JPH03156415A - Optical device and method for optical beam scanning - Google Patents

Abstract

PURPOSE:To simply correct a change in the intensity of an optical beam due to a position on a scanning line by arranging a plane mirror so that the intensity of an incident optical beam to a face to be scanned is fixed on the scanning line. CONSTITUTION:The plane mirror 6 is arranged on the face vertical to a scanning plane so that a normal 9 drawing on the reflection face of the mirror 6 forms an inclination angle alpha with the optical axis AX of an image forming optical system 5. The angle alpha is 1/2 the angle beta formed by an optical beam 10 projected from a light source unit 1 and the axis AX of the system 5 and its direction is the light source unit direction. Then the plane mirror 6 is inclined from the scanning plane. The inclination angle is set up so that the optical beam is reflected on the face 8 to be scanned arranged on the light source (1) side from the optical axis AX of the system 5 and the optical beam coincident with the optical axis AX arrives at the center B of the scanning line 8. Consequently, the intensity variation of the optical beam due to the scanning position can be effective corrected without generating difficulty in production.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light beam scanning optical device such as a laser beam printer.

[Conventional technology]

2. Description of the Related Art In a scanning optical device that scans a light beam, a method of deflecting the light beam by changing the angle of a light beam reflecting surface, such as a rotating polygon mirror, is widely used as a light beam deflection means.

FIG. 7 is a configuration diagram showing an example of a conventional light beam scanning optical device.

This optical device includes a light source unit 1, a rotating polygon mirror 2 that deflects a light beam, an imaging optical system 5 that focuses the deflected light beam onto a scanned surface 7, and a light beam from the imaging optical system 5. It is composed of a plane mirror 6 that changes the direction of the beam toward the surface to be scanned 7 and the surface to be scanned 7 .

The operation of the optical device having the above configuration will now be described.

The light beam 10 exiting the light source unit 1 is reflected by the rotating polygon mirror 2, and is deflected into condylar light beams 10a, 10b, and 10o according to the rotation of the rotating polygon @2. The plane formed by this deflected light beam is defined as a scanning plane.

Further, the angle θ formed by the light beam deflected by the rotating polygon mirror 2 and the optical axis AX of the imaging optical system 50 is defined as the deflection angle θ. In FIG. 7, the value of the deflection angle θ is determined by the optical axis AX of the imaging optical system.
On the other hand, the case where the light is deflected to the side opposite to the light source unit is considered positive.

The light beam deflected by the rotating polygon mirror 2 is focused by the imaging optical system 5.

The light beam exiting the imaging optical system 5 is reflected by a plane mirror 6,
The surface to be scanned 7 is scanned linearly. This straight line is the scanning line 8
shall be.

The surface to be scanned 7 is, for example, a photosensitive recording medium, and information is recorded by irradiation with a light beam.

In the scanning optical device as described above, when a light beam is deflected by the rotating polygon mirror 2, the value of the deflection angle θ changes depending on the angle of incidence of the light beam on the reflecting surface 4 of the rotating polygon mirror.

Here, it is generally known that the reflectance of a light beam reflecting medium changes depending on the incident angle of the light beam.

Therefore, when the light beam scans the scanned surface 7, the intensity of the light beam changes depending on the scanning position, which changes depending on the deflection angle.

Next, FIG. 8(a) shows the position on the scanning line on the horizontal axis and the intensity of the light beam on the vertical axis (changes in intensity with respect to the position on the scanning line).

In such a scanning optical device, the light beam that scans the surface to be scanned has an energy distribution in a cross section perpendicular to the beam traveling direction that is approximately equal to the distance from the beam center.
It has a so-called Gaussian distribution shape. (Hereafter, this will be referred to as the Gax beam.) Figure 8 (b) is similar to Figure 8 (a).
This figure shows the energy distribution of the light beam at positions C and C on the scanning line when there is a change in the intensity of the light beam at the positions on the scanning line shown in FIG.

In FIG. 8(b), the horizontal axis shows the distance from the beam center, the vertical axis shows the optical energy, and the straight line 51 shows the photosensitivity level 31 of the recording medium, which is the surface to be scanned.
It is recorded on the recording medium when a larger light energy is irradiated.

Therefore, the beam diameter of the light beam recorded on the recording medium is ω1 at scanning position A and ω at scanning position C.

Therefore, even if the same character is recorded, the thickness of the line of that character will be the same.

For example, in the case of a laser printer, this causes variations in printing and causes deterioration of printing quality.

An example of an optical device that solves the above-mentioned problems is the one described in Japanese Patent Application Laid-Open No. 63-92913.

In the conventional scanning optical device described above, in order to correct the change in the intensity of the light beam due to the difference in position on the scanning line, the reflective surface of the plane mirror 60 in FIG. 7 is coated or the like along the scanning direction of the light beam. The reflectance is changed based on the reflection rate.

[Problem to be solved by the invention]

However, the above-mentioned conventional technology has a problem in that it is extremely difficult to coat the reflecting surface so that it has an appropriate reflectance depending on the location. Furthermore, when assembling such a plane mirror, it must be mounted with high precision so that the reflectance will be an appropriate value in response to changes in the intensity of the light beam depending on the position on the scanning line, which makes assembly difficult. There is also a peak.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to realize a scanning optical device that can easily correct changes in the intensity of a light beam depending on the position on a scanning line.

[Means to solve the problem]

In order to solve the above problems, a light beam scanning optical device according to the present invention is as follows.

That is, the optical P-A scanning optical device according to the present invention includes a light beam generation source, a deflection device, an imaging optical system, and a plane mirror, and the plane mirror is configured to deflect the light beam incident on the surface to be scanned. The intensity is placed at a constant position on the scanning line.

The plane mirror is placed between the imaging optical system and the surface to be scanned, and the plane mirror is placed perpendicular to the scanning plane, and the normal line to the reflection surface of the light beam of the plane mirror and the above-mentioned resultant plane are arranged perpendicularly to the scanning plane. It is preferable that the imaging optical system be arranged at such an angle that the angle formed with the optical axis is half of the angle formed between the optical axis and the light beam directed from the light beam generation source toward the deflection device. , but is not limited to this.

Further, the position of the plane mirror can be more easily determined by making the reflectance characteristics for the light beam on the reflection surface of the plane mirror the same as the reflectance characteristics for the light beam at the reflection r of the deflection device.

In addition, between the imaging optical system and the plane mirror, a parallel plate having a transmittance that has the same characteristics as the reflectance of the rotating polygon mirror for the light beam is installed to reflect the light beam incident on the scanned surface. It may be arranged at a position where the intensity is constant on the scanning line.

A light beam scanning method for achieving the above object is such that the plane mirror reflects the light beam at different reflection angles depending on the point of incidence, so that the light beam incident on the surface to be scanned has a constant intensity on the scanning line. K so that it becomes.

Also, a plane mirror is placed between the imaging optical system and the surface to be scanned,
The angle formed by the normal to the light beam reflecting surface of the plane mirror and the optical axis of the imaging optical system is the angle formed by the light beam directed from the light beam generation source toward the deflection device and the optical axis. 1/2
It is preferable that the plane mirror be placed at a position such that the plane mirror is tilted so that the plane mirror reflects the light at different angles depending on the incident point, but the invention is not limited thereto.

[Effect]

When a light beam is deflected by a rotating polygon mirror, changes in the angle of incidence of the light beam on the reflecting surface of the rotating polygon mirror will be explained.

FIG. 5 schematically shows how the light beam 10 is deflected in the vicinity of the reflective surface 4 of the one-rotation polygon @2 as the reflective surface 4 moves.

1 is a light source unit, 10 is a light beam, 4a, 4b.

4o is a reflective surface, 10a, 10. is the light beam reflected by each reflective surface, ψ4. ψ is the incident angle of the light beam, β is the angle between the optical axis X of the imaging optical system 5 and the incident light beam, and θ is the optical axis A
It shows the angle formed by X and the reflected light beam, that is, the polarization angle.

The angle of incidence ψ of the light beam on the reflecting surface 4 is from ψ to ψ.

, the reflected light beams are sequentially deflected from light beam 10a (negative deflection angle) to light beam 10o (positive deflection angle, maximum) K.

At this time, the reflectance of the light beam changes depending on the incident angle, as shown in FIG. 4, for example, and therefore the intensity of the light beam changes depending on the deflection angle.

Here, the plane fM6 disposed between the imaging optical system 5 and the surface to be scanned 7 is set as in the configuration of the present invention described above. That is, the change in the angle of incidence of the deflected light beam on the plane mirror 6 is set to be opposite to that on the reflecting surface 4 of the rotating polygon mirror 2 described above. In this way, the angle of incidence of the light beam on the plane mirror 6 is large when the deflection angle 0 is negative (when it is deflected toward the light source unit side from the optical axis AX), and small when the deflection angle is positive. Become.

Furthermore, the reflectance characteristics of the plane mirror 6 for the light beam are as follows:
Assuming that the reflectance of the reflective surface of the rotating polygon mirror has the same characteristics, the reflectance of the light beam emitted from the light source unit 1 on the reflective surface 4 of the rotating polygon mirror 2 and the reflectance on the plane mirror 6 are inversely proportional to each other. Become.

Therefore, the plane mirror 6 according to the present invention acts to cancel out the change in the intensity of the light beam caused by the rotating polygon mirror 2, which corresponds to the deflection angle.

This makes it possible to correct changes in the intensity of the light beam that correspond to the deflection angle, so that the intensity remains the same on the scanning line 8.

〔Example〕

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

FIG. 1 shows the configuration of an embodiment of the present invention.

The scanning optical device according to this embodiment includes a light source unit 1, a rotating polygon mirror 2, a motor 3, an imaging optical system 5, a plane mirror 6, and a surface to be scanned 7.

Next, its operation will be explained. The light source unit 1 is
It includes a light source and a light beam shaping optical system, and emits a nearly parallel light beam. The light source is a semiconductor laser in this example.

The rotating polygon mirror 2 is rotated by a motor 3 in the direction of the arrow shown in the figure. The light beam 10 exiting the light source unit 1 is
It is reflected by the reflective surface 4 of the rotating polygon @2.

As shown in the figure, as the rotating polygon mirror 2 rotates in the direction of the arrow, the light beam reflected by the reflecting surface 4 is sequentially 1
051.10b, it will change direction and be deflected 10oO.

In this embodiment, the rotating polygon mirror 2 has eight reflective surfaces, and one
The light beams 10a to 100 are deflected by the two reflecting surfaces, that is, one scan is performed, and eight scans are performed while the rotating polygon mirror 2 rotates once.

The imaging optical system 5 is composed of two lenses, a first lens having negative power and a second lens having positive power.

The imaging optical system 5 includes a rotary polygon mirror 2 that provides an image of 10a to 10o.
It functions to focus the deflected light beam on the scanned surface 7.

In addition to the function of focusing the light beam described above, the imaging optical system 5 has the function that when the light beam scans the surface to be scanned 7, the position on the scanning line 8 is proportional to the deflection angle θ (so-called fθ characteristic). It acts to bend the optical path of the light beam.

The plane mirror 6 has the function of reflecting the light beam from the imaging optical system 5 to a predetermined scanning position on the surface to be scanned 7, and at the same time reflects the non-uniform intensity of the light beam corresponding to the deflection angle of the light beam according to the present invention. It has the effect of correcting gender.

The plane mirror 6 is arranged at a predetermined angle within the scanning plane.

FIG. 2 is a block diagram of the embodiment shown in FIG. 1 when viewed from above the scanning plane.

The arrangement of the plane mirror 6 will be explained with reference to FIG.

As shown in FIG. 2, first, the plane mirror 6 is arranged on a plane perpendicular to the scanning plane so that the normal 9 erected to the reflection plane forms an inclination angle α with the optical axis AX of the imaging optical system 5. Ru. The angle α is
It is assumed that the angle β between the light beam 10 emitted from the light source unit 1 and the optical axis AX of the imaging optical system 5 is 1/2, and its direction is in the direction of the light source unit.

Next, the plane mirror 6 is tilted relative to the scanning plane. The tilt angle is such that the light beam is reflected onto the scanned surface 8 placed closer to the light source unit 1 than the optical axis AX of the imaging optical system 5, and the light beam that coincides with the optical axis AX is Tilt it so that it reaches the center B of the scanning line 8. Since this angle is the same for all incident light beams, it can be any angle that satisfies the above conditions.

Furthermore, the reflective surface of the plane mirror 6 is made of the same material as the reflective surface of the rotating polygon mirror 2.

By arranging the plane mirror 6 as described above, the plane mirror 6
The characteristic of the reflectance of the light beam corresponding to the deflection angle θ is
It has a characteristic opposite to the reflectance characteristic of the rotating polygon mirror 2, and can correct changes in the intensity of the light beam that vary depending on the deflection angle.

The details of this action will be explained later.

The surface to be scanned 7 is, for example, a photosensitive drum surface in a laser printer or the like, and a charging or discharging phenomenon occurs in a portion irradiated with a light beam, and a signal is recorded. The light beam scans the scanned surface 8 in a straight line (scanning line 8) and records a signal on the scanned surface, and the scanned surface 7 rotates, for example, in the direction of the arrow in FIG. The signal recorded in the process is transmitted to the next process.

Next, with reference to FIG. 3, an explanation will be given of the effect of the plane g86 to correct variations in the intensity of the light beam corresponding to the deflection angle θ.

First, when the light beam is deflected by the rotating polygon mirror 2,
The reason why the intensity of the light beam changes depending on the deflection angle θ will be explained.

As shown in FIG. 3, the light beam 1 exiting the light source unit 1
0 is reflected by the reflecting surface 4 of the rotating polygon mirror 2, and the reflecting surface 4 changes its position as 4a, 4b, and 4o according to the rotation of the rotating polygon mirror 2 (in the direction of the arrow).

At this time, the angle of incidence of the light beam 10 on the reflecting surface 4 (reflecting surface 4
The angle formed by the normal to the incident light beam 10) increases monotonically from ψ to ψ.

In this embodiment, the optical axis person X of the light beam 10 and the imaging optical system 5 is
The angle β between the two is 55 degrees, and the deflection angle θ of the light beam is at most ±50 degrees with respect to the optical axis AX of the imaging optical system 5.

As shown in Fig. 3, the light beam 100 is directed to 1 reflecting surface
If the angle of incidence is ψ, then ψ=(θ+β
)/2 ......(1).

Therefore, in this example, ψ changes from ψ,=175 degrees to ψ,
=42.5 degrees.

A graph of this change is shown by the broken line 21 in Figure @5.

Figure 4 shows an example of the change in reflectance with respect to the incident angle of the light beam on the reflecting surface 4 of the rotating polygon mirror 2 used in this example. The horizontal axis shows the incident angle ψ of the light beam, and the vertical axis shows the reflectance of the light beam.In this way, the reflectance of a light beam using a metal etc. as a reflective surface generally changes depending on the incident angle of the light beam. do.

As mentioned above, in this example, the incident angle of the light beam is ψ,
As shown in Figure 4, the reflectance of the light beam is approximately A change of 10% is K.

When there is such a change in reflectance, the intensity of the light beam reflected by the rotating polygon mirror changes depending on the value of the incident angle of the light beam, and the change shows a certain relationship with the light beam deflection angle. The state of the change is as indicated by the broken line 25 in FIG.

In FIG. 6, the horizontal axis is the deflection angle θ of the light beam, and the vertical axis is a relative value with respect to the intensity of the light beam when θ=0 degrees.

When the intensity of the light beam changes in accordance with the deflection angle θ, the intensity of the light beam incident on the scanned surface 71C changes depending on the location. As mentioned above, in laser printers and the like, printing becomes uneven and the printing quality is significantly degraded.

In the present invention, as described above, by arranging the plane @6 at an angle compared to the conventional arrangement, it is possible to correct changes in the intensity of the light beam above the plane @6.

In this embodiment, attention is paid to the light beam incident on the plane mirror 6. The light beam incident on this plane mirror 6 and the imaging optical system 5
The angle formed by the optical axis AX with respect to the optical axis AX changes almost linearly with respect to the deflection angle θ of the light beam, as shown by the dashed-dotted line 22 in FIG. Further, its inclination is approximately the same as the characteristic 21 (indicated by a broken line) of the incident angle of the light beam on the reflecting surface 4 of the rotating polygon mirror.

The reason for this is that, as described above, the imaging optical system 5 has the so-called fθ characteristic, so the optical path of the light beam deflected by the rotating polygon mirror 2 at an angle θ is bent by the imaging optical system 5, and the optical beam is focused. This is because after passing through the image optical system 5, the angle formed with the optical axis AX becomes much smaller than the deflection angle θ.

Generally, an imaging optical system called an fθ lens has similar characteristics.

In this embodiment, the angle formed between the light beam after passing through the imaging optical system 5 and the optical axis AX is approximately 1/2 of the deflection angle θ, and the characteristics with respect to the deflection angle θ are as shown in FIG. The dashed line 22 shows the characteristics of the angle of incidence on the rotating polygon mirror.
It is almost parallel to 1.

By using the above characteristics, by arranging the plane mirror 6 at an angle as shown in FIG. 2, the angle of incidence of the light beam on the plane mirror 6 is determined by the solid line shown in FIG. 2
It can be changed as shown in 3.

The characteristic of the angle of incidence of the light beam on the plane mirror 6 shown by the solid line 25 is the characteristic 2 of the angle of incidence of the light beam on the reflecting surface 4 of the rotating polygon mirror.
Compared to 1, the absolute values are almost equal, and the positive and negative slopes are opposite.

Here, if the reflecting surface of the plane mirror 6 is made of the same material as the reflecting surface 4 of the rotating polygon mirror 2, the reflectance characteristics with respect to the angle of incidence of the light beam on the plane mirror 6 will be the same as that of the reflecting surface 4 of the rotating polygon mirror 2. Same as reflectance characteristics - busy.

Due to this, the change in beam intensity due to the reflectance of the light beam corresponding to the deflection angle θ on the plane mirror 6Vc can be made to have a characteristic as shown by the dashed-dotted line 26 in FIG.

The intensity of the light beam incident on the scanned surface 7Vc depends on the product of the reflectance on the reflecting surface 4 of the rotating polygon mirror and the reflectance on the plane mirror 6.

Therefore, the intensity of the light beam on the scanned surface 7 is the product of the characteristics of the broken line 25 and the dashed-dotted line 26 in FIG. can be kept constant.

The above-mentioned angle between the light beam exiting the imaging optical system 5 and the optical axis AX of the imaging optical system varies slightly depending on the design of the imaging optical system having fθ characteristics, and accordingly, Although the reflectance characteristics shown by the dotted chain 11126 in the figure are slightly improved, the changes in the light beam intensity are significantly improved compared to the characteristics of the change in the light beam intensity with respect to the deflection angle in the conventional optical system, as shown by the broken line 25. There is no change in the fact that it can be relaxed.

FIG. 9 is a block diagram of a second embodiment of the present invention. In this embodiment, a transparent parallel plate is installed between the imaging optical system 5 and the surface to be scanned 70, and the light beam of the parallel plate is K is set so that the transmittance characteristics for the light beam are the same as the reflectance characteristics of the rotating polygon mirror with respect to the incident angle of the light beam. By arranging such a parallel plate at an angle in the same way as the plane mirror of the above embodiment according to the above concept, changes in the intensity of the light beam corresponding to the deflection angle θ can be corrected and made uniform.

Further, in these embodiments, a rotating polygonal mirror is used as the deflection device, but the present invention is also effective in the case of other deflection devices that use a reflecting mirror, such as a single-type galvano mirror.

Furthermore, the present invention is effective not only for optical systems for laser printers but also for other scanning optical systems where unevenness in light intensity is a problem, such as recording devices for photosensitive films such as microfilms.

〔Effect of the invention〕

As described above, according to the present invention, there is no increase in the number of elements compared to conventional optical devices, and assembly precision such as positioning is not required.1. It is possible to realize a scanning optical device that satisfactorily corrects variations in the intensity of a light beam with respect to a scanning position without any manufacturing difficulties.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the configuration of an embodiment of the present invention, Fig. 2 is an optical path diagram when the embodiment shown in Fig. 1 is viewed from above the scanning plane, and Fig. 3 is a reflection of a rotating polygon mirror. An enlarged view of the optical path near the surface, Figure 4 is a graph showing the reflectance characteristics with respect to the beam incidence angle on the light beam reflection surface of the rotating polygon mirror, and Figure 5 is the light beam incidence angle or optical axis with respect to the deflection angle of the light beam. AX
FIG. 6 is a graph showing the change in the angle formed by the light beam, FIG.
The figure shows an optical path diagram in a conventional light beam optical device, Fig. 8 (
FIG. 8(a) is a graph showing variations in light beam intensity corresponding to positions on a scanning line in a conventional optical system, and FIG. 8(b) is a graph showing energy distribution of a light beam on a surface to be scanned. 9ηIJ 8 iris'2a＞'t'or91JA
lf1g2. L1... Light source unit, 2... Rotating polygon mirror, 3... Motor, 4, 4a, 4b, 4o... Reflection surface of rotating polygon mirror, 5... Imaging optical system, 6...・Plane mirror, 7...Scanned surface, 8...Scanning line, 9...Normal to the reflecting surface of the plane mirror, 10...Light beam, 10a
, 10b... A light beam reflected by a rotating polygon mirror,
51...Sensitivity level of the recording medium, 41...Parallel plate, α...Angle between the normal to the reflecting surface of the plane mirror and the optical axis of the imaging optical system, β...Light source unit and rotation The angle between the light beam between the polygon mirrors and the optical axis of the imaging optical system, θ...
・Deflection angle, ψ2. ψ,...Angle of incidence of the light beam on the rotating polygon mirror, ψ41ψ5 ψ6...Angle of incidence of the light beam on the plane mirror, AX...Optical axis of the imaging optical system, ω...Position on the scanning line Diameter of the light beam recorded on the recording medium at 1 m, ω...Diameter of the light beam recorded on the recording medium at position C on the scanning line. Figure 1 2nd mouth 4- Repulsion surface 10-11 beam No. 60 Beam Sendo circle No. 7 [¥1 7 Coffin stolen items No. 0

Claims (1)

[Claims] 1. A light beam generation source, a deflection device that deflects the light beam emitted from the light beam generation source using a reflective surface, and a light beam deflected by the deflection device onto a surface to be scanned. A light beam scanning optical device comprising an imaging optical system for converging and scanning at a constant speed on the surface to be scanned, and a plane mirror placed between the imaging optical system and the surface to be scanned. A light beam scanning optical device, wherein the plane mirror is arranged at a position where the intensity of the light beam incident on the surface to be scanned is constant on a scanning line. 2. A plane mirror is placed between the imaging optical system and the scanned surface,
The plane mirror is placed perpendicular to the scanning plane, and the angle between the normal to the light beam reflection surface of the plane mirror and the optical axis of the imaging optical system is from the light beam generation source to the deflection device. 2. The light beam scanning optical device according to claim 1, wherein the light beam scanning optical device is disposed at a position that is one-half of the angle formed by the optical axis. 3. The light beam scanning optical device according to claim 1 or 2, wherein the reflectance characteristics for the light beam on the reflective surface of the plane mirror are made the same as the reflectance characteristics for the light beam on the reflective surface of the deflection device. . 4. A light beam generation source, a deflection device that deflects the light beam emitted from the light beam generation source by a reflective surface, and a deflection device that focuses the light beam deflected by the deflection device onto a surface to be scanned and scans the surface to be scanned. In a light beam scanning optical device comprising an imaging optical system for performing uniform velocity scanning on a surface and a plane mirror placed between the imaging optical system and the surface to be scanned, the imaging optical system comprises: A parallel plate having a transmittance that has the same characteristics as the reflectance of the rotating polygon mirror for the light beam is installed between the system and the plane mirror so that the intensity of the light beam incident on the surface to be scanned is on the scanning line. A light beam scanning optical device characterized in that the light beam scanning optical device is arranged at a constant position. 5. A laser beam printer comprising the light beam scanning optical device according to claim 1, 2, 3 or 4. 6. Deflect the light beam emitted from the light beam generation source by the reflecting surface of the deflection device, make the deflected light beam enter a plane mirror via the imaging optical system, and make the light beam reflected by the plane mirror In a light beam scanning method in which scanning is performed by irradiating the surface to be scanned, the light beam incident on the surface to be scanned is reflected by the plane mirror at different angles of reflection depending on the point of incidence.
A light beam scanning method that scans a surface to be scanned with a light beam so that its intensity remains constant on a scanning line. 7. A plane mirror is placed between the imaging optical system and the surface to be scanned, and the angle between the normal to the light beam reflection surface of the plane mirror and the optical axis of the imaging optical system is the angle between the optical axis of the imaging optical system and the optical axis of the imaging optical system. The plane mirror is arranged at a position that is half the angle formed by the optical axis and the light beam directed from the source to the deflection device, and the plane mirror is tilted so that the reflection angle differs depending on the incident point. 7. The light beam scanning method according to claim 6, wherein the light beam is reflected. 8. When recording characters and figures on a recording medium on a surface to be scanned using the light beam scanning method according to claim 6 or 7,
A recording method characterized in that the intensity of the light beam in the scanning line on the surface to be scanned is made uniform, and when characters and figures to be recorded are the same, they are recorded with the same thickness.