CN1308656C - device for measuring laser beam parallelism - Google Patents

Abstract

A device for measuring the parallelism of a laser beam. The present invention uses a beam to be detected, an aperture, a converging lens, a semi-transparent and semi-reflecting mirror, two cylindrical lenses, two four-quadrant detectors and a computer to form a measuring device; a converging objective lens, a semi-transparent and semi-reflecting mirror, two cylindrical lenses and two four-quadrant detectors constitute a beam parallelism detector, and the beam parallelism is detected based on the astigmatism method focusing error detection. The differential method is used to eliminate the detection error caused by the off-axis incident light. The optical system can be designed to have any sensitivity and linear range; it is particularly suitable for measuring high-quality small-caliber, small-divergence-angle laser beams with rotational symmetry.

Description

Device for measuring the parallelism of laser beams

technical field

The invention belongs to laser technology and is a device for measuring the parallelism of laser beams. It is mainly used in the detection of the divergence angle of the collimated laser beam and the measurement of the divergence angle of the small divergence angle and rotationally symmetrical laser beam.

Background technique

Laser collimator for measuring the coaxiality of large mechanical holes and shafting and the straightness, flatness and parallelism of the plane, laser range finder, laser atmospheric monitoring and wireless optical communication, all need collimated laser beams , the parallelism of the laser beam has a great influence on the performance of the measuring instrument and the communication quality. Therefore, the application range of the detection of the parallelism of the collimated laser beam is relatively large. The parallelism of the collimated laser beam is measured by the far-field divergence angle of the beam.

At present, the measurement of parallelism of collimated laser beams is mainly realized by interferometric methods. The measured beam is divided into two beams, and then interferes at an appropriate position. If the incident beam is parallel light, the resulting interference fringes are straight or no fringes. This method has higher measurement accuracy. But there are also the following defects:

1) The interferometer is expensive;

2) Generally, the interferometer has a large volume and is inconvenient to use;

3) Vibration has a great influence on the measurement;

4) The angle range that can be measured is small.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies in the prior art and provide a device for measuring the parallelism of laser beams, which can quickly and easily measure the parallelism of laser beams.

Basic idea of the present invention is:

The invention measures the beam parallelism based on the astigmatic focus error detection, and the beam parallelism detector is composed of a converging objective lens, a half-transparent mirror, two cylindrical lenses and two four-quadrant detectors. And the differential method is used to eliminate the detection error caused by the off-axis incident light.

Technical solution of the present invention is as follows:

A device for measuring the parallelism of laser beams, which is composed of: a diaphragm, a converging lens, a half-mirror, a first cylindrical lens, and a first four-quadrant detector are sequentially arranged on the same optical axis; The reflected light direction of the half mirror, that is, the direction perpendicular to the optical axis is followed by the second cylindrical lens and the second four-quadrant detector, and the first cylindrical lens and the second cylindrical lens are related to the semi-transparent The splitting surfaces of the half-mirror are symmetrical, and the signal output ends of the first four-quadrant detector and the second four-quadrant detector are connected with the input ends of the computer;

The division slit of the first four-quadrant detector is 45° to the astigmatic direction of the first cylindrical lens, and the division slit of the second four-quadrant detector is 45° to the astigmatism direction of the second cylindrical lens. The direction is 45°, the long axis of the light spot on the first four-quadrant detector corresponds to the short axis of the light spot on the second four-quadrant detector, and the short axis of the light spot on the first four-quadrant detector is the same as the short axis of the light spot on the second four-quadrant detector Corresponds to the major axis on the four-quadrant detector;

The method for measuring beam parallelism using the described device for measuring beam parallelism comprises the following steps:

① Align the optical axis of the device of the present invention with the light beam to be measured, so that the light beam to be measured is incident along the optical axis;

②Start the device for automatic measurement, and obtain the error signal through computer processing

In the formula: A ₁ , A ₂ , A ₃ , and A ₄ are the areas of the light spots illuminated on the four quadrants of the first four-quadrant detector; B ₁ , B ₂ , B ₃ , and B ₄ are the areas illuminated on the second The area of the light spots of the four quadrants of the four-quadrant detector;

In the linear region, the relationship between H and the divergence angle θ can be expressed as H=Kθ, where K is a coefficient related to the gain of the detector, the focal length of the converging lens, and the focal length of the cylindrical lens.

The converging lens, the first cylindrical lens and the second cylindrical lens are all achromatic lenses.

Compared with the prior art, the present invention has the following advantages:

1. Low cost;

2. The instrument is small in size, quick and easy to measure;

3. The measurement accuracy mainly depends on the processing accuracy and assembly accuracy of each optical component, and the impact of vibration is small;

4. By designing the optical system - choosing the focal length of the converging lens and the cylindrical lens, the distance between the converging lens and the cylindrical lens, and the position of the four-quadrant detector, to have any sensitivity and linear range; especially suitable for measuring high-quality small caliber, rotationally symmetric laser beam with small divergence angle.

5. Both the converging lens and the cylindrical lens can be made into achromatic lenses within a certain range, that is, they can be used when light beams of different wavelengths are incident without adjusting the optical path.

Description of drawings

FIG. 1 is a schematic structural diagram of an embodiment of the device for measuring the parallelism of laser beams according to the present invention.

FIG. 2 is a top view of the second four-quadrant detector 8 in FIG. 1 .

FIG. 3 is a right side view of the first four-quadrant detector 7 in FIG. 1 .

Detailed ways

The present invention will be further described below in conjunction with drawings and embodiments.

Please refer to FIG. 1 first. FIG. 1 is a schematic structural diagram of an embodiment of the device for measuring the parallelism of laser beams according to the present invention. As can be seen from the figure, the composition of the device for measuring laser beam parallelism in the present invention is: a diaphragm 2, a converging lens 3, a half-mirror 4, a first cylindrical lens 5, and the first four-quadrant detection are arranged successively on the same optical axis. Device 7, in the reflected light direction of the half mirror 4, that is, the direction perpendicular to the optical axis is followed by the second cylindrical lens 6, the second four-quadrant detector 8, the first cylindrical lens 5 and the second cylindrical lens 6 are symmetrical about the splitting surface of the half mirror 4, and the signal output terminals of the first four-quadrant detector 7 and the second four-quadrant detector 8 are connected with the input terminals of the computer 9 . The division slit of the first four-quadrant detector 7 is 45° to the astigmatic direction of the first cylindrical lens 5, and the division slit of the second four-quadrant detector 8 is connected to the second cylindrical lens 5. The astigmatism direction of 6 is 45 °, and the major axis of light spot on the first four-quadrant detector 7 is corresponding to the short axis of light spot on the second four-quadrant detector 8, and the light spot is on the first four-quadrant detector 7. The minor axis corresponds to the major axis of the light spot on the second four-quadrant detector 8 . The converging lens 3, the first cylindrical lens 5 and the second cylindrical lens 6 are all achromatic lenses.

The method for measuring beam parallelism using the device for measuring laser beam parallelism of the present invention comprises the following steps:

① Align the optical axis of the device of the present invention with the light beam to be measured, so that the light beam to be measured is incident along the optical axis;

②Start the device for automatic measurement, and obtain the error signal through computer processing

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}{\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}{\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}$

In the formula: A ₁ , A ₂ , A ₃ , and A ₄ are the areas of the light spots shining on the four quadrants 701, 702, 703, and 704 of the first four-quadrant detector 7, respectively, see FIG. 3 ;

B ₁ , B ₂ , B ₃ , and B ₄ are the areas of the light spots shining on the four quadrants 801, 802, 803, and 804 of the second four-quadrant detector 8, respectively, see FIG. 2 ;

In the linear region, the relationship between H and the divergence angle θ can be expressed as H=Kθ, where K is a coefficient related to the gain of the detector, the focal length of the converging lens, and the focal length of the cylindrical lens.

Working process of the present invention is as follows:

The inspected light beam 1 passes through the diaphragm 2 and then passes through the converging lens 3, so that the incident light beam becomes a converging light beam; 50% of the converging light beam is transmitted by the half-mirror 4 and then incident on the first column lens 5. Produce astigmatism on the astigmatism direction of lens 5; In addition, 50% is incident on the second rod lens 6 after being reflected by half-transparent mirror 4, and on the astigmatism direction of second rod lens 6 after the second rod lens 6 produce astigmatism. The optical axis of the first cylindrical lens 5 coincides with the optical axis of the converging lens 3 , and the positions of the first cylindrical lens 5 and the second cylindrical lens 6 are symmetrical with respect to the dichroic plane of the half mirror 4 .

The placement of the cylindrical lens and the four-quadrant detector makes the short axis of the light spot on the first four-quadrant detector 7 correspond to the long axis on the second four-quadrant detector 8, and the light spot on the first four-quadrant detector 7 The long axis on corresponds to the short axis on the second four-quadrant detector 8 . In this way, the error when the measured beam is off-axis can be eliminated, and the sensitivity of the final error signal to angle will not be affected, because the corresponding quadrants are subtracted.

The first four-quadrant detector 7 and the second four-quadrant detector 8 placed at appropriate positions receive the light beams passing through the first cylindrical lens 5 and the second cylindrical lens 6 respectively, and convert them into electrical signals for current-voltage conversion , after being pre-amplified and sent to the computer 9 for a series of calculations, the divergence angle of the incident beam 1 can be obtained. The parallelism of the beam is measured by the divergence angle of the beam.

The areas of the light spots illuminated on the four quadrants 701, 702, 703, and 704 of the first four-quadrant detector 7 are respectively A ₁ , A ₂ , A ₃ , and A ₄ , and the areas illuminated on the four quadrants of the second four-quadrant detector 8 The areas of the light spots in the quadrants 801, 802, 803, and 804 are B ₁ , B ₂ , B ₃ , and B ₄ , respectively. The error signal obtained after adding, subtracting and normalizing the electrical signals output by the first four-quadrant detector 7 and the second four-quadrant detector 8:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}{\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}{\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}$

In the linear region, the relationship between H and the divergence angle θ can be expressed as H=Kθ

Among them, K is a coefficient related to the gain of the detector, the focal length of the converging lens, and the focal length of the cylindrical lens. H is proportional to the divergence angle of the measured beam in the linear region. For more accurate measurement, it can be calibrated, and then the divergence angle of the measured beam can be directly obtained from the obtained error signal.

In the present embodiment, the aperture of aperture 2 is D=8mm; The focal length of converging lens 3 is 20.2mm; The focal length of the first cylindrical lens 5, the second cylindrical lens 6 is 1000mm; The first four-quadrant detector 7 and the first The distance between the cylindrical lens 5 and the distance between the second four-quadrant detector 8 and the second cylindrical lens 6 are 20mm; the side length of the first four-quadrant detector 7, the second four-quadrant detector 8 single quadrant is 0.08mm; incident light power is 5mW; the maximum measurable divergence angle is 2mrad.

H is proportional to the incident light power, and the error signal obtained is normalized: divided by the incident light power, H0 is obtained.

The corresponding relationship between H0 value and divergence angle θ is as follows: Divergence angle (rad) 0 0.0002 0.0004 0.0006 0.0008 0.0010 0.0012 Normalized H0 0 0.0317 0.0628 0.0927 0.1211 0.1476 0.1720 Beam divergence (rad) 0 0.00002 0.00004 0.00006 0.00008 Normalized H0 0 0.0032 0.0064 0.0095 0.0127

Claims (2)

1. A device for measuring the parallelism of laser beams is characterized in that its composition is: a diaphragm (2), a converging lens (3), a half-transparent mirror (4), and a first cylindrical lens are successively provided with the same optical axis (5), the first four-quadrant detector (7), in the reflected light direction of described half mirror (4), promptly perpendicular to described optical axis direction is successively the second cylinder lens (6), The second four-quadrant detector (8), the first cylindrical lens (5) and the second cylindrical lens (6) are symmetrical about the splitting plane of the half-transparent mirror (4), and the first four The signal output terminals of the quadrant detector (7) and the second four-quadrant detector (8) are connected with the input terminals of the computer (9); The division slit of the first four-quadrant detector (7) is 45° to the astigmatism direction of the first cylindrical lens (5), and the division slit of the second four-quadrant detector (8) is 45° to the astigmatism direction of the first cylindrical lens (5). The astigmatic direction of the second cylindrical lens (6) is 45°, and the long axis of the light spot on the first four-quadrant detector (7) corresponds to the short axis of the light spot on the second four-quadrant detector (8) , the short axis of the light spot on the first four-quadrant detector (7) corresponds to the long axis of the light spot on the second four-quadrant detector (8); The method for measuring beam parallelism using the device for measuring laser beam parallelism comprises the following steps: ① Align the optical axis of the device of the present invention with the light beam to be measured, so that the light beam to be measured is incident along the optical axis; ②Start the device for automatic measurement, and obtain the error signal through computer processing $\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}{\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; )</span>}{\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}$ In the formula: A ₁ , A ₂ , A ₃ , and A ₄ are the areas of the light spots shining on the four quadrants (701), (702), (703), (704) of the first four-quadrant detector (7) respectively ; B ₁ , B ₂ , B ₃ , and B ₄ are the areas of the light spots shining on the four quadrants (801), (802), (803), and (804) of the second four-quadrant detector (8) respectively; In the linear region, the relationship between H and the divergence angle θ can be expressed as H=Kθ, where K is a coefficient related to the gain of the detector, the focal length of the converging lens, and the focal length of the cylindrical lens. 2. The device for measuring parallelism of laser beams according to claim 1, characterized in that said converging lens (3), first cylindrical lens (5) and second cylindrical lens (6) are all achromatic lenses.

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