JP2001296109A - Diameter-measuring device for light spot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for measuring light spot diameter which can accurately measure the shape of a light spot of a laser beam. SOLUTION: This diameter-measuring device is provided with a photodetecting element 3, which outputs a light receiving information signal when a laser beam L is made incident, a light-shielding means which drives a slit 1a so that the slit 1a traverses the optical axis X of the laser beam L, and a track changing means which changes the track of the slit 1a, with respect to the optical axis X. This measuring instrument is also provide with an arithmetic means, which finds the diameter of the light spot formed of the laser beam L, based on the moving speed of the slit 1a and the light-receiving information from the photodetecting element 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light spot diameter measuring apparatus for measuring a light spot shape of a laser beam by a slit method.

[0002]

2. Description of the Related Art A scanning optical system for converging a laser beam as a light spot on a surface to be scanned and scanning the surface to be scanned is widely known for various image forming apparatuses such as laser printers and digital copying machines. Recently, “higher density and multi-beam scanning” by a scanning optical system are intended, and higher precision is required for measuring the light spot diameter. In particular, as the density increases, the depth of focus of light spots becomes shallower, and high-precision measurement of minute spots has become an important measurement technique.

[0003] Conventionally, as a device for measuring a light spot, there is a device using a narrow slit system or a two-dimensional CCD crossing the front of a photodetector. FIG.
1 shows a configuration of a main part of a conventional measuring device using a slit method. In this conventional example, there is a light shielding means comprising a cylindrical body 1 having a slit 1a in front of the light detecting element 3, and the cylindrical body 1 provided with the slit 1a is rotated by a motor 2 in the direction of arrow a. The slit 1a is arranged so as to cross the light spot L 'of the laser L. FIG.
When the slit 1a crosses the light spot L 'as shown in (a), the output from the light detecting element 1 changes as shown in FIG. In general, the highest output value from the photodetector 1 is 1
The width of the 3.5% position is the spot diameter d. The spot diameter d is calculated by the control unit based on the light receiving information signal from the light detecting element 3 and the moving speed of the slit 1a.

Further, the above-mentioned conventional slit method can only measure one-dimensionally with respect to the spot diameter L '. On the other hand, in the apparatus shown in FIG. 7, two-dimensional measurement is performed by providing two inclined slits. In this example, the rotating shaft 2
When two slits 1b and 1c, each of which is inclined at ± 45 ° with respect to a, cross the spot diameter L 'as shown in FIG. 8 (a), the output from the photodetector 3 becomes FIG.
It changes as shown in FIG. According to this example, the slit 1
spot diameter _{d 1} is the c, the light spot diameter _{d 2} is obtained by the slit 1b. When the three-dimensionally displaying the two-way output of d ₁ and d _2, the three-dimensional spot shape as shown in FIG. 9 is obtained. According to the slit method, φ
Measurement of a minute spot of about 20 μm is possible.

In the two-dimensional CCD system, a light spot L 'is formed by a two-dimensional light receiving surface in a stationary state without using a slit.
Can be detected. Unlike the conventional slit method described above, this method is advantageous in that the entire image of the spot is captured.

[0006]

However, in the CCD system in which light is received by a two-dimensional pixel array, although the spot shape is excellent in reproducibility, there is a limit to the CCD pixel pitch, and thus a limit to the measurable spot diameter. is there. At present, the spot diameter to be measured is at least φ100
It is required to be about μm, and the resolution of a small spot smaller than this diameter is relatively insufficient.

On the other hand, in the conventional slit method, φ20 μm
Although it is advantageous in that a small spot of about m can be measured, the measurement is only performed in several directions due to the inclination of the slit. Simply tilting the slit cannot specify the exact shape of the entire spot. For example, only information on the diameter in two directions in which two slits are inclined does not represent an accurate ellipse as the light spot shape.

Accordingly, the present invention has been made in view of these facts. It is an object of the present invention to measure a minute spot which cannot obtain a sufficient resolution with a two-dimensional CCD and to measure the entire spot. It is an object of the present invention to provide a light spot diameter measuring device capable of measuring an accurate shape of the light spot.

[0009]

In order to achieve the above object, a light spot diameter measuring apparatus according to the present invention comprises: a light detecting element for outputting a light receiving information signal in accordance with a light receiving amount of an incident laser; Light shielding means for driving the slit such that the slit traverses the optical axis for irradiating the element, trajectory variable means for changing the trajectory direction of the slit with respect to the optical axis, moving speed of the slit, and Calculating means for calculating the light spot diameter of the laser based on the received light information signal.

The trajectory changing means can be constituted by a rotation mechanism for rotating the light shielding means about the optical axis.

It is preferable that the calculation means obtains the light spot shape of the laser based on a plurality of light receiving information signals obtained at each rotation position of the light shielding means. Also in this case, the calculation means may be configured such that each rotation amount of the light shielding means is 180 ° or less in order to obtain the plurality of light reception information signals.

Further, the arithmetic means may be configured to determine a three-dimensional light spot shape based on a light receiving information signal from a light detecting element at each rotation position of the light shielding means.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a measuring apparatus to which the present invention is applied will be described below with reference to the drawings. FIG. 1 is a side view showing the entire configuration of a measuring apparatus according to the present invention, and FIG. 2 is a perspective view of the apparatus shown in FIG.

The configuration of this device is roughly divided into a light spot measuring unit A and a rotation mechanism B thereof. The light spot measuring unit A includes a cylindrical body 1, a first motor 2 for driving the cylindrical body 1, and a light detecting element 3.

The cylindrical body 1 has a very narrow slit 1a in the direction of the first rotation axis 2a. This cylinder 1
Are drivably supported on a rotating shaft on the first motor 2. The first rotating shaft 2a is connected to the laser L to be measured.
Is substantially perpendicular to the optical axis X, and the cylindrical body 1 has a slit 1
The rotation trajectory a is supported at a position where it passes through the optical axis X, thereby constituting a light shielding means.

The rotation mechanism B is a trajectory changing means, and comprises a housing 4 and a second motor 5. In the illustrated example, the rotation mechanism B
The rotation shaft of the second motor 5 is fixed to the rear part of the optical disk, and the light spot measurement unit A in the housing 4 is rotatably supported. Case 4
Has an opening 4a into which the laser beam L enters, and the optical axis X entering from the opening 4a is the second rotation axis 5a.
Is to be matched. Thereby, even if the housing 4 rotates, the incident optical path of the laser L is secured.

In the illustrated example, a second rotation axis 5a is set on the extension of the optical axis X, and the slit 1
The first rotation shaft 2a for driving the first rotation axis a intersects at right angles. When the second motor 5 is driven, the first rotating shaft 2a rotates about the second rotating shaft 5a, and thereby the slit 1 is rotated about the second rotating shaft 5a and the optical axis X.
The orbit direction of a is variable. That is, the position where the slit 1a crosses the laser L is not changed, but the trajectory changing means is configured such that the direction (orbit direction) crossing the slit 1a is rotated with respect to the optical axis X.

According to the rotation mechanism A, the direction of the trajectory of the slit 1a crossing the laser L becomes free, and the spot diameter can be measured by setting the trajectory direction to an arbitrary angle. Also, regardless of the rotational position of the housing 4,
The longitudinal direction of the slit 1a always crosses the perpendicular direction of the optical axis X. Therefore, in the present invention, the long direction of the slit and the direction of its orbit are always in a fixed relationship,
The same conditions are measured in all orbital directions.

The arithmetic means 6, which also serves as a control section of the present apparatus, is connected to the first motor 2 and the second motor 5, controls the driving of each of them, and based on the light receiving information signal from the light detecting element 3. The light spot diameter of the laser L is calculated for each orbit direction of the slit 1a.

Next, a measurement procedure using the above-described apparatus will be described. The first motor 2 is driven to rotate the cylindrical body 1 in the direction of arrow a to rotate the slit 1a. The rotating slit 1a makes the photodetector 3 intermittently receive the laser beam L incident from the opening 4a, crossing the laser beam L every rotation. The output of the light detecting means 3 is taken into the calculating means 6. The calculating means 6 obtains the waveform of the light receiving information signal based on the change in the voltage value of the light detecting means 3.
It is stored as light reception information at a specific rotation position of the first rotation shaft 2a about a. This light receiving operation is performed at a plurality of rotational positions (orbital directions) while changing the orbital direction of the slit 1a by driving the second motor 5.

FIG. 3 illustrates a change in the orbital direction of the slit 1a. In this example, the housing 4 is rotated by 15 ° to set 12 different trajectories. The output from the light detecting element 3 is measured at each rotation position, and a signal waveform is captured. Further, as is apparent from this example, in order to measure almost the entire area (0 ° to 360 °) with respect to the spot shape, after all, the rotation range of the slit 1a is sufficient to be about 180 °. From 165 °.

The signal waveform obtained at each rotation position is shown in FIG.
This is a bell shape as shown in (b), which corresponds to the beam cross-sectional intensity incident and shielded by both side edges of the slit 1a. As shown in FIG. 4, if each of the rotation positions at 15 ° intervals is set on the X and Y plane coordinates, and the output of the photodetector 3 at each rotation position is set on the vertical axis Z, the three-dimensional shape of the light spot is obtained. Information is obtained.

The beam diameter is calculated by calculating a time difference facing each other at 1 / e (13.5%) of the maximum value of each signal waveform, and multiplying this time difference by the moving speed of the slit 1a to calculate a beam diameter. The entire beam spot shape can be accurately measured from the beam diameter at each rotation position. Further, by setting the rotation position more finely, it is possible to measure a spot shape with higher accuracy, and to provide a measuring apparatus which is extremely suitable for measuring a small and high-density light spot diameter of about φ20 μm. be able to.

[0024]

As is apparent from the above description, the measuring device according to the present invention comprises a photodetector for outputting a light reception information signal in accordance with the amount of incident laser light, and a light for irradiating the photodetector. Light shielding means for driving the slit so that the slit traverses the axis, trajectory changing means for changing the trajectory direction of the slit with respect to the optical axis, and a moving speed of the slit and a light receiving information signal from the light detecting element. And a calculation means for calculating the diameter of the laser light spot, the beam diameter can be measured in any direction in which the slit crosses the light spot, and accurate information on the entire light spot can be obtained.

[Brief description of the drawings]

FIG. 1 is a side view showing the overall configuration of a measuring device according to the present invention.

FIG. 2 is a perspective view of the apparatus of FIG.

FIG. 3 is a schematic view illustrating a change in the orbital direction of a slit.

FIG. 4 is a waveform diagram showing a three-dimensional shape of a light spot measured by a measuring device according to the present invention.

FIG. 5 is a perspective view showing a configuration of a main part of a conventional measuring device.

6A and 6B show a measuring method of the apparatus shown in FIG. 5, wherein FIG. 6A is a schematic diagram showing the movement of a slit, and FIG. 6B is a waveform diagram obtained from a photodetector.

FIG. 7 is a perspective view showing another configuration of a conventional measuring device.

8A and 8B show a measuring method of the apparatus shown in FIG. 7, wherein FIG. 8A is a schematic diagram showing the movement of a slit, and FIG. 8B is a waveform diagram obtained from a photodetector.

FIG. 9 is a three-dimensional waveform diagram showing a light spot shape measured by the apparatus of FIG. 7;

[Explanation of symbols]

 1a slit 3 light detecting element 6 calculating means A rotating mechanism L laser X optical axis

Claims (5)

[Claims] 1. A light detecting element for outputting a light receiving information signal in accordance with a light receiving amount of an incident laser, a light shielding means for driving the slit so that the slit traverses the laser irradiating the light detecting element, and the laser. Trajectory varying means for variably changing the trajectory direction of the slit with respect to the optical axis, and calculating means for determining the light spot diameter of the laser based on the moving speed of the slit and a light receiving information signal from the photodetector. A light spot diameter measuring device, characterized in that: 2. The light spot diameter measuring apparatus according to claim 1, wherein said orbit changing means is a rotating mechanism for rotating said light shielding means about said optical axis. 3. The method according to claim 1, wherein said calculating means obtains a light spot shape of said laser based on a plurality of light receiving information signals obtained at each rotation position of said light shielding means. 3. A light spot diameter measuring apparatus according to claim 1. 4. The light spot according to claim 1, wherein said calculating means sets each rotation amount of said light blocking means to 180 ° or less in order to obtain said plurality of light receiving information signals. Diameter measuring device. 5. The method according to claim 1, wherein said calculating means obtains a three-dimensional light spot shape based on a light receiving information signal from a light detecting element at each rotation position of said light shielding means. 5. The light spot diameter measuring device according to any one of 4.