CN107167301B - The method of testing laser device beam quality Improvement - Google Patents
The method of testing laser device beam quality Improvement Download PDFInfo
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- CN107167301B CN107167301B CN201710560143.1A CN201710560143A CN107167301B CN 107167301 B CN107167301 B CN 107167301B CN 201710560143 A CN201710560143 A CN 201710560143A CN 107167301 B CN107167301 B CN 107167301B
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Abstract
The present invention provides a kind of method of testing laser device beam quality Improvement, and by measuring the near-field intensity distribution and far-field intensity distribution of Laser Output Beam, power P IR value in the ring of light beam is calculated.According to the potentiality that power P IR value evaluation beam quality is promoted in ring.The measurement of power P IR value is convenient in ring, calculates simple, explicit physical meaning, is a kind of method of easy, quick, effectively evaluating laser beam quality Improvement.
Description
Technical Field
The invention relates to the technical field of laser, in particular to a method for testing the beam quality improvement potential of a laser.
Background
Beam quality is an important parameter in describing lasers. The quality of the light beam determines the long-distance use effect of the laser beam. Due to the influences of factors such as thermal deformation of optical elements, thermal distortion of optical media and the like, the quality of a light beam directly output by a laser is generally poor, and a self-adaptive optical system is required to further improve the quality of the light beam. However, the effect of improving the beam quality is not only related to the performance of the adaptive optics system, but also to the characteristics of the laser output beam. The potential for beam quality improvement varies among different types of lasers. By adopting the same adaptive optical system, the quality of the light beam output by some lasers can be greatly improved, and the quality of the light beam output by some lasers can be only slightly improved. Although various methods are available for testing the beam quality of the laser, a simple and effective test method is still lacking for the potential improvement of the beam quality of the laser.
Disclosure of Invention
In order to solve the above technical problems, an object of the present invention is to provide a method for testing the beam quality improvement potential of a laser.
The invention provides a method for testing the beam quality improvement potential of a laser, which comprises the following steps:
step S100: after measuring the near field intensity distribution and the far field intensity distribution of the output beam of the laser, calculating the low-frequency power P according to the formulas (1) to (2)1And high frequency power P2，
Wherein,for polar representation of the far field intensity distribution, R1Radius of the first diffractive dark ring of the far field of the light beam, R2The radius of the fourth diffraction dark ring of the far field of the light beam;
step S200: and calculating the power PIR in the loop according to the formula (3):
wherein, P1At low frequency power, P2Is high-frequency power;
step S300: judging whether the power PIR in the ring is close to 1 or 0, if the power PIR in the ring is close to 1, the potential of improving the beam quality of the laser is large; if the ring power PIR is close to 0, the potential for beam quality improvement of the laser is small.
Further, the radius R of the first diffraction dark ring of the far field of the light beam1And radius R of the fourth diffraction dark ring of the far field of the light beam2Calculating according to formulas (4) to (5):
wherein λ is the wavelength of the laser beam, f is the focal length of the far-field measuring lens, and D is the equivalent diameter of the laser beam.
Further, the equivalent diameter D of the laser beam is calculated by the following formula:
wherein σ2The second moment of the near field intensity.
Further, the second moment σ of the near-field light intensity2Calculated according to the following formula:
wherein,is a polar representation of the near field intensity distribution.
The invention has the technical effects that:
1. the invention provides a method for testing the quality improvement potential of a laser beam, which can obtain the value of the power PIR in a loop only by measuring the near-field intensity distribution and the far-field intensity distribution of the high-energy laser output beam and carrying out simple calculation, evaluate the improvement potential of the quality of the laser beam by the value of the power PIR in the loop which can effectively reflect the far-field intensity distribution condition of the laser output beam, and effectively represent the improvement potential of the quality of the laser output beam. The method is simple and rapid.
2. The invention provides a method for testing the quality improvement potential of a laser beam, which is particularly suitable for evaluating the quality improvement potential of a high-energy laser beam.
The above and other aspects of the invention will be apparent from and elucidated with reference to the following description of various embodiments presented in a method of testing the beam quality improvement potential of a laser according to the invention.
Drawings
FIG. 1 is a schematic flow chart of a method for testing the beam quality improvement potential of a laser provided by the present invention;
FIG. 2 is a schematic illustration of the optical path used to measure the near field intensity distribution and the far field intensity distribution in a preferred embodiment of the present invention;
FIG. 3 is an initial beam quality factor β in a preferred embodiment of the invention0The result of the beam quality of the 4.2 high-energy laser after being corrected by the adaptive optics system of the unit 61 is shown schematically;
FIG. 4 is an initial beam quality factor β for a preferred embodiment of the invention0The result of the beam quality of the high-energy laser of 4.2 after being corrected by the adaptive optics system of the unit 91 is shown schematically;
FIG. 5 is an initial beam quality factor β in a preferred embodiment of the invention0The beam quality result of the high-energy laser of 4.2 corrected by the adaptive optics system of the 127 unit is shown schematically.
Illustration of the drawings:
1. a high-energy laser; 2. a high-reflection mirror; 3. an attenuation sheet; 4. a beam splitter; 5. a near field measurement CCD camera; 6. a far field measurement lens (focal length f); 7. and a far-field measurement CCD camera.
Detailed Description
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention.
The method for testing the beam quality improvement potential of the laser is particularly suitable for the high-energy laser 1. The high-energy laser 1 here is a continuous wave laser having an average output power of 10kW or more.
Referring to fig. 1, the method for testing the beam quality improvement potential of the laser provided by the invention comprises the following steps:
step S100: measuring laser outputAfter the near field intensity distribution and the far field intensity distribution of the light beam, the low frequency power P is calculated according to the formulas (1) to (2)1And high frequency power P2，
Wherein,for polar representation of the far field intensity distribution, R1Radius of the first diffractive dark ring of the far field of the light beam, R2The radius of the fourth diffraction dark ring of the far field of the light beam;
step S200: calculating the power PIR in the loop according to the formula (3),
wherein, P1Is the sum of low frequency power and P2Is high-frequency power;
step S300: judging whether the power PIR in the ring is close to 1 or 0, if the power PIR in the ring is close to 1, the potential of improving the beam quality of the laser is large; if the ring power PIR is close to 0, the potential for beam quality improvement of the laser is small.
The potential for improvement in the quality of the laser beam depends primarily on the spatial frequency content of the output beam wavefront distortion. Generally, if the spatial frequency of wavefront distortion is mainly low frequency component, the potential for improving the quality of laser beam is great; if the spatial frequency of the wavefront distortion is dominated by the high frequency component, the potential for improving the beam quality of the laser is small.
According to the method provided by the invention, the improvement potential of the laser beam quality is obtained by analyzing the far-field intensity distribution condition of the laser output beam. The ring power PIR value represents the share of low-frequency distortion components in the output beam in the total distortion components, and the potential of improving the quality of the output beam of the laser can be effectively represented. P1The power between the first diffraction dark ring and the fourth diffraction dark ring in the far-field intensity distribution of the light beam is represented, and low-frequency distortion components in the light beam are reflected; p2Representing the power outside the fourth diffractive dark ring in the far field intensity distribution of the beam, reflects the high frequency distortion component in the beam. 0.7024 is the ratio of the power between the first through fourth diffractive dark rings to the power outside the first diffractive dark ring in the far field intensity distribution of the ideal light beam, here as a normalization parameter.
The ring power PIR value is between 0 and 1 and represents the fraction of the low frequency distortion component in the output beam in the total distortion component. If the ring power PIR value of a certain light beam is close to 1, the light beam is mainly divided by low-frequency distortion, the wavefront of the light beam is easy to correct by an adaptive optical system, and the potential for improving the quality of the light beam is large; if the ring power PIR value of a certain light beam is close to 0, it indicates that the light beam is mainly dominated by high-frequency distortion, the wavefront is difficult to be corrected by the adaptive optics system, and the potential for improving the beam quality is small. Therefore, whether various laser beams are worth further correcting and improving the beam quality is simply and conveniently evaluated through the ring power PIR value.
The near field intensity distribution and the far field intensity distribution in the method provided by the invention can be determined according to a conventional method. For example, using the optical path shown in fig. 2, the near field intensity distribution and the far field intensity distribution of the laser output beam are measured. The polar coordinate of the near field intensity distribution is expressed asThe polar coordinate of the far field intensity distribution is expressed as
Preferably, R1Radius of the first diffractive dark ring of the far field of the light beam, R2The radius of the fourth diffractive dark ring in the far field of the light beam can be obtained according to the obtained near field intensity distribution and the far field intensity distribution according to the prior method. The method comprises the following specific steps:
where λ is the wavelength of the laser beam, f is the focal length of the far-field measurement lens 6, and D is the equivalent diameter of the laser beam.
Preferably, the equivalent diameter D of the laser beam can be obtained by the following formula:
wherein σ2The second moment of the near field intensity.
Preferably, the second moment σ of the intensity of the near-field light2Can be obtained by the following formula:
wherein,is a polar representation of the near field intensity distribution of the optical beam.
The method provided by the invention is explained in detail below by combining specific simulation examples.
First, referring to fig. 2, an optical path is constructed to measure the near-field intensity distribution and the far-field intensity distribution of the output beam of the high-energy laser 1. The optical path comprises a high-energy laser 1, a high-reflection mirror 2, an attenuation sheet 3, a spectroscope 4 and a far-field measuring lens 6 which are connected in sequence. After the laser beam is divided into two paths by the spectroscope 4, the first laser beam enters the near-field measurement CCD camera 5 to be captured. The other laser beam enters a far field measurement CCD camera 7 after passing through a far field measurement lens 6.
The light beam output by the high-energy laser 1 is divided into two parts after being reflected by the high-reflection mirror 2 (the reflectivity is more than 99.8%), and the reflected light with larger power is not processed. The transmitted light with smaller power passes through the attenuation sheet 3 (the uniformity is better than 0.01, and the optical density depends on the intensity of the light beam) and then is attenuated to the milliwatt level. The attenuated light beam is divided into two paths by a spectroscope 4 (the splitting ratio is 50:50), one path of the light beam is incident into a near-field measurement CCD camera 5 (the number of pixels is more than 640 multiplied by 480, and the dynamic range is more than 8bit) to measure the near-field intensity distribution of the light beam, and the other path of the light beam is incident into a far-field measurement CCD camera 7 (the number of pixels is more than 640 multiplied by 480, and the dynamic range is more than 8bit) after passing through a far-field measurement lens 6 (the equivalent focal length is f) to measure the far-field intensity distribution of the.
Next, according to equations (1) to (7), a value of the ring-in-loop power PIR of the light beam is calculated.
In order to illustrate the effectiveness of the PIR value of power in the ring to describe the beam quality improvement potential of the high-energy laser 1, the beam quality improvement conditions of the high-energy laser 1 with different wavefront distortions are numerically simulated, in numerical calculation, the output beam of the high-energy laser 1 has different wavefront distortion conditions, 176 kinds of wavefront distortions are randomly generated, the wavefront distortions have different spatial frequency distributions, and the magnitudes of the wavefront distortions are adjusted so that the output beam quality factor β of the high-energy laser 1 is enabled to be equal to04.2, calculating the PIR value of the light beam in the 176 cases according to the formulas (1) to (7), then performing wavefront correction on the 176 high-energy laser beams by adopting ideal adaptive optical systems of 61 units, 91 units and 127 units respectively, and calculating the beam quality factors β after correction of the 176 high-energy laser beams respectively1. PIR value and corrected beam quality of high-energy laser beamFactor β1The relationships between them are shown in FIGS. 3 to 5.
From the obtained result, the improvement condition of the beam quality of the high-energy laser 1 is not only related to the capability of the adaptive optics system, but also closely related to the PIR value of the beam, for the same adaptive optics system, the larger the PIR value of the output beam of the high-energy laser 1 is, the higher the beam quality factor β corrected by the adaptive optics system is1The smaller the size, the more the beam quality of the high-energy laser 1 is improved. As can be seen from FIG. 2, for the adaptive optics system with 61 units, the PIR value of the output beam of the high-energy laser 1 is greater than 0.83, which indicates that the beam quality of the output beam has a great potential to be improved, and the beam quality factor can be improved from 4.2 to a level close to 1; for the adaptive optics system with 91 units, the PIR value of the output beam of the high-energy laser 1 is greater than 0.7, which indicates that the beam quality of the high-energy laser has a huge improvement potential, and the beam quality factor of the high-energy laser can be improved to a level close to 1 from 4.2; for the adaptive optics system with 127 units, the PIR value of the output beam of the high-energy laser 1 is greater than 0.35, which indicates that the beam quality improvement potential is very large, and the beam quality factor can be improved to a level close to 1 from 4.2. In conclusion, the ring power PIR value of the output beam of the high-energy laser 1 can effectively represent the potential for improving the beam quality, and the larger the ring power PIR value is, the larger the potential for improving the beam quality is.
It will be clear to a person skilled in the art that the scope of the present invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the present invention as defined in the attached claims. While the invention has been illustrated and described in detail in the drawings and the description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments.
Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the term "comprising" does not exclude other steps or elements, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims shall not be construed as limiting the scope of the invention.
Claims (4)
1. A method for testing the beam quality improvement potential of a laser is characterized by comprising the following steps:
step S100: after measuring the near field intensity distribution and the far field intensity distribution of the output beam of the laser, calculating the low-frequency power P according to the formulas (1) to (2)1And high frequency power P2，
Wherein,for polar representation of the far field intensity distribution, R1Radius of the first diffractive dark ring of the far field of the light beam, R2The radius of the fourth diffraction dark ring of the far field of the light beam;
step S200: and calculating the power PIR in the loop according to the formula (3):
wherein, P1For said low frequency power, P2Is the high frequency power;
step S300: judging whether the power PIR in the ring is close to 1 or 0, if the power PIR in the ring is close to 1, the potential of improving the beam quality of the laser is large; if the power PIR in the ring is close to 0, the potential of improving the beam quality of the laser is small; the larger the power PIR value in the ring is, the larger the potential of the quality improvement of the laser beam is, and the smaller the power PIR value in the ring is, the smaller the potential of the quality improvement of the laser beam is.
2. The method of claim 1 wherein the radius R of the far field first diffractive dark ring of the light beam is1And radius R of the fourth diffraction dark ring of the far field of the light beam2Calculating according to formulas (4) to (5):
wherein λ is the wavelength of the laser beam, f is the focal length of the far-field measuring lens, and D is the equivalent diameter of the laser beam.
3. The method of claim 2, wherein the equivalent diameter D of the laser beam is calculated as:
wherein σ2The second moment of the near field intensity.
4. The method of claim 3 wherein the second moment σ of the near field intensity is2Calculated according to the following formula:
wherein,is a polar coordinate representation of the near field intensity distribution of the optical beam.
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