Influence of aerodynamic window flow field on beam quality by shearing interferometry Chen Jixing, Liu Tianwei, Jiang Zongfu, Li Wenzhao Institute of Directional Energy Technology, College of Science and Technology, National University of Defense Technology, Changsha 410073, Hunan, China The measurement principle solves the difficulty that the interference fringes are difficult to interpret. The effect of the flow field of the freely swirling aerodynamic window on the beam quality under steady state is experimentally studied. The Strehl ratio is used as the evaluation standard. The measurement gives the influence of the free vortex aerodynamic window on the beam quality under steady working conditions. . The results show that when the free vortex aerodynamic window works under the theoretical design conditions, the influence on the beam quality is relatively small, which can better meet the task requirements.
With the development of high-power lasers, the research and development of aerodynamic windows is becoming more and more important. The study of the influence of the flow field of aerodynamic window on the beam quality is one of the important aspects. 4 It is usually measured by schlieren holography. These methods have a common shortcoming to the test of the child's environment and ugly play against the thousands of experiments; far-field spot measurement measurement has a knot, not 4 points, difficult to achieve higher precision, this article uses lateral shear interference The instrument is used for the same measurement, which reduces the experimental requirements, simplifies the experimental device, makes the experiment easier, and can achieve a relatively high measurement accuracy 5! However, this method has the disadvantage that the interference fringes are difficult to interpret. This paper properly handles this question, and gives the measurement result of the influence of the flow field of the free vortex aerodynamic window on the optical wavefront. 1 Measurement principle Guangxu transparent transparent colorless flow, its refraction The rate of +3 can change the phase or propagation direction of the wavefront, and the amplitude will not change. The phase change can be transformed into the change of the intensity distribution by the interferometry method, and the interference spectrum can be obtained by analyzing the interference fringes. The distortion of the front phase is as small as the actual measurement condition. Therefore, in the following discussion, the deflection of the beam in the flow field is ignored, and the phase change of the optical wave is considered!
1.1 Transverse shear interference Transverse shear interference is to shear the measured wavefront into two. The two wavefronts are offset by a fixed distance and overlap. The interference is different from the ordinary interferometer. The transverse shear interference does not require the reference wavefront, and the two wavefronts After the same path, the comparative interference occurs, which determines that the transverse shear interference is not sensitive to the vibration temperature disturbance. When the measurement environment requirements are different, the characteristics of the comparison also determine that the transverse shear interference fringe reflects the variation gradient of the wavefront instead of Directly reflecting the shape of the wavefront, this is the difficulty of using this method. 41 Set the wavefront to be measured, square cut, cut clear. Then the light field before the cut wave is 1 command +51. The light field of the cut is 1 blade and the stripe is the field 1 and it is difficult to 1 to more than 1 strip. The 1 wave continued wavefront recovery could not enter the hall. At the same time, when there was no shearing amount for the Xiaobian, which was difficult to interpret, the equal-thickness interference fringe factory added the modulation of equal thickness. In the D1, the order of the stripes of the Ding 1 changes sequentially in order, 1 to get the relative. The interference level is selected along the cutting edge and the test point is taken. The 77 is the reference point number, and the reference point spacing is only equal to the thickness of the corpse. Know by the formula 5, reference point. 1. The interference level at the interference level is the interference level at the point of the 6th system. When the plant has airflow, the relationship is changed by the 7th, 8th type, and the derivation of the mountain is used to make the seventh. At the wavefront at point 4, the wavefront of the nowhere is the change of the wavefront at the point where there is airflow and no airflow. The Liangqi River is obtained from the same reference point 1 in the two states before and after the Di gas. Similarly, in the direction of shearing, the relationship between the wavefront change and its difference value can also be obtained. For the analysis of transverse shear interference fringes, the difference value of the wavefront variation in the shear direction at all reference points can be obtained. The change of ice in the wavefront is a hypothesis that the polymorphic small slow-changing function is used. From the 12th formula, the preferred term coefficient can be eliminated, and the wavefront variation is obtained by this method. The influence of the flow field on the wavefront is obtained. It can eliminate the wavefront distortion caused by other factors in the experiment, such as the influence of the deformation of the mirror, etc. 1.2 The treatment of the interference is measured by the experimentally measured stripe. Using human 1 to determine the deviation of the center of the stripe at the center of the stripe, the work is very hot and the error is also large. The automatic processing of the interference fringe by the exposed machine improves the efficiency and accuracy of the interference fringe of the experimental stripe. First, noise reduction processing is required. In the experiment, Wiener filtering is used to process the shape. Eliminating high-frequency noise Due to the experimental 1 carrier technology, the interference fringes can be adjusted to reflect the characteristic stripe of the information of the straight stripe; along the direction perpendicular to the stripe, find all local minima and maximal values ​​of the pixel values ​​on the line. The value, that is, the center position of all the light and dark stripes on the line; the scan is perpendicular to all the lines of the stripe, and the center position of the light and dark stripes can be determined, thereby obtaining the relative interference order of each interference fringe for the relative thousand level of the reference point. The linear interpolation method can be used to determine the relative interference level of each reference point required for wavefront recovery by determining the relative order of the interference fringes.
The cabinet 141 is a horizontal shearing of the ten-striped pavilion obtained by the flow, and a center of the interference fringe obtained by the filtering of the knot of 1 is a dimension. It can be seen from 10 that the center of the interference fringe is relatively accurate, there is no pseudo fringe and the number of fringes is reduced, and a satisfactory result is obtained. 1.3 The beam quality is evaluated by the phase error of the light wave, and the mountain in the far field is the Fraunhofer diffraction. The intensity on the optical axis is such that if the wavefront is particularly shy, then this is limited by the diffraction limit. The Strehl ratio is defined as the actual peak power obtained by the 16th type, and the diffraction limit peak power is 20. The soil can be written as 57=161. The mountain 5 finds the item under the condition of small aberration approximation, and expands and only takes the first two items, and only depends on the wavefront error. And very sensitive to wavefront errors. therefore. Can be used for m bundle j tribute. In this sheet, t uUK is taken to calculate the distortion of the wavefront after the laser beam passes through the flow field of the pneumatic window. 3f. The calculated Strehl ratio is 0.9594 2 Experimental and results å® plane, the laser is transmitted in 2 directions, and the airflow direction is positive.
According to the characteristics of the free-pneumatic air window, it is known that the airflow density non-uniformity mainly occurs in the positive direction along the airflow direction 16; the density of the direction can be considered to be uniform, and has little effect on the wavefront. In the experiment, only the wave along the airflow direction The front change was measured, and the shear direction was along the direction of the air flow. The cut amount was 5=1.5, for example, the result of the first set of the positive set. Therefore, the total pressure of the gas supply to the gas supply was 0.9, and the sealing pressure ratio was 1 3 is the first machine measurement result. At this time, the total pressure of the pneumatic window into the gas supply is 51刖, and the sealing pressure ratio is 2.841. It is the wavefront distortion before and after the gas-filling, and the calculated Strehl ratio is 22. It can be seen from this that at this time, the influence of the airflow on the wavefront is relatively large, and the wavefront high-order distortion Mingkun pays the two sets of experimental results. It can be known that the aerodynamic pressure is 1. The card ratio of the pneumatic window is relatively high. At this time, the aerodynamic window works near the design working state. The calculated Strehl ratio is 959, indicating that the actual peak intensity and the diffraction limit peak intensity are very close, and the aerodynamic window flow field has little effect on the beam quality; The pressure is 51 river, when, the ratio is 1622, which shows that under this working condition, the influence of the aerodynamic window on the beam quality is relatively large. The whole measurement result is consistent with the theoretical design result of the aerodynamic window!
3 Conclusions The paper proposes the use of transverse shear interferometer to measure the influence of aerodynamic window on beam quality, reduce the requirements of the experimental environment, improve the measurement accuracy in harsh environments, and experimentally measure the flow field of free vortex pneumatic window under different working conditions. The effect of the beam quality, the measurement results are given, and a preliminary analysis is carried out. It can be seen from the experimental results that the transverse shearing interferometry can satisfactorily meet the measurement requirements of the flow field of the aerodynamic window and the influence of the beam quality. It has a good application prospect in the optical performance of the aerodynamic window. 1 Liu Tianhua, Jiang Zongfu, Wei Chenghua ,Wait. Preliminary experimental study on the principle of free-spinning pneumatic window and its working performance. 1 China Laser, 2000, 712327.
I7I Sun Xiangxiang. The digital image handles the elbow. Shijiazhuang Hebei Industrial Press, 1983. 0 name 6100, 1 grid. , 3 such as 2 cents 1 grid 16 he 1431Press519838 Zhou Renzhong. Adaptive optics. North Brother Defense Industry Press, 1996. Department 0. 8. 10, 8. Dad, 1 plus 160, 1 He Tu 1688, 9 Liu Tianhua, Li Wenzhao, Jiang Zongfu, and so on. Using the far-field method, the optical properties of the free-rotating aerodynamic window are strong laser and particle beam, 200201314.
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