point inside the marking object. Unlike the case of a crack, such a change in the optical characteristics does not destroy the marking object or cause a decrease in strength. Further, in the above method, the region where the refractive index has changed diffracts visible light. Therefore, macroscopically, the formed mark is recognized as a change in brightness or color.

[0010] According to another aspect of the present invention, a pattern composed of portions having different optical characteristics is formed inside,
And an optical member formed of a material that transmits visible light, wherein the pattern is a pattern that diffracts visible light.

[0011] By the diffraction of visible light, a mark composed of a pattern composed of portions having different optical characteristics is recognized as a change in brightness or color. This mark can be used as an identification code for the device. Further, the optical member can be given a value as a decorative article with a colorful mark.

According to another aspect of the present invention, the object to be processed is irradiated with a pulsed laser beam by changing the NA of the objective lens and the energy per pulse, thereby forming an altered region at the focal point of the laser beam. A first step, a second step of determining the relationship between the length of the formed altered region, the NA and the energy per pulse, a third step of determining the length of the altered region to be formed, From the relationship determined in the process and the length of the altered region to be formed, the NA to be used
And a fourth step of determining the energy per pulse;
A laser beam is focused on the workpiece with the determined NA and the energy per pulse, and a fifth step of forming a deteriorated region is provided.

By appropriately selecting the NA and the energy per pulse, it is possible to form an altered region having a desired length.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A marking device and method according to an embodiment of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a perspective view schematically showing a marking device 10 according to an embodiment of the present invention. Marking device 1
Reference numeral 0 denotes a laser light source 11 that generates laser light in a wavelength range that passes through the transparent glass substrate 1 as a marking target, a beam shaper 12 that shapes the beam shape of the laser light emitted from the laser light source 11, and a transparent glass A galvano scanner 13 for moving the convergence position of the laser light formed in the substrate 1 along a predetermined pattern, and an fθ lens 1 for condensing the laser light at a desired depth in the transparent glass substrate 1
4 and a stage 15 on which the transparent glass substrate 1 is placed and which is appropriately moved in the XY plane.

As the laser light source 11, for example, a mode-locked Ti: sapphire laser can be used.
The laser light source 11 has, for example, a pulse width of 130 fs and a wavelength of 8
A pulsed laser beam having a wavelength of 00 nm, an average output of 1 W, and a repetition frequency of 1 kHz is output. As the laser light source 11,
Ti: In addition to sapphire laser, YAG laser, YLF
A laser diode (LD) pumped solid-state laser oscillator such as a laser can also be used. Various laser light sources that generate harmonics of the fundamental wave output from the laser oscillators can also be used.

The galvano scanner 13 includes a mirror driving device that rotationally drives a pair of galvanometer mirrors 13a and a high-brightness position detecting device. The galvano scanner 13 scans a beam spot formed in the transparent glass substrate 1 by the fθ lens 14 with XY.
It can be moved to any point in the plane. The galvano scanner 13 is controlled by the computer 20 via the drive unit 13b. The computer 20 synchronizes the drive of the galvano scanner 13 with the pulse oscillation of the laser light source 11.

The fθ lens 14 not only focuses the laser light on the transparent glass substrate 1 but also keeps the focus of the laser light at a constant depth during scanning by the galvano scanner 13. It is needless to say that the same effect can be obtained by moving the fθ lens 14 in the Z direction instead of moving the transparent glass substrate 1 in the Z direction by operating the stage 15.

At the focal point of the laser beam formed by the fθ lens 14, an altered portion having a change in the refractive index is formed. By scanning such a condensing point by the galvano scanner 13, a desired pattern including a deteriorated portion can be formed. When such a pattern constitutes, for example, a diffraction grating that diffracts visible light, this pattern is visually recognized by the diffracted light.

The stage 15 holds the far-light glass substrate 1 in XY
The mark formation position is adjusted by moving the mark to an arbitrary position in the plane. By driving the galvano scanner 13, a unit diffraction pattern including a deteriorated portion is formed. By appropriately operating the stage 15,
A plurality of unit diffraction patterns can be formed at arbitrary positions in the transparent glass substrate 1. Thus, a display device in which marks representing figures, characters, symbols, and the like are embedded is obtained. The operation of the stage 15 is controlled by the computer 20, and is synchronized with the Carpano scanner 13 and the laser light source 11.

The stage 15 can finely move the transparent glass substrate 1 in the Z direction. Thereby, the depth of the mark formed in the transparent glass substrate 1 can be adjusted. For example, a first depth in the transparent glass substrate 1
By forming the second mark and forming the second mark at the second depth, a mark having a multilayer structure can be formed. Furthermore, the marks arranged three-dimensionally can be formed by moving the stage 15 stepwise in three dimensions while forming diffraction marks by using the galvano scanner 13 or the like.

The transparent glass substrate 1 only needs to transmit laser light from the laser light source 11 and generate efficient multiphoton absorption of the laser light. However, in order to visually recognize the diffraction mark formed inside, it is necessary that the diffraction mark substantially transmits visible light. For example, GeO ₂ —SiO ₂ glass or the like can be used. It has also been confirmed that diffraction marks can be formed on various materials such as soda-lime glass and quartz glass.

The operation of the apparatus shown in FIG. 1 will be described below. First, the transparent glass substrate 1 is placed on the stage 15, and a portion where a diffraction mark is to be formed is moved directly below the fθ lens 14 (step S1).

Next, the galvano scanner 13 is operated in synchronization with the laser light source 11 to scan the focal point of the laser light (step S2). At this time, since the laser light source 11 generates an ultrashort pulse on the order of femtoseconds, multiphoton absorption occurs efficiently at the focal point. If such multiphoton absorption is utilized, energy can be injected by infrared laser light which does not originally absorb. As a result, a relatively large change in optical characteristics such as a refractive index can be caused only at the converging point. Such a change in the characteristics is caused by the transparent glass substrate 1
Is an optical non-linear phenomenon formed due to a change in density, a change in a bonding state, or the like, and permanently remains in glass to form a deteriorated portion. Such a deteriorated portion is formed in the transparent glass substrate 1 along the scanning locus of the galvano scanner 13.

When the laser beam is scanned so that the altered portion forms a Bragg diffraction grating, a Bragg diffraction grating is formed. When visible light enters this diffraction grating, light diffracted in a direction corresponding to the grating interval is emitted. For example, when the diffraction grating is illuminated with white light and observed at different angles, the mark appears to change to a rainbow color. Furthermore, when this diffraction grating is illuminated with monochromatic light, light diffracted at a specific angle corresponding to the wavelength of the monochromatic light is emitted. When this is observed through a filter that transmits only monochromatic light, a high S
The mark can be detected by the / N ratio. Note that the contour of the scanning area forming the diffraction grating is not limited to a rectangle, but may be a circle or another figure.

Next, the scanning of the laser beam is temporarily stopped, and the stage 15 is operated to move the transparent glass substrate 1.
As a result, the focal point of the laser beam is moved to a position where a diffraction grating is to be formed next (step S3).

As in step S2, the galvano scanner 13 is operated so that the laser light source 11 and the laser light source 11 are synchronized with each other, and scans the focal point of the laser light. Thereby, a diffraction grating can be formed also at this position (step S4).

By repeating the above steps S3 and S4, diffraction gratings can be sequentially formed at desired positions. Marks that are recognized as figures, characters, and symbols as a whole can be formed in the transparent glass substrate 1.
This mark may be any pattern as long as it can be visually recognized, may be an identification code, or may be a decoration having no meaning in itself.

In the marking device of FIG. 1 described above,
The laser beam is scanned in the in-plane direction of the transparent glass substrate 1 by the galvano scanner 13 to form a diffraction grating.
Laser light can be scanned using a drive system of the stage 15 instead of the galvano scanner 13. In this case, since it is not necessary to operate the galvano scanner 13, the galvano scanner 13 can be replaced with a simple deflecting mirror. Also, instead of the fθ lens 14,
An ordinary objective lens, for example, a microscope objective lens can be used. It is desirable that the drive system of the stage 15 be operated at high speed and with high accuracy.

Furthermore, the diffraction grating can be formed by scanning the laser beam using the galvano scanner 13 and the drive system of the stage 15 together. In this case, for example, relatively high-speed scanning by the galvano scanner 13 is defined as main scanning, and relatively low-speed scanning by the drive system of the stage 15 is defined as sub-scanning.

Hereinafter, a specific example of manufacturing a mark will be described. In the following example, a diffraction mark was formed by scanning a laser beam using only the drive system of the stage 15. Also, instead of the fθ lens 14, the focal length is 10
A microscope objective with a numerical aperture (NA) of 0.23 mm was used. The energy per pulse of the laser beam passing through this lens is about 0.2 to 0.4 μJ / pulse.

FIGS. 2A and 2B are a front view and a plan view, respectively, of a deteriorated region formed around the focal point by a single-pulse laser beam. FIG. 2A is a diagram of the altered region viewed from a direction perpendicular to the optical axis direction.
(B) is a diagram viewed along the optical axis direction. The intensity distribution in the beam cross section of the laser light is infinitely rotationally symmetric with respect to the optical axis OA. The deteriorated region 1a obtained in the example has a rod shape along the optical axis OA, a diameter AD of about 1 μm and a length A
L was about 20 to 30 μm.

Note that, despite the fact that the focal depth of the condenser lens is about 5 μm, the altered region 1a
It extends to 0 μm. This phenomenon occurs because
It is considered that the self-condensing effect due to the optical Kerr effect is balanced with the diffraction. Further, it is considered that the self-condensing effect is caused by thermal nonlinearity.

Next, another embodiment in which the laser light focusing condition is changed will be described. A lens with a focal length of 100 mm and NA of 0.05, energy per pulse 2 μJ
/ Length of about 50
An altered region having a diameter of 0 μm and a diameter of about 1 to 2 μm was formed. The laser used was Ti: sapphire laser,
The repetition period is 1 kHz, the wavelength is 800 nm, and the pulse width is about 130 fs.

For reference, the self-condensing effect in the latter embodiment was evaluated by calculating the temperature rise after condensing one pulse light in the glass. In order to calculate the temperature rise, the following three-dimensional heat diffusion equation (1) was analyzed.

[0036]

１u / ∂t = a ｛(∂ ² / ∂x ² ) u + (∂ ² / ∂y ² ) u + (∂ ² / ∂z ² ) u｝ (1) where u Is the temperature, t is the time, and a is the diffusion coefficient. The energy absorption of the laser pulse is Lambert-Bee
Following r's law, the initial temperature distribution was assumed to be Gaussian. As the temperature u at t = 0, 10 ⁶ K was used, and as a heat temperature coefficient of glass, -10 ^-7 was used. Since the repetition frequency of the laser pulse is 1 kHz, the pulse interval was 1 ms. As a result of the calculation, the residual temperature rise is
1 irradiated with a pulse laser beam having a pulse width of 130 fs
It was about 10 ° C. after ms. After all, when the number of incident pulses increases, the thermal self-focusing effect becomes important.

FIG. 3 shows the trajectory of the focal point of the laser beam when the stage 15 is operated. The horizontal direction in FIG. 3 is the main scanning direction, and the vertical direction is the sub-scanning direction. The speed of the main scanning is 0.1 mm / s, and the interval between the scanning lines (the pitch of the sub-scanning) is 4 μm. By this scanning, 1 mm x 1 mm
A Bragg diffraction grating is formed in the range of the square.

Since the main scanning speed is 0.1 mm / s, the interval between the affected areas in the main scanning direction is 0.1 μm.
Since the diameter of the altered region formed in one shot is 1-2 μm, the altered regions are arranged continuously in the main scanning direction.

FIG. 4 shows a diffraction grating formed in a scanning area in the transparent glass substrate 1. FIG. 4A shows a step of manufacturing the first-layer Bragg diffraction grating 30. FIG.
(B) shows a step of manufacturing the second-layer Bragg diffraction grating 30. The direction of the grating vector of the diffraction grating is in the X direction, and the main scanning direction of the focal point of the laser beam is in the Y direction.
Consider an XYZ orthogonal coordinate system as a direction.

The diffraction grating is constituted by a Bragg diffraction grating 30 having a two-layer structure overlapping in the Z direction. The thickness T of the Bragg diffraction grating 30 for one layer is 30 μm. The first-layer Bragg diffraction grating 30 and the second-layer Bragg diffraction grating 3
The displacement S in the optical axis direction (Z direction) from 0 was set to 30 μm, which is almost equal to the thickness T. The diffraction grating 30 of the second layer
When the diffraction grating of the layer is moved in parallel in the Z direction by the displacement S, the diffraction grating of the second layer overlaps the diffraction grating of the second layer. Thereby, the thickness 6
A 0 μm diffraction grating is obtained. Although the details will be described later, the diffraction efficiency of the obtained diffraction mark was about ten and several percent.

Hereinafter, the change in the refractive index occurring in the Bragg diffraction grating 30 will be described. Kogelnik's coupled mode theory gives equation (2) to evaluate the magnitude of the refractive index change.

[0042]

Η = sin ² (πn ₁ T / λ ₀ cos θ _B ) (2) where η is the diffraction efficiency, n ₁ is the intensity of the refractive index change, T is the thickness of the grating, λ ₀ Represents the wavelength of the incident beam, and θ _B represents the incident angle of Bragg. The Bragg condition is

[0043]

K _s = k _i + K (3) Here, k _s is the diffraction wave vector, k _i is the incident wave vector, K is representative of the grating vector.

The refractive index distribution is assumed to be sinusoidal in the above theory. The refractive index change of the formed grating is different from a sine wave, and has a shape like a comb-shaped function. This is because the change in the refractive index caused by the laser pulse is localized near the focal point. In this evaluation, it was assumed that the formed diffraction grating was a superposition of sinusoidal diffraction gratings. The refractive index change n (x) is

[0045]

(4) n (x) = (Σ^m _{L = 1}n_Lcos (Lπx / Λ) (4) Where m is an integer and x is a diffraction grating vector
Coordinates along the direction of n _LIs a sinusoidal refractive index diffraction grating
Represents the period of each diffraction grating.

The refractive index distribution was evaluated by using the above equations (2), (3) and (4). Since the change in the refractive index is usually small (about 10 ^-3 ), Born's first-order approximation was used. In this first approximation, it is assumed that light rays diffracted by one grating are not diffracted by another diffraction grating. High-order diffracted light was obtained by changing the angle of incidence using a light beam of a He-Ne laser as an incident light beam. Although it was possible to observe up to the fifth-order diffracted light, since the intensity of the diffracted light of the higher order than the third order is less than 0.1% of the zero-order light,
In Equation (4), even the third-order diffracted light is included.

Table 1 below shows the measurement results at the stage when only the first layer Bragg diffraction grating 30 was manufactured.

[0048]

[Table 1]

FIG. 5 shows the distribution of the evaluated refractive index change. The horizontal axis represents the displacement from the reference point in the direction along the grating vector in the unit of “μm”, and the vertical axis represents the refractive index change n (x). FIG. 5 shows that the amount of change in the refractive index is 1.5 × 10
^-3 . The total scattering loss of the formed diffraction grating is 15%. The high scattering loss and low diffraction efficiency are believed to be due to local destruction and inhomogeneities such as voids. It is considered that the refractive index increases in the region around the void due to the increase in the density of the glass, and the refractive index decreases in the region around the void. The refractive index change evaluated in this experiment is considered to be a value obtained by averaging the refractive indices of a region where only the refractive index has changed without generating voids and a void portion.

Equation (2) shows that the diffraction efficiency increases as the thickness of the diffraction grating increases. In the case where a two-layer diffraction grating is manufactured by moving the focal point along the optical axis in order to increase the thickness of the diffraction grating (see FIG. 4B),
The diffraction efficiency of the first-order diffracted light increased to 13%.

In the above embodiment, the pitch of the Bragg diffraction grating 30 is fixed at 4 μm. However, the pitch of the diffraction grating may be a periodic modulation. For example, the pitch of the diffraction grating is 4 μm, 5 μm, 6 μm, 7 μm,
The modulation may be applied so that the pitch monotonically increases, such as 4 μm, 5 μm, 4 μm, 5 μm,.
Modulation may be applied so that the pitch periodically varies, for example, μm,.

In the above embodiment, the case where the Bragg diffraction grating is used as the diffraction grating has been described. However, instead of the Bragg diffraction grating, for example, a Fresnel zone plate can be used. This makes it possible to form a constant light and dark pattern or the like. Further, the diffraction grating not only allows the mark to be visually recognized, but also functions as a beam splitter that disperses light of a specific wavelength (color).

Hereinafter, an example of manufacturing a Fresnel zone plate will be described. The zone plate converges off-axis divergent light symmetrically to a point on the optical axis. The width Λ _L of the L-th zone is given by the following equation. Λ _L = λ / (2 sin θ _L ) θ _L = tan ⁻¹ (r _L / f) (5) where θ _L is the L-th diffraction angle, λ is the wavelength of the incident light, r _L indicates the outer radius of the L-th zone, and f indicates the distance to the focal point. In the experiment, λ = 633 nm, f = 50 m
m, is the r _L = 4 to 5 mm, the period lambda _L is 4.0 to 3.2
μm. The size of the zone plate is 1mm x 1
mm. A He-Ne laser beam (wavelength 633 nm) diverging from the lens is applied to the zone plate,
The diffracted light with A of 0.1 was collected on the light receiving surface of the CCD. FIG.
(A) and (b) show the X direction and Y of the focal point, respectively.
3 shows an intensity distribution of a cross section along a direction. The spot diameter was about 80 μm, and the diffraction efficiency was 2.9%. Diffraction limited operation (about 4μm) due to aberration of thick zone plate
Was not obtained.

Hereinafter, a diffraction grating composed of a spot array will be described. FIG. 7 is a plan view conceptually illustrating the arrangement of the produced spot arrays. This diffraction grating
A matrix MS of 25 × 25 points is formed at a pitch of 4 μm, and this matrix MS is converted into a matrix of 3 × at a pitch of about 200 μm.
It is obtained by arranging at three places.

Hereinafter, the manufacturing conditions of the diffraction grating will be described. As the laser light source 11, a Ti: sapphire laser is used. The repetition frequency is 1 kHz, the wavelength is 800 nm,
The pulse width is 130 fs. The numerical aperture NA of the objective lens for condensing the laser beam on the transparent glass substrate 1 is 0.3
It is. The energy per pulse during writing at the focal point was 0.68 μJ / pulse, and the exposure time at each focal point was 1 s. With the diffraction grating obtained as described above, clear visibility due to diffraction was obtained rather than simply increasing the number of marks.

Next, another embodiment of the present invention will be described. The energy per pulse is 1.9 μJ / pulse, the focal length of the objective lens is 100 mm, and the NA is 0.0
As No. 5, a Ti: sapphire laser was focused inside the glass substrate. The repetition frequency and wavelength of the pulse oscillation are the same as in the above embodiment.

FIG. 8 is an enlarged front view of a deteriorated region formed by changing the exposure time. It can be seen that when the exposure time is increased, the altered region extends toward the upstream side of the laser beam. The deteriorated region when the exposure time was set to 0.5 minutes was difficult to recognize, and the deteriorated region when the exposure time was set to 0.25 minutes was hardly observed.

Next, the irradiation time was set to 2 minutes, and the altered area was formed by changing the energy per pulse. It was found that when the energy per pulse increased, the altered region extended toward the upstream side of the laser beam. The energy per pulse is 1.8 μJ / pulse, 2, 3 μJ /
When the pulse is set to 2.8 μJ / pulse, 3.5 μJ / pulse, and 4.4 μJ / pulse, the length of the altered region is:
450 μm, 500 μm, 800 μm, 900 respectively
μm, and 1000 μm.

The energy per pulse is 0.9-1.
At 8 μJ / pulse, one thread-like altered region was formed. However, the energy per pulse is 2.3 ~
At 7.0 μJ / pulse, an altered region was formed as if a plurality of thread-like portions were bound. In order to form an altered region composed of one thread-like portion, it is preferable that the energy per pulse be 0.9 to 1.8 μJ / pulse.

The energy per pulse is 10 μm.
When it was larger than J / pulse, an altered region in which the granular portions were irregularly arranged along the optical axis of the laser beam was formed. Therefore, in order to form a thin thread-like altered region,
It is preferable that the energy per pulse be 10 μJ / pulse or less.

It has been found that there is a suitable range for NA and energy per pulse in order to form an altered region consisting of one thread-like portion. NA of 0.05, 0.
The preferable values of the energy per pulse at 1 and 0.3 are 1.1 to 2.3 μJ / pulse and 0.9, respectively.
２．０2.0 μJ / pulse and 0.3-0.5 μJ / pulse.

When the altered area is formed under these conditions, the altered area becomes longer as the exposure time increases. However, it was found that when the exposure time reached a certain length, the increase in the length of the altered region was saturated. When the NA is 0.05, the saturation time is about 30 minutes, and the length of the altered region at that time is about 50 minutes.
It was 0 μm. The saturation time when NA is 0.1 is about 10
Min, and the length of the altered region at that time was about 200 μm. When the NA is 0.3, the saturation time is about 5 minutes,
The length of the altered region at that time was about 40 μm. Therefore, it is understood that it is necessary to reduce NA in order to form a long altered region.

Hereinafter, a method of forming a deteriorated region having a desired length will be described. A deteriorated region is formed in the object to be processed with various NAs and energy per pulse in advance, and the relationship between NA, energy per pulse, and the saturation length of the deteriorated region is examined. From this relationship, the NA and the energy per pulse at which the saturation length of the altered region is substantially equal to the length of the desired altered region are determined. By performing the laser processing under the determined conditions, it is possible to form an altered region having a desired length. The longer the deteriorated area, the higher the visibility of the mark. Further, when the object to be processed is thin, it is preferable to shorten the altered region in accordance with the thickness.

In the above embodiment, a pulse laser beam having a pulse width of 130 fs was used. However, it was confirmed that a similar altered region could be formed by using a pulse laser beam having a pulse width on the order of picoseconds.

The mark formed in the above embodiment can be used as a component identification code. In addition, a member such as glass marked inside can visually recognize diffracted lights of various colors, and thus can have a value as a decorative article.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0067]

As described above, according to the present invention,
By forming a diffraction grating in the altered region in which the optical property has changed, a mark that is easily visible can be obtained. Also,
By appropriately selecting the NA of the objective lens and the energy per pulse, a deteriorated region having a desired length can be formed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a structure of a marking device that performs a method for marking a light transmitting material according to an embodiment of the present invention.

FIG. 2 is a side view and a front view of a deteriorated portion formed by the apparatus of FIG. 1;

FIG. 3 is a diagram illustrating a scanning pattern of a laser beam.

FIG. 4 is a diagram showing a structure of a Bragg diffraction grating formed in a glass substrate.

FIG. 5 is a graph illustrating a change in the diffraction index of the Bragg diffraction grating of FIG. 4;

FIG. 6 is a diagram illustrating light collection by a Fresnel zone plate.

FIG. 7 is a diagram illustrating a diffraction pattern formed of a spot array.

FIG. 8 is an enlarged front view of a deteriorated region formed by changing an exposure time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent glass substrate 10 Marking device 11 Laser light source 12 Beam shaper 13 Galvano scanner 13a Galvano mirror 14 Lens 15 Stage 20 Computer 30 Bragg diffraction grating OA Optical axis

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 5/18 G02B 5/18 F term (Reference) 2H049 AA06 AA12 AA33 AA45 AA60 AA65 4E068 AB01 CA11 CB08 CE02 CE04 DA11 DB13 4G059 AA11 AB19 AC09

Claims (7)

[Claims] A step of preparing a marking object; a step of converging laser light in a wavelength range that transmits a material forming the marking object into the marking object to absorb multiphotons; Moving the convergence position of the laser beam so that the region whose refractive index has changed due to photon absorption constitutes a diffraction pattern for diffracting visible light. 2. The marking method according to claim 1, wherein the diffraction pattern is a Bragg diffraction pattern. 3. The step of moving the convergence position, the step of moving the convergence position so as to form a first pattern arranged along a certain virtual plane; Moving the convergence position so as to form a second pattern obtained by translating in the normal direction. 4. A stage on which a marking target is placed, a light source that generates laser light in a wavelength range that transmits a material forming the marking target, and the laser light from the light source is applied to the marking target. An optical system that converges inside and multi-photon absorption, and a condensed position formed by multi-photon absorption at the convergence position of the laser beam so that the converged position is configured to form a diffraction grating that diffracts visible light. And a moving means for moving. 5. An optical member having a pattern formed of portions having different optical characteristics formed therein and made of a material that transmits visible light, wherein the pattern is a pattern that diffracts visible light. The optical member as described above. 6. The object to be processed is provided with an NA of the objective lens and 1
A first step of changing the energy per pulse to irradiate a pulsed laser beam to form a deteriorated region at the focal point of the laser beam; and determining the length of the formed deteriorated region, the NA, and the energy per pulse. A second step for determining the relationship, a third step for determining the length of the altered region to be formed, and the NA and one pulse to be used from the relationship determined in the second step and the length of the altered region to be formed. A marking method comprising: a fourth step of determining an energy per unit area; and a fifth step of condensing a laser beam on the object to be processed with the determined NA and energy per pulse to form an altered region. 7. The marking method according to claim 6, wherein in the first step, the altered region is exposed to a laser beam until the length of the altered region is saturated to form an altered region having a saturated length.