Patent Description:
<CIT> (PTL <NUM>) discloses a diffractive optical element (DOE) that converts a circular laser beam into a line beam. The line beam is used to process a workpiece. <CIT> describes a diffraction optical element, lighting system, and sensor device.

A diffractive optical device of the present disclosure is provided, in accordance with claim <NUM>. The diffractive optical device includes at least one diffractive optical element. The at least one diffractive optical element generates light having a first order and light having a second order from a laser beam input to the at least one diffractive optical element, and superimposes the light having the first order and the light having the second order on each other on an optical axis of the laser beam to cause interference between the light having the first order and the light having the second order, the light having the first order and the light having the second order having diffraction orders different from each other. The at least one diffractive optical element includes a first phase pattern and a second phase pattern. The first phase pattern converts the laser beam into a line beam. The second phase pattern diffracts the laser beam in a short axis direction of the line beam to generate the light having the first order and the light having the second order. A first focal plane of the light having the first order is located at a position different from a second focal plane of the light having the second order on the optical axis of the laser beam.

In order to obtain a line beam, a diffractive optical element converges a laser beam more intensely in the short axis direction of the line beam than in the long axis direction of the line beam. When displaced from the focal plane of the diffractive optical element, the line beam is diverged abruptly in the short axis direction of the line beam. Therefore, the focal depth of the line beam is short. When a workpiece is processed using such a line beam having a short focal depth, processing characteristics for the workpiece are greatly varied in response to only a slight change being made in a distance between the diffractive optical element and the workpiece. It is an object of the present disclosure to provide a diffractive optical device by which a line beam having a longer focal depth can be obtained.

According to the diffractive optical device of the present disclosure, a line beam having a longer focal depth can be obtained.

First, embodiments of the present disclosure are listed and described.

Therefore, a line beam having a longer focal depth can be obtained. The light intensity distribution of the line beam becomes more uniform in the short axis direction of the line beam without exerting an influence in the long axis direction of the line beam. The first phase pattern and the second phase pattern may be more precisely positioned with respect to each other.

Details of embodiments will be described below with reference to figures. It should be noted that in the figures, the same or corresponding portions are denoted by the same reference characters, and will not be described repeatedly. At least parts of the configurations of the embodiments described below may be combined appropriately.

A laser beam irradiation device <NUM> of a first embodiment will be described with reference to <FIG>. As shown in <FIG>, laser beam irradiation device <NUM> is, for example, a device that irradiates a workpiece <NUM> with a line beam <NUM>. Workpiece <NUM> is processed using line beam <NUM>, for example. Workpiece <NUM> is, for example, a semiconductor wafer, a glass substrate, a thin film formed on a substrate or the like. Laser beam irradiation device <NUM> includes a laser light source <NUM> and a diffractive optical device <NUM>.

Laser light source <NUM> is, for example, a solid-state laser or a gas laser. Examples of the solid-state laser include a fiber laser, a semiconductor laser, and a YAG laser. Examples of the gas laser include a carbon dioxide gas laser. Laser beam <NUM> output from laser light source <NUM> is input to diffractive optical device <NUM>. As shown in <FIG>, laser beam <NUM> has a circular cross sectional shape, for example. The light intensity distribution of laser beam <NUM> in the cross section of laser beam <NUM> is, for example, Gaussian distribution. In the present specification, the cross section of the light beam (for example, laser beam <NUM> or line beam <NUM>) refers to a cross section thereof perpendicular to the optical axis of the light beam (optical axis <NUM> of laser beam <NUM> or optical axis <NUM> of diffractive optical device <NUM>). The cross sectional shape of the light beam (for example, laser beam <NUM> or line beam <NUM>) refers to the shape of the light beam in the cross section perpendicular to the optical axis of the light beam (for example, optical axis <NUM> of laser beam <NUM> or optical axis <NUM> of diffractive optical device <NUM>). In the present specification, a direction along optical axis <NUM> is referred to as "z axis direction".

Diffractive optical device <NUM> can convert laser beam <NUM> (see <FIG>) into a line beam <NUM> (see <FIG>) that is more elongated than laser beam <NUM>. That is, diffractive optical device <NUM> can convert laser beam <NUM> into a line beam <NUM> having an aspect ratio larger than the aspect ratio of laser beam <NUM>. The aspect ratio of a beam represents a degree of elongation of the beam. In the present specification, the long axis direction of line beam <NUM> is referred to as "x axis direction", and the short axis direction of line beam <NUM> is referred to as "y axis direction". Further, diffractive optical device <NUM> can attain a long focal depth of line beam <NUM>.

As shown in <FIG>, diffractive optical device <NUM> includes at least one diffractive optical element (diffractive optical element <NUM>). The at least one diffractive optical element is composed of an optical material transparent to laser beam <NUM>, such as glass or a transparent resin.

The at least one diffractive optical element (diffractive optical element <NUM>) includes a first phase pattern <NUM> shown in <FIG> and a second phase pattern <NUM> shown in <FIG>. Generally, a phase pattern provides, to a light beam passing through the phase pattern, a phase corresponding to the local thickness of a diffractive optical element in which the phase pattern is formed. The phase pattern changes the wavefront of the light beam to converge or diffract the light beam, for example. Each of first phase pattern <NUM> and second phase pattern <NUM> is formed by patterning a surface of a plate transparent to laser beam <NUM> using, for example, a photolithography process.

In the present embodiment, the at least one diffractive optical element is constituted of one diffractive optical element <NUM> including a light incident surface 12a and a light exit surface 12b. First phase pattern <NUM> and second phase pattern <NUM> are formed in light exit surface 12b of diffractive optical element <NUM>. That is, as shown in <FIG>, diffractive optical element <NUM> includes a phase pattern <NUM> in which first phase pattern <NUM> and second phase pattern <NUM> are overlapped with each other, and phase pattern <NUM> is formed in light exit surface 12b of diffractive optical element <NUM>.

As shown in <FIG>, the at least one diffractive optical element (diffractive optical element <NUM>) generates light <NUM> having a first order and light <NUM> having a second order from laser beam <NUM> input to the at least one diffractive optical element (diffractive optical element <NUM>), and superimposes light <NUM> having the first order and light <NUM> having the second order on each other on optical axis <NUM> of laser beam <NUM> to cause interference between light <NUM> having the first order and light <NUM> having the second order. Light <NUM> having the first order and light <NUM> having the second order have diffraction orders different from each other. A first focal plane <NUM> of light <NUM> having the first order is located at a position different from a second focal plane <NUM> of light <NUM> having the second order on optical axis <NUM> of laser beam <NUM>.

First phase pattern <NUM> converts laser beam <NUM> into line beam <NUM> (see <FIG>) that is more elongated than laser beam <NUM>. First phase pattern <NUM> converges laser beam <NUM> in the short axis direction (y axis direction) of line beam <NUM>. First phase pattern <NUM> has a positive refractive power in the short axis direction (y axis direction) of line beam <NUM>.

Second phase pattern <NUM> diffracts laser beam <NUM> in the short axis direction (y axis direction) of line beam <NUM> to generate light <NUM> having the first order and light <NUM> having the second order. Light <NUM> having the first order is, for example, a +<NUM>-order diffraction beam. Light <NUM> having the second order is, for example, a -<NUM>-order diffraction beam.

Specifically, as shown in <FIG>, second phase pattern <NUM> includes a central phase pattern 15a and peripheral phase patterns 15b. Peripheral phase patterns 15b are disposed on both sides relative to central phase pattern 15a in the short axis direction (y axis direction) of line beam <NUM>. Central phase pattern 15a extends over a width d with respect to y=<NUM>. For example, central phase pattern 15a extends between a first line defined by y=d/<NUM> and a second line defined by y=-d/<NUM>. Central phase pattern 15a provides a first optical phase to the laser beam input to second phase pattern <NUM>. Each of peripheral phase patterns 15b provides a second optical phase different from the first optical phase to the laser beam input to second phase pattern <NUM>. A difference between the first optical phase and the second optical phase is π.

Second phase pattern <NUM> may be uniform in the long axis direction (x axis direction) of line beam <NUM>. Specifically, central phase pattern 15a may be uniform in the long axis direction (x axis direction) of line beam <NUM>, and peripheral phase pattern 15b may be uniform in the long axis direction (x axis direction) of line beam <NUM>. Therefore, second phase pattern <NUM> may diffract laser beam <NUM> only in the short axis direction (y axis direction) of line beam <NUM>.

The first refractive power of second phase pattern <NUM> for light <NUM> having the first order in the short axis direction (y axis direction) of line beam <NUM> is different from the second refractive power of second phase pattern <NUM> for light <NUM> having the second order in the short axis direction (y axis direction) of line beam <NUM>. For example, the first refractive power may be greater than the second refractive power. Therefore, first focal plane <NUM> of light <NUM> having the first order is located at a position different from second focal plane <NUM> of light <NUM> having the second order on optical axis <NUM> of laser beam <NUM>.

For example, second phase pattern <NUM> has a positive refractive power for light <NUM> having the first order (for example, the +<NUM>-order diffraction beam) in the short axis direction (y axis direction) of line beam <NUM>. Second phase pattern <NUM> has a negative refractive power for light <NUM> having the second order (for example, the -<NUM>-order diffraction beam) in the short axis direction (y axis direction) of line beam <NUM>. Due to the positive refractive power of first phase pattern <NUM> and the positive refractive power of second phase pattern <NUM> for light <NUM> having the first order, first focal plane <NUM> of light <NUM> having the first order is located close to diffractive optical device <NUM> (or the at least one diffractive optical element (diffractive optical element <NUM>)) relative to focal plane <NUM> on optical axis <NUM> of laser beam <NUM> as shown in <FIG>. On the other hand, due to the positive refractive power of first phase pattern <NUM> and the negative refractive power of second phase pattern <NUM> for light <NUM> having the second order, second focal plane <NUM> of light <NUM> having the second order is located distant away from diffractive optical device <NUM> (or the at least one diffractive optical element (diffractive optical element <NUM>)) relative to focal plane <NUM> on optical axis <NUM> of laser beam <NUM> as shown in <FIG>.

It should be noted that in the present specification, focal plane <NUM> is defined as a plane in which the length of a line beam formed only by first phase pattern <NUM> in the short axis direction (y axis direction) is minimum as in a below-described Comparative Example, among planes perpendicular to optical axis <NUM> (z axis). In the present specification, focal plane <NUM> may be referred to as "focal plane <NUM> of diffractive optical device <NUM>". As shown in <FIG>, focal plane <NUM> of diffractive optical device <NUM> is a plane defined by z=<NUM>. Focal plane <NUM> of diffractive optical device <NUM> is located on a surface of workpiece <NUM> or is located inside workpiece <NUM>, for example.

Thus, first focal plane <NUM> of light <NUM> having the first order is located at a position different from second focal plane <NUM> of light <NUM> having the second order. Light <NUM> having the first order and light <NUM> having the second order are superimposed on each other on optical axis <NUM> of laser beam <NUM> (optical axis <NUM> of diffractive optical device <NUM>) to cause interference therebetween. Therefore, the focal depth of line beam <NUM> can be made long.

For example, as shown in <FIG>, focal depth Dz of line beam <NUM> can be made long. In the present specification, focal depth Dz is defined as a length thereof on optical axis <NUM> (z axis), in which the optical axis direction relative light intensity of line beam <NUM> is more than or equal to <NUM>. The optical axis direction relative light intensity of line beam <NUM> is obtained by dividing the light intensity of line beam <NUM> on optical axis <NUM> (z axis) by the maximum light intensity of line beam <NUM> on optical axis <NUM> (z axis).

The optical axis direction relative light intensity of line beam <NUM> is preferably more than or equal to <NUM> between a first position P<NUM> and a second position P<NUM> in an optical axis direction relative light intensity profile of line beam <NUM>. In the present specification, the optical axis direction relative light intensity profile refers to a distribution of optical axis direction relative light intensity on the optical axis (z axis). Therefore, the light intensity in a region irradiated with line beam <NUM> becomes more uniform. A variation in processing of workpiece <NUM> in the region irradiated with line beam <NUM> can be reduced. First position P<NUM> in the optical axis direction relative light intensity profile of line beam <NUM> is a position on optical axis <NUM> at which the optical axis direction relative light intensity of line beam <NUM> is <NUM> in the optical axis direction relative light intensity profile of line beam <NUM>, and is a position furthest away from diffractive optical device <NUM> (or laser light source <NUM>). Second position P<NUM> in the optical axis direction relative light intensity profile of line beam <NUM> is a position on optical axis <NUM> at which the optical axis direction relative light intensity of line beam <NUM> is <NUM> in the optical axis direction relative light intensity profile of line beam <NUM>, and is a position closest to diffractive optical device <NUM> (or laser light source <NUM>).

As shown in <FIG>, the light intensity peak of line beam <NUM> on the short axis (y axis) of line beam <NUM> in focal plane <NUM> of diffractive optical device <NUM> is flattened. That is, the relative light intensity profile of line beam <NUM> on the short axis (y axis) of line beam <NUM> in focal plane <NUM> of diffractive optical device <NUM> (hereinafter, referred to as "short axis direction relative light intensity profile of line beam <NUM>") has a flat top shape. Therefore, the light intensity in the region irradiated with line beam <NUM> becomes more uniform. The variation in processing of workpiece <NUM> in the region irradiated with line beam <NUM> can be reduced.

In the present specification, the short axis direction relative light intensity profile of line beam <NUM> refers to a distribution of short axis direction relative light intensity on the short axis (y axis) of line beam <NUM> in focal plane <NUM>. The short axis direction relative light intensity of line beam <NUM> is obtained by dividing the light intensity of line beam <NUM> on the short axis (y axis) of line beam <NUM> in focal plane <NUM> by the maximum light intensity of line beam <NUM> on the short axis (y axis) of line beam <NUM> in focal plane <NUM>.

The short axis direction relative light intensity profile of line beam <NUM> with a flat top shape means that a ratio W<NUM>/W<NUM> of a <NUM> peak width W<NUM> (see <FIG>) of the short axis direction relative light intensity profile of line beam <NUM> to a <NUM>/e<NUM> peak width W<NUM> (see <FIG>) in the short axis direction relative light intensity profile of line beam <NUM> is more than or equal to <NUM>, and that the short axis direction relative light intensity profile of line beam <NUM> is more than or equal to <NUM> between a third position P<NUM> (see <FIG>) and a fourth position P<NUM> (see <FIG>) in the short axis direction relative light intensity profile of line beam <NUM>.

<NUM> peak width W<NUM> of the short axis direction relative light intensity profile of line beam <NUM> is defined as a length thereof on the short axis (y axis) in focal plane <NUM>, at which the short axis direction relative light intensity of line beam <NUM> is more than or equal to <NUM>. <NUM>/e<NUM> peak width W<NUM> of the short axis direction relative light intensity profile of line beam <NUM> is defined as a length thereof on the short axis (y axis) in focal plane <NUM>, at which the short axis direction relative light intensity of line beam <NUM> is more than or equal to <NUM>/e<NUM>. Third position P<NUM> in the short axis direction relative light intensity profile of line beam <NUM> is a position at which the short axis direction relative light intensity of line beam <NUM> is <NUM> in the short axis direction relative light intensity profile of line beam <NUM>, and is a position furthest away from optical axis <NUM> in the +y axis direction. Fourth position P<NUM> in the short axis direction relative light intensity profile of line beam <NUM> is a position at which the short axis direction relative light intensity of line beam <NUM> is <NUM> in the short axis direction relative light intensity profile of line beam <NUM>, and is a position furthest away from optical axis <NUM> in the -y axis direction.

Diffractive optical device <NUM> of the present embodiment can reduce the diameter of laser beam <NUM> required to obtain the short axis direction relative light intensity profile of line beam <NUM> having a small short axis direction width close to the diffraction limit and having a flat top shape. Therefore, diffractive optical device <NUM> can be downsized. The cost of diffractive optical device <NUM> can be reduced. First phase pattern <NUM> and second phase pattern <NUM> can be formed with higher precision.

As shown in <FIG>, the light intensity peak of line beam <NUM> on the long axis (x axis) of line beam <NUM> in focal plane <NUM> of diffractive optical device <NUM> is flattened. That is, the relative light intensity profile of line beam <NUM> on the long axis (x axis) of line beam <NUM> (hereinafter, referred to as "long axis direction relative light intensity profile of line beam <NUM>") in focal plane <NUM> of diffractive optical device <NUM> has a flat top shape. For example, a ratio W<NUM>/W<NUM> of a <NUM> peak width W<NUM> of the long axis direction relative light intensity profile of line beam <NUM> to a <NUM>/e<NUM> peak width W<NUM> of the long axis direction relative light intensity profile of line beam <NUM> is more than or equal to <NUM>.

In the present specification, the long axis direction relative light intensity profile of line beam <NUM> refers to a distribution of long axis relative light intensity on the long axis (x axis) of line beam <NUM> in focal plane <NUM>. The long axis relative light intensity of line beam <NUM> is obtained by dividing the light intensity of line beam <NUM> on the long axis (x axis) of line beam <NUM> in focal plane <NUM> by the maximum light intensity of line beam <NUM> on the long axis (x axis) of line beam <NUM> in focal plane <NUM>. <NUM> peak width W<NUM> of the long axis direction relative light intensity profile of line beam <NUM> is defined as a length thereof on the long axis (x axis) in focal plane <NUM>, at which the long axis relative light intensity of line beam <NUM> is more than or equal to <NUM>. <NUM>/e<NUM> peak width W<NUM> of the long axis direction relative light intensity profile of line beam <NUM> is defined as a length thereof on the long axis (x axis) in focal plane <NUM>, at which the long axis relative light intensity of line beam <NUM> is more than or equal to <NUM>/e<NUM>.

An aspect ratio of line beam <NUM> is defined in focal plane <NUM>. Specifically, the aspect ratio of line beam <NUM> is defined as a ratio W<NUM>/W<NUM> of <NUM>/e<NUM> peak width W<NUM> (see <FIG>) of the long axis direction relative light intensity profile of line beam <NUM> to <NUM>/e<NUM> peak width W<NUM> (see <FIG>) of the short axis direction relative light intensity profile of line beam <NUM>. An aspect ratio of laser beam <NUM> is also defined in the same manner as aspect ratio W<NUM>/W<NUM> of line beam <NUM>. For example, when laser beam <NUM> has a circular shape, the aspect ratio of laser beam <NUM> is <NUM>.

In one example of the present embodiment, laser beam <NUM> has a circular cross sectional shape, the light intensity distribution of laser beam <NUM> in the cross section thereof is Gaussian distribution, laser beam <NUM> has a wavelength λ, light <NUM> having the first order is a +<NUM>-order diffraction beam, and light <NUM> having the second order is a -<NUM>-order diffraction beam. The <NUM>/e<NUM> beam diameter of laser beam <NUM> is defined as ω. The <NUM>/e<NUM> beam diameter of laser beam <NUM> is a diameter of laser beam <NUM> with which the relative light intensity of laser beam <NUM> in the cross section thereof is <NUM>/e<NUM>. The relative light intensity of laser beam <NUM> in the cross section thereof is obtained by dividing the light intensity of laser beam <NUM> in the cross section of laser beam <NUM> by the maximum light intensity of laser beam <NUM> in the cross section of laser beam <NUM> (the light intensity of laser beam <NUM> at the center of the cross section of laser beam <NUM>).

First refractive power P+<NUM> of second phase pattern <NUM> for the +<NUM>-order diffraction beam in the short axis direction (y axis direction) of line beam <NUM> and second refractive power P-<NUM> of second phase pattern <NUM> for the -<NUM>-order diffraction beam in the short axis direction (y axis direction) of line beam <NUM> are given by the following formula (<NUM>):
<MAT>.

Coefficient C may satisfy the below-described formula (<NUM>). Therefore, the optical axis direction relative light intensity of line beam <NUM> can be more than or equal to <NUM> between first position P<NUM> and second position P<NUM> in the optical axis direction relative light intensity profile of line beam <NUM> (see <FIG>). The light intensity in the region irradiated with line beam <NUM> becomes more uniform. The variation in processing of workpiece <NUM> in the region irradiated with line beam <NUM> can be reduced.

Coefficient C may satisfy the below-described formula (<NUM>). Therefore, the focal depth of diffractive optical device <NUM> of the present embodiment (see, for example, <FIG>) is <NUM> times or more as large as the focal depth of the diffractive optical device of the Comparative Example (see <FIG>) which does not include second phase pattern <NUM> (see <FIG>). Even when laser beam <NUM> is more intensely converged in the short axis direction (y axis direction) of line beam <NUM> by using diffractive optical device <NUM>, focal depth Dz of line beam <NUM> can be made further longer.

Coefficient C may satisfy the below-described formula (<NUM>). Therefore, with diffractive optical device <NUM> of the present embodiment, the short axis direction relative light intensity profile of line beam <NUM> with a flat top shape can be obtained. The light intensity in the region irradiated with line beam <NUM> becomes more uniform. The variation in processing of workpiece <NUM> in the region irradiated with line beam <NUM> can be reduced.

In the above one example of the present embodiment, width d of central phase pattern 15a is given by the following formula (<NUM>):
<MAT>.

Examples <NUM> to <NUM>, each of which is a specific example of the present embodiment, will be described in comparison to a Comparative Example. In each of Examples <NUM> to <NUM> and the Comparative Example, laser beam <NUM> has a circular cross sectional shape, the aspect ratio of laser beam <NUM> is <NUM>, and <NUM>/e<NUM> beam diameter ω of laser beam <NUM> is <NUM>. The light intensity distribution of laser beam <NUM> in the cross section of laser beam <NUM> is Gaussian distribution. Wavelength λ of laser beam <NUM> is <NUM>. A focal distance f of diffractive optical device <NUM> is <NUM>. Focal distance f is a distance between diffractive optical device <NUM> and focal plane <NUM> in the optical axis direction (z axis direction). As shown in each of <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, <NUM> peak width W<NUM> of the long axis direction relative light intensity profile of line beam <NUM> is <NUM>, and <NUM>/e<NUM> peak width W<NUM> of the long axis direction relative light intensity profile of line beam <NUM> is <NUM>.

A diffractive optical element of the Comparative Example includes only a phase pattern shown in <FIG>. That is, the phase pattern of the Comparative Example is constituted of only a first phase pattern <NUM> of Example <NUM>, and does not include a second phase pattern <NUM> of Example <NUM> shown in <FIG>. Therefore, in the diffractive optical element of the Comparative Example, width d of central phase pattern 15a is regarded as being infinite. Since the diffractive optical element of the Comparative Example does not generate light <NUM> having the first order (for example, the +<NUM>-order diffraction beam) and light <NUM> having the second order (for example, the -<NUM>-order diffraction beam), coefficient C is regarded as zero.

A line beam <NUM> having a defocus profile shown in <FIG> is obtained by the diffractive optical element of the Comparative Example. Referring to <FIG>, focal depth Dz of line beam <NUM> is <NUM>. The relative light intensity on optical axis <NUM> in focal plane <NUM> (z=<NUM>) is <NUM>. The optical axis direction relative light intensity of line beam <NUM> is more than or equal to <NUM> between first position P<NUM> and second position P<NUM> in the optical axis direction relative light intensity profile of line beam <NUM>.

Referring to <FIG>, <NUM> peak width W<NUM> of the short axis direction relative light intensity profile of line beam <NUM> is <NUM>, and <NUM>/e<NUM> peak width W<NUM> of the short axis direction relative light intensity profile of line beam <NUM> is <NUM>. Aspect ratio W<NUM>/W<NUM> of line beam <NUM> is <NUM>. Ratio W<NUM>/W<NUM> is <NUM>, which is less than <NUM>. Therefore, the short axis direction relative light intensity profile of line beam <NUM> does not have a flat top shape.

A diffractive optical element <NUM> of Example <NUM> includes phase pattern <NUM> shown in <FIG>. Phase pattern <NUM> of the present example is a phase pattern in which first phase pattern <NUM> shown in <FIG> and second phase pattern <NUM> shown in <FIG> are overlapped with each other. Central phase pattern 15a of second phase pattern <NUM> provides a first optical phase of π to laser beam <NUM>. Each of peripheral phase patterns 15b of second phase pattern <NUM> provides a second optical phase of <NUM> to laser beam <NUM>. Since diffractive optical element <NUM> of the present example includes second phase pattern <NUM>, diffractive optical element <NUM> generates a +<NUM>-order diffraction beam as light <NUM> having the first order and generates a -<NUM>-order diffraction beam as light <NUM> having the second order. In the present example, width d of central phase pattern 15a is <NUM>, and coefficient C is <NUM>.

A line beam <NUM> having a defocus profile shown in <FIG> is obtained by diffractive optical element <NUM> of the present example. Referring to <FIG>, focal depth Dz of line beam <NUM> is <NUM>. The relative light intensity on optical axis <NUM> in focal plane <NUM> (z=<NUM>) is <NUM>. The optical axis direction relative light intensity of line beam <NUM> is more than or equal to <NUM> between first position P<NUM> and second position P<NUM> in the optical axis direction relative light intensity profile of line beam <NUM>.

Referring to <FIG>, <NUM> peak width W<NUM> of the short axis direction relative light intensity profile of line beam <NUM> is <NUM>, and <NUM>/e<NUM> peak width W<NUM> of the short axis direction relative light intensity profile of line beam <NUM> is <NUM>. Aspect ratio W<NUM>/W<NUM> of line beam <NUM> is <NUM>. Ratio W<NUM>/W<NUM> is <NUM>, which is more than or equal to <NUM>. The short axis direction relative light intensity profile of line beam <NUM> is more than or equal to <NUM> between third position P<NUM> and fourth position P<NUM> in the short axis direction relative light intensity profile of line beam <NUM>. Therefore, the short axis direction relative light intensity profile of line beam <NUM> has a flat top shape.

A diffractive optical element <NUM> of Example <NUM> includes a phase pattern <NUM> shown in <FIG>. Phase pattern <NUM> of the present example is a phase pattern in which first phase pattern <NUM> shown in <FIG> and a second phase pattern <NUM> shown in <FIG> are overlapped with each other. Second phase pattern <NUM> of the present example is similar to second phase pattern <NUM> of Example <NUM>, but width d of central phase pattern 15a of the present example is <NUM>. In the present example, coefficient C is <NUM>.

Referring to <FIG>, <NUM> peak width W<NUM> of the short axis direction relative light intensity profile of line beam <NUM> is <NUM>, and <NUM>/e<NUM> peak width W<NUM> of the short axis direction relative light intensity profile of line beam <NUM> is <NUM>. Aspect ratio W<NUM>/W<NUM> of line beam <NUM> is <NUM>. In the short axis direction relative light intensity profile of line beam <NUM>, there is a portion in which the optical axis direction relative light intensity of line beam <NUM> is less than <NUM> between third position P<NUM> and fourth position P<NUM> in the short axis direction relative light intensity profile of line beam <NUM>. For example, in the short axis direction relative light intensity profile of line beam <NUM>, the short axis direction relative light intensity of line beam <NUM> on optical axis <NUM> (y=<NUM>) is <NUM>. Therefore, the short axis direction relative light intensity profile of line beam <NUM> does not have a flat top shape.

A line beam <NUM> having a defocus profile shown in <FIG> is obtained by diffractive optical element <NUM> of the present example. Referring to <FIG>, focal depth Dz of line beam <NUM> is <NUM>. In the optical axis direction relative light intensity profile of line beam <NUM>, there is a portion in which the optical axis direction relative light intensity of line beam <NUM> is less than <NUM> between first position P<NUM> and second position P<NUM> in the optical axis direction relative light intensity profile of line beam <NUM>. For example, the relative light intensity on optical axis <NUM> in focal plane <NUM> (z=<NUM>) is <NUM>.

<FIG> shows a change in focal depth Dz with respect to coefficient C and a change in the relative light intensity on the optical axis at z=<NUM> with respect to coefficient C in each of Examples <NUM> to <NUM> and the Comparative Example. Table <NUM> shows the numerical values of the parameters of each of Examples <NUM> to <NUM> and the Comparative Example. Table <NUM> shows the numerical values of the parameters of each of Examples <NUM> to <NUM>.

Modifications of the present embodiment will be described. In a first modification of the present embodiment, first phase pattern <NUM> and second phase pattern <NUM> may be formed in light incident surface 12a of diffractive optical element <NUM>. That is, diffractive optical element <NUM> may include phase pattern <NUM> (see <FIG>) in which first phase pattern <NUM> and second phase pattern <NUM> are overlapped with each other, and phase pattern <NUM> may be formed in light incident surface 12a of diffractive optical element <NUM>. In a second modification of the present embodiment, first phase pattern <NUM> may be formed in light incident surface 12a of diffractive optical element <NUM>, and second phase pattern <NUM> may be formed in light exit surface 12b of diffractive optical element <NUM>. In a third modification of the present embodiment, first phase pattern <NUM> may be formed in light exit surface 12b of diffractive optical element <NUM>, and second phase pattern <NUM> may be formed in light incident surface 12a of diffractive optical element <NUM>.

A laser beam irradiation device 1b of a second embodiment will be described with reference to <FIG>. Laser beam irradiation device 1b of the present embodiment has a configuration similar to that of laser beam irradiation device <NUM> of the first embodiment, but is mainly different therefrom in terms of the configuration of diffractive optical device <NUM>.

Diffractive optical device <NUM> of the present embodiment includes a first diffractive optical element (diffractive optical element <NUM>) and a second diffractive optical element (diffractive optical element <NUM>). Diffractive optical element <NUM> and diffractive optical element <NUM> are disposed along optical axis <NUM> of diffractive optical device <NUM>. Diffractive optical element <NUM> is disposed on the light incident side of laser beam <NUM> relative to diffractive optical element <NUM>. First phase pattern <NUM> is formed in diffractive optical element <NUM>, and second phase pattern <NUM> is formed in diffractive optical element <NUM>. Particularly, first phase pattern <NUM> is formed in one of light incident surface 12a or light exit surface 12b of diffractive optical element <NUM>. Second phase pattern <NUM> is formed in one of light incident surface 17a or light exit surface 17b of diffractive optical element <NUM>.

In a modification of the present embodiment, first phase pattern <NUM> may be formed in diffractive optical element <NUM>, and second phase pattern <NUM> may be formed in diffractive optical element <NUM>. Particularly, first phase pattern <NUM> is formed in one of light incident surface 17a or light exit surface 17b of diffractive optical element <NUM>. Second phase pattern <NUM> is formed in one of light incident surface 12a or light exit surface 12b of diffractive optical element <NUM>.

The first and second embodiments and modifications thereof disclosed herein are illustrative and non-restrictive in any respect. The scope of the present invention is defined by the terms of the claims, rather than the first and second embodiments and modifications thereof described above, and is intended to include any modifications within the scope of the claims.

Claim 1:
A diffractive optical device (<NUM>) comprising at least one diffractive optical element (<NUM>, <NUM>), wherein
the at least one diffractive optical element (<NUM>, <NUM>) generates light having a first order (<NUM>) and light having a second order (<NUM>) from a laser beam (<NUM>) input to the at least one diffractive optical element (<NUM>, <NUM>), and superimposes the light having the first order (<NUM>) and the light having the second order (<NUM>) on each other on an optical axis (<NUM>) of the laser beam (<NUM>) to cause interference between the light having the first order (<NUM>) and the light having the second order (<NUM>), the light having the first order (<NUM>) and the light having the second order (<NUM>) having diffraction orders different from each other,
the at least one diffractive optical element (<NUM>, <NUM>) includes a first phase pattern (<NUM>) and a second phase pattern (<NUM>),
the first phase pattern (<NUM>) converts the laser beam (<NUM>) into a line beam (<NUM>), the second phase pattern (<NUM>) diffracts the laser beam (<NUM>) in a short axis direction of the line beam (<NUM>) to generate the light having the first order (<NUM>) and the light having the second order (<NUM>),
a first focal plane (<NUM>) of the light having the first order (<NUM>) is located at a position different from a second focal plane (<NUM>) of the light having the second order (<NUM>) on the optical axis (<NUM>)
the second phase pattern (<NUM>) includes a central phase pattern (15a) and peripheral phase patterns (15b) disposed on both sides relative to the central phase pattern (15a) in the short axis direction,
the central phase pattern (15a) provides a first optical phase to the laser beam (<NUM>),
each of the peripheral phase patterns (15b) provides a second optical phase different from the first optical phase to the laser beam (<NUM>), and
a difference between the first optical phase and the second optical phase is π.