JPH0572030A - Spot-diameter measuring apparatus - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a spot diameter measuring device capable of realizing highly accurate measurement in a short measuring time. [Configuration] rotates while reflecting the light beam L ₁ on one surface of the polygon mirror 21 rotating, by entering this way the light beam L ₁ to be scanned pivoted to the photodetector 22 through the slit 23 When the diameter of the light flux L ₁ is obtained, a period of half or more of the maximum value of the light intensity on the light intensity distribution characteristic detected by the photodetector 22 is detected by the clock pulse and the half width time The luminous flux diameter is detected based on the interval.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot diameter side measuring device, which is useful when measuring the spot diameter of a laser beam or the like.

[0002]

2. Description of the Related Art The spot diameter of a laser beam must be measured rapidly while maintaining high accuracy. As a measuring device of this kind according to the prior art, a device for scanning a chopper equipped with a knife edge is known.

FIG. 4 is a block diagram showing a spot diameter measuring device according to the prior art, and FIG. 5 is a graph showing the relationship between the laser beam scanning output and the knife edge position of the chopper.

As shown in FIG. 4, when scanning is performed with the knife edge 2 of the chopper 1 arranged on the optical path of the laser beam I as the object to be measured, the laser beam I that is not blocked by the knife edge 2 during the scanning process. Is input to the detector 4 after passing through the condenser lens 3, it changes depending on the position of the knife edge 2 as shown in FIG. In FIG. 5, the vertical axis represents the scanning output of the laser beam I. The state where the scanning output is 100% is the case where the knife edge 2 does not block the laser beam I at all, and the state where the scanning output is 0% is the laser beam. In this state, I is completely blocked by the knife edge 2. The horizontal axis L shows the position of the knife edge. In this case, the spot diameter (denoted by W) of the laser beam I is defined as W = 0.78l where the difference between the knife edges corresponding to 90% and 10% of the scanning output is 1, and the scanning output is 90%. % And 10%, the knife edge positions L ₁ and L ₂ can be easily obtained by ₁ = L ₂ −L ₁ . That is, the output from the above-mentioned detector 4 is input to the sampling gate 5, where the sampling gate 5 performs a sampling process, the waveform is temporarily stored in the waveform storage device 6 and then processed by the processing device 7.
Since the value of the spot diameter of the laser beam as a result of the processing by the processing device 7 is displayed on the display device 8, it is recorded and displayed even when the spot diameter of the laser beam changes momentarily or the laser output changes. Such an operation is controlled by the control device 9.

The spot diameter can be measured even in such a conventional apparatus, but it has the following problems.

1) Since the chopper is mechanically reciprocated, the vibration given to the optical device is large.

2) Since the chopper is reciprocating, the number of scannings of the laser beam per unit time is small and the response is poor.

3) Only a simple laser beam pattern can be accurately measured.

A method for measuring the spot diameter of a laser beam which solves the above-mentioned problems is disclosed in Japanese Patent Laid-Open No. 194321/1982.
There is a technique disclosed in the publication. This is because the laser beam I to be measured has a one-dimensional condensing lens 11 as shown in FIG.
Rotary encoder 1 as only one-way component via
A polygonal mirror 12 rotated by a driving device provided with a laser beam 3 is irradiated with a reflected laser beam I ′ scanned by the polygonal mirror 12, and a light receiving element 15 having a slit 16 on the front surface thereof is provided.
Light received signal II from the light receiving element 15 and an angle signal III obtained from the rotary encoder 13.
The threshold value IV preset by the spot diameter calculation threshold rate setting unit 17 is input to the calculation processing unit 19, and the calculation processing unit 19 calculates the maximum value of the received light signal I and the threshold ratio IV to obtain a threshold value. Then, the received light value of the received light signal II is compared with a threshold value, the rotation angle range where the received light value is equal to or greater than the threshold value is obtained from the angle signal, and the rotation angle range at this time is converted into dimensions to obtain the beam spot diameter. Is obtained and is displayed on the display unit 18.

[0010]

The spot diameter measuring method shown in FIG. 6 has the advantages that vibrations have less adverse effects on optical equipment and that accurate measurement is possible.
Since the spot diameter is detected by calculation based on the rotation angle of the polygon mirror 12 and the light intensity detected by the light receiving element 15, the structure of the counter for calculation becomes complicated and the response time becomes slow, so that measurement speed is increased. However, the problem remains.

In view of the above-mentioned conventional technique, it is an object of the present invention to provide a spot diameter measuring device capable of realizing highly accurate measurement in a short measuring time.

[0012]

The structure of the present invention which achieves the above object is as follows.

A polygonal mirror which reflects the luminous flux of the spot light emitted from the light source and is driven to rotate so that the reflected luminous flux rotates, and a luminous flux which is reflected by one surface of the polygonal mirror and rotates, are detected. The maximum value of the light intensity of is stored, and the time when the light intensity of the light beam reflected by the next surface of the polygon mirror becomes a predetermined ratio with respect to the maximum value is stored. And a light flux diameter detecting means for obtaining the light flux diameter of the light flux from the above.

[0014]

According to the present invention having the above-described structure, the width of the predetermined ratio on the light intensity distribution characteristic can be obtained based on the time when the light intensity of the reflected light flux becomes a predetermined ratio with respect to its maximum value. It is possible to detect the luminous flux diameter of the luminous flux based on this width.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is an explanatory view showing the outline of the configuration of an embodiment of the present invention. As shown in the figure, the polygon mirror 21, which is a polygon mirror, passes through the center of one surface of the polygon mirror 21,
Arranged at a position where a center line along the axial direction of 1a (a direction perpendicular to the plane of the drawing) and a center line of a light beam L ₁ which is a spot light emitted from a light source intersect with the rotation thereof. It is configured to be rotatable. Thus, the polygon mirror 21 rotates by reflecting the light beam L ₁ incident on its one surface.

The photodetector 22 is the polygon mirror 21.
Of the polygon through a slit 23 extending upward in the drawing of the one surface, passing through the center of the one surface and orthogonal to the center line of the light flux L ₁ , and extending parallel to the axial direction of the rotating shaft 21a. The light flux L _{1 which} is rotated by the mirror 21 is made incident.

The light source 24, the collimator lens 25, and the photodetector 26 are for synchronizing the timing of measurement. Of these, the light source 24 and the collimator lens 25 are arranged above the other surface of the polygon mirror 21 at a position which is a line symmetrical with respect to the vertical center line of the polygon mirror 21. Thus, the optical axis of the collimator lens 25 is orthogonal to the center line of the light beam L ₁ at the center of the other surface of the polygon mirror 21.
The photodetector 26 is arranged at a position such that its center is on the center line of the light beam L ₁ . Thus, the luminous flux L ₁
Is reflected by the one surface of the polygon mirror 21 and the photodetector 2
A state equivalent to the state of being incident on the beam No. ₂ can be realized by the light beam L ₂ emitted from the light source 24 being reflected by the other surface of the polygon mirror 21 and being incident on the photodetector 26. ..

FIG. 2 is a block diagram showing the luminous flux diameter detecting means according to this embodiment. This luminous flux diameter detecting means detects the luminous flux L ₁ which is reflected by the polygon mirror 21 and is rotated by the photodetector 22, stores the maximum value of the optical intensity of this luminous flux L ₁ , and detects the next value of the polygon mirror 21. The time when the light intensity of the light beam L ₁ reflected by the surface becomes a predetermined ratio (half in this embodiment) to the maximum value is stored, and the time of the light beam L ₁ is calculated from this time and the rotation speed of the polygon mirror 21. The light beam diameter is obtained, and the photodetector 22 shown in FIG. 1 and the light source 24 constituting the synchronous system, the collimator lens 25, and the photodetector 2 are used.
6 is included.

As shown in FIG. 2, the photodetector 22 converts the incident light beam L ₁ into an electric signal, and outputs a light intensity signal S ₁ representing the light intensity of this light beam L ₁ via the amplifier 27 to A /
It is supplied to the D converter 28. The A / D converter 28 converts the light intensity signal S ₁ into a digital signal and supplies the digital signal to the peak hold circuit 29 and the half-value period detection circuit 30. The oscillator 11 receives the clock pulse S ₂ that defines the sampling timing from the A / D converter 28 and the peak hold circuit 2.
9 and the half value period detection circuit 30. Thus, at the rising edge of the clock pulse S ₂ , the light intensity signal S ₁ which is the output signal of the photodetector 22 is taken into the A / D converter 28 and converted into a digital signal, and this digital signal is also held by the peak hold circuit 29. And half-value period detection circuit 3
0 is supplied. The peak hold circuit 29 stores the maximum value of the light intensity signal S ₁ during the _first scanning period by the polygon mirror 21, that is, the period in which the light flux L ₁ is rotated on one surface of the polygon mirror 21. The half-value period detection circuit 30 reaches a half of the maximum value of the light intensity signal S ₁ that gradually increases in the next scanning period by the polygon mirror 21, that is, in the period in which the light flux L ₁ is rotated on the next surface of the polygon mirror 21. The time until the time when the value reaches half the maximum value is detected again by referring to the stored contents of the peak hold circuit 29 and the light intensity obtained as a result of this detection. A half-value period signal S ₃ representing a time that is a value that is at least half the maximum value of the signal S ₁ is sent to the spot diameter calculation unit 34.

The photodetector 26, which constitutes a synchronous system, converts the incident light beam L ₂ into an electric signal, and sends a trigger signal S ₃ based on a light intensity signal representing the light intensity of this light beam L ₂ via an amplifier 32. And supplies it to the A / D converter 28 and the counter 33. Thus, the A / D converter 28 is, for example, the light flux L ₂
Of the light intensity signal S ₁ is started by the supply of the trigger signal S ₃ which is generated at the time when the incidence of is detected, and the counter 33 outputs the trigger signal S ₃ every time the light signal L ₃ is supplied, that is, every time the light beam L ₁ is scanned. The state becomes High or Low.

Either the peak hold circuit 29 or the half value period detection circuit 30 operates depending on the output state of the counter 33. That is, the scanning period with the light flux L ₁ is
Is the scanning period for detecting the maximum value of the light intensity signal S ₁ ,
It is necessary to identify whether it is the scanning period for detecting the half-value period of the maximum value, but by updating the contents of the counter 33 for each scanning and using the output signal as a switching signal, which of the scanning periods is described. Then, one of the peak hold circuit 29 and the half-value period detection circuit 30 is selectively operated.

The driver 35 drives the motor 36 and sends a rotation speed signal S ₄ representing the rotation speed of the motor 36 to the spot diameter calculator 34. Motor 36
Is driven by the driver 35 to drive the polygon mirror 21.
To rotate.

The spot diameter calculator 34 determines the half-value period signal S
The beam diameter of the beam L ₁ is obtained based on ₃ and the rotation speed signal S _4, and a beam diameter signal S ₅ representing this beam diameter is transmitted.

According to the above embodiment, based on the time when the light intensity of the luminous flux L ₁ becomes half the maximum value,
The half width on the light intensity distribution characteristic of the light flux L ₁ can be obtained as the number of clock pulses S ₂ corresponding to this half width.

More specifically, the photodetector 22 detects
Luminous flux L₁The light intensity distribution characteristics of the polygon mirror 21
The characteristics become as shown in FIG. Because
The maximum light intensity is shown in the light intensity distribution characteristics as shown in Fig. 3.
The threshold value is half the value, and this threshold
The full width at half maximum W, which is the period during which the value is greater than
₁It is possible to calculate the luminous flux diameter of.

The detection of the luminous flux diameter as described above is performed by the photodetector 26.
When the first rotation / scanning of the light flux L ₁ by one surface of the polygon mirror 21 which is driven by the motor 36 and is driven by the rising edge of the trigger signal S ₃ based on the above, is defined by the output state of the counter 33. For example, in the peak hold period, the maximum value of the light flux L ₁ is detected, and the output state of the counter 33 changes during the second rotation / scanning of the light flux L ₁ by the next surface of the polygon mirror 21. Therefore, for example, the half-value width detection period comes, and the half-value period detection circuit 1
When the value is 0, the half-value period is detected based on the clock pulse S _2, and the half-value period signal S ₃ is transmitted. Then, the spot diameter calculator 34 calculates the diameter of the light flux L ₁ .

[0028]

As described above in detail with reference to the embodiments, according to the present invention, a period of a predetermined ratio with respect to the maximum value of the light intensity on the light intensity distribution of the light beam which is a measurement target and is incident through the slit. Is detected as the time interval, the predetermined measurement of the spot diameter can be performed quickly and with high accuracy.

Incidentally, the number of divisions of the rotary encoder 13 in the device according to the prior art shown in FIG. 6 is 18,0.
Assuming 00 pulses / revolution, the electrical response speed range required for calculation is usually (100 / 18,000) × 10 ³ × 6
It is about 0 = 333 (rotation / minute).

On the other hand, in the device according to the present invention, the number of samplings is 10,000 and the clock frequency is 3.
If it is 2MHz, (3.2 × 10 ⁶ / 10,000)
It becomes x (1/8) x 60 = 2,400 rotations / minute, and it can be seen that the measurement speed is dramatically improved as compared with the conventional technique.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of a configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a light flux detecting means according to the embodiment.

FIG. 3 is a graph showing a light intensity distribution of a light beam L ₁ detected in the above embodiment.

FIG. 4 is a block diagram showing a spot diameter measuring device according to a conventional technique.

5 is a graph showing the relationship between the laser beam scanning output and the knife edge position of the chopper in FIG.

FIG. 6 is a block diagram showing another conventional spot diameter measuring device.

[Explanation of symbols]

21 polygon mirror 22, 26 photodetector 23 slit L ₁ luminous flux

Claims (1)

[Claims] 1. A polygonal mirror which reflects a light flux of spot light emitted from a light source and is rotationally driven so that the reflected light flux rotates, and detects a light flux which is reflected by one surface of the polygonal mirror and rotates. The maximum value of the light intensity of this light beam is stored, and the time at which the light intensity of the light beam reflected by the next surface of the polygon mirror becomes a predetermined ratio with respect to the maximum value is stored. A spot diameter measuring device, comprising: a light beam diameter detecting means for obtaining a light beam diameter of a light beam from a rotation speed.