JP3522444B2 - Light beam modulator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam modulator that modulates a light beam with an acousto-optic modulator.

[0002]

2. Description of the Related Art An acousto-optic modulator (AOM) is an optical element that is widely used in an image recording apparatus for the purpose of modulating a light beam such as a laser beam emitted from a laser light source. This acousto-optic modulator propagates ultrasonic waves in an acoustic medium by applying ultrasonic waves transmitted from an ultrasonic transducer called a transducer to an acoustic medium made of crystals such as tellurium dioxide (TeO ₂ ). Then, it is a device that modulates a light beam by utilizing the diffraction of light by the acousto-optic interaction.

In this acousto-optic modulator, the smaller the beam diameter of the light beam incident on the acoustic medium, the higher the modulation speed. Therefore, an optical system such as a lens is arranged in front of the acousto-optic modulator, and the acousto-optic modulator is arranged. The focused light beam is made incident on the modulator. As a result, a light beam having a high energy density is incident on the acoustic medium of the acousto-optic modulator. Further, in an image recording apparatus or the like, when performing high-speed recording or recording on a photosensitive material having low sensitivity, a high energy light beam emitted from a high-power laser light source or the like is used. Therefore, even in this case, a light beam having a high energy density is incident on the acoustic medium of the acousto-optic modulator.

As described above, when the light beam having a high energy density is incident on the acoustic medium of the acousto-optic modulator, the acoustic medium is gradually deteriorated, and the acoustic medium itself is black at the incident position of the light beam. There is a phenomenon in which the coating on the surface of the acoustic medium is broken or the coating is damaged. In such a case, there arises a problem that the light quantity of the light beam after being modulated by the acousto-optic modulator is reduced. For this reason, the acousto-optic modulator is replaced with a new one after performing modulation for a certain period.

[0005]

Each acousto-optic modulator has various subtle errors that occur during the manufacturing process and the like. Among these errors, as an error that has a great influence on the light beam modulator, there is an error in parallelism between the entrance surface and the exit surface of the acoustic medium.

This error will be described with reference to FIGS. 6 and 7. FIG. 6 shows that, by exchanging the acousto-optic modulator, the emission surface 4b of the acoustic medium 2 after the change is changed by an angle Δθ with respect to the emission surface 4a of the acoustic medium 2 before the exchange of the acousto-optic modulator. In the case, it is a schematic diagram showing how the emission angle of the light beam B as the primary light emitted from the acoustic medium 2 changes.

Before replacing the acousto-optic modulator,
The light beam B incident from the incident surface 3 of the acoustic medium 2 is diffracted at the diffraction point 5 in the acoustic medium 2 by the ultrasonic wave propagating in the acoustic medium 2 in the vertical direction shown in FIG. It is incident on the surface 4a at an angle θ ₀ . When the refractive index of the acoustic medium 2 is n, the angle of the emitted light emitted from the emitting surface 4a is n · θ ₀ . On the other hand, when the emission surface of the acoustic medium 2 is changed from 4a to 4b by the angle Δθ by exchanging the acousto-optic modulator, the light beam B incident from the incident surface 3 of the acoustic medium 2 is The light is diffracted at the inner diffraction point 5 and is incident on the emission surface 4b of the acoustic medium 2 at an angle θ ₀ + Δθ. Then, the exit surface 4b
The angle of the emitted light emitted from the
(Θ ₀ + Δθ). Therefore, the change α in the angle of the emitted light caused by replacing the acousto-optic modulator is as shown in FIG.
As shown in, the following values are obtained.

Α = (n−1) · Δθ

As shown in FIG. 7, in the device in which the acousto-optic modulator 6 and the optical system 7 are combined, when the angle of the modulated light beam B emitted from the acousto-optic modulator 6 changes by the above α. When the optical path length from the acousto-optic modulator 6 to the optical system 7 is L, the incident height difference Δh of the light beam B entering the optical system 7 is approximately represented by the following value.

Δh = L (n-1) · Δθ

In this equation, for example, the optical path length L from the acousto-optic modulator 6 to the optical system 7 is 100 mm, the refractive index n of the acoustic medium 2 is 2.4, and the error Δθ of the emission surface of the acoustic medium 2 is 0. When set to 0.5 ° (8.7 × 10 ⁻³ rad), the above α is about 0.7 °, and the above Δh is about 1.2 m.
m. As described above, when the angle of incidence or the height of incidence on the optical system 7 changes significantly, there arises a problem that the shape of the light beam deteriorates due to coma aberration, astigmatism, or the like of the optical system 7.

Therefore, in the conventional device, every time the acousto-optic modulator 2 is replaced, the position of the optical system 7 is adjusted again according to the light beam B emitted from the acousto-optic modulator 2. Work was needed.

The present invention has been made to solve the above problems, and it is an object of the present invention to provide a light beam modulator capable of easily adjusting the emission angle of a light beam emitted from an acousto-optic modulator. To aim.

[0014]

According to a first aspect of the present invention, a light source for emitting a light beam and an ultrasonic wave oscillated from an ultrasonic oscillator are propagated in an acoustic medium and are incident on the acoustic medium. An acousto-optic modulator that emits the generated light beam as diffracted light, and an optical beam that is disposed in the optical path between the light source and the acousto-optic modulator, and that emits the light beam emitted from the light source of the acousto-optic modulator. It is characterized by comprising a condensing lens for converging in an acoustic medium and a moving means for translating a light beam emitted from the light source and incident on the condensing lens.

According to a second aspect of the present invention, in the first aspect of the invention, a confirmation means for confirming the emission angle of the light beam emitted from the acousto-optic modulator is further provided.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION First, the basic idea of the present invention will be described with reference to FIGS. FIG. 4 is a schematic diagram showing a state in which the angle of the emitting surface 4 of the acoustic medium 2 is changed by Δθ, and similarly to FIG. 6 described above, 4a indicates the emitting surface of the acoustic medium 2 before the acousto-optic modulator is replaced. Show 4
b shows the emission surface of the acoustic medium 2 after replacement. However,
In this figure, after replacing the acousto-optic modulator,
The incident angle of the light beam Bb incident on the acoustic medium 2 is changed by Δθ (n−1) with respect to the incident angle of the light beam Ba before replacement.

As shown in this figure, before exchanging the acousto-optic modulator, the emission angle of the light beam Ba incident on the acoustic medium 2 from the emission surface 4a is nθ ₀ , as in the case of FIG.
Becomes On the other hand, after the acousto-optic modulator is replaced, the incident angle of the light beam Bb incident on the acoustic medium 2 is Δθ (n−
Since only 1) is changed, the emission angle of the light beam Bb from the emission surface 4b becomes nθ-Δθ with respect to the emission surface 4b after the replacement of the acousto-optic modulator, as shown in FIG. To the exit surface 4a of the same as the light beam Ba.
It becomes ₀ . Therefore, by changing the angle of the light beam B incident on the incident surface 3 of the acoustic medium 2, the angle of the light beam B emitted from the acousto-optic modulator is made constant before and after the replacement of the acousto-optic modulator. be able to.

In this case, before and after the replacement of the acousto-optic modulator, the light beams Ba and Bb as the primary light emitted from the acoustic medium 2 are the traveling directions of the light beam B in the acoustic medium 2 ( Assuming that the thickness d with respect to the horizontal direction in FIG. 4) is d and that the diffraction point 5 due to the ultrasonic wave propagating in the acoustic medium 2 in the vertical direction shown in FIG. 4 is at the center of the acoustic medium 2, the following distance y However, the height of the emission position is different.

Y = (d / 2) .multidot. (1-1 / n) .multidot..DELTA..theta.

In this equation, as in the case of FIG. 6, the refractive index n of the acoustic medium 2 is 2.4, and the error Δθ of the emitting surface of the acoustic medium 2 is 0.5 ° (8.7 × 10 ⁻³ rad). When the thickness d of the acoustic medium 2 is 10 mm, the above y is about 0.0
It becomes 25 mm. Before and after replacing the acousto-optic modulator,
Since the output angles of the light beams Ba and Bb from the acousto-optic modulator are the same, this distance y is constant regardless of the arrangement of the lens system thereafter. Therefore, with the above configuration,
Compared with the conventional case shown in FIG. 7, the change in the emitted light from the acousto-optic modulator before and after the replacement of the acousto-optic modulator is significantly increased to such an extent that the optical performance is not substantially affected. It is possible to reduce.

In order to change the incident angle of the light beam Bb incident on the acoustic medium 2 of the acousto-optic modulator by the above-mentioned angle Δθ (n-1), it is effective to use the structure shown in FIG. 5, for example. Is. That is, between the light source 10 such as a laser light source that emits the light beam B and the acousto-optic modulator 6,
A mirror 9 that can reciprocate in one direction and deflects the light beam B at a right angle, and a condenser lens 8 that has a focal length f and focuses the light beam B into the acoustic medium 2 of the acousto-optic modulator 6 are arranged. To do. The optical path length of the condenser lens 8 and the acoustic medium 2 of the acousto-optic modulator 6 to the diffraction point 5 is made substantially equal to the focal length f. With such a configuration, after the acousto-optic modulator 6 is replaced, the mirror 9 is moved so that the light beam B incident on the condensing lens 8 is directed in the vertical direction (that is, the acoustic wave of the acousto-optic modulator 6 is shown in FIG. 5). Medium 2
In the ultrasonic wave propagation direction), the incident angle of the light beam Bb incident on the acoustic medium 2 of the acousto-optic modulator 6 can be changed by Δθ (n−1). it can.

M = fΔθ (n-1)

Therefore, the light beam B incident on the condenser lens 8 for focusing the light beam B in the acousto-optic modulator 6.
By translating, the emission angle of the light beam B emitted from the acousto-optic modulator 6 can be adjusted to be substantially the same before and after the replacement of the acousto-optic modulator 6.

Next, an embodiment of the present invention based on the above concept will be described. FIG. 1 shows the first of the present invention.
It is a schematic diagram of a light beam modulator according to an embodiment.

This optical beam modulator has a laser beam B
A laser light source 10 for emitting a laser beam, a mirror 9 for deflecting the laser beam B emitted from the laser light source 10 by 90 °,
A condenser lens 8 for condensing the laser beam B deflected by the mirror 9, an acousto-optical modulator 6 for modulating the laser beam B condensed by the condensing lens 8, and a modulation by the acousto-optical modulator 6. The optical system 12 for guiding the generated laser beam B1 as the primary light to the recording surface in the subsequent stage, and the laser beam B0 as the zero-order light emitted from the acousto-optic modulator 6.
Position detector 13 for confirming the emission angle of the.

The laser light source 10 is, for example, a laser light source using argon gas and has a beam diameter of 700.
The laser beam B of μm is emitted. As the condenser lens 8, for example, one having a focal length f of 56 mm is used, and the condenser lens 8 is separated from the optical path length from the diffraction point in the acoustic medium 2 of the acousto-optic modulator 6 by the focal distance f. The laser light source 10
The laser beam B from the laser is focused on the acoustic medium 2 of the acousto-optic modulator 6 in a state of being narrowed to 50 μm.

The mirror 9 is a flat mirror support 22.
The laser beam B from the laser light source 10 is deflected by 90 ° in the direction of the condenser lens 8. The support 22 that supports the mirror 9 is driven by a pulse motor (not shown) to emit a laser beam B emitted from a laser light source.
It is configured to be able to reciprocate in a direction parallel to the emission direction of (1) (direction of arrow A shown in FIG. 1). Therefore, the mirror 9 supported by the support 22 slightly moves in the direction of arrow A, so that the incident height of the laser beam B incident on the condenser lens 8 changes.

In this embodiment, the mirror 9 is reciprocally movable in the direction parallel to the emitting direction of the laser beam B emitted from the laser light source (the direction of arrow A shown in FIG. 1). The mirror 9 is configured to be reciprocally movable in a direction parallel to the incident direction of the laser beam B incident on the condenser lens 8 (direction orthogonal to the arrow A direction shown in FIG. 1), so that the laser beam B is incident on the condenser lens 8. The incident height of the laser beam B may be changed. That is, in this embodiment, the laser beam B incident on the condenser lens 8 may be translated in a direction parallel to the propagation direction of the ultrasonic wave in the acoustic medium 2 in the acousto-optic modulator 6.

The position detector 13 is provided with a photodiode 24 arranged via a pinhole 23 in the optical path of the laser beam B0 as the 0th order light emitted from the acousto-optic modulator 6.
And a display device 25 for displaying the light quantity value of the laser beam B0 detected by the photodiode 24. The position detecting device 13 detects the consistency between the irradiation position of the laser beam B0 and the position of the pinhole 23,
This is for confirming the emission angle of the laser beam B0. That is, since the laser beam generally has a Gaussian distribution, if the diameter of the pinhole 23 is set smaller than the beam diameter of the laser beam B0, the laser beam B
When the irradiation position of 0 coincides with the pinhole 23, the light amount of the laser beam B0 passing through the pinhole 23 and reaching the photodiode 24 becomes maximum. Therefore, by detecting the light amount of the photodiode 24, it is possible to confirm the emission angle of the laser beam B0 as the 0th order light.

Generally, it is known that the angle formed by the 0th-order light and the 1st-order light emitted from the acousto-optic modulator 6 is constant regardless of the incident angle of the laser beam B on the acousto-optic modulator 6. Has been. Therefore, in a state where the laser beam B1 as the primary light emitted from the acousto-optic modulator 6 can be suitably incident on the optical system 12, the laser beam B0 as the 0-order light emitted from the acousto-optic modulator 6 is By previously disposing the pinhole 23 at the irradiation position, even when the acousto-optic modulator 6 is replaced, the light amount of the laser beam B0 is detected and the irradiation position of the laser beam B0 as the 0th-order light is detected. If is matched with the pinhole position, 1
The laser beam B1 as the next light is incident on the optical system 12 in the subsequent stage at an appropriate position.

In the above optical beam modulator, when replacing the deteriorated acousto-optic modulator 6 with a new acousto-optic modulator 6, the incident surface 3 and the exit surface 4 of the acoustic medium 2 of the acousto-optic modulator 6 are replaced. The emission angle of the laser beam B emitted from the acousto-optic modulator 6 changes before and after the replacement due to the error in the parallelism. Therefore, as described above, the light beam B incident on the condenser lens 8 is translated by the distance M by the movement of the mirror 9, and the incident angle of the light beam B incident on the acoustic medium 2 of the acousto-optic modulator 6 is increased. Is changed by Δθ (n−1) to adjust the emission angle of the laser beam B.

That is, after the acousto-optic modulator 6 is installed, the laser light source 10 is turned on and the mirror 9 is driven via the support 22 by driving a pulse motor (not shown).
Is moved in the direction of arrow A in FIG. 1, and the laser beam B0 as the 0th order light emitted from the acousto-optic modulator 6 is irradiated near the pinhole 23. Then, the mirror 9 is detected while the light quantity of the laser beam B0 is detected by the photodiode 24.
1 in the direction of arrow A in FIG.
Control is performed so that the detected value of is maximized. This control may be performed by an operator manually driving the pulse motor while checking the display device 25, or may be performed by feedback control based on the output value of the photodiode 24. If it is confirmed that the detection value of the photodiode 24 has become maximum, the mirror 9 is stopped.

In this state, the mirror 9 has moved by the distance M described above, and the irradiation position of the laser beam B0 as the 0th order light emitted from the acousto-optic modulator 6 after the replacement is in the pinhole 23. It almost coincides with the center. Therefore, the laser beam B1 as the primary light emitted from the acousto-optic modulator 6 after the replacement also enters the optical system 12 in the subsequent stage at a suitable position.

As described above, in the light beam modulator according to this embodiment, the mirror 9 is moved in one direction to move the laser beam B incident on the condenser lens 8 in parallel, thereby performing acousto-optical modulation. It is possible to easily correct the deviation of the emission angle of the laser beam B due to the replacement of the device 6. Further, since the position detector 13 detects the irradiation position of the laser beam B0 as the 0th-order light emitted from the acousto-optic modulator 6, the movement amount of the mirror 9 can be controlled, and thus the movement of the mirror 9 can be performed. The amount can be easily controlled.

In the light beam modulator according to this embodiment, the angle formed by the 0th-order light and the 1st-order light emitted from the acousto-optic modulator 6 is constant regardless of the incident angle of the laser beam B. By utilizing this, the position detection device 13 detects the irradiation position of the 0th-order light not particularly used for image recording in the laser beam B emitted from the acousto-optic modulator 6. When replacing the modulator 6,
The laser beam B emitted from the acousto-optic modulator 6 can be detected with good reproducibility. That is, in order to measure the primary light used for image recording or the like with the position detection device 13, it is necessary to install the position detection device 13 in the optical path of the primary light only at the time of the measurement. Thirteen
The reproducibility of the mounting position of the beam affects the accuracy of the irradiation position detection. However, in the case of measuring the 0th-order light, the position detector 13 can be left fixed to the device, so that the problem of reproducibility and the like does not occur. However, the present invention is not limited to such a form, and the irradiation position of the primary light is confirmed by the position detection device 13 or the like by disposing a half mirror in the optical path of the primary light, for example. You may do it.

Further, in the above-mentioned embodiment, the position detecting device 13 detects the light amount of the laser beam B0 passing through the pinhole 23 by the photodiode 24. Acousto-optic modulator 6 such as CCD camera and cross mark
Various structures can be adopted as long as the irradiation position of the laser beam B0 emitted from can be confirmed by some means.

Next, another embodiment of the present invention will be described. FIG. 2 is a schematic diagram of a light beam modulator according to the second embodiment of the present invention.

The light beam modulator according to this embodiment differs from the first embodiment in that a parallel prism 29 is used as a means for moving the laser beam B incident on the condenser lens 8 in parallel. . That is, in this embodiment, the parallel prisms 29 having planes parallel to each other are supported by the support means 32, and the laser light source 10
The laser beam B incident on the condenser lens 8 is translated in parallel by arranging it in the optical path of the laser beam B emitted further from the optical path. The amount of movement of the laser beam B is measured by the parallel prism 29 in the direction of arrow C in FIG.
The angle can be changed by rotating in the direction and adjusting the inclination angle.

In this embodiment, when the acousto-optic modulator 6 is replaced, the laser beam B0 as the 0th-order light emitted from the acousto-optic modulator 6 is emitted as in the case of the first embodiment described above. The light is emitted from the acousto-optic modulator 6 by controlling the tilt angle of the parallel prism 29 based on the position detection device 13 for confirming the irradiation position.
The emission angle of the laser beam B1 as the next light can be adjusted.

Next, still another embodiment of the present invention will be described. FIG. 3 is a schematic diagram of a light beam modulator according to a third embodiment of the present invention.

In the first and second embodiments described above,
In order to adjust the parallelism error between the incident surface 3 and the output surface 4 of the acoustic medium 2 of the acousto-optic modulator 6 in the direction parallel to the propagation direction of ultrasonic waves in the acoustic medium 2, the condenser lens 8 is used.
The laser beam B incident on is translated in a direction corresponding to the propagation direction of ultrasonic waves in the acoustic medium 2, but in the third embodiment, a direction perpendicular to the propagation direction of ultrasonic waves in the acoustic medium 2. To adjust the parallelism error of
The first point is that the laser beam B incident on the condenser lens 8 is translated in two directions, a direction corresponding to the propagation direction of ultrasonic waves in the acoustic medium 2 and a direction perpendicular thereto.
This is different from the second embodiment.

That is, in the light beam modulator according to this embodiment, a direction parallel to the emission direction of the laser beam B supported by the support 42 and emitted from the laser light source 10 (direction of arrow D in FIG. 3). A first mirror 39 that is reciprocally movable to deflect the laser beam B by 90 °, and a direction perpendicular to the traveling direction of the laser beam B that is supported by a support 52 and deflected by the first mirror 39 ( A second mirror 49 which is capable of reciprocating in the direction of arrow E in FIG. 3 and deflects this laser beam B by 90 °. In this light beam modulator, when the first mirror 39 is moved in the direction of arrow D in FIG. 3, the laser beam B incident on the condenser lens 8 is an ultrasonic wave in the acoustic medium 2 of the acousto-optic modulator 6. Of the laser beam B incident on the condenser lens 8 when the second mirror 49 is moved in the direction of arrow E in FIG. The acoustic medium 2 is moved in a direction parallel to the propagation direction of ultrasonic waves.

Therefore, before and after the replacement of the acousto-optic modulator 6, an error in parallelism between the incident surface 3 and the exit surface 4 of the acoustic medium 2 in the direction parallel to the propagation direction of ultrasonic waves in the acoustic medium 2. Is Δθ, it suffices to move the second mirror 49 in the direction of the arrow E by the above-mentioned distance M. Further, in the acoustic medium 2 of the incident surface 3 and the outgoing surface 4 of the acoustic medium 2. The error of parallelism in the direction perpendicular to the ultrasonic wave propagation direction is Δθ
In this case, the first mirror 39 needs to be moved in the direction of arrow D by the distance M described above. In this case, the movement amount of each of the mirrors 39 and 49 is the same as in the above-described first and second embodiments, and the irradiation position of the laser beam B0 as the 0th-order light emitted from the acousto-optic modulator 6 is confirmed. The control may be performed on the basis of the position detection device 13 for performing the operation. However, in this embodiment, since the laser beam B0 as the 0th order light emitted from the acousto-optic modulator 6 moves two-dimensionally, for example, a two-dimensional CCD camera or the like is used, and the laser beam B0 is used. B
It is preferable that the irradiation position in the XY direction can be confirmed.

[0044]

According to the first aspect of the invention, the light beam incident on the condenser lens is moved in parallel,
The emission angle of the light beam can be easily adjusted. For this reason, when the acousto-optic modulator is replaced, even if there is an error in the parallelism of the acoustic medium of the acousto-optic modulator before and after the replacement, the error is practically achieved by simple adjustment. It is possible to prevent the influence.

According to the second aspect of the present invention, since there is further provided confirmation means for confirming the emission angle of the light beam emitted from the acousto-optic modulator, the emission angle of the light beam confirmed by this confirmation means is set. Based on this, the amount of movement of the light beam that enters the condenser lens can be controlled. For this reason,
It becomes possible to more easily perform the adjustment when replacing the acousto-optic modulator.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a light beam modulator according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of a light beam modulator according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram of a light beam modulator according to a third embodiment of the invention.

FIG. 4 is a schematic diagram showing the basic principle of the present invention.

FIG. 5 is a schematic diagram showing the basic principle of the present invention.

FIG. 6 is a schematic diagram showing a deviation of an emission angle of a light beam due to replacement of an acousto-optic modulator.

FIG. 7 is a schematic diagram showing a deviation of an emission angle of a light beam due to replacement of an acousto-optic modulator.

[Explanation of symbols]

2 acoustic medium 3 Incident surface 4 Exit surface 6 Acousto-optic modulator 8 Condensing lens 9 mirror 10 Laser light source 12 Optical system 13 Position detector 22 Support 23 pinholes 24 photodiode 29 parallel prism 32 support 39 mirror 42 Support 49 mirror 52 Support B laser beam F focal length

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-3-109527 (JP, A) JP-A-62-147435 (JP, A) Practical application Sho-58-59016 (JP, U) (58) Field (Int.Cl. ⁷ , DB name) G02F 1/33 G02F 1/11

Claims (2)

(57) [Claims] 1. A light source that emits a light beam, and an acousto-optic modulator that propagates an ultrasonic wave oscillated from an ultrasonic transducer in an acoustic medium and emits the light beam incident in the acoustic medium as diffracted light. And a condenser lens disposed in an optical path between the light source and the acousto-optic modulator, for converging a light beam emitted from the light source into an acoustic medium of the acousto-optic modulator, the light source A light beam modulator, comprising: a moving unit that moves in parallel the light beam that is emitted from and is incident on the condenser lens. 2. The light beam modulator according to claim 1, further comprising a confirmation unit that confirms an emission angle of the light beam emitted from the acousto-optic modulator.