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高功率激光装置中通过测量光束强度分布来评价近场光束质量。然而测量结果为一稳态分布,并不能真实反映经噪声扰动后光束的强弱调制演变特性,可能会忽略传输过程中存在的调制较为严重的区域。针对此问题着重研究了光束经噪声扰动后的近场传输演化特性,进而对近场分布测量的局限性进行深化理解和补充。同时,为简化分析单因素局部缺陷影响下不同传播距离处的近场分布变化规律,引入等效菲涅耳数来表征近场强度调制特性。结果表明,当实测近场分布中存在较弱调制信息时,测量位置之前可能存在更为严重的调制区域。以调制为π的相位型缺陷为例,其最大调制相对于入射光强度可增大9倍。
Near-field beam quality is evaluated by measuring the beam intensity distribution in high-power laser devices. However, the measured result is a steady-state distribution, which can not truly reflect the evolution characteristics of the intensity modulation of the light beam after the noise disturbance and may ignore the more heavily modulated area during the transmission. Focusing on this problem, the evolution characteristics of the near-field propagation of light beams after noise disturbance are studied emphatically, and the limitations of near-field distribution measurement are further understood and supplemented. At the same time, in order to simplify the analysis of the variation of near-field distribution under different propagation distances under the influence of single-factor local defects, the equivalent Fresnel number was introduced to characterize the near-field intensity modulation. The results show that when there is weak modulation information in the measured near-field distribution, there may be a more serious modulation region before the measurement position. Taking a phase defect modulated at π as an example, its maximum modulation can be increased nine times relative to the incident light intensity.