JPH09258012A - Optical element for generating laser beam and laser beam generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element for generating a laser beam and a laser beam generating device capable of intensifying the intensity of a middle peak after ensuring a focal depth to some extent. SOLUTION: After a laser beam of a spherical wave transmitted from a semiconductor laser element 1 is converted into a plane wave by a collimator lens 2, it is made incident on an optical element 3 for generating a laser beam. A surface having light refracting action in the optical element 3 for generating a laser beam, that is a surface of a light outgoing side, is formed by two ridges D', D" when viewed on a cross section cut by a plane including the optical axis (z-axis) to form such a laser beam being converted out of the optical axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam generation optical element capable of generating a laser beam having a relatively small spot diameter and a remarkably large depth of focus as compared with an ordinary laser beam having the same spot diameter. The present invention relates to a laser beam generation device including the laser beam generation optical element and suitable when applied to a device such as a laser processing 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. 9 shows an optical system that focuses the Gaussian beam. In this optical system, an objective lens 22 is used as a means for condensing the laser beam 21. Further, FIG. 10 is a view of the objective lens 22 seen from the direction of the optical axis 4, and the lines in the drawing show 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 beam center intensity is 80% or more of the beam center intensity at the position where the spot diameter is the minimum, that is, the so-called depth of focus Z, is such that the spot diameter becomes the minimum as shown in the following equation (2). It is well known that it is proportional to the square of the beam diameter at the position (the radius of the beam at the position where 1 / e ² of the peak intensity) 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, the case of the laser processing machine shown in FIG. 11 will be described as an example. As shown in FIG. 11A, the laser beam emitted from the laser beam generator 100 has an optical path of 90 ° by a mirror 101. After the conversion, the light is condensed by the objective lens 102, and the condensed spot is guided to the processing object 106 therebelow.

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 and the like.

FIG. 12 shows a conventional example of an 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.

In FIG. 13, the axicon 13 is shown with an 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) However, Z: distance in the optical axis direction r: distance in the direction perpendicular to the optical axis α, β: positive constants Due to the above cross-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. 14A, 14B, and 14C show optical elements using holograms, respectively.

That is, as shown in FIG. 14A, similarly to the Fresnel lens, the thickness of the refracting surface may be returned to the reference surface 17 every time the optical path difference becomes 1/2 of the wavelength λ. In this case, the hologram 16 has a sawtooth-shaped cross section as shown in FIG.

As a simpler hologram, the holograms shown in FIGS. 2B and 2C can be considered. In the case shown in FIG. 6B, the optical path difference is equal to the wavelength λ like a Fresnel strip plate.
The thickness is changed with a radius of 1/2 of the cycle as a cycle, and in the example shown in FIG. 7C, the transmittance is inverted with a radius of 1/2 of the wavelength λ as a cycle. That is, the transmissive portion and the non-transmissive portion are alternately provided in this cycle. In the cases of FIGS. 2B and 2C, it is clear that the hologram 16 is a set of concentric circles. In addition, FIG.
In (c), parts corresponding to those in (a) of the figure are designated by the same reference numerals.

FIG. 15 is a view of the hologram 16 which is optically equivalent to the axicon 13 as seen from the optical axis 4 direction. In this case, since the traveling direction of the light emitted from the hologram 16 is the same at any position in the direction perpendicular to the optical axis 4, the pattern of the hologram 16 is a set of concentric circles of equal pitch in the direction perpendicular to the optical axis 4. become.

In the optical system shown in FIG. 12, the electric field distribution in the direction perpendicular to the optical axis 14 as seen in a cross section including the optical axis 14 is
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. 16 shows the changes in the focused spot diameters of the basic Bessel beam and the Gaussian beam as seen in the optical axis direction, in comparison with the case of a spot diameter of 40 μm. In the figure, (1) represents a Bessel beam, and (2) represents a Gaussian beam. Further, Table 1 shows specific spot diameters in the optical axis direction of both beams shown in FIG.

[0022]

[Table 1]

The depth of focus of the Gaussian beam in Table 1 was calculated based on the above equation (2). In addition, the depth of focus in the case of a Bessel beam is also defined as a range in which the central intensity of the beam is 80% or more with respect to the central intensity of the beam at the position where the spot diameter is the minimum (similar to the Gaussian beam). The range in which the central intensity is 80% or more was measured from the graph of Δθ = 0 in FIG. 4).

As is apparent from FIG. 16, in the Bessel beam, the focused spot diameter is constant at 40 μm regardless of the position in the optical axis direction (mm), whereas in the Gaussian beam, the focused spot diameter 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 seen that the Bessel beam can have a significantly larger (deeper) depth of focus than the Gaussian beam.

[0025]

By the way, in the above Bessel beam, the light intensity in the radial direction of the axicon 13 is as shown in FIG.
It has many sub-peaks.

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 a Bessel beam as described above is used for a device such as a laser beam machine, which is not required to have a sub-peak and requires only a high peak intensity of the central spot. I couldn't. 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 used in many applications, such as laser beam machines, laser printers, optical pickups, and bar code readers, the focal depth does not need to be as deep as the Bessel beam, and the conventional Gaussian beam is used. Just a little deeper than the beam gives very useful results. 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.

The present invention has been made in view of the above circumstances, and a novel laser capable of suppressing the occurrence of a sub-peak and increasing the intensity of the central spot peak while securing a certain depth of focus. An object of the present invention is to provide a beam generation optical element and a laser beam generation device including the laser beam generation optical element.

[0030]

In the optical element for generating a laser beam according to the present invention, in an arbitrary plane including the optical axis, beams within a half plane defined by the optical axis converge outside the optical axis. As described above, the above-mentioned object is achieved by the optical element which emits the beam.

Preferably, the optical element is a lens, and a curve representing a ridgeline in a half plane defined by the optical axis in an arbitrary section including the optical axis of the lens is a non-linear function, and the curve is It is discontinuous on the optical axis.

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

The laser beam generator of the present invention is
The optical element according to any one of claims 1 to 3 is provided, whereby the above object is achieved.

Here, when the optical element is a lens, the function of the ridge is, for example, a higher-order function of the third order or higher,
And a discontinuous function can be used.

The operation will be described below with reference to FIG.

In the case of an ordinary Bessel beam as shown in FIG. 12, a light beam forming a long focus laser beam (hereinafter, a laser beam having a larger depth of focus than a Gaussian beam is referred to as a long focus laser beam) is the optical axis. It is parallel light that intersects. 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, according to the laser beam generating optical element of the present invention, for example, as shown in FIG. 1, the light beams C ′ and C ″ forming the laser beam intersect the optical axis 4, and Since the light beams converge on the off-optical axis 4, the light intensity per unit space inside the light beams C ′ and C ″ improves 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.

On the other hand, the laser beam emitted from the laser beam generating optical element 3 is divided into two light beams C ′ and C ″ as shown in FIG. 1. One light beam C ′ intersects the optical axis 4, Further, it becomes a light beam that converges toward a point E ′ outside the optical axis 4, and the other light beam C ″ becomes a light beam that intersects the optical axis 4 and converges toward a point E ″ outside the optical axis 4. here,
Since E ′ and E ″ are symmetrical with respect to the optical axis 4, the light beams C ′ and C ″ intersect. For this reason, at the intersecting portions, the wavefronts of the light beams C ′ and C ″ interfere with each other, and the long focal point having an amplitude distribution similar to the 0th-order Bessel function of the first kind in the direction perpendicular to the optical axis 4. A laser beam is formed, that is, a laser beam having a far greater depth of focus than a Gaussian beam is formed.

Therefore, by using the laser beam generator equipped with the laser beam generating optical element of the present invention, a laser beam having a practically sufficient depth of focus and a high central spot intensity can be obtained. Therefore, for example, when applied to a laser processing machine, it is not necessary to finely adjust the focus 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 bar code reader, the bar code can be read without moving the reading device even if the position of the bar code changes.

When applied to an optical pickup,
The signal of the optical disk can be read without using a movable mechanism for focus adjustment.

Further, by using a hologram, it is possible to easily realize the above laser beam generating optical element.

[0044]

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

(First Embodiment) FIG. 1 shows a first embodiment of a laser beam generator according to the present invention. This laser beam generator comprises a semiconductor laser element 1, a collimator lens 2, and a laser beam generating optical element (laser beam generating optical element of the present invention) 3.

The laser beam C of the spherical wave 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.

Here, unlike the Bessel beam, the angle θ formed with the optical axis 4 in the traveling direction of the light refracted at the one ridge D ′ changes depending on the height r from the optical axis 4. Therefore, θ is a function of r and is represented by θ (r) below.

Laser Beam Generating Optical Element 3 of the Present Invention
Is an optical element that forms a laser beam that converges off the optical axis. Therefore, θ (r) increases as the distance from the optical axis 4 increases.

From the geometrical relationship shown in FIG. 1, θ (r)
Is expressed by the following equation (4) as an example.

Θ (r) = θ ₀ −Δθ (R−r) / R (4) where R: is the outer diameter (radius) of the optical element 3 Δθ: is a constant that determines the strength of convergence. , An angle formed by a straight line refracted at the position of r = R toward the convergence point E ′ and a straight line refracted at the position of r = 0 toward the convergence point E ′ In the light refracted at the other ridge D ″ Similarly, the relationship of the above formula (4) is established. Note that the light refracted at the ridge D ″ converges at the convergence point E ″. Further, the actual optical system is rotationally symmetric with respect to the optical axis 4. Therefore, the relationship of the equation (4) is similarly established for any cross section seen from a plane including the optical axis 4 other than the cross section shown in FIG.

A function f representing the above-mentioned edge lines D'and D "
(R) and g (r) are expressed by the following equations (5) and (6), respectively, and are functions that cannot be differentiated on the optical axis.

[0052]

[Equation 2]

[0053]

(Equation 3)

With reference to FIG. 2 below, the above (5),
The process of deriving the equation (6) will be described. The following equation (7) is established by the geometrical relationship shown in FIG.

Θ ₁ = π−α, θ ₂ = θ ₁ + θ (7) This θ is θ (r) in the above equation (2).

Now, assume that the function of the curve corresponding to the ridge D'is expressed by the following equation (8).

Z = f (r) (8) Since the tangent line 5 of this curve can be obtained by differentiating the function z = f (r), it is expressed by the following equation (9).

Z = f '(r) .r + m (9) where m is the intersection of the tangent line 5 and the z axis.

Here, the inclination f '(r) of the tangent line 5 is as shown in FIG.
It is expressed by the following equation (10) according to the geometrical relationship shown in.

F ′ (r) = tan α (r) (10) Here, assuming that the refractive index is n, the following equation (11) is established according to Snell's law.

N sin θ ₁ = sin θ ₂ (11) When the relationship of the above equation (7) is substituted into this equation (11), the following equation (12) is established.

Nsin (π−α) = sin (π−α + θ) (12) When formula (12) is rearranged, the following formula (13) is obtained.

Nsin α = sin (α−θ) (13) Since α = α (r) and θ = θ (r), (1
Equation (3) can be rewritten as equation (14) below.

Nsinα (r) = sin {α (r) −θ (r)} = sinα (r) cosθ (r) −cosα (r) sinθ (r) (14) (14) Both sides of the formula are sinα. Dividing by (r) gives (1
Expressions 5a) and (15b) are established.

N = cos θ (r) − {tan α (r)} ⁻¹ · sin θ (r) (15a) {n-cos θ (r)} / sin θ (r) = − {tan α (r)} ⁻¹ (15b) Therefore, tan α (r) = − sin θ (r) / {n−cos θ (r)} (16)

Substituting the relationship of the above equation (10) into the equation (16), the following equation (17) is established.

F ′ (r) = − sin θ (r) / {n−cos θ (r)} (17) Therefore, the ridge line D ′ is represented by the above formula (5) by integrating the above formula (17). Is a function that is

Similarly, the ridgeline D ″ is represented by the above equation (6).

Here, depending on how θ (r) is given,
In some cases, the indefinite integral in the formula cannot be executed. In that case, the form of the function can be determined by performing the numerical integration.

As an example, s = Δθ / R, t = θ ₀ −Δ
When θ and θ (r) = sr + t are set, the above f (r) can be rewritten as the following equation (18).

F (r) = − (1 / s) · log {n−cos (sr + t)} + c (18) Here, when f (0) = z ₀ , the following formula (19) is established. .

F (0) = z ₀ = − (1 / s) · log (n−cost) + c (19) Therefore, the integration constant c is expressed by the following equation (20).

C = z ₀ + (1 / s) · log (n-cost) (20) Therefore, the above equation (5) can be rewritten as the following equation (21).

Z = f (r) = − (1 / s) · log {n-cos (sr + t)} + (1 / s) · log (n-cost) + z ₀ (21) FIG. 3 shows It is the figure which looked at the optical element 3 for laser beam generation from the direction of the optical axis 4, and the center is discontinuous and the other part is a continuous curved surface. The lines in the figure are contour lines.

Now, the laser beam emitted from the laser beam generating optical element 3 having the refracting surface having the above-mentioned shape is shown in FIG.
As shown in FIG. 2, it is divided into two light beams C ′ and C ″. One light beam C ′ intersects the optical axis 4 and is located at a point E ′ outside the optical axis 4.
The other light flux C ″ is a light flux that converges toward the optical axis 4 and the other light flux C ″ intersects the optical axis 4 and converges toward a point E ″ outside the optical axis 4. Here, since E ′ and E ″ are symmetrical to each other with respect to the optical axis 4, the light beams C ′ and C ″ intersect. For this reason, at the intersecting portions, the wavefronts of the light beams C ′ and C ″ interfere with each other, and the long focal point having an amplitude distribution similar to the 0th-order Bessel function of the first kind in the direction perpendicular to the optical axis 4. A laser beam is formed, i.e.
A laser beam having a far greater depth of focus than a Gaussian beam is formed.

Here, the reason why the peak intensity of the focused spot is improved by the laser beam generating optical element 3 will be described. In the case of an ordinary Bessel beam as shown in FIG. 12, the light flux forming the long focus laser beam is parallel light intersecting 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 of the present invention, as shown in FIG. 1, the light beams C ′ and C ″ forming the long focus laser beam intersect the optical axis 4, and Since the light beam converges on the off-axis axis 4, the light beam C ′,
The light intensity per unit space inside C ″ is improved in the optical axis direction. That is, according to this laser beam generating optical element 3, both the light fluxes C ′ and C ″ are directed toward the convergence point E ′ and the point E ″. The light intensity per unit space can be improved as compared with the case of the Bessel beam because it travels in a narrowed state. The peak intensity can also be improved compared to the case of the Bessel beam.

An example of numerical calculation of the peak intensity of the focused spot is shown below. The luminous flux from the beam generating opening of the laser beam generating optical element 3 is expressed by the above formula (5),
Consider a case where the light is converged to the outside of the optical axis 4 in the form shown by the equation (6). At this time, the amplitude distribution U (r) in the radial direction at the beam generating aperture is expressed by the following equation (22).

U (r) = J ₀ {β (r) · r} (22) where β (r) = (2π / λ) sin θ (r) Amplitude distribution U in the radial direction at this opening (R) below (2
Fresnel integration represented by the equation (3) was performed to simulate a change in the peak intensity I of the focused spot viewed in the optical axis direction, represented by the following equation (24).

[0080]

(Equation 4)

However, A: constant k = 2π / λ r: radial coordinate at z = 0 ρ: radial coordinate at z = z i: imaginary number I (z, ρ) = | E (z, ρ) | ² (24) In addition, the above equations (22) and (23) are expressed by “A.J.C.
ox and Joseph D'Anna; Opt.
Lett. Vol. 17, No. 4 (1922) 232 ″, so a detailed description is omitted here.

FIG. 4 shows the result of the above simulation. From FIG. 4, as compared with the case where the light flux is parallel light (Δθ = 0) as in the case of forming a Bessel beam, the peak of the focused spot increases as the degree of convergence of the light flux (Δθ) increases. It can be seen that the strength is improved.

[0083] 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. The intensity distribution in the direction perpendicular to the optical axis of the long focus laser beam at this time is as shown in FIG. 5, which is similar to the intensity distribution of the conventional Bessel beam of FIG. 12, but at a position away from the optical axis 4. It can be seen that the unnecessary sub-peak is suppressed in.

Next, the effect of using such a laser beam generator in a laser beam processing 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.

Therefore, the depth of focus does not need to be as large as the Bessel beam described above. On the other hand, the depth of focus of the laser beam formed by the laser beam generating optical element 3 of the present invention is significantly larger than that of the Gaussian beam. Therefore, according to the present invention, as shown in FIG. 6B, it is possible to sufficiently secure the depth of focus corresponding to the total of the unevenness 107 and the thickness d of the processing object 106. 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.

Here, in the case of this embodiment, assuming that the peak intensity required for the laser processing machine is 8, Δθ = 3θ ₀ /
4 was used. The focused spot diameter by this optical element was 40 μm. A normal Gaussian beam should have a focal depth of 1.48 mm, but by using the optical element of the present invention, a focal depth of 9 mm, which is 6 times deeper or more, could be realized. Further, the peak intensity of the central spot was up to 9 times that of the Bessel beam.

Even when the laser beam generator of the first embodiment is applied to other devices such as a laser printer, an optical pickup and a bar code reader, fine adjustment becomes unnecessary and a movable mechanism becomes unnecessary. There is an advantage such as.

(Second Embodiment) FIG. 7 shows a second embodiment of the laser beam generator according to the present invention. In the second embodiment, a hologram 3'which is optically equivalent to the laser beam generating optical element 3 is used as the laser beam generating optical element, and the other configurations are the same as those in FIG. Therefore, corresponding parts are denoted by the same reference numerals, and detailed description thereof will be omitted.

It should be noted that FIG. 8 shows this hologram 3'as an optical axis 4
In the hologram 3 ′, the traveling direction of the light emitted from the hologram 3 ′ is different at each position in the direction perpendicular to the optical axis 4, and the diffraction angle increases as the distance from the optical axis 4 increases. Therefore, the pattern of hologram 3'is
It is a collection of concentric circles whose pitch decreases in the direction of the optical axis 4.

As a method of producing such a hologram 3 ', the method of producing a hologram equivalent to the axicon 13 for forming the above Bessel beam can be applied as it is. That is, the thickness of the refracting surface is equal to 1
A hologram with a sawtooth-shaped cross section or an optical path difference of 1 wavelength
The transmittance may be inverted with a radius of / 2 as the period, or a hologram formed by changing the thickness may be used.

Also in the second embodiment, it is possible to form a laser beam in which the light intensity of the central spot is larger than that of the Bessel beam and the depth of focus is significantly larger than that of the Gaussian beam. It is possible to exert an effect.

[0092]

As described above, by using the laser beam generating optical element of the present invention, it is possible to obtain a laser beam having a large depth of focus and a large light intensity at the central spot.

Therefore, when the laser beam generator equipped with this laser beam generating optical element is applied to, for example, a laser beam machine, it is not necessary to finely adjust the focal position corresponding to the unevenness of the workpiece. . That is, the troublesome adjustment work becomes unnecessary. Further, a laser beam having a high center peak can be obtained. As a result, a laser processing machine with excellent processing efficiency can be realized.

When applied to a laser beam printer, there is an advantage that the position adjustment of the photoconductor can be simplified.

When applied to a bar code reader, there is an advantage that the bar code can be read without moving the reading device even if the position of the bar code changes.

When applied to an optical pickup,
Since a movable mechanism for focus adjustment is not necessary, cost reduction and simplification of the device configuration can be achieved.

In particular, when the laser beam generating optical element is composed of a hologram, there is an advantage that the laser beam generating optical element can be easily manufactured.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a first embodiment of a laser beam generator of the present invention.

FIG. 2 is an explanatory view used for obtaining a ridge line of the laser beam generating optical element of FIG. 1 in a function form.

FIG. 3 is a view of the laser beam generating optical element of FIG. 1 seen from the optical axis direction.

4 is a graph showing the relationship between the peak intensity of a focused spot and the optical axis direction in the laser beam generating optical element of FIG.

5 is a graph showing changes in the intensity of a focused spot viewed in the radial direction in the laser beam generating optical element of FIG.

6A and 6B show a case where the laser beam generator of the present invention is applied to a laser processing machine, FIG. 6A is a schematic view, and FIG. 6B is a partially enlarged view of FIG. 6A.

FIG. 7 is a schematic diagram showing a second embodiment of the laser beam generator of the present invention.

FIG. 8 is a view of the laser beam generating optical element of FIG. 7 viewed from the optical axis direction.

FIG. 9 is a schematic diagram showing an optical system that forms a Gaussian beam.

FIG. 10 is a view of an objective lens used in the optical system of FIG. 9 viewed from the optical axis direction.

11A and 11B show a case where an optical system for forming a Gaussian beam is applied to a laser beam machine, FIG. 11A is a schematic view, and FIG. 11B is a partially enlarged view of FIG. 11A.

FIG. 12 is a schematic diagram showing an optical system that forms a Bessel beam.

FIG. 13 is a diagram of an axicon used in the optical system of FIG. 11, viewed from the optical axis direction.

14A, 14B, and 14C are schematic diagrams respectively showing holograms which are different from each other and are optically equivalent to an axicon.

FIG. 15 is a diagram of a hologram optically equivalent to an axicon, as viewed from the optical axis direction.

FIG. 16 is a graph showing changes in the intensity of a focused spot in the optical axis directions of the Bessel beam and the Gaussian beam.

FIG. 17 is a graph showing the relationship between the peak intensity of the focused spot and the radial direction in the optical system that forms the Bessel beam.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser element 2 ... Collimating lens 3 ... Optical element for laser beam generation 3 '... Optical element for laser beam generation consisting of hologram 4 ... Optical axis C', C "... Luminous flux D ', D" ... Ridge line

Claims (4)

[Claims] 1. A laser beam generator comprising an optical element that emits a beam within a half plane defined by the optical axis so that the beams are converged outside the optical axis in an arbitrary plane including the optical axis. Optical element. 2. The optical element is a lens, and a curve representing a ridgeline in a half plane divided by the optical axis in an arbitrary section including the optical axis of the lens is a non-linear function, and the curve is the The laser beam generating optical element according to claim 1, wherein the optical element is discontinuous along the optical axis. 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 any one of claims 1 to 3.