CN110160470B - Device and method for detecting laser beam collimation - Google Patents
Device and method for detecting laser beam collimation Download PDFInfo
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- CN110160470B CN110160470B CN201910366226.6A CN201910366226A CN110160470B CN 110160470 B CN110160470 B CN 110160470B CN 201910366226 A CN201910366226 A CN 201910366226A CN 110160470 B CN110160470 B CN 110160470B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/26—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes
- G01B11/27—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes for testing the alignment of axes
- G01B11/272—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes for testing the alignment of axes using photoelectric detection means
Abstract
A device and a method for detecting the collimation of a laser beam are provided, the device comprises a Fresnel biprism, a CCD camera and a computer connected with the CCD. The device has the characteristics of simple structure, convenient operation, low cost, high sensitivity and high measurement precision, has extremely high practical value, and can be widely applied to various aspects such as scientific research, production and the like.
Description
Technical Field
The invention belongs to the field of optical instrument measurement, and particularly relates to a device and a method for detecting laser beam collimation.
Background
The rapid development of laser technology makes high-precision collimated light beam play an increasingly important role in scientific experiments and engineering projects. Various devices and methods for detecting optical alignment exist so far, and are mainly classified into the following two categories: one is to utilize Talbot self-imaging and the gate-stack phenomenon, and the other is to shear the interference method. The former has the disadvantages of complex structure, complex operation and poor practicability, and is difficult to popularize and apply, while the latter has the advantages of simple structure, convenient operation, low cost and the like, and the most common parallel plate shearing interferometer has the disadvantages of strict requirement on the parallelism of parallel plates, low sensitivity, low interference fringe observation by naked eyes and low discrimination precision.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a detection device and a detection method for laser beam collimation, and the device has the characteristics of simple structure, high detection precision, low cost and easiness in popularization. Can be widely used in scientific research, production and other aspects.
The technical solution of the invention is as follows:
the device for detecting the collimation of the laser beam is characterized by comprising a Fresnel biprism main section and a CCD camera receiving screen which are sequentially arranged along an optical axis, wherein the output end of the CCD camera is connected with the input end of a computer, a laser beam to be detected is injected into the center of the Fresnel biprism main section along the optical axis, and the CCD camera receives interference information and presents an image on a display screen of the computer.
The Fresnel biprism is made of common transparent materials.
The range of the included angle theta between the two edge surfaces of the Fresnel biprism and the main section is 0 degree < theta <5 degrees.
The method for detecting the collimation of the laser beam by using the detection device is characterized by comprising the following steps of:
1) the Fresnel biprism of the detection device and the receiving screen surface of the CCD camera are sequentially arranged along the direction of the optical axis of the laser beam to be detected, and the output end of the CCD camera is connected with the input end of a computer;
2) the CCD camera collects interference fringes of the laser beam to be detected, the interference fringes are input into the computer, whether the interference fringes are parallel or not is judged, if a plurality of interference fringes are parallel, the next step is carried out, and if not, the laser beam to be detected is an uncollimated light beam;
3) and rotating the Fresnel biprism by 90 degrees along the optical axis, collecting the interference fringes of the laser beam to be detected by the CCD camera, inputting the interference fringes into the computer, judging whether the interference fringes are parallel or not, and if the interference fringes are parallel, determining that the light beam to be detected is collimated light.
The interference fringe image can also be quantitatively analyzed by a computer: and establishing a rectangular coordinate system to calculate the slope of each bright (dark) stripe by randomly picking points to calculate the point, wherein the smaller the fluctuation range of the slope value is, the better the collimation of the laser beam 1 is, and when the slopes of any point on all the bright (dark) stripes are equal, the light beam to be measured is ideal collimated light.
The Fresnel biprism can rotate at any angle along the optical axis, the main section of the prism faces the incident laser beam to be measured, the size of the caliber of the main section of the prism is not limited, the design can be adjusted according to the size of the caliber of the beam in practical application, and the caliber of the main section of the prism is ensured to be sufficiently larger than the caliber of the beam to be measured.
The material of the fresnel biprism can be selected from common transparent materials, such as BK7, quartz, etc., and the material is not limited in practical application.
The injection angle of the light beam to be detected when the light beam is incident on the main section of the Fresnel biprism is not strictly required to be 90 degrees, and the detection collimation result is not greatly influenced when the light beam is obliquely incident at a certain angle. In addition, the light spots of the light beams on the main cross section of the prism are distributed up and down symmetrically about the center of the main cross section of the prism as far as possible, but certain deviation is allowed.
When the laser beam is a collimated beam, according to the law of refraction, the beam emergent from the upper prism surface and the beam emergent from the lower prism surface are a cluster of parallel light, the two beams of parallel light are deflected towards the prism, and are overlapped and interfered in the forward transmission process to generate parallel equidistant interference fringes.
The stripe distance is only related to the included angle theta between the edge surface of the Fresnel biprism and the main section, the refractive index n and the wavelength lambda of the laser beam, and the stripe distance formula is as follows:
nsinθ＝sinα；
f(θ,α)＝2ncos(α-θ)/cosα*sinθ+2sin(α-θ)-2cos(α-θ)tanα；
a fringe spacing Δ x ═ λ/f (θ, α);
alpha is a refraction angle of a light beam incident on a prism surface-air interface, the size of n is determined by an actually adopted Fresnel prism material, and the larger theta is, the smaller the distance between interference fringes is, so that the theta range is limited to be 0 degrees < theta <5 degrees in order to ensure that the interference fringes on a computer are obvious.
The distribution of the overall aperture size of the interference fringe pattern along the optical axis is as follows: the aperture of the interference fringe pattern is 0 at the prism ridge position, and the farther the back edge optical axis is from the ridge, the greater the aperture is at the distance from the ridge
The aperture of the interference fringe pattern at the position reaches the maximum, and the aperture gradually becomes smaller when the interference fringe pattern is continuously away from the ridge along the axial direction
Position ofThe aperture of the interference fringe pattern is reduced to 0 again, and no interference fringe exists at the position which is far away from the ridge along the axial direction, so that the CCD receiving screen is required to be placed at the position which is far away from the ridge of the prism along the optical axis to ensure that the CCD receiving screen acquires the interference fringe pattern with the aperture as large as possible
And at the position, wherein r is the radius of the laser beam to be measured.
When any interference pattern generated before and after the prism rotates by 90 degrees is a non-parallel interference fringe, the light beam to be measured is non-collimated light.
Preferably, when the aperture of the interference pattern exceeds the aperture of the receiving screen of the CCD camera, a standard microscope objective lens which is highly transparent to the wavelength of the laser to be detected can be added between the Fresnel biprism and the CCD, and the interference pattern is projected onto the receiving screen of the CCD after being reduced in aperture so as to be convenient for detection. Before the collimation of the light beam to be detected is formally detected, a collimator (an ideal collimated light source) is needed to calibrate the standard microscope objective, so that the microscope objective is prevented from carrying out non-collimation operation on the light beam to be detected.
The invention has the following technical effects:
the invention makes the laser beam to be measured incident to the center of the main section of the Fresnel biprism along the optical axis, and the laser beam is divided into two beams of light with coherent characteristics after passing through the upper and lower prism surfaces, the two beams of light are overlapped and interfered in space, the interference signals are received by a CCD camera, and the interference signals are converted into electric signals by a computer connected with a CCD and then displayed, and the electric signals can be further used for quantitative analysis and processing. Only when the laser beam to be measured is collimated light, interference signals displayed by the prism before and after the prism rotates by 90 degrees along the optical axis are light and dark alternate fringes with parallel equal intervals, and when the laser beam to be measured is non-collimated light, the interference fringes generated by the prism before and after the prism rotates by 90 degrees are not all parallel, so that whether the laser to be measured is collimated light or not can be judged according to whether the interference fringes before and after the prism rotates by 90 degrees are all parallel. The device has the characteristics of simple structure, convenient operation, low cost, high sensitivity and high measurement precision, has extremely high practical value, and can be widely applied to various aspects such as scientific research, production and the like.
Drawings
FIG. 1 is a schematic structural diagram of a laser beam collimation detection device according to the present invention
FIG. 2 is a front view of a device of the present invention with collimated light incident along the optical axis
FIG. 3 is a front view of the device for detecting the collimation of a large-aperture light beam according to the present invention
FIG. 4 is a front view of a collimated oblique light incidence device of the present invention
FIG. 5 is a front view of a device of the present invention with non-collimated light incident along the optical axis
Detailed Description
The present invention will be further described with reference to the following examples and drawings, but the scope of the present invention should not be limited thereto.
Referring to fig. 1, fig. 1 is a schematic structural diagram of a laser beam collimation detection device of the present invention, and it can be seen from the diagram that the laser beam collimation detection device of the present invention includes a fresnel biprism 2 and a receiving screen of a CCD camera 3 arranged in sequence along an optical axis, an output end of the CCD camera 3 is connected to an input end of a computer 4, a laser beam 1 to be measured is injected into a center of a main section of the fresnel biprism 2 along the optical axis, and the CCD camera 3 receives interference information and presents an image on a display screen of the computer 4.
The main section of the Fresnel biprism 2 faces the incidence direction of the light beam to be measured, the main section of the Fresnel biprism and the CCD receiving screen surface are coaxial in the vertical plane, and the axial distance between the main section of the Fresnel biprism and the CCD receiving screen surface is
The laser beam 1 vertically enters the center of the main section of the Fresnel biprism 2 along the optical axis, and when reaching two edges, the same beam is divided into an upper beam and a lower beam of coherent light by taking the ridge as a boundary, the light path emitted by the upper edge surface deflects downwards, the light path emitted by the lower edge surface deflects upwards, and the two beams of light meet and interfere in a space transmitted forwards. The CCD camera 3 is used for receiving the interference fringes and converting optical signals of the interference fringes into electric signals through the connection of the CCD camera 3 and the computer 4, so that the interference fringes can be conveniently observed and the method is used for quantitative calculation and the like.
The method for detecting the collimation of the laser beam by using the detection device comprises the following steps:
1) the Fresnel biprism 2 and the receiving screen of the CCD camera 3 of the detection device of claim 1 are sequentially arranged along the direction of the optical axis of the incidence of the laser beam to be detected, and the output end of the CCD camera 3 is connected with the input end of the computer 4;
2) the CCD camera 3 collects interference fringes of the laser beam to be detected, inputs the interference fringes into the computer 4, judges whether the interference fringes are parallel, if a plurality of interference fringes are parallel, the next step is carried out, otherwise, the laser beam to be detected is a non-collimated beam;
3) and rotating the Fresnel biprism 2 by 90 degrees along the optical axis, collecting the interference fringes of the laser beam to be detected by the CCD camera 3, inputting the interference fringes into the computer 4, judging whether the interference fringes are parallel or not, and if the interference fringes are parallel, determining that the laser beam to be detected is collimated light.
Taking the laser beam to be measured as the collimated light, as shown in fig. 1 and fig. 2. Laser beam 1 incides 2 main cross sections centers of fresnel biprism along the optical axis, the light beam incident angle is 0, consequently not take place to deflect when passing through main cross section, transmit two faceted pebbles forward always, because two faceted pebbles have certain contained angle and contained angle with main cross section to equal, can know by the law of refraction, same light beam divide into two bundles of coherent light from two faceted pebbles after the emergence, and all deflect to the direction of prismatic ridge, the refraction angle of two bundles of light equals, the light of two faceted pebbles outgoing is parallel light respectively about promptly, and the direction of propagation equals with the contained angle of water flat line. The two beams are overlapped and interfered in a forward transmission space range, so that interference fringes are received on the CCD camera 3, parallel and equally spaced bright and dark alternate fringes are displayed on the computer 4, and the interference fringes are still parallel and equally spaced after the Fresnel biprism is rotated by 90 degrees because collimated light is injected. According to the calculation of the optical path difference of the light and dark fringes, the optical path difference of the two coherent light rays corresponding to any bright point is even times of the half wavelength, and the optical path difference of the two coherent light rays corresponding to any dark point is odd times of the half wavelength, so that the interference fringe distance formula is obtained as follows:
nsinθ＝sinα；
f(θ,α)＝2ncos(α-θ)/cosα*sinθ+2sin(α-θ)-2cos(α-θ)tanα；
a fringe spacing Δ x ═ λ/f (θ, α);
where α is the angle of refraction of the beam incident at the facet-air interface. It can be seen that the fringe spacing Δ x is only related to the angle θ between the facets of the fresnel biprism and the principal cross-section, the refractive index n, and the wavelength λ of the laser beam.
When the computer quantitatively analyzes the interference fringe image, a rectangular coordinate system can be established to calculate the slope of any point in each bright (dark) fringe for analyzing the collimation degree of the light beam to be detected. Points are widely randomly taken in each bright (dark) stripe to calculate the slope, and the smaller the fluctuation range of the slope value is, the better the collimation of the laser beam 1 is, and the more sampling points are, the more accurate the sampling points are. When the slopes of any point on all the bright (dark) stripes are equal, the light beam to be measured is the ideal collimated light.
When the aperture of the interference pattern exceeds the aperture of the receiving screen of the CCD, a standard microscope objective 5 can be added between the Fresnel biprism and the CCD to reduce the aperture of the interference pattern and project the reduced interference pattern onto the CCD. The structure is shown in fig. 3. Before formally detecting the collimation of the laser beam 1, a collimator (ideal collimation light source) is needed to calibrate the microscope objective 5, so that the microscope objective 5 itself is prevented from performing non-collimation operation on the laser beam 1.
The laser beam 1 is not required to be incident on the Fresnel biprism strictly along the optical axis, the collimation measurement result is not influenced when the laser beam is obliquely incident at a certain angle, as shown in FIG. 4, when a laser beam 1 obliquely enters the center of the main cross section of a prism 2, the beam path is shifted as a whole after passing through the main cross section, the refraction angles are equal, and when the laser beam reaches the upper and lower facets, because the two edge surfaces and the main section have certain included angles, the incident angle of the light beam on the upper edge surface is different from the incident angle of the light beam on the lower edge surface, so the refraction angle is different, the included angles of the upper light beam and the lower light beam relative to the horizontal line are different, however, the refraction angles of the outgoing beams of the upper edge surface are all the same, so that the outgoing beams of the lower edge surface are a cluster of parallel beams deviated from the original optical path downwards.
When the laser beam 1 is non-collimated light, such as a divergent beam shown in fig. 5, it is considered that the light and the main cross section of the prism have different included angles only in the vertical direction, and only the distribution of the light paths in a certain vertical plane is considered. The following explains the direction of the light beam emitted from the prism surface: the light beams emitted from the prism surface are not parallel any more, and the included angle of the emitted light beams relative to the horizontal changes along with the direction of the emitting position on the prism surface away from the prism as follows: the emergent light beam at the position close to the ridge deflects downwards relative to the horizontal position, the included angle between the emergent light beam and the horizontal line is smaller as the emergent light beam is farther away from the ridge until the emergent light beam is gradually horizontal, and the emergent light beam deflects upwards relative to the horizontal position after the emergent light beam is gradually horizontal, and the included angle between the emergent light beam and the horizontal line is larger and larger. The distribution of the outgoing light beams of the lower edge surface and the outgoing light beams of the upper edge surface is completely symmetrical about a horizontal plane where the edges are located, so that the generated interference fringes are not parallel and equally spaced. Meanwhile, the incident light and the main section of the prism have different included angles in the horizontal direction, and the emergent light of the prism surface is more complicated in distribution. The interference fringes are no longer parallel equally spaced bright and dark interference fringes when non-collimated light is incident on the detection device, so the detection system can be used to distinguish between collimated and non-collimated light.
Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Experiments show that the device has the characteristics of simple structure, convenience in operation, low cost, high sensitivity and high measurement precision, has extremely high practical value, and can be widely applied to various aspects such as scientific research and production.
Claims (4)
1. The device for detecting the collimation of the laser beam is characterized by comprising a Fresnel biprism (2) and a receiving screen of a CCD camera (3) which are sequentially arranged along an optical axis, wherein the output end of the CCD camera (3) is connected with the input end of a computer (4), a laser beam (1) to be detected is injected into the center of the main section of the Fresnel biprism (2) along the optical axis, and the CCD camera (3) receives interference information and presents an image on a display screen of the computer (4);
the included angle between the two edge surfaces of the Fresnel biprism (2) and the main section
Is in the range of 0 DEG<
<5°；
The main section of the Fresnel biprism faces the incident direction of the light beam to be measured, the main section of the Fresnel biprism and the CCD receiving screen surface are coaxial in the vertical plane, and the axial distance between the main section of the Fresnel biprism and the CCD receiving screen surface is
，
Is the radius of the laser beam to be measured,
is the refraction angle of the light beam incident on the prism surface-air interface of the Fresnel biprism (2).
2. The apparatus according to claim 1, wherein the Fresnel biprism material is a transparent material.
3. A method for detecting the collimation of a laser beam using the detection device of claim 1, the method comprising the steps of:
1) the Fresnel biprism (2) of the detection device and the receiving screen of the CCD camera (3) are sequentially arranged along the direction of the optical axis of the incidence of the laser beam to be detected, and the output end of the CCD camera (3) is connected with the input end of the computer (4);
2) the CCD camera (3) collects interference fringes of the laser beam to be detected, the interference fringes are input into the computer (4), whether the interference fringes are parallel or not is judged, if a plurality of interference fringes are parallel, the next step is carried out, and if not, the laser beam to be detected is a non-collimated light beam;
3) and rotating the Fresnel biprism (2) by 90 degrees along the optical axis, collecting the interference fringes of the laser beam to be detected by the CCD camera (3), inputting the interference fringes into the computer (4), judging whether the interference fringes are parallel or not, and judging whether a plurality of interference fringes are parallel or not, wherein the light beam to be detected is collimated light.
4. The method for detecting the collimation of a laser beam as claimed in claim 3, wherein the interference fringe image is further analyzed quantitatively by a computer: and establishing a rectangular coordinate system to calculate the slope of each bright stripe or each dark stripe by randomly picking points to calculate the point, wherein the smaller the fluctuation range of the slope value is, the better the collimation of the laser beam (1) is, and when the slopes of any point on all the bright stripes or the dark stripes are equal, the light beam to be measured is the ideal collimated light.
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