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Evaluation method of laser beam quality of low-numerical aperture large-mode field area fiber

A numerical aperture and beam quality technology, applied in the direction of testing optical performance, etc., can solve the problems that it is difficult to reflect the quality of the laser beam exiting the fiber, and the relative phase irrelevance between modes

Active Publication Date: 2016-05-11
NAT UNIV OF DEFENSE TECH
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Problems solved by technology

However, theoretical studies have shown that the propagation characteristics of a beam are only related to the composition of high-order modes in the beam, and have nothing to do with the relative phase between modes [RumaoTao, LongHuang, PuZhou, LeiSi, and ZejinLiu, “Propagation of high-power fiber laser with high-order-mode content,” PhotonicsResearch2015, 3(4),192-199]
Therefore, traditional M 2 The factor is difficult to reflect the beam quality of the laser exiting the fiber with low numerical aperture and large mode field area

Method used

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  • Evaluation method of laser beam quality of low-numerical aperture large-mode field area fiber
  • Evaluation method of laser beam quality of low-numerical aperture large-mode field area fiber
  • Evaluation method of laser beam quality of low-numerical aperture large-mode field area fiber

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Embodiment 1

[0088] See attached Figure 6 As shown, the laser beam 1 output from the fiber with low numerical aperture and large mode field area is collimated by the collimation system 2 and then continues to transmit. The light intensity distribution in the near field is measured by a CCD camera 7 at the laser output plane 3 , and the spot data is recorded and processed by a computer 6 . After the laser beam travels a distance z, a CCD camera 7 is used to detect the light intensity distribution of the transmitted beam at the plane 4, and the distance between the plane 4 and the collimation system is measured. Substitute the light intensity distribution detected by the CCD camera 7 at planes 3 and 4 into equations (14a, b) and (15a, b) to calculate the beam size. The corrected M 2 factor to evaluate the beam quality of the output laser.

Embodiment 2

[0090] See attached Figure 7 As shown, the laser light 1 output from the optical fiber with low numerical aperture and large mode field area passes through the collimation system 2 and is divided into two parts by the high reflection mirror 73. Part of the laser light, that is, the transmitted beam 75 is first imaged on the CCD camera 7, and the measured near-field spot is recorded by the computer 6, and then the transmitted beam 75 is focused on the CCD camera 7 to measure the far-field spot through the focusing optical system 76. The light spot measured by the CCD camera 7 uses (14a, b) and (15a, b) formulas to calculate the far field light spot size after the near field, and finally substitute the calculated light spot size and the focal length f (z=f) of the focusing system into the formula (17a, b) can get the correction M 2 factor to evaluate the beam quality of the output laser.

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Abstract

The invention relates to an evaluation method of laser beam quality of a low-numerical aperture large-mode field area fiber. According to the invention, effects on an M2 factor imposed by inter-mode relative phases can be eliminated, so the M2 factor which is only related to inter-mode power proportion but not related to the inter-mode relative phases can be obtained. The M2 factor modified with the method can precisely reflect mode components and laser beam quality of the low-numerical aperture large-mode field area fiber. The closer to 1 the numerical value of the M2 factor is, the better the laser beam quality is. In this way, effects on laser beam quality imposed by the inter-mode relative phases are eliminated, and a disadvantage is overcome that it is hard to evaluate the laser beam quality of the low-numerical aperture large-mode field area fiber via an M2 factor.

Description

technical field [0001] The invention relates to a method for evaluating the beam quality of a fiber laser beam with a low numerical aperture and a large mode field area, in particular to a method using a modified M 2 A method to evaluate the beam quality of low numerical aperture large mode field area fiber laser using the factor definition formula. Background technique [0002] Beam quality is an extremely important parameter in laser application technology. It is a performance index for evaluating laser characteristics in terms of quality. It has very important guiding significance for the design, manufacture, detection and application of lasers. At present, there are many methods to evaluate the beam quality of the laser, such as M 2 Factor, barrel power, Strehl ratio, etc. [Feng Guoying, Zhou Shouhuan, "Discussion on Comprehensive Evaluation of Laser Beam Quality," China Laser, 2009, 36, 1643-1653], where M 2 The factor is defined as the ratio of the product of the spo...

Claims

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Application Information

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IPC IPC(8): G01M11/02
CPCG01M11/02
Inventor 陶汝茂支冬马阎星冷进勇马鹏飞王小林周朴司磊许晓军陈金宝刘泽金
Owner NAT UNIV OF DEFENSE TECH
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