JPS6112526B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser beam beam diameter measuring device.

Laser beams are used in fields such as optical communications and POS, but in the various devices that make up the optical system, such as laser beam transmission media, it is necessary to accurately know the diameter of the laser beam and adjust it accordingly. Since it is necessary to design the beam diameter, it is desired to develop a device that can measure the beam diameter more easily and quickly than before. Conventionally, when measuring the beam diameter of such a laser beam, a Ronchi plate made of a pinhole, a knife edge, or a transparent plate with many black stripes is placed in the laser beam path, and the passing light is detected by a photodetector. A method is adopted in which the maximum value and the minimum value of the output signal are compared. However, in such a measurement method,
For example, in the case of pinholes, a large number of pinholes with different diameters are used to measure the intensity of the passing light for each, which is cumbersome to operate, takes time to measure, and requires a shielding plate with many pinholes. In addition, there were disadvantages in that errors occurred due to fluctuations in the output of the laser beam, making it impossible to accurately measure the beam diameter.

The present invention solves these drawbacks and provides an apparatus that is not affected by fluctuations in the output of laser light and can automatically measure the beam diameter of laser light.

Embodiments of the present invention will be described below based on the drawings. 1st
In the figure, 1 is a laser resonator, 2 is a first photodetector into which the laser beam (indicated by a broken line) emitted from the non-output side mirror of the laser resonator 1 is input, and 3 is an output side mirror of the laser resonator 1. A laser beam shielding plate 4 is attached to the front surface of the second photodetector 3, and a laser beam shielding plate 4 is attached to the photodetector light receiving surface of the laser beam shielding plate 4. An opening 5 with a diameter of about 50μ is formed at a corresponding position. Reference numeral 6 denotes a motor, the rotational force of which is transmitted to the second photodetector 3 through a rope 7. As a result, the second photodetector 3 is moved in the direction A perpendicular to the traveling direction of the laser beam, and the aperture 5 is scanned across the laser beam. 8 is the second photodetector 3
is a spring that applies an elastic force in a direction opposite to the direction of tension by the motor 6. Reference numerals 9 and 10 are amplifiers for amplifying the output signals of the first and second photodetectors 2 and 3, respectively. Reference numeral 11 is a divider having two inputs as the outputs of the amplifiers 9 and 10, and the outputs of the amplifiers 9 and 10 are respectively amplified. If E ₂ and E ₁ , then the output is k(E ₁ /
E ₂ ) (k is a constant) is obtained. 12 is the divider 11
A peak value holding circuit that detects and holds the peak value of the output differentiates the divider output and determines the peak value by detecting its zero crossing point. 13 is a multiplier which inputs this peak value and performs an operation of X1/ _e2 . It should be noted here that the beam diameter of a normal laser beam is, if it is a single mode, the laser beam intensity is 1/e ₂ = 0.189 (e = 2.302585) of the peak value, that is, up to 18.9% of the maximum light intensity. It is defined as. That is, the minimum value when measuring the laser beam diameter in the multiplier 13 is given. 14 is a comparator that outputs an output when the two output signals of the divider 11 and multiplier 13 are added and the values of both signals become equal; 15 is a chopper attached to the motor 6; the rotation speed thereof is detected by the photocoupler 16; be done.

A counting circuit 17 counts the number of rotations of the chopper 15 to which a pulse signal from the photocoupler 16 is applied. It is configured to stop the counting operation upon receiving the output signal. In addition to the photocoupler 16, a rotary encoder may be used to detect the motor rotation speed. 18 is a multiplier with a constant magnification that multiplies the contents of the counting circuit 17 by a constant constant, and this constant is determined to convert the number of pulses input to the counting circuit into the moving distance of the second photodetector 3. Ru. Reference numeral 19 denotes a display such as a digital meter on which the value converted to distance by the multiplier 18 is displayed.

Next, the operation of the measuring device having the above configuration will be explained using FIG. 2. At the current time t ₀ , laser resonator 1
is in an oscillation state and emits a laser beam, and if the motor 6 is driven and the second photodetector 3 and shielding plate 4 start moving across the laser beam, the output of the divider 11 is: As shown in FIG. 2a, the peak value gradually increases, and at time _t1 , the peak value is detected and held by the peak value holding circuit 12. The period T ₁ from time t ₀ to t ₁ can be called a peak value detection period. The peak value of the divider output detected at time t ₁ is added to the next-stage multiplier 13 to calculate X1/e ₂ , and the value is input to the comparator 14 . After this time _t1 , the output of the divider 11 now starts to gradually decrease. Note that after this time _t1 , the counting operation of the counting circuit 17 is started by the peak value detection output b, and the output pulses d of the photocoupler 16 are counted. In this way, divider 1
When the output of 1 decreases and its value becomes equal to the output value of the multiplier 13 (let this time be t ₂ ), the comparator 14 outputs c and the counting operation of the counting circuit 17 stops. do. Therefore, the counting circuit 17
operates for a period T ₂ from time t ₁ to t ₂ , and the number of pulses counted during that period (shown by the solid line in figure d) is
The signal is input to the multiplier 18 and converted into the actual moving distance of the second photodetector 3, which is displayed on the display 19.
Here, the period _T2 can be called a beam diameter detection period, and the numerical value thus obtained on the display 19 indicates the beam radius.

Such a measurement device of the present invention assumes that the intensity of the laser beam has a Gaussian distribution, and that the distribution up to the peak value (first half) is equal to the distribution after reaching the peak value (second half). In the first half, the peak value was detected, and in the second half, the moving distance of the second photodetector was measured from the peak value until the value decreased to 1/e ₂ of the peak value. It is. Therefore, by scanning the second photodetector once, the laser beam diameter can be automatically measured. In actual measurements, we used a rotary encoder that generates 180 pulses per motor rotation, and one motor rotation corresponds to a photodetector movement of 0.5 mm.
The measurement error is ±1% when designed to correspond to
It was below. Furthermore, in the present invention, even if the light intensity of the laser beam fluctuates and the output intensity of the second photodetector 3 changes to, for example, aE ₁ , the first photodetector 2
Similarly, the output of aE ₂ changes to aE 2 , so this variation is canceled out in the divider 11 and its output is not affected.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the embodiment. 1... Laser resonator, 2... First photodetector, 3
... second photodetector, 4 ... shielding plate, 5 ... aperture,
6... Motor, 11... Divider, 12... Peak value holding circuit, 13, 18... Multiplier, 14... Comparator, 17... Counting circuit, 19... Display.

Claims (1)

[Claims] 1. A laser resonator, a first photodetector that receives laser light emitted from the non-output side of the laser resonator, and a first photodetector that receives the laser light emitted from the output side of the laser resonator. a second photodetector for receiving light, a laser beam shielding plate provided in front of the light receiving part of the second photodetector and having an opening, and the second photodetector and the shielding plate are arranged in a direction perpendicular to the traveling direction of the laser beam. a scanning means for scanning, a divider for calculating the ratio of the outputs of the first and second photodetectors, a peak value holding circuit for detecting and holding the peak value of the output of the divider, and the peak value a multiplier that provides an output of 1/e ₂ ; a comparator that compares the output of the multiplier with the output of the multiplier; and a counter that counts the distance traveled by the scanning means of the second photodetector and the shielding plate. circuit, and a display that displays the count contents of the counting circuit, and the counting circuit starts counting in response to a peak value detection signal from the peak value holding circuit, and the values of the two signals input to the comparator are A laser beam diameter measuring device that stops counting based on the signal output when the values are equal.