JPH10186115A - Optical element for generating laser beam and laser beam generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam generator capable of increasing the peak intensity of a center spot while securing the depth of a focus to some extent and fixing peak intensity in the depth of the focus as much as possible. SOLUTION: A laser beam C of a spherical wave projected from a semiconductor laser element 1 is converted into a plane wave by a collimator lens 2 and made incident on a laser beam generating optical element 30. The ridge line of the element 30 is divided into four sections 31, 31, 32, 32 and the incident beam is divided into beams C1', C1" projected from the sections 31, 31 and beams C2', C2" projected from the sections 32, 32. The beams C1', C1" intersect with an optical axis and are converged on convergent points E1', E1" other than the optical axis and the beams C2', C2" also intersect with the optical axis and are converged on convergent points E2', E2" other than the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element for generating a laser beam capable of generating a laser beam having a relatively small spot diameter and a remarkably large focal depth as compared with a normal laser beam having the same spot diameter. The present invention relates to a laser beam generating device which is provided with the laser beam generating optical element and is suitable for application to devices such as a laser beam machine, a laser printer, an optical pickup and a bar code reader.

[0002]

2. Description of the Related Art Hitherto, in an optical system using a laser beam, a so-called Gaussian beam, in which the intensity distribution becomes a Gaussian distribution with respect to the optical axis, has been used. FIG. 7 shows an optical system for focusing a Gaussian beam. In this optical system, an objective lens 22 is used as a means for condensing the laser beam 21. FIG. 8 is a view of the objective lens 22 viewed from the optical axis direction, and the lines in the figure indicate contour lines. The cross-sectional shape of the objective lens 22 is represented by the following equation (1), and has a continuous curve at the intersection with the optical axis 4.

[0003]

(Equation 1)

Where C ₀ : curvature of a reference spherical surface K: conic constant a _m : aspherical surface coefficient Z: distance in the direction of the optical axis r: distance in the direction perpendicular to the optical axis When condensed using,
The range in which the center intensity of the beam is 80% or more of the center intensity of the beam at the position where the spot diameter is minimum, the so-called depth of focus Z, is such that the spot diameter is minimized as shown in the following equation (2). It is well known that the beam diameter at a certain position (the radius of the beam at a position where the peak intensity is 1 / e ² ) is proportional to the square of ω ₀ .

Z = ± 1.44ω ₀ ² / λ (2) where λ: wavelength From the equation (2), it can be seen that the focal depth Z becomes very shallow when the spot diameter is reduced. For this reason, in applications that need to condense into a narrow beam near the theoretical limit, such as laser processing machines, laser printers, laser beam printers, optical pickups and bar code readers using the above optical system, focus There was an inconvenience that the position had to be finely adjusted.

For example, taking the case of a laser processing machine shown in FIG. 9 as an example, as shown in FIG. 1A, a laser beam emitted from a laser beam generator 100 is:
After the optical path is changed by 90 ° by the mirror 101, the light is condensed by the objective lens 102, and the condensed spot is guided to the processing object 106 thereunder.

FIG. 1B shows the condensed light spot portion in an enlarged manner. As is clear from this drawing, the conventional optical system has a small depth of focus, so that the unevenness 107 and the thickness of the object 106 are reduced. It is necessary to finely adjust the focal position of the optical system according to the distance d. That is, since the depth of focus is small, a troublesome fine adjustment of the focus position is required in order to efficiently guide the condensed spot to a target location.

Similarly, in a laser beam printer, it is necessary to finely adjust the focal position by precisely adjusting the position of the photosensitive member. In a barcode reader, it is necessary to finely adjust the position where the barcode is placed. In addition, the optical pickup needs a movable mechanism for focus adjustment.

As described above, there have been various problems in the conventional general condensing optical system, such as the necessity of fine adjustment of the focal position and a mechanism associated therewith.

In order to solve these problems, as a laser beam having a very large depth of focus and a relatively small spot diameter, an electric field distribution in the radial direction perpendicular to the optical axis is obtained.
A Bessel beam (non-diffractive beam) having a zero-order Bessel function of the first kind has been devised. For details of the Bessel beam, see (1) Durnin: J.M. Opt. Soc. Am.
A4 (1987) 651. (2) Uehara: Applied physics (19
90) 746, etc.

FIG. 10 shows an example of a conventional optical system for generating a basic Bessel beam. This optical system includes a semiconductor laser element 11, a collimator lens 12, and an axicon 13 which is a conical lens. The operation will be described below.

The laser light A of the spherical wave emitted from the semiconductor laser 11 is converted into a plane wave by the collimator lens 12 and then enters the axicon 13. Axicon 13
In the section taken along the plane including the optical axis 14, the optical axis 1
Curves representing the ridges B 'and B "of the surface having the effect of refracting light in the half plane defined by 4 are straight lines, and the traveling direction of the light after refraction is independent of the height from the optical axis. That is, the refracted light becomes plane waves A ′ and A ″, and the traveling directions of the two half planes defined by the optical axis are different.

Since the function representing the surface to be refracted is rotationally symmetric with respect to the optical axis, it may be considered in a section including the optical axis. In this cross section, the function representing the refracting surface of the axicon 13 is two straight lines intersecting at the optical axis and having different inclinations, and is discontinuous in the functional axis on the optical axis.

FIG. 11 shows the axicon 13 connected to the optical axis 14.
FIG. 3 is a diagram viewed from a direction, and lines in the figure indicate contour lines. The cross-sectional shape of the axicon 13 is represented by the following equation (3).

Z = ± αr + β (3) where Z: distance in the optical axis direction r: distance in the direction perpendicular to the optical axis α, β: positive constant Because of the above sectional shape, as shown in FIG. Axicon 1
The laser beam emitted from 3 is refracted by the ridgeline B ′ in a half plane defined by the optical axis 14, and becomes a plane wave A ′ traveling in a direction crossing the optical axis 14 at an angle θ. Similarly,
In the opposite half plane defined by the optical axis 14, the plane wave A ″ is refracted by the ridge line B ″ and travels in a direction that also crosses the optical axis 14 at an angle θ. However, the traveling direction of the plane wave A ″ is a direction axially symmetric with the plane wave A ′ with respect to the optical axis.

By using a hologram, an optical element optically equivalent to the axicon 13 can be produced. However, the details are omitted here.

In the optical system shown in FIG. 10, the electric field distribution in a direction perpendicular to the optical axis 14 when viewed in a section including the optical axis 14 is as follows.
The plane waves A ′ and A ″ interfere with each other to form a Bessel beam proportional to the 0th-order Bessel function of the first kind.

FIG. 12 shows the change in the focused spot diameter of the basic Bessel beam and Gaussian beam as viewed in the optical axis direction in comparison with a case where the spot diameter is 40 μm. In the figure, (1) represents a Bessel beam, and (2) represents a Gaussian beam. Table 1 shows specific spot diameters in the optical axis direction of both beams shown in FIG.

[0019]

[Table 1]

The focal depth of the Gaussian beam in Table 1 was calculated based on the above equation (2). The depth of focus in the case of the Bessel beam is also defined as a range in which the center intensity of the beam is 80% or more of the center intensity of the beam at the position where the spot diameter is minimized, similarly to the Gaussian beam ( From the graph of △ θ = 0 in FIG.
%).

As apparent from FIG. 12, the focused spot diameter of the Bessel beam is constant at 40 μm regardless of the position in the optical axis direction (mm), whereas the focused spot diameter of the Gaussian beam is 40 μm. In some areas, the optical axis direction is
It is an extremely limited area of 150 mm. Therefore, as is clear from this point and the numerical values shown in Table 1, it can be understood that the depth of focus of the Bessel beam can be much larger (deeper) than that of the Gaussian beam.

By the way, in the above-mentioned Bessel beam, the light intensity in the radial direction of the axicon 13 is as shown in FIG. 13, and has a number of sub-peaks in the radial direction. For this reason, the intensity of the central spot is usually about several percent of the total light intensity.

Therefore, the laser beam generator for generating the above-described Bessel beam is used for an apparatus such as a laser beam machine which does not require a sub-peak and requires only a high peak intensity at the center spot. I couldn't do that. In general, there is a trade-off relationship between the depth of focus and the peak intensity of the central spot in a laser beam, and it is not possible to achieve both at the same time. It is possible.

When the laser beam generator is applied to many uses, for example, a laser processing machine, a laser printer, an optical pickup, and a bar code reader, the focal depth does not need to be as deep as the Bessel beam. Very useful results can be obtained just slightly deeper than the beam. That is, in order to apply to these devices, the intensity of the central peak is higher than the depth of focus, and the absence of the sub-peak is more effective in improving the processing capability and the detection accuracy. This is because it is desirable. Therefore, the above-described Bessel beam has a problem in this point.

In order to solve the above problems, a laser beam generating optical element proposed by the present applicant in Japanese Patent Application No. 8-70777 and a laser beam generating apparatus using the laser beam generating optical element have been proposed. There is.

FIG. 14 shows this laser beam generator. This laser beam generating device includes a semiconductor laser element 1, a collimating lens 2, and an optical element 3 for generating a laser beam.

The spherical laser beam C emitted from the semiconductor laser device 1 is converted into a plane wave by the collimator lens 2 and then enters the laser beam generating optical device 3. The surface of the laser beam generating optical element 3 having the function of refracting light, that is, the surface on the emission side, has two ridgelines D ′ and D ′ when viewed in a section cut by a plane including the optical axis 4 (z axis). Is formed.

The equations representing the ridge lines D 'and D "and the derivation process thereof are described in Japanese Patent Application No. 8-70777.
Since the contents are the same as those of the present invention described later, they are omitted here.

The laser beam emitted from the laser beam generating optical element 3 having the refraction surface having the above-mentioned shape is shown in FIG.
As shown in FIG. 4, the light flux is divided into two light fluxes C ′ and C ″. One light flux C ′ intersects with the optical axis 4 and converges toward a point E ′ outside the optical axis 4, and the other light flux C ′. The light beam C "intersects the optical axis 4 and converges toward a point E" outside the optical axis 4. Here, E 'and E "are symmetrical with respect to the optical axis 4. , The light beams C ′ and C ″ intersect with each other. Therefore, the wavefronts of the light beams C ′ and C ″ interfere with each other at the portion where they cross each other, and the optical axis 4
A long-focus laser beam having an amplitude distribution similar to the first-order zero-order Bessel function in the direction perpendicular to the laser beam is formed. That is, a laser beam having a significantly larger depth of focus than a Gaussian beam is formed.

Here, the reason why the laser beam generating optical element 3 improves the peak intensity of the focused spot will be described. In the case of a normal Bessel beam as shown in FIG. 10, the light beam forming the long-focus laser beam is a parallel light crossing the optical axis. At this time, the light intensity per unit space inside the light beam is constant when viewed in the optical axis direction.

On the other hand, in the laser beam generating optical element 3, as shown in FIG. 14, the light beams C ′ and C ″ forming the long focal point laser beam intersect with the optical axis 4 and are out of the optical axis. 4, the light intensity per unit space inside the light beams C ′ and C ″ is improved in the optical axis direction. That is, according to the laser beam generating optical element 3, since the light fluxes C ′ and C ″ both travel toward the convergence points E ′ and E ″, the light intensity per unit space is It can be improved compared to the case of the beam. Therefore, the peak intensity of the converging spot formed by the intersection of the converging light fluxes C ′ and C ″ can be improved as compared with the case of the Bessel beam.

FIG. 15 shows the result of a simulation in which the peak intensity of the condensed spot is specifically calculated numerically. FIG.
From FIG. 5, the peak intensity of the condensed spot increases as the degree of convergence of the light beam (△ θ) increases, as compared with the case where the light beam is parallel light (△ θ = 0) as in the case of forming a Bessel beam. It can be seen that is improved.

[0033] For example, △ θ = 0, i.e., as compared to the peak intensity of the Bessel beam, △ theta = peak intensity of the central spot of the long focal laser beam 3q _0/4 is increased about 9 times. At this time, the intensity distribution of the long focal point laser beam in the direction perpendicular to the optical axis is as shown in FIG. 16 and is similar to the intensity distribution of the conventional Bessel beam of FIG. It can be seen that unnecessary side peaks are suppressed in the above.

Next, the effect of using such a laser beam generator in a laser beam machine will be described with reference to FIG. Here, the depth of focus actually used only needs to be a depth corresponding to the sum of the size and the thickness d of the unevenness 107 of the object 106 to be irradiated with the laser beam. Not all light paths to object 106 need be. Therefore, it is only necessary that a long-focus laser beam can be formed in a region distant from the beam generating aperture in the region of the long-focus laser beam determined geometrically, that is, in the vicinity of the irradiation target.

For this reason, the focal depth does not need to be as large as the above-mentioned Bessel beam. On the other hand, the depth of focus of the laser beam formed by the laser beam generating optical element 3 is much larger than that of a Gaussian beam. For this reason,
As shown in FIG. 17B, a sufficient depth of focus corresponding to the sum of the unevenness 107 and the thickness d of the processing target 106 can be secured. Therefore, there is no need to finely adjust the focal position of the optical system during processing. Further, since the light intensity of the central spot can be increased as compared with the Bessel beam, there is an advantage that the processing efficiency can be improved accordingly.

[0036]

However, the laser beam generator proposed by the present applicant in Japanese Patent Application No. 8-70777 is applied to devices such as a laser beam machine, a laser printer, an optical pickup and a bar code reader. If so, there is still room for improvement as shown below.

That is, as shown in FIG. 15, in the laser beam generator proposed earlier by the present applicant, before and after the position in the optical axis direction where the peak intensity of the condensed spot viewed in the optical axis direction becomes maximum. The change in light intensity is large.

Here, a laser processing machine, a laser printer,
In devices such as an optical pickup and a barcode reader, it is desirable that the peak intensity within the depth of focus be as constant as possible. The reason is that if the peak intensity within the depth of focus is substantially constant, fine adjustment of the focus position and the like becomes unnecessary.

That is, when applied to a laser beam machine, there is no need to finely adjust the focal position corresponding to the unevenness of the workpiece. When applied to a laser beam printer, the position adjustment of the photosensitive member is simplified. When applied to a barcode reader, the barcode can be read without moving the reader even if the position of the barcode changes.When applied to an optical pickup, a movable mechanism for focus adjustment This is because there is an advantage that it is not necessary to use

Therefore, at present, there is still room for improvement in the laser beam generator proposed by the present applicant.

The present invention has been made in view of such circumstances, and it is necessary to secure a certain depth of focus, increase the peak intensity of the center spot, and make the peak intensity within the depth of focus as constant as possible. To provide a laser beam generating optical element capable of performing laser beam generation, and a laser beam generating apparatus suitable for use in devices such as a laser processing machine, a laser printer, an optical pickup, and a bar code reader, including the laser beam generating optical element. With the goal.

[0042]

According to the optical element for generating a laser beam of the present invention, in an arbitrary plane including an optical axis, a beam in a half plane defined by the optical axis is positioned at a different position outside the optical axis. The optical element emits a plurality of beams from within the half plane so as to converge in each case, thereby achieving the above object.

Preferably, the optical element is a lens, and a ridge in a half plane defined by the optical axis in an arbitrary cross section including the optical axis of the lens is constituted by a plurality of sections. The shape of each section is represented by a different non-linear function, and each section is functionally discontinuous with each other.

Preferably, the optical element is a hologram optically equivalent to the lens.

Further, the laser beam generating apparatus of the present invention
Any one of the above optical elements is provided, thereby achieving the above object.

The operation of the present invention will be described below with reference to FIGS. FIG. 1 shows that the ridge line in the half plane of the laser beam generating optical element 30 has two sections 31 and 3.
2 is shown.

In the optical system shown in FIG. 1, the light beams C1 'and C1 "forming the laser beam emitted from the section 31 intersect with the optical axis (Z-axis) and converge points E1' and E1" off the optical axis.
Has converged. The light beams C2 'and C2 "forming the laser beam emitted from the section 32 intersect with the optical axis and converge at convergence points E2' and E2" off the optical axis.

Here, the change in the condensed spot formed by the intersection of the light fluxes C1 'and C1 "as viewed in the optical axis direction becomes an intensity distribution (1) as shown in FIG.
The change in the focused spot formed by the intersection of 2 ′ and C2 ″ as viewed in the optical axis direction is the intensity distribution (2) in FIG.

When the intensity distributions (1) and (2) are located at different peak positions, the two intensity distributions (1) and (2) are superposed to provide a high peak intensity and an optical axis. An intensity distribution (3) having a substantially constant intensity in the direction is obtained. In the present invention, in order to obtain such an intensity distribution (3), the above configuration is employed.

Because of having such an intensity distribution (3), it is apparent from comparison with FIG. 15 that the use of the laser beam generating apparatus provided with the laser beam generating optical element of the present invention makes it practically practical. A long focal length laser beam having a sufficient depth of focus, a high intensity of the central spot, and a substantially constant intensity in the optical axis direction can be obtained.

As a result, for example, when the laser beam generator of the present invention is applied to a laser beam machine, there is no need to finely adjust the focal position corresponding to the unevenness of the workpiece.

When the laser beam generator of the present invention is applied to a laser beam printer, the adjustment of the position of the photosensitive member can be simplified.

When the laser beam generator of the present invention is applied to a bar code reader, the bar code can be read without moving the reader even if the position of the bar code changes.

When the laser beam generator of the present invention is applied to an optical pickup, signals can be read without using a movable mechanism for adjusting the focus.

When a hologram optically equivalent to a lens is used, the above-described laser beam generating optical element can be easily manufactured.

The shape of the section will be clarified in an embodiment described later.

[0057]

Embodiments of the present invention will be specifically described below with reference to the drawings.

(Embodiment 1) FIGS. 1 and 2 show Embodiment 1 of a laser beam generator according to the present invention. This laser beam generator includes a semiconductor laser element 1, a collimating lens 2, and an optical element 30 for generating a laser beam. Here, the laser beam generating optical element 30 is configured by a lens in which a ridge line in a half plane defined by the optical axis in an arbitrary cross section including the optical axis (Z axis) is formed by two sections 31 and 32. I have. The shape of the two sections 31, 32 is
Each of the sections 31, 3 is represented by a different nonlinear function and
2 are non-continuous with each other. The ridges of the two half planes are discontinuous with each other on the optical axis. That is, in FIG. 1, the two sections 31, 31 are also discontinuous with each other in the optical axis. FIG. 2 shows the laser beam generating optical element 30 viewed from the optical axis direction.

In the above configuration, the spherical laser beam C emitted from the semiconductor laser element 1 is converted into a plane wave by the collimating lens 2 and then enters the laser beam generating optical element 30. The laser beam generating optical element 30 includes four sections 31, 31, 32,
As shown in FIG. 1, the incident beam is split into the light beams C1 ′ and C1 ′ emitted from the sections 31 and 31.
1 "and the light fluxes C2 ', C2 emitted from the sections 32, 32
2 ".

Here, the light fluxes C1 'and C1 "cross the optical axis and converge at convergence points E1' and E1" outside the optical axis. The light beams C2 'and C2 "also intersect with the optical axis and converge at convergence points E2' and E2" outside the optical axis.

Next, the light flux C1 ', C1 "or the light flux C
Laser beam generating optical element 3 forming 2 ′, C2 ″
The specific shape of the ridge line 0, that is, the ridge line 3 of the sections 31 and 32
The functions representing 1 and 32 will be described.

First, the ridge line of the laser beam generating optical element 30 is divided into the two sections 31 and 32 at the position of the radius R1, and the light beam C1 'refracted by the ridge lines 31 and 32 of the sections 31 and 32. , C2 ″ traveling direction Z axis (optical axis)
The angles θ ₃₁ and θ ₃₂ are functions of the distance r from the optical axis, and are expressed by the following equations (4) and (5).

Θ ₃₁ (r) = θ 1 −Δθ 1 (R−r) / R (0 ≦ r ≦ R 1) (4) θ ₃₂ (r) = θ 2 −Δθ 2 (R−r) / R (R 1 ≦ r ≦ R) (5) where: R: outer diameter (radius) of the laser beam generating optical element θ1: when the ridgeline 31 is not sectioned, light is refracted at r = R and heads toward the convergence point E1 ′. Is the angle formed by the Z axis θ2: the angle formed by the light refracted at r = R and directed toward the convergence point E2 ′ when the ridgeline 32 is not partitioned Δθ1, Δθ2: constants that determine the intensity of convergence When the ridge lines 31 and 32 are not partitioned, respectively, the light is refracted at the position of r = R and is directed toward the convergence points E1 ′ and E2 ′ and the light is refracted at the position of r = 0 and the convergence points E1 ′ and E2 Function f31 (r), f32 representing ridgelines 31, 32 above
(R) is represented by the following equations (6) and (7).

[0064]

(Equation 2)

Since the derivation process of the above equations (6) and (7) is the same, the derivation process of the equation (6) will be described below with reference to FIG. The following equation (8) is established by the geometric relationship shown in FIG.

Θ ₁ ′ = π−α ′, θ ₂ ′ = θ ₁ ′ + θ ₃₁ (8) It is assumed that the following equation (9) is used as a function of a curve corresponding to the ridgeline 31.

Z = f31 (r) (9) Since the tangent line 5 to this curve can be obtained by differentiating the function z = f31 (r), it is expressed by the following equation (10).

Z = f′31 (r) · r + m (10) where m is the intersection of the tangent 5 and the z-axis.

Here, the slope f '(r) of the tangent line 5 is calculated as shown in FIG.
Is expressed by the following equation (11) according to the geometric relationship shown in FIG.

F′31 (r) = tanα ′ (r) (11) Here, assuming that the refractive index is n, the following equation (12) holds according to Snell's law.

N sin θ ₁ ′ = sin θ ₂ ′ (12) By substituting the relationship of the above equation (8) into the equation (12), the following equation (13) is established.

Nsin (π−α ′) = sin (π−α ′ + θ ₃₁ ) (13) When the expression (13) is rearranged, the following expression (14) is obtained.

Nsin α ′ = sin (α′−θ ₃₁ ) (14) Since α ′ = α ′ (r) and θ ₃₁ = θ ₃₁ (r), the expression (14) is given by the following expression (15). Rewritten as an expression.

N sin α ′ (r) = sin {α ′ (r) −θ ₃₁ (r)} = sin α ′ (r) cos θ ₃₁ (r) −cos α ′ (r) sin θ ₃₁ (r) (15) ( By dividing both sides of the expression (15) by sinα ′ (r), the following expressions (16a) and (16b) are established.

N = cos θ ₃₁ (r) − {tan α ′ (r)} ^{− 1} · sin θ ₃₁ (r) (16a) {n−cos θ ₃₁ (r)} / sin θ ₃₁ (r) = − {tan α ′ (R)｝ ⁻¹ (16b) Therefore, tan α ′ (r) = − sin θ ₃₁ (r) / {n-cos θ ₃₁ (r)} (17)

When the relationship of the above equation (11) is substituted into the equation (17), the following equation (18) is established.

F′31 (r) = − sin θ1r) / ｛n
−cos θ1r)｝ (18) Therefore, the ridgeline 31 is
A function represented by the above equation (6) is obtained by integrating the above equation (18).

Here, depending on the way of giving θ ₃₁ (r), the indefinite integration in the equation may not be executed. In this case, the form of the function is determined by performing the numerical integration. it can.

As an example, s = △ θ ₃₁ / R, t = θ 1-
If Δθ31, θ ₃₁ (r) = sr + t, the above f31
(R) is rewritten as the following equation (19).

F31 (r) = − (1 / s) · log {n−cos (sr + t)} + C (19) Here, if f31 (0) = z ₀ , the following equation (20) is established. .

F31 (0) = z ₀ = − (1 / s) · log (n-cost) + C (20) Accordingly, the integration constant C is expressed by the following equation (21).

C = z ₀ + (1 / s) · log (n-cost) (21) Accordingly, the above equation (6) can be rewritten as the following equation (22).

Z = f31 (r) = − (1 / s) · log {n−cos (sr + t)} + (1 / s) · log (n−cost) + z ₀ (22) Here, in general, θ1 ≠ θ2, △ θ1 ≠ △ θ2,
At the radius R1, θ ₃₁ (R1) ≠ θ ₃₂ (R1).
Therefore, if the function of the curve of the ridgeline 32 is z = f32 (r), f31 (R1) ≠ f32 (R1), and the ridgelines 31 and 32 of the laser beam generating optical element 3 are discontinuous at the position of the radius R1 ( Functionally discontinuous).

The light flux C1 ', C1 "or the light flux C1
A method for calculating the peak intensity of the converging spot formed by the intersection of 2 ′ and C2 ″ is disclosed in Japanese Patent Application No. 8-70.
No. 777, the description is omitted here.

The point E at which the light beams C1 'and C1 "converge.
1 ′ and E1 ″ are points E at which the light fluxes C2 ′ and C2 ″ converge.
2 ′, E2 ″, and as shown in FIG.
The change in the converged spot formed by the intersection of 1 ′ and C1 ″ as viewed in the optical axis direction is defined as an intensity distribution (1), and the light flux C
Assuming that the change in the condensed spot formed by the intersection of 2 ′ and C2 ″ in the optical axis direction is an intensity distribution (2), the intensity distributions (1) and (2) have different peak positions.
When the peak positions of the intensity distributions 1 and 2 are slightly different from each other, the superposition of the two intensity distributions (1) and (2) results in an intensity distribution in which the peak intensity is high and the intensity in the optical axis direction is almost constant ( 3) is obtained.

According to the laser beam generator of the first embodiment, a long focal length laser beam having a practically sufficient depth of focus, a high intensity of the central spot, and a substantially constant intensity in the optical axis direction can be obtained. As a result, for example, when the laser beam generator of the present invention is applied to a laser beam machine, it is not necessary to finely adjust the focal position corresponding to the unevenness of the workpiece.
When applied to a laser beam printer, the position adjustment of the photoconductor can be simplified.When applied to a barcode reader, the barcode is read without moving the reading device even if the position of the barcode changes. be able to,
When applied to an optical pickup, it is possible to obtain an effect that a signal can be read without using a movable mechanism for focus adjustment.

In the first embodiment, the ridge line in the half plane is 2
Although the description has been given of the case where the image is divided into three, it is also possible to divide the image into three or more. The function representing the m-th ridgeline when the ridgeline of the laser beam generating optical element 3 is divided into a plurality of (n, n ≧ 2) sections will be described below.

First, the angle θ _3m (r) formed between the light beam refracted at the m-th ridge line and the Z-axis in the traveling direction is expressed by the following equation (23).

Θ _3m (r) = θm− △ θm (R−r) / R (23) where Rm−1 ≦ r ≦ Rm (2 ≦ m ≦ n) 0 ≦ r ≦ R1 (m = 1) Rn = R (m = n) θm: When the m-th ridge line is not partitioned, the angle formed by the light refracted at r = R and directed toward the convergence point Em ′ with the Z axis Δθm: Obtain the convergence strength When the m-th ridge line is not partitioned, a straight line refracted at the position of r = R toward the convergence point Em ′ and a straight line refracted at the position of r = 0 toward the convergence point Em ′ Therefore, the function f3m (r) representing the m-th edge is represented by the following equation (24).

[0090]

(Equation 3)

This deriving process is the same as in the case of the above equation (6).

Also in this case, θm-1 ≠ θm, △ θm-1
≠ △ θm, and θ _3m-1 (Rm−
1) It becomes ≠ θ _3m (Rm-1). Therefore, f3m-1
(Rm-1) ≠ f3m (Rm-1), and the ridge is discontinuous at the radius R1.

(Embodiment 2) FIGS. 5 and 6 show Embodiment 2 of the laser beam generator of the present invention. Embodiment 2
In this embodiment, a hologram 30 ′ optically equivalent to the laser beam generating optical element 30 is used as the laser beam generating optical element, and the other configuration is the same as that of the first embodiment. Therefore, corresponding parts are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 6 shows a state in which the hologram 30 'is viewed from the optical axis direction.

The traveling direction of the light emitted from the hologram 30 'is different at each position in the direction perpendicular to the optical axis, and the diffraction angle increases as the distance from the optical axis increases. Therefore, the hologram 3
The pattern of 0 'is a group of concentric circles having a smaller pitch in the optical axis direction.

[0095] As such a hologram 30 ', specifically, the following may be used. A method in which the thickness of the refraction surface is returned to the reference surface every time the optical path difference becomes 1/2 of the wavelength, and a hologram having a sawtooth-shaped cross section or a radius at which the optical path difference becomes 1/2 of the wavelength is set as a period. A hologram in which the transmittance is inverted or the thickness is changed can be used.

Since the hologram 30 'is optically equivalent to the laser beam generating optical element 30, the laser beam generating apparatus of the second embodiment can be used as a laser beam machine, laser beam printer, bar code reader, optical When applied to a pickup, the same effects as described in the first embodiment can be obtained.

In addition, since a hologram can be easily manufactured as compared with a lens, there is an advantage that a cheaper optical element for generating a laser beam can be realized.

[0098]

As described above, by using the laser beam generating optical element of the present invention, it is possible to generate a laser beam having a high peak intensity and an intensity distribution in which the intensity in the optical axis direction is almost constant. . For this reason, if a laser beam generating apparatus equipped with the laser beam generating optical element of the present invention is used, a long focal length with a practically sufficient depth of focus, a high intensity of the central spot, and a substantially constant intensity in the optical axis direction is obtained. A laser beam can be obtained.

As a result, for example, when the laser beam generator of the present invention is applied to a laser beam machine, there is no need to finely adjust the focal position corresponding to the unevenness of the workpiece.
Processing efficiency can be improved.

When the laser beam generator of the present invention is applied to a laser beam printer, the adjustment of the position of the photoreceptor can be simplified, which is advantageous in reducing the size and simplification of the device configuration. is there.

When the laser beam generator of the present invention is applied to a bar code reader, the bar code can be read without moving the reader even if the position of the bar code changes, so that the reading efficiency is improved. it can.

When the laser beam generating apparatus of the present invention is applied to an optical pickup, signals can be read without using a movable mechanism for focus adjustment, so that the structure of the apparatus can be reduced in size and simplified. Is advantageous.

Further, according to the laser beam generating optical element of the third aspect, since this optical element is a hologram, it can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing a first embodiment of a laser beam generator according to the present invention.

FIG. 2 is a diagram illustrating a laser beam generating optical element according to a first embodiment of the present invention, as viewed from an optical axis direction.

FIG. 3 is an explanatory diagram showing Embodiment 1 of the laser beam generating apparatus of the present invention, which is used to obtain a ridge line of a laser beam generating optical element in the form of a function.

FIG. 4 is a graph showing a relationship between a peak intensity of a condensed spot and a position in an optical axis direction according to the first embodiment of the laser beam generator of the present invention.

FIG. 5 is a schematic side view showing Embodiment 2 of the laser beam generator of the present invention.

FIG. 6 is a diagram illustrating a second embodiment of the laser beam generator according to the present invention, in which a hologram is viewed from an optical axis direction.

FIG. 7 is a schematic side view showing an optical system that forms a Gaussian beam.

FIG. 8 is a view of an objective lens used in the optical system of FIG. 7 as viewed from an optical axis direction.

9A and 9B show a case where an optical system for forming a Gaussian beam is applied to a laser beam machine. FIG. 9A is a schematic diagram, and FIG. 9B is a partially enlarged view of FIG.

FIG. 10 is a schematic side view showing an optical system that forms a Bessel beam.

FIG. 11 is a diagram of an axicon used in the optical system of FIG. 11, viewed from the optical axis direction.

FIG. 12 is a graph showing a change in intensity of a focused spot in the optical axis direction of a Bessel beam and a Gaussian beam.

FIG. 13 is a graph showing a relationship between a peak intensity of a condensed spot and a radial direction in an optical system that forms a Bessel beam.

FIG. 14 is a schematic side view showing a laser beam generating device previously proposed by the present applicant.

FIG. 15 is a graph showing a relationship between a peak intensity of a converging spot and a position in an optical axis direction in a laser beam generating optical element provided in the laser beam generating apparatus of FIG.

FIG. 16 is a graph showing a change in intensity of a converged spot as viewed in the moving half direction in a laser beam generating optical element provided in the laser beam generating apparatus of FIG.

17A and 17B show a case where the laser beam generator of FIG. 14 is applied to a laser beam machine. FIG. 17A is a schematic diagram, and FIG. 17B is a partially enlarged view of FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 semiconductor laser element 2 collimating lens 30 laser beam generating optical element 31 and 32 composed of lens 31 ridge ridge section of laser beam generating optical element 30 hologram

Claims (4)

[Claims] 1. A plurality of beams from a half plane defined by the optical axis in an arbitrary plane including the optical axis such that the beams converge at different positions outside the optical axis. An optical element for generating a laser beam, comprising an optical element that emits light. 2. The optical element is a lens, and a ridge line in a half plane defined by the optical axis in an arbitrary cross section including the optical axis of the lens is constituted by a plurality of sections. Compartment shapes are represented by different nonlinear functions,
2. The laser beam generating optical element according to claim 1, wherein each section is functionally discontinuous with respect to each other. 3. The laser beam generating optical element according to claim 1, wherein said optical element is a hologram optically equivalent to said lens. 4. A laser beam generator comprising the optical element according to claim 1.