JPH04123016A - Phase shift element and laser device using the same - Google Patents

Abstract

PURPOSE:To realize a laser beam with a small beam spot while holding the depth of focus large without varying the NA(numerical aperture) of an image formation optical system by using the specific phase shift element. CONSTITUTION:The light transmission part of the phase shift element 4 is divided into two transparent areas which are a 1st area 11 and a 2nd area 12 and laser beam which passes through the 2nd area 12 is longer in optical path length than laser beam which passes through the 1st area 11 by a half as long as the wavelength. Then luminous flux emitted from a light source part 1 composed of a laser, etc., is converged by a condenser lens 3. The phase shift element 4 is arranged in the vicinity of a beam waist which is formed at this time and light passing through the phase shift element 4 is made incident on a cylindrical lens 6 from a collimator lens 5. Consequently, a spot which is smaller than the beam spot diameter determined by the NA of the optical system can be formed on a specific surface while the depth of focus is held large.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a phase shift element and a laser device using the same, and particularly to a phase shift element that divides a laser beam passage region into a plurality of regions,
By using a phase shift element that imparts a predetermined phase difference between the laser beams passing through each region, the beam spot diameter of the laser beam can be adjusted to form images with high accuracy. The present invention relates to a phase shift element for astigmatic adjustment and a laser device using the same.

(Prior Art) In recent years, there has been a demand for laser devices that input and output image information using laser light to be able to form and reproduce image information with high resolution.

Generally, in order to form and reproduce image information with high resolution,
For example, the beam spot diameter of the laser light (laser beam) during human output may be made smaller. It is known that the beam spot diameter can be reduced by using an optical system with a large NA (numerical aperture).

FIG. 14 is a schematic diagram of the main parts of an optical scanning device used in a conventional laser printer or the like.

In FIG. 14, reference numeral 91 denotes a light source section consisting of a laser or the like, and a laser beam emitted from the light source section 91 is converted into substantially parallel light by a collimator lens 92 and enters a rotating polygon mirror 93. The rotating polygon mirror 93 is rotating at a constant speed in the direction of the arrow, and the laser beam incident on the point P of the reflecting surface 93a of the rotating polygon mirror 93 is reflected and deflected and scanned in the main scanning section. The light enters an f-theta lens system 94 as an image optical system. The laser beam that has passed through the f-theta lens system 94 forms an image on a surface to be scanned 95, and optically scans the surface by linearly moving at a substantially constant speed.

For example, in order to achieve high resolution when forming an image on a surface to be scanned such as a photoreceptor, the NA of the f-theta lens system 94 is increased, and the beam spot diameter formed on the surface to be scanned 95 is increased. 96
All you have to do is make it smaller.

However, it is very difficult to construct an optical system with a large NA, and theoretically, an optical system in air has a NA of 1.
I can't go beyond that. Furthermore, as the NA increases, the depth of focus decreases rapidly, resulting in severe image plane setting errors and difficulty in manufacturing and adjusting the device.

Generally, the beam spot diameter and focal depth on the image plane of a laser device using a laser light source are expressed by the following equation.

Spot diameter = λ/(2・NA) ・・・・・・(a
) Depth of focus = ±λ/(2・NA2) ...(b
) Here, λ is the wavelength, k is a constant (k≧1.64) representing the degree of beam intensity in the periphery of the pupil of the imaging optical system, and the beam spot diameter is the 1/e2 value of the peak intensity.

For reference, wavelength λ = 0.78 in equations (a) and (b).
Table 1 shows the relationship between the beam spot diameter on the scanned surface and the depth of focus for various NAs calculated assuming that μm and constant = 1.7.

Table 1 Furthermore, as a laser light source used in a laser device, a semiconductor laser has an astigmatism difference due to its structure. That is, as shown in FIG. 13(A), the size of the light emitting area is different between the direction parallel to the semiconductor junction surface (X direction) and the direction perpendicular to the semiconductor junction surface (X direction). Therefore, the radius of curvature of the wavefront at a point away from the laser light source differs in two directions, a parallel direction and a perpendicular direction, as shown in FIG. 13(B).

Therefore, when high-speed light from a laser light source is imaged using a rotationally symmetrical lens system, the best imaging position differs in the two directions, the X direction and the I'll come.

Conventionally, this type of astigmatic difference has been corrected by arranging a cylindrical lens in the optical path and adjusting the position of the cylindrical lens.

(Problems to be Solved by the Invention) As is clear from Table 1 above, for example, for laser devices such as laser printers, the NA of the imaging optical system is 0.0.
2 or more, that is, when the spot diameter is less than 33 μm, the depth of focus becomes less than ±1 mm.

Generally, when the depth of focus is less than ±1 mm, manufacturing becomes very difficult due to problems such as setting the position of the photoreceptor and flatness of the photoreceptor. Therefore, it is generally difficult to increase the NA of the imaging optical system by 002 or more.

Furthermore, for objective lenses for optical disks, objective lenses for microscopes, etc., the beam spot diameter is approximately 0.7 μm, which is the limit, and it is theoretically difficult to obtain a spot diameter smaller than that. .

As described above, there is a problem in that it is theoretically and mechanically difficult to obtain a laser beam with a small spot diameter in the conventional laser device.

In addition, when an optical system used in a laser device or a rotationally symmetrical lens system is used, if a cylindrical lens is used to correct the astigmatism difference when a semiconductor laser is used, the radius of curvature of the cylindrical lens increases. There was a problem that it became difficult to produce.

The present invention utilizes a phase shift element configured to impart a predetermined phase difference to the laser beam passing through each of the plurality of regions through which the laser beam passes, thereby adjusting the NA of the imaging optical system. By realizing a laser beam with a smaller beam spot diameter while maintaining a large depth of focus without changing the depth of focus, and by arranging the phase shift element at an appropriate position in the optical path of the laser device, the astigmatic difference of the laser light source can be reduced. An object of the present invention is to provide a phase shift element that can easily obtain high optical performance such as good correction, and a laser device using the same.

(Means for Solving the Problems) The phase shift element of the present invention includes a first region that is transparent to light of a predetermined wavelength, and a predetermined region around the first region that is transparent to light passing through the first region. It is characterized by providing a second region having a phase difference of . Further, the phase difference at this time is 180 degrees.

Further, the laser device of the present invention may include a first lens transparent to the laser beam near the light emitting end face of the laser light source, near a position conjugate with the light emitting end face, or near the beam waist of the laser light emitted from the laser light source. The present invention is characterized in that a phase shift element having a region and a second region having a predetermined phase difference with respect to the laser beam passing through the first region is arranged around the first region. A semiconductor laser or a cassette laser is used as the laser light source, and the beam waist is formed by condensing the laser light emitted from the laser light source using a condensing optical system.

(Example) Fig. 1 is a schematic view of the main part showing one embodiment of the phase shift element of the present invention, Fig. 1 (A) is a perspective view, and Fig. 1 (B) is a central axis (optical axis). FIG.

In Fig. 1, 4 is a phase shift element, and 11 is a circular or elliptical beam of a predetermined wavelength centered on the optical axis (laser beam L).
12 is a circular or elliptical ring-shaped second region provided around the first region 11 and transparent to the laser beam; 13 is a laser surrounding the second @ region 12; This is a light-shielding area that is opaque to light.

In this way, the light transmitting portion of the phase shift element 4 is located in the first region 1.
It is divided into two transparent areas, a transparent area 1 and a second area 12. A predetermined phase difference is given between the two light fluxes passing through the two regions 11 and 12.

In this embodiment, the optical path length of the laser light passing through the second region @12 is set to be longer by one-half wavelength than that of the laser light passing through the first region @11.

That is, the phase shift element 4 directs the passing light flux to the first region 1.
The light beam is divided into two light beams: a light beam that passes through the second region 1 and a light beam that passes through the second region 12, and a phase difference of 180° is given between the two light beams at this time.

Such a phase shift element can be manufactured relatively easily. For example, using parallel plate glass that has been polished on both sides to a fine grain size as a substrate, and assuming that the wavelength of the laser beam is λ, a vapor deposited material with a refractive index n is applied only to the second region 12 or the first region, and the thickness is d−λ/(2
It can be manufactured by forming a thin film of (n-1)) by vacuum evaporation and applying a light-absorbing paint to the light-shielding slope.

Next, the principle of reducing the beam spot diameter of laser light by using a phase shift element will be explained.

FIGS. 2A and 2B are explanatory diagrams showing the wavefront state and amplitude distribution when a plane wave light beam enters and passes through the phase shift element 4 of this embodiment. Such a situation occurs, for example, when the phase shift element 4 is disposed near the beam waist of the laser beam in a laser device.

In the figure, when a plane wave laser beam is incident on the phase shift element 4 from the left side of the drawing, the first. 2nd area 1
1.12 conceptually shows wavefronts of light beams having a predetermined phase difference with each other.

As shown in FIG. 2(A), the laser beam enters the phase shift element 4 from the left, but since the phase shift element 4 is arranged near the beam waist position, the laser beam becomes almost a plane wave near the incident position. There is. When this plane wave enters the phase shift element 4, an optical path difference of 1/2 wavelength occurs between the plane wave that passed through the first region @11 and the plane wave that passed through the second region 12, as shown in the figure. It emits as a wavefront of a certain shape. Therefore, the complex amplitude distribution of the laser beam immediately after being emitted from the phase shift element 4 is as shown in FIG. 2(B).

In Figure 2 (B), 3 and X are the coordinates perpendicular to the optical axis, UO
(X) is the complex amplitude distribution of the laser beam at the coordinate X,
14 represents the complex amplitude distribution of the beam that has passed through the first region 11 of the phase shift element 4, and 15a and 15b represent the complex amplitude distribution of the beam that has passed through the second region 12 of the phase shift element 4.

Uo(X) is a complex number, but the phase is 0 degrees and 180 degrees
Since it is a complex amplitude distribution with only two values, the imaginary component is zero, and it can be expressed only on the real axis as shown in the figure. For simplicity, the figure is drawn assuming that the intensity of the laser beam is constant regardless of the position 1jlx.

Next, a description will be given of what kind of intensity distribution can be obtained on the image plane when the phase shift element 4 is regarded as an object plane and an aberration-free optical system is used to form an image. For simplicity, the phase shift element is
The explanation will be made assuming that it is a one-dimensional element in the direction and that the magnification of the optical system is 1.

First, when the numerical aperture of the optical system is infinitely large, the complex amplitude distribution on the object plane (FIG. 2(B)) is directly reproduced as the complex amplitude distribution on the image plane. However, in reality, since the numerical aperture of the optical system is finite, spreading due to diffraction occurs, and a complex amplitude distribution U, (x') as shown in FIG. 3(A) is formed on the image plane.

In the figure, X' is the coordinate on the image plane, 16°17a
, 17b are the complex amplitude distributions 14, 17b in FIG. 2(B), respectively.
15a and 15b. This can be explained using a formula.

The complex amplitude distribution ul(X') on the image plane is the complex amplitude distribution U on the object plane. (x) and point spread complex amplitude distribution K(X'), it can be expressed by the following equation.

Ll, (x')-1Llo(x)・ to (x'-x)・
dx...11) Here U. 3 with different phases
If the approximation to consider it as a set of point light sources holds true, then δ(
Llo(x) = C・δ(×)−δ(x−a)−δ(x
+a) -12) It's been quite a while. However, a is the distance from the optical axis to the center of the complex amplitude distribution 15a or 15b, and C is a constant corresponding to the ratio of the energy in the part of the complex amplitude 14 and the energy in the part of the complex amplitude 15a or 15b. It is. Substituting equation (2) into equation (1) yields (1)
The formula is 1, (x') = Cs (x') - K (x'÷a) - (x' - a) (3), and the complex amplitude of the image plane It can be seen that the distribution is represented by the addition of three point spread complex amplitude distributions.

The first, second, third, or third term on the right side of equation (3)
Complex amplitude distributions 16 and 17a in Figure (A).

17b. In addition, the complex amplitude distribution 16°17a, 1
7b etc. are drawn with the secondary maximum of the small dots omitted for simplicity. If the approximation of considering the object surface as a set of three point light sources does not hold, then if the intensity of the object surface is 1, then the complex amplitude distribution U of the object surface. (x) is given. However, ao is the distance from the optical axis to the boundary between the first region 11 and the second region-12, and a is the distance from the optical axis to the boundary between the second region 12 and the light-shielding region 13. (4
) into equation (1), the image plane complex distribution u, (X'
) is expressed as follows.

(5) The first, second, third, or third term on the right side of equation
These are the complex amplitude distributions 16° 17a and 17b in Figure (A).

As mentioned above, when an object with a complex amplitude distribution as shown in Figure 2 (B) is imaged by an optical system, the image plane complex amplitude distribution is as shown in Figure 3 (
It has been explained that A) is expressed by adding the three complex amplitude distributions 16.17a and 17b.

Now, in FIG. 3(A), 17a and 17b' are curves 17a each representing a complex amplitude distribution.

The curve 17b is folded back to the X' axis, and by comparing the curves 17a'' and 17b'' with the curve 16, the magnitude of the amplitude can be compared. From the figure, the base of curve 16 and curves 17a' and 17b'
It can be seen that they almost overlap, and it is desirable to have such a relationship in order to obtain a small spot diameter.

Three complex amplitude distributions 16° 17a, 17 in Fig. 3(A)
The curve 18 in FIG. 3(B) is expressed as one complex amplitude distribution by adding b. Compared to the curve 16, the spread of the curve 18 in the X' direction is improved and smaller.

A curve 19 in FIG. 3(C) is a curve showing the image plane intensity distribution. The intensity distribution 1(x') is obtained from the complex amplitude distribution ul(X'') by 1(x') - U + x') tll(x') - 11J,
(x”)+2−·(6).

As described above, in this embodiment, the phase shift element as shown in FIGS. An imaging spot diameter smaller than the imaging spot diameter determined from the number (numerical aperture, NA) is obtained.

Next, the principle by which the phase shift element according to the present invention can correct the astigmatism difference of a semiconductor laser will be explained using simulation results.

FIG. 4(A) is a schematic diagram when this phase shift element 4 is placed near the beam waist position of the laser beam, and FIG.
B) is an explanatory diagram showing the results of a simulation of the intensity distribution on the image plane by the imaging lens of FIG.

In this embodiment, for simplicity, calculations are performed using a system that is symmetric about the rotational axis. In FIG. 4(B), the phase shift element has a concentric structure, consisting of a first region 11 with radius A from the central axis (optical axis) and a second region 12 with radius β outside the first region 11, and between the passing light beams. It is set to have a phase difference of 180 degrees. The outside of the second region B is a light-shielding region. Such a phase shift element 4 is placed near the beam waist position formed by condensing the laser beam, and is imaged by an imaging lens assumed to be an aberration-free lens.

Here, the beam waist radius is W. , the wavelength of the laser light is λ
, the effective F number on the image plane side of the imaging lens is FNO,
A simulation to determine the intensity distribution on the image plane was performed using ordinary diffraction theory.

FIG. 4(B) shows Wo=1.0. czm, λ=0.632
The figure shows the intensity distribution on the image plane when the value of A is changed from 0.5 μm to 2.0 μm, with FNO=1.0 and B=2.0 μm. However, the intensity distribution is normalized by the maximum value, and the parameters Wo, A, and B are shown on the scale on the image plane, which is the actual size multiplied by the magnification of the imaging lens.

As shown in FIG. 4(B), when A=2 μm, A=B, and there is no phase inversion region, which is the same as simply inserting an aperture. In this case, Fig. 13 (
As can be expected from B), since the light divergence origin is shifted from the position of the phase shift element, the beam spot diameter can be made smaller to some extent by defocusing the image plane. When half [A] becomes 1 μm, the spot diameter on the image plane becomes smaller due to the effect of phase inversion. When the radius A becomes 0.7 μm, the beam spot diameter on the image plane becomes even smaller and almost matches the Airy pattern of the imaging lens. An Airy pattern is a diffraction image produced on an image plane when a point light source is imaged by an imaging lens that is assumed to be a rotationally symmetric achromatic lens. Then, when the radius A=0.7 μm, it can be interpreted that there is a virtual point light source exactly at the position of the phase shift element.

As a result, the phase shift element can be considered as an element having an optical function that can bring the origin of light divergence of the laser beam to the position of the phase shift element. At the same time, as mentioned above, the divergence angle of the laser beam is increased,
It can be thought of as an element that can reduce the beam spot diameter by making the laser beam incident on the entire effective diameter of the imaging lens.

As described above, when the optical system is rotationally symmetrical, the phase shift element can control the position of the origin of light divergence.

In the case of a semiconductor laser where the beam spot diameter is rotationally asymmetric, it is considered that the origin of light divergence is in two cross sections as shown in FIG. 13(B).

Therefore, if a phase shift element is used, the position of the light divergence origin can be moved to the position of the phase shift element within each cross section. In this way, the positions of the origins of light divergence, which were initially different in each cross section, can be moved to the same position.

In this embodiment, using this principle, the radius A of the phase shift element is
, B and the arrangement position in the laser optical path are appropriately set to correct the astigmatism difference of the semiconductor laser. Note that the phase difference between the laser beams passing through the first region @11 and the N2 region 12 may be any phase difference that is limited to 180 degrees.

Next, various embodiments of a laser device using the phase shift element of this embodiment will be described.

FIG. 5 is a schematic diagram of a main part of a first embodiment of a laser device using the phase shift element of the present invention.

In the figure, reference numeral 1 denotes a light source section consisting of a laser or the like, and the light beam emitted from the light source section 1 is made into substantially parallel light by a collimator lens 2, and then condensed by a condenser lens 3. At this time, a beam waist is formed near the focal point. A phase shift element 4 is disposed near the beam waist, and the light that has passed through the phase shift element 4 is converted into parallel light by a collimator lens 5 and enters a cylindrical lens 6 having refractive power in the sub-scanning direction. The cylindrical lens 6 forms a linear image of the light beam in the sub-scanning direction, which enters the rotating polygon mirror 7 and is reflected. The light beam reflected and deflected by the rotating polygon mirror 7 forms a beam spot 1o on the scanned surface 9 via the f-theta lens system 8.

Note that since the rotating polygon mirror 7 is rotating at a constant speed in the direction of the arrow, the laser spot 10 optically scans the surface to be scanned 9 as it rotates.

In this embodiment, by using the phase shift element 4 in the above configuration, the surface to be scanned can be scanned with a small beam spot diameter without reducing the depth of focus. As a result, a laser device capable of forming and reading images with high resolution, for example, has been achieved.

6 to 9 are schematic diagrams of main parts of second to fifth embodiments of laser devices using the phase shift element of the present invention. In the figure,
Elements that are the same as those shown in the first embodiment of FIG. 5 are given the same reference numerals.

In the second embodiment shown in FIG. 6, a semiconductor laser 1 is used as a light source.
A phase shift element 4 is arranged near the emission end face of the laser beam. The laser beam emitted from the light emitting point of the semiconductor laser 1 passes through a phase shift element 4 disposed in the vicinity thereof, and then becomes a parallel beam of light at the collimator lens 2 and enters the cylindrical lens 6 . The light is incident on the cylindrical lens 6. The structure after passing through the cylindrical lens 6 is the same as that of the first embodiment shown in FIG.

In this embodiment, the position immediately after the laser beam emitting end face of the semiconductor laser 1 is near the beam waist, so the phase shift element 4 is placed at that position to reduce the beam spot diameter according to the principle described above. .

This embodiment has a simplified optical system compared to the first embodiment shown in FIG.

In the third embodiment shown in FIG.
, consisting of a laser. 21 is a first condensing lens; 22
is an A10 modulator, 23 is a second condenser lens, 24 is a collimator lens, and 25 is a beam expander. In the figure, the laser beam emitted from the He-Ne laser 20 is
The beam is condensed by a first condensing lens 21, and subjected to intensity modulation by an A10 modulator 22 disposed near the condensing point.

The laser beam emitted from the A10 modulator 22 is again focused by the second focusing lens 23.

A phase shift element 4 is placed near the beam waist position formed at this time. The laser beam emitted from the phase shift element 4 is collimated by a collimator lens 24 , and the beam diameter is expanded by a beam expander 25 before entering the cylindrical lens 6 . After passing through the cylindrical lens, the beam spot IO is formed on the scanned surface 9 in the same manner as in the first embodiment shown in FIG.

In this embodiment, the gas laser is used as a light source by condensing the laser beam emitted from the gas laser with the second condensing lens 23 to form a beam waist, and arranging the phase shift element having the above-described configuration near the beam waist. In the fourth embodiment shown in FIG. 8, which allows the same effect as described above to be obtained in a laser device, the laser beam from the light source section 1 is rotated from the scanned surface 9 side through an f-theta lens system 8. It is characterized in that the light is guided to a polygonal mirror 7.

In the figure, reference numeral 41 denotes a transmission type phase shift element, which is provided approximately on the same plane as the scanned surface 9.

In this embodiment, the f-theta lens 8 is a tilt correction optical system in which the mirror surface of the rotating polygon mirror 7 and the surface to be scanned 9 are in a substantially conjugate relationship with respect to the sub-scanning direction.

In the figure, the laser beam emitted from the light emitting point of the semiconductor laser 1 passes through the collimator lens 2 to become a parallel beam, and is then focused by the condensing lens 3 to the surface to be scanned 9.
A beam waist is formed near the extended line of.

The phase shift element 41 is arranged near the beam waist position. A laser beam is incident on the phase shift element 41 from an oblique direction, or a laser beam of approximately 1/2 wavelength is emitted after passing through two regions for a beam incident obliquely at a certain angle. It is made to have an optical path difference. The laser beam emitted from the phase shift element 41 is f
The light passes through the -θ lens 8 and forms a line image near the mirror surface of the rotating polygon mirror 7. The laser beam is then reflected by the same mirror, passes through the f-theta lens 8 again, and passes through the scanned surface 9.
A beam spot 10 is formed above. Dom Spot 1
0 rotates the rotating polygon mirror 7 in the direction of the arrow, and scans the surface to be scanned 9 with light in the direction of the arrow.

This embodiment does not require a cylindrical lens for line image formation, so in addition to simplifying the optical system, the beam waist diameter formed near the phase shift element 41 or the beam spot diameter when no phase shift element is used. Since they are about the same size, there is an advantage that the phase shift element 41 can be manufactured easily.

Furthermore, in this embodiment, since the laser beam is incident on the phase shift element 41 from an oblique direction, the laser beam reflected by the phase shift element hardly returns to the semiconductor laser, so that stable laser oscillation is possible. It has the characteristic of becoming.

The fifth embodiment shown in FIG. 9 differs from the fourth embodiment shown in FIG. 8 in that a reflective phase shift element is used instead of a transmission phase shift element, and the other configurations are the same. be.

The reflective phase shift element 42 of this embodiment is made so that the optical path difference between the laser beams emitted from two regions is 1/2 wavelength for a laser beam having a specific oblique incident angle. ing. When a reflective phase shift element with oblique incidence is used in this manner, the optical system as a whole becomes compact, and at the same time, stable laser oscillation is possible because the reflected light does not return to the laser.

FIG. 10 is a schematic diagram of the main parts of an optical system according to a sixth embodiment when the phase shift element of the present invention is applied to an optical pickup detection system for an optical memory.

In the figure, reference numeral 1 denotes a light source section consisting of a laser or the like, and the light beam emitted from the light source section 1 is condensed by a condenser lens 81 to form a beam waist near the condensing position. A phase shift element 4 is arranged near the beam waist position, and the light beam emitted from the phase shift element 4 passes through a splitter 84 and is condensed by an objective lens 82 to an optical memory medium 8.
A beam spot is formed on 3.

In this embodiment, a small beam spot is formed on the surface of the optical memory medium 83 by using the phase shift element 4. The reflected light from the optical memory medium 83 passes through the objective lens 82, is reflected by the beam splitter 84, and enters the photodetector 85. In this way, the photodetector 8
5, signals on the optical memory medium 83 are read at high density.

In this embodiment, one phase shift element 4.1 is arranged at the beam waist position, but it may be arranged at a position other than the beam waist, for example, near the light source 1, or one or more phase shift elements may be arranged. It may be arranged and configured.

FIG. 11 is a schematic diagram of a main part of an optical system according to a seventh embodiment in which the astigmatism difference of a semiconductor laser is corrected using the phase shift element of the present invention.

In the figure, a rotationally asymmetrical laser beam emitted from a light source section 1 made of a semiconductor laser is focused by a first condenser lens 21 to form a rotationally asymmetrical beam spot. A phase shift element 4 similar to that explained in FIG. 4 is arranged near this beam spot position. The phase difference of the light flux passing through the first region @ 11 and the second inclined wall 12 shown in FIG. 4(B) of this phase shift element 4 is 180 degrees, and the radius thereof is A=0.7 mm and B= It is 2 μm.

The laser beam that has passed through the phase shift element 4 is condensed by the second condenser lens 23 to form a beam spot on the image plane 86 .

In this embodiment, the light emitting surface of the semiconductor laser 1, the phase shift element 4, and the image surface 86 are in an optically conjugate relationship with each other.

In this embodiment, by arranging the phase shift element 4 in the vicinity of the condensing point of the first condensing lens 21, the light divergence origin of the laser beam can be adjusted in both the X direction and the phase direction. It is set to be the position of the shift element 4. As a result, a good beam spot with no astigmatism difference is formed on the image plane 86.

As described above, according to this embodiment, it is possible to construct a laser device that can obtain a good beam spot without astigmatism as a laser light source compatible with various systems in which the phase shift element 4 is regarded as a new point light source. .

Note that the shape of the phase shift element according to each of the above embodiments is not limited to that shown in FIG.
Those shown in Figures (A) to (F) are applicable.

In the figure, 11 indicates a first region, 12 indicates a second region, and the shaded area indicates a light-shielding region. The first region 11 and the second region 12 are configured so that there is a phase difference of 180 degrees (1/2 wavelength) between the passing light beams.

In addition to the embodiments described above, the laser device of the present invention can be applied to, for example, a laser beam printer, a laser microscope, a reticle drawing device using a scanning optical system, and the like.

(Effects of the Invention) According to the present invention, by arranging the phase shift element as described above at a predetermined position of the optical system, it is possible to correct the astigmatism difference of laser light when a semiconductor laser is used, and The aim is to achieve a laser device that can form a spot diameter smaller than the beam spot diameter determined by the NA of the optical system on a predetermined surface while maintaining a large depth of focus, and can achieve high resolution in image formation, for example. can.

Further, according to the present invention, unlike the case where the phase shift method is applied to an exposure apparatus (stepper) for manufacturing semiconductor devices, it is not necessary to form a phase shift region along all the open patterns on the reticle surface. It has the advantage that the entire apparatus can be simplified because the shift region need only be placed at one location near the optical axis of the optical system.

[Brief explanation of the drawing]

FIGS. 1(A) and (B) are schematic diagrams of main parts of the phase shift element of the present invention, and FIGS. 2(A) and (B) are explanations showing the wavefront state of the light flux passing through the phase shift element of the present invention. Figure, Figure 3 (A
) to (C) are explanatory diagrams of the complex amplitude distribution of the light beam passing through the phase shift element of the present invention and the intensity distribution on the image plane, and FIG.
) and (B) are explanatory diagrams of the simulation results of the optical system when correcting the astigmatism difference of laser light using the phase shift element of the present invention, and FIGS. 5 to 11 each illustrate the phase shift element of the present invention. FIG. 12 is an explanatory diagram of another embodiment of the phase shift element of the present invention, and FIG. 13 is a diagram of a conventional semiconductor laser. FIG. 14, which is an explanatory diagram showing the astigmatism difference, is a schematic diagram of the main part of a conventional laser device. In the figure, 1 is a light source, 2 and 5 are collimator lenses, and 3 and 8
1 is a condenser lens, 4, 41.42 is a phase shift element, 6
is a cylindrical lens, 7 is a rotating polygon mirror, 8 is f-θ
Lens system, 9 is a surface to be scanned, 10 is a beam spot, 11
is the first region, 12 is the second region, 13 is the light shielding region, 20 is H
6Nc laser, 21 is a first condensing lens, 22 is an A10 modulator, 23 is a second condensing lens, 24 is a collimator lens, 25 is a beam expander 82 is an objective lens, 83
84 is a beam splitter, and 185 is a photodetector. Figure 1-Y-Figure State of the wavefront before and after the phase shift element arranged near the beam waist position Complex 4&i @ distribution immediately after exit from the object surface (phase shift element) August 30, 1991

Claims (5)

[Claims] (1) A first region that is transparent to light of a predetermined wavelength and a second region that has a predetermined phase difference with respect to light passing through the first region is provided around the first region. Phase shift element. (2) The phase shift element according to claim 1, wherein the predetermined phase difference is 180 degrees. (3) A first lens transparent to the laser beam located near the light emitting end face of the laser light source, near a position conjugate to the light emitting end face, or near the beam waist of the laser light emitted from the laser light source.
A laser device comprising a phase shift element having a region and a second region having a predetermined phase difference around the first region with respect to a laser beam passing through the first region. (4) The laser device according to claim 3, wherein the predetermined phase difference is 180 degrees. (5) The laser device according to claim 4, wherein the beam waist is formed by condensing laser light emitted from the laser light source using a condensing optical system.