JPH0247070A - Optical beam scanner - Google Patents

Abstract

PURPOSE:To prevent a gradation in a predetermined direction from generating at a visible image by generating a linearly polarized beam from a light source, and so determining the relatively rotating position of an acoustic optical light modulator with the light path of an optical beam incident to the modulator as an axis that the sectional shape of the beam emitted from the modulator approaches mostly to a circular shape. CONSTITUTION:A relatively rotating position between a light source 1 and an acoustic optical light modulator 3 with the light path of a linearly polarized beam 2 incident to the modulator 3 is so determined that the polarized plane of the beam incident to the modulator 3 becomes the long axis direction of the beam or in a direction perpendicular thereto. Since the beam 2' emitted form the modulator 3 is only one polarized component, the sectional shape of the beam 2' becomes substantially circular shape on a recording sheet 4, and necessity of correcting the fading being generated in a direction corresponding to the major axis direction of the ellipse of an image generated when the sectional shape of the beam 2 is substantially elliptical is eliminated in an image reader or an image recorder using an optical beam scanner.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a light source that generates a light beam, and an acousto-optic light modulator that adjusts or modulates the intensity of the light beam and emits the light beam.
Hereinafter, it will be referred to as AOM. ) and a scanning means for two-dimensionally scanning an object to be scanned with a light beam emitted from the AOM.

(Prior Art) It is practiced in various fields to read a recorded radiation image to obtain an image signal, perform appropriate image processing on the image signal, and then reproduce and record the image. For example, an X-ray image is recorded using an X-ray film with a low gamma value designed to be compatible with later image processing, and the X-ray image is read from the film on which it is recorded and converted into an electrical signal. A system that can obtain reproduced images with good image quality performance such as contrast sharpness and graininess by performing image processing on this electrical signal (image signal) and then reproducing it as a visible image in a photocopy etc. has been developed (see Japanese Patent Publication No. 61-5193).

In addition, the applicant has proposed radiation (X-rays, α-rays).

When irradiated with β rays, γ rays, electron beams, ultraviolet rays, etc., a part of this radiation energy is accumulated, and then when irradiated with excitation light such as visible light, stimulable fluorescence exhibits stimulated luminescence depending on the accumulated energy. A radiation image of a subject such as a human body is photographed and recorded on a -H sheet of stimulable phosphor using a stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam. The resulting photostimulated luminescence is read in a charging manner to obtain image data, and based on this image data, a radiation image of the subject can be recorded on recording materials such as photographic materials, CRTs, etc. Radiation image recording and reproducing systems that output visual images have already been proposed (Japanese Patent Application Laid-open Nos. 55-12429, 56-11395, 55-
No. 183472, No. 5B-104645, No. 55-1
16340 etc.).

This system has the practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, in a stimulable phosphor, it is recognized that the amount of emitted light that is stimulated to emit light due to excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range.
Therefore, even if the amount of radiation exposure varies considerably due to various imaging conditions, the amount of stimulated luminescence emitted from the stimulable phosphor sheet can be read by the photoelectric conversion means by setting the reading gain to an appropriate value. By converting the radiation image into an electric signal and using this electric signal to output the radiation image as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT, a radiation image that is not affected by fluctuations in radiation exposure amount can be obtained. be able to.

An image reading device that obtains an image signal by reading an image such as a radiation image recorded on a recording sheet such as the above-mentioned X-ray film or stimulable phosphor sheet, and modulates a light beam based on the image signal obtained by reading the image. However, an image recording device that reproduces and records images on a recording sheet such as a photosensitive film using a modulated light beam usually includes a light source that generates a light beam, and a light source that generates a light beam.
AOM that adjusts or modulates the intensity of the light beam and emits it
and a light beam scanning device including a scanning means for main-scanning a recording sheet, which is a scanned object, with a light beam emitted from the AOM and sub-scanning in a direction substantially perpendicular to the main-scanning direction. ing.

In the image reading device, the light beam scanning device scans the recording sheet with a pre-beam having a substantially constant amount of light;
The light representing the image obtained from each scanning point on the recording sheet (
It is configured to obtain an image signal by reading stimulated luminescence light emitted from a stimulable phosphor sheet, light transmitted through an X-ray film, light reflected by an X-ray film, etc.

Further, in the image recording device, the light beam scanning device is used to modulate a light beam with an AOM based on the image signal obtained by the image reading device, and the modulated light beam is scanned on the recording sheet. It is configured to scan and reproduce and record images on the recording sheet.

(Problem to be Solved by the Invention) When an image based on an image signal obtained from a recording sheet is displayed in the above-mentioned image reading device on, for example, a CRT display device, or when an image is reproduced and recorded on a recording sheet in the above-mentioned image recording device. There is a problem in that, in some cases, the displayed or recorded image may be blurred (deterioration in image sharpness or contrast) in a predetermined direction. Until now, it was thought that this degree of blurring was due to the capabilities of the device. However, when blurring occurs in a predetermined direction, the image becomes difficult to see, and there is also a risk of erroneous judgment when observing the details of the image.

Therefore, when the inventors pursued the cause of this problem, A.
It turned out that OM was the cause.

AOM divides the light beam into a 0-order beam and a 1st-order beam by causing a sound wave (usually an ultrasonic wave) to interfere with an incident light beam.By changing the intensity of the sound wave, the 0-order beam and the 1st-order beam are separated. It adjusts or modulates the intensity, and is used for the purpose of adjusting the intensity of the light irradiated onto the recording sheet to be constant, or temporally modulating the intensity of the light irradiated onto the recording sheet. used.

When sound waves propagate within the AOM, the AOM generates heat. Furthermore, heat is not generated uniformly, but temperature distribution occurs within the AOM. This temperature distribution is determined by the structure of the AOM, the method of mounting the AOM, etc. Further, the temperature gradient varies depending on the power (average power over a predetermined period of time) that drives the AOM.

When the temperature inside the AOM changes and a temperature gradient occurs, the temperature change directly causes mechanical distortion in the AOM, and this distortion causes light refraction inside the AOM. yielding a rate distribution and also A
It has been found that the OM has birefringence, and as a result, the cross section of the light beam emitted from the AOM takes on a substantially elliptical shape extending in a predetermined direction, causing image blurring in the direction of the long axis of the ellipse.

Further, as a result of experiments, it was found that the fact that the AOM has birefringence is the main reason why the cross section becomes approximately oval.

However, as long as an AOM is used, the occurrence of temperature gradients, distortions, etc. inside the AOM is unavoidable.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a light beam scanning device in which the diameter of the light beam emitted from the AOM is substantially circular, thereby suppressing the occurrence of image blur. It is something.

(Means for Solving the Problems) A light beam scanning device of the present invention includes a light source that generates a light beam, an acousto-optic light modulator (AOM) that adjusts or modulates the intensity of the light beam and emits the light beam, and a target. A light beam scanning device comprising a scanning means for main-scanning a scanning body with a light beam emitted from the modulator and sub-scanning in a direction substantially perpendicular to the main-scanning direction, wherein the light source emits a linearly polarized beam. The light source and the modulator are aligned with the optical path of the light beam incident on the modulator as the axis so that the cross-sectional shape of the light beam emitted from the modulator becomes as close as possible to a circle. It is characterized in that a relative rotational position is determined.

The light source may originally emit a linearly polarized beam, or may have a polarizer placed on the optical path of the emitted light beam.

Further, the light beam emitted from the AOM may be either a zero-order beam or a first-order beam.

(Function) As described above, the main reason why the cross-sectional shape of the tip beam emitted from the AOM becomes approximately elliptical is that the AOM becomes birefringent due to heat generation, distortion, etc. When a light beam has birefringence, the refractive index for each of the two linearly polarized components of the incident light beam is different, and each polarized component is emitted in a slightly specific direction. When viewed as a whole, the cross section of the light beam becomes a substantially elliptical shape that spreads in a predetermined direction. In addition, it has been confirmed that factors other than birefringence are small and can be ignored with respect to the fact that the cross section of the light beam is approximately elliptical.

Since the light source of the light beam scanning device of the present invention generates a linearly polarized beam, when the light source and the AOM are relatively rotated around the optical path of the light beam incident on the AOM, the light beam emitted from the AOM is rotated. The cross-section of the light beam that is emitted alternately becomes approximately circular and approximately elliptical.

In the light beam scanning device of the present invention, the light source generates a linearly polarized beam as described above, and the AOM is scanned so that the cross-sectional shape of the light beam emitted from the AOM becomes closest to a circle.
A light source and an AO centering on the optical path of the light beam incident on M.
Since the relative rotational position with M is determined, AOM
Even if there is heat generation or distortion in the AOM, the cross section of the light beam emitted from the AOM will be approximately circular, and in image reading devices and image recording devices using this light beam scanning device, the cross section of the light beam will be approximately elliptical. There is no need to correct blur that would otherwise occur in a direction corresponding to the long axis of the oval, and an image with excellent viewing characteristics can finally be obtained.

(Example) Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of a light beam scanning device of the present invention.

This light beam scanning device consists of a laser light source 1 that generates a light beam 2, an AOM 3 mounted on a mount 3' that modulates the light beam 2, and a light beam 2' (0-order beam or 1-order beam) emitted from the AOM 3. The scanning optical system 5 (here, only the rotating polygon mirror 5a is shown) main scans the recording sheet 4, which is the object to be scanned, in the X direction using It is composed of sheet conveying means 6 that performs sub-scanning. The scanning optical system 5
and the sheet conveying means 6 constitute the scanning means of the present invention. The light source 1 is composed of a laser 1a and a polarizer 1b for converting the light beam emitted from the laser 1a into a linearly polarized beam. Alternatively, a semiconductor laser or the like that directly outputs a linearly polarized beam may be used as the light source 1. Here, in the AOM 3, the ultrasonic waves are propagating in the direction of arrow Z shown in the figure. The light beam 2' emitted from the AOM3 has birefringence due to the conversion of the ultrasonic energy of the AOM into thermal energy, etc., and due to this, each polarization component of the light beam emitted from the AOM3 They have light paths in slightly different directions.

Therefore, the cross-sectional shape of the light beam 2' on the recording sheet 4 becomes approximately oval. According to experiments conducted by the present inventors, the direction in which the oval shape is formed with its long axis varies depending on the structure of the AOM3, the method of attaching the AOMB to the mounting plate 3', etc.; , Once the method of attachment to the mounting plate 3' is determined, the direction is almost determined, and the driving power of the AOM (ultrasonic energy propagating inside the AOM, etc.)
Changing , only the degree of spread changes.

In the light beam scanning device of the present invention, the linearly polarized beam 2 that is incident on the AOM 3 is configured such that the plane of polarization of the linearly polarized beam 2 that is incident on the AOM 3 is in the long axis direction of the above-mentioned light beam or in a direction perpendicular to this. The relative rotational positions of the light source 1 and the AOM 3 are determined with the optical path as an axis. A.O.
Since the light beam 2' emitted from M3 has only one polarization component, the cross-sectional shape of the light beam 2' on the recording sheet 4 is approximately circular. In the image recording apparatus, there is no need to correct the blurring in the direction of the image corresponding to the long axis of the ellipse, which occurs when the cross-sectional shape of the light beam 2 is substantially elliptical.

FIG. 2 is a perspective view of an embodiment of an image reading and recording apparatus using the light beam scanning device shown in FIG. This image reading/recording device has the functions of an image reading device using the above-mentioned stimulable phosphor sheet and an image recording device for reproducing and recording images on a photosensitive film. Components corresponding to those shown in FIG. 1 are given the same numbers.

First, a case where this image reading/recording device is used as an image reading device will be explained.

A parallel light beam 2 emitted from a laser light source
The beam enters the beam expander 7, is adjusted to a predetermined beam diameter, and then enters the AOM 3.

The zero-order light beam 2' emitted from the AOM 3 passes through a half mirror 8 for monitoring the amount of light, and then enters a rotating polygon mirror 5a rotating in the direction of arrow A, where it is reflected and deflected. In this embodiment, a scanning optical system 5 is composed of a rotating polygon mirror 5a and a scanning lens 5b. The reflected and deflected light beam 2' passes through a scanning lens 5b such as an fθ lens, and then is conveyed (sub-scanned) in the direction of arrow Y by a sheet conveying means 6 (sub-scanning means) on which a radiation image is accumulated and recorded. The stimulable phosphor sheet 9 is repeatedly scanned in the main scanning direction (direction of arrow X shown in the figure) which is substantially perpendicular to the sub-scanning direction. That is, two-dimensional scanning is performed by the light beam 2' over the entire surface of the stimulable phosphor sheet 9 by the main scanning and sub-scanning.

The stimulable phosphor sheet 9 scanned by the above scanning emits stimulated light according to the image information accumulated and recorded at each scanning point, and this emitted light is transmitted to the main scanning line in the vicinity of the stimulable phosphor sheet 9. The light enters a transparent light guide 10 having a parallel incident end surface 10a from the incident end surface 1Qa. This light guide IO has an incident end surface 10a formed in a planar shape, and is formed so as to gradually become cylindrical toward the rear end side, and is provided on the exit end surface with a substantially cylindrical shape at the rear end portion tob. It is coupled to a photomultiplier 11. The stimulated luminescent light entering from the input end surface 10a is guided to the rear end lOb, and is transmitted to the photomultiplier 11 via an optical filter (not shown) that selectively transmits the stimulated luminescent light. Further, at a position opposite to the incident end surface 10a of the light guide 10 across the main scanning line, a light guide is provided extending in the main scanning direction to direct the incident stimulated luminescence light to the incident end surface 10a.
A reflecting mirror 12 is provided to reflect the light toward 0a. The stimulated luminescent light is converted into an electrical signal (analog image signal) Sl in a photomultiplier 11.

Here, even if the AOMB becomes birefringent due to heat generation, distortion, etc. within the AOMB as described above, the cross-sectional shape of the light beam 2' on the stimulable phosphor sheet 9 is made to be approximately circular, that is, Light beam 2' emitted from AOMB
is incident on the 80M3 such that the plane of polarization is in the long direction of the AOM3 or in a direction perpendicular thereto, where the beam emitted from the AOM3 becomes an oval when an unpolarized light beam is incident on the AOMB. The relative rotational position of the light source and the AOMB is determined with the optical path of the light beam 2 as an axis.

Further, the light beam 2' reflected by the half mirror 8 is monitored for its light intensity by a photodetector 13, and the AOMB is driven so that the light intensity is constant via an AOM driver 28 for driving the AOMB. Ru.

On the other hand, the synchronized beam 15 emitted from the laser light source 14 enters the rotating polygon mirror 5a, is reflected and deflected, and is reflected by the mirror 16.
The beam is reflected by the beam, enters the synchronous beam detector 17, and scans the grid 17a of the synchronous beam detector 17. The grid 17a has a large number of slits L7b lined up in the direction of the scanning path, and the synchronous beam 15 passes backward only when it irradiates these slits 17b.
When the intermediate position between 7b and slit 17b is irradiated,
The optical path is blocked by the slit plate 17a. slit 17
The monitor light that has passed through b enters the light guide 17c, propagates inside the light guide 17c, and reaches the photomultiplier 17.
d, and is converted into an electrical signal S3. electrical signal S
3 corresponds to the fact that the synchronous beam 15 is intermittently interrupted when scanning over the grid 17a, resulting in a pulse signal of, for example, 100 KHz that changes repeatedly. This pulse signal is sent to the A/D converter 23 and used as a sampling timing signal when sampling an analog image signal.

The analog image signal S1 output from the photomultiplier 11 is amplified by the amplifier 21, and then sampled and digitized by the A/D converter 23 in synchronization with the sampling timing signal S3. The digital image signal S2 obtained in this way is stored in the storage means 24, and then sent to the image processing means 25 as necessary to undergo necessary image processing. The image signal subjected to image processing by the image processing means is sent again to the storage means 24 and stored therein.

In this case, if the cross-sectional shape of the light beam 2' scanning the stimulable phosphor sheet 9 is approximately oval, the obtained image signal S2 corresponds to the direction of the long sleeve of the oval. However, since this image reading and recording device uses the light beam scanning device of the present invention, this does not occur and the obtained image signal S
Even if an image is reproduced and recorded as described below based on 2, the image will not be blurred in a predetermined direction and will be an image that is suitable for viewing.

Next, the case where an image is reproduced and recorded using the image reading and recording apparatus shown in FIG. 2 will be described. Duplicate explanations of points common to the case of image reading will be omitted.

When playing and recording images, 1 output from AOMB
The next light beam 2' is used and this first order light beam 2'
An image is reproduced and recorded on the photosensitive film 29 by main scanning the photosensitive film 29 conveyed in the direction of the arrow Y in the X direction. Although the zero-order light beam 2' and the first-order light beam 2' differ in the direction in which they are emitted from the AOM 3, they are shown here as having the same optical path for the sake of simplicity. Due to this difference, the main scanning lines are slightly different between the stimulable phosphor sheet 9 and the photosensitive film 29, but this can be corrected by adjusting the timing of driving the AOM 3, etc. Furthermore, although the stimulable phosphor sheet 9 and the photosensitive film 29 are drawn to refer to the same sheet, they represent the stimulable phosphor sheet 9 during reading, and the photosensitive film 29 during recording. do.

The image signal S2 read from the storage means 24 is input to the D/A converter 26 and converted into an analog image signal 82'. The AOM driver 28 drives the AOM 3 so that an image based on this analog image signal is reproduced and recorded. Since the cross-sectional shape of the light beam 2' on the photosensitive film 29 is approximately circular, the image reproduced and recorded on the photosensitive film 29 will not be blurred in a predetermined direction.

In the above embodiment, a system using a stimulable phosphor sheet has been described, but the light beam scanning device of the present invention is not limited to a system using a stimulable phosphor sheet. It goes without saying that the present invention can also be implemented in systems that scan line films to obtain image signals.

Furthermore, in the above embodiment, an example was explained in which the light beam scanning device is applied to an image reading/recording device that can perform both image reading and reproduction/recording, but the light beam scanning device of the present invention can only read images. The present invention can also be applied independently to an image reading device that performs image reading or an image recording device that only performs reproduction and recording of images.

(Effects of the Invention) In the light beam scanning device of the present invention, the light source generates a linearly polarized beam, and the light beam incident on the AOM is arranged so that the cross-sectional shape of the light beam emitted from the AOM becomes closest to a circle. Since the relative rotational position of the light source and the AOM is determined with the optical path of the beam as the axis, the diameter of the light beam emitted from the AOM is approximately circular, and an image reading device incorporating this light beam scanning device There is no possibility that blurring in a predetermined direction will occur in a visible image finally obtained using an image recording device or the like.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of a light beam scanning device of the present invention, and FIG. 2 is a perspective view showing an embodiment of an image reading and recording device using the light beam scanning device shown in FIG. It is a diagram. 1... Light source la... Laser 1b... Polarizer 2.2'
, 2'... Light beam 3... AOM (acousto-optic light modulator) 4... Recording sheet 5... Scanning optical system 5a... Rotating polygon mirror
9...Stormable phosphor sheet 11...Photomultiplier 29...Photosensitive film Fig. 1

Claims (1)

[Scope of Claims] A light source that generates a light beam, an acousto-optic light modulator that adjusts or modulates the intensity of the light beam, and emits the light beam; In the light beam scanning device, the light beam scanning device includes a scanning means for scanning and sub-scanning in a direction substantially perpendicular to the main scanning direction, wherein the light source generates a linearly polarized beam, and the light beam emitted from the modulator The relative rotational position of the light source and the modulator is determined with respect to the optical path of the light beam incident on the modulator such that the cross-sectional shape of the light beam becomes closest to a circle. A light beam scanning device.