JPH10246876A - Laser modulation optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the laser modulation optical system which can make the pulse response time of an acousto-optic element shorter than before without lowering the durability of the medium of the element. SOLUTION: The laser light emitted from a laser light source 1 is made incident on the acousto-optic element 20 through two cylindrical lenses 11 and 12 as a beam shape setting means. A condenser lens 31 is arranged in front of the acousto-optic element 20. The two cylindrical lenses 11 and 12 both contain the optical axis, have positive power only in planes parallel to the propagation direction of a sound wave, and expand the beam diameter only in a direction P parallel to the propagation direction of the sound wave of the luminous flux incident on the condenser lens 31 so that the beam diameter DP in the direction P is larger than the beam diameter DH in a direction H. The sectional shape of the laser light at a convergence position on the acousto- optic element 20 is such an elliptic shape that the diameter in the direction P is shorter than the diameter in the direction H.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulation optical system of a device using a laser as a light source such as a scanning type drawing device, and more particularly to a laser light source such as a gas laser which cannot directly modulate and a modulation device. And a laser modulation optical system configured by combining the acousto-optical element.

[0002]

2. Description of the Related Art Conventionally, a raster scanning type drawing apparatus has used a laser modulation optical system constituted by combining a gas laser and an acousto-optic element. The laser light modulated by the optical system is deflected by a deflector such as a polygon mirror, and forms a beam spot on a photosensitive material surface to be drawn via a scanning lens such as an fθ lens.

In order to improve the drawing speed of the drawing apparatus, it is necessary to increase the scanning speed of the beam spot on the surface of the photosensitive material and to shorten the pulse response time of the acousto-optic device. The pulse response time tr of the acousto-optic element is
The beam diameter of the light beam incident on the acousto-optic element is d, and the sound speed is v
Is known to be approximately given by tr = 0.65 d / v. That is, the smaller the beam diameter is, the shorter the pulse response time of the acousto-optic element can be. In addition, since the acousto-optic element is arranged so as to coincide with the beam waist position of the converging laser beam, the above beam diameter means the minimum beam diameter at the beam waist position.

[0004]

However, if the beam diameter of the incident light beam is reduced in order to shorten the pulse response time of the acousto-optic element, the energy of the laser light is concentrated on a partial area of the acousto-optic element. In other words, the energy density per unit area becomes excessively large in some regions, and this energy may reduce the durability of the medium of the acousto-optic element and damage the element. Therefore, the beam diameter of the incident light beam is set to a value as small as possible without deteriorating the durability of the element, and there is a limit in shortening the pulse response time.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and has a laser capable of shortening the pulse response time of an acousto-optic device without reducing the durability of the medium. It is an object to provide a modulation optical system.

[0006]

The laser modulation optical system according to the present invention focuses on the fact that the beam diameter affecting the pulse response time of the acousto-optic element is only the diameter in the direction parallel to the propagation direction of the sound wave. The cross-sectional shape of the light beam incident on the acousto-optic element at the beam waist position was set so that the width in the direction parallel to the sound wave propagation direction on the acousto-optic element was shorter than the width in the direction perpendicular to the sound wave propagation direction. It is characterized by the following.

That is, the laser modulation optical system according to the present invention is provided with a laser light source, a condensing lens for condensing laser light emitted from the laser light source, and a laser light condensing position by the condensing lens. An acousto-optic element that modulates laser light by propagating sound waves on a medium in a direction substantially perpendicular to the direction of travel of the laser, Beam shape setting means for setting the cross-sectional shape of the laser light such that the width in the direction parallel to the propagation direction of the sound wave on the acousto-optic element is shorter than the width in the direction perpendicular to the propagation direction of the sound wave. Features.

By setting in this way, even if the cross-sectional area is the same, that is, even if the energy density per unit area is the same, compared with the case of using a circular light beam, The pulse response time can be shortened.

When the condenser lens is a lens rotationally symmetric about the optical axis, the beam shape setting means can be constituted as an anamorphic beam expander disposed between the laser light source and the condenser lens. The anamorphic beam expander is composed of two cylindrical lenses or two wedge prisms,
The width of the light beam incident on the condenser lens in the direction parallel to the sound wave propagation direction is set to be longer than the width in the direction perpendicular to the sound wave propagation direction. Further, as the beam shape setting means, an anamorphic lens that gives astigmatic difference to the light beam incident on the acousto-optic element can be used.

[0010] The cross-sectional shape of the laser beam incident on the acousto-optic element can be elliptical. When the diameter in the direction parallel to the propagation direction of the sound wave is a and the diameter in the direction perpendicular to the propagation direction of the sound wave is approximately 4a, the pulse response time is reduced to about half at the same energy density as a circular beam having a diameter of 2a. Can be.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a laser modulation optical system according to the present invention is applied to a raster scan type drawing apparatus will be described below. FIG. 1 is a perspective view showing the arrangement of the entire optical system of the apparatus. Laser light emitted from a gas laser light source 1 such as a helium neon laser is applied to two cylindrical lenses 11, 1 constituting a first anamorphic beam expander 10, which is a beam shape setting means.
The light is incident on the acousto-optic element 20 through 2. Before and after the acousto-optic element 20, a condenser lens 31 for converging the light incident on the acousto-optic element 20 and a collimating lens 32 for returning the outgoing light to parallel light are arranged, and these lenses are rotationally symmetric. A beam expander is configured.

The luminous flux modulated by the acousto-optic element 20 passes through a second anamorphic beam expander 40 comprising two cylindrical lenses 41 and 42 having power in a direction orthogonal to the first anamorphic beam expander 10. The light is transmitted and is dynamically reflected and deflected by the polygon mirror 2 serving as a deflector. The deflected laser light is reflected by the fixed mirror 3 and converges via the fθ lens 4 which is a scanning lens to form a laser spot on the drawing target surface 5 holding the photoconductor.

As shown in FIG. 2, the acousto-optic element 20 is configured by attaching a transducer (piezoelectric element) 21 to a transparent dielectric medium 22 such as tellurium dioxide. This element generates ultrasonic waves that propagate in the medium 22 in the direction P in the figure by applying a sound wave frequency, and diffracts an incident light beam by elastic deformation of the medium and a change in the refractive index due to the ultrasonic waves.
In this example, the diffracted light when the ultrasonic frequency is applied is guided to the drawing target surface 5 and used for drawing, and the transmitted light when the ultrasonic frequency is not applied is cut off. The acousto-optic device 20 changes with the change of the scanning position of the laser spot on the drawing target surface 5 due to the rotation of the polygon mirror 2.
Is driven in accordance with the drawing signal, so that the drawing target surface 5 is
An exposure pattern is formed thereon by turning on / off the laser light.

FIGS. 3A and 3B are developed views showing the optical path of the optical system together with the light beam, and FIG. 3A is a cross section in the direction H orthogonal to the propagation direction of the ultrasonic wave on the acousto-optic element 20. B) shows cross sections in a direction P parallel to the propagation direction of the ultrasonic wave.

Beam waist position on the acousto-optic device 20
The beam diameter of the laser beam at the (condensing position) is
It is determined by the F number of the optical system including 1. Here, the condenser lens 31 is rotationally symmetric, the focal length is the same in any direction, and the incident light beam is a parallel light beam. It depends only on the beam diameter of the incident light beam.

Two cylindrical lenses 11, 1 constituting a first anamorphic beam expander 10
2 has a positive power only in a plane including the optical axis and parallel to the direction of propagation of the sound wave, and has a beam diameter DP in a direction P parallel to the direction of propagation of the sound wave of the light beam incident on the condenser lens 31.
Has a function of expanding the beam diameter only in the direction P so that the beam diameter becomes larger than the beam diameter DH in the direction H. Thereby, the cross-sectional shape of the laser light condensed by the condensing lens 31 at the condensing position on the acousto-optic element 20 has a diameter in the direction P parallel to the propagation direction of the sound wave as shown in FIG. The ellipse is shorter than the diameter in the direction H perpendicular to the propagation direction.

With this setting, even if the cross-sectional area is the same, that is, even if the energy density per unit area is the same, as compared with the case where a circular light beam is used, The pulse response time can be shortened. The cross-sectional shape of the laser beam can be elliptical. For example, when the diameter in the direction parallel to the propagation direction of the sound wave is a, and the diameter in the direction perpendicular to the propagation direction of the sound wave is almost an ellipse of 4a, the same cross-sectional area as that of a circle with a diameter of 2a And the pulse response time can be reduced to about half.

On the other hand, the second anamorphic beam expander 40 has a function of shaping a laser beam having an elliptical cross section that has passed through the collimator lens 32 and has been converted into a parallel beam. By returning the cross-sectional shape of the laser beam to a circle by the second anamorphic beam expander 40, the spot shape on the drawing target surface can be made circular.

As the beam shape setting means for setting the cross-sectional shape of the laser beam at the condensing position on the acousto-optic element, in addition to the anamorphic beam expander using the cylindrical lens shown in the above example, FIG. An anamorphic beam expander composed of two wedge prisms 51 and 52 as shown can be used, and an anamorphic lens that gives astigmatic difference to a light beam incident on the acousto-optic element 20 can also be used.

When an anamorphic lens is used, a cylindrical lens may be provided between the condenser lens and the acousto-optic element, or the condenser lens itself may be configured as a toric lens. By generating an astigmatic difference in the light beam and adjusting the beam waist position in the direction parallel to the direction of propagation of the sound wave to the position of the acousto-optic element, the beam waist position in the direction perpendicular to this will be separated from the acousto-optic element, As a result, the beam diameter on the acousto-optic element can be made smaller in the direction parallel to the propagation direction and larger in the direction perpendicular to the propagation direction, and the same effect as when an anamorphic beam expander is used can be obtained.

[0021]

As described above, according to the present invention, the beam diameter in the direction parallel to the propagation direction of the sound wave which affects the pulse response time can be reduced without increasing the energy density on the acousto-optic device. Therefore, the pulse response time of the acousto-optic element can be shortened without reducing the durability of the medium.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating an arrangement of an entire optical system of a drawing apparatus according to an embodiment.

FIG. 2 is a plan view showing a configuration of an acousto-optic element.

FIG. 3 is an explanatory diagram showing an optical path of the optical system shown in FIG.

FIG. 4 is an explanatory diagram showing another example of the beam shape setting means.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 10 1st anamorphic beam expander 20 Acousto-optic element 31 Condensing lens 40 2nd anamorphic beam expander

Claims (9)

[Claims] 1. A laser light source; a condenser lens for condensing laser light emitted from the laser light source; An acousto-optic element that modulates the laser light by propagating sound waves over a medium in a direction, a laser disposed between the laser light source and the acousto-optic element, and a laser at the condensing position on the acousto-optic element Beam shape setting means for setting a cross-sectional shape of the light such that a width in a direction parallel to the propagation direction of the sound wave on the acousto-optic element is shorter than a width in a direction perpendicular to the propagation direction of the sound wave. Laser modulation optical system. 2. The condensing lens is a lens that is rotationally symmetric about an optical axis, and the beam shape setting means is disposed between the laser light source and the condensing lens, and enters the condensing lens. The laser modulation optical system according to claim 1, wherein the laser modulation optical system is an anamorphic beam expander that sets a width of a light beam in a direction parallel to the sound wave propagation direction to be longer than a width in a direction perpendicular to the sound wave propagation direction. . 3. The laser modulation optical system according to claim 2, wherein the anamorphic beam expander includes two cylindrical lenses. 4. The laser modulation optical system according to claim 2, wherein said anamorphic beam expander includes two wedge prisms. 5. The anamorphic beam expander according to claim 2, wherein the anamorphic beam expander has a function of expanding a beam diameter of a light beam incident on the condenser lens in a direction parallel to a propagation direction of the sound wave. A laser modulation optical system according to any of the above. 6. The laser modulation optical system according to claim 1, wherein a cross-sectional shape of the laser light incident on the acousto-optic element is an elliptical shape. 7. The cross-sectional shape, wherein a is a diameter in a direction parallel to the direction of propagation of the sound wave, and a diameter in a direction perpendicular to the direction of propagation of the sound wave is approximately 4a. Item 7. A laser modulation optical system according to Item 6. 8. The laser modulation optical system according to claim 1, wherein the beam shape setting means is an anamorphic lens that gives astigmatic difference to a light beam incident on the acousto-optic element. 9. A laser light source; a condensing lens for condensing laser light emitted from the laser light source; An acousto-optic element that modulates the laser light by propagating sound waves on a medium in a direction, disposed between the laser light source and the condenser lens;
A first anamorphic beam expander for setting a width of a light beam incident on the condenser lens in a direction parallel to the propagation direction of the sound wave to be longer than a width in a direction perpendicular to the propagation direction of the sound wave; A second laser beam is disposed at a position where the emitted light beam enters, and the laser beam having an elliptical cross section is shaped into a circle.
An anamorphic beam expander, a deflector for dynamically deflecting a light beam emitted from the second anamorphic beam expander, and a scanning lens for converging the light beam deflected by the deflector on a surface to be scanned. Characteristic scanning optical system.