用激光显示焊接气流是近几年发展起来的一种新的显示方法。由于其图象条纹的复杂性,有必要对其成象原理进行研究。本文对折射率在成象中的作用进行了试验研究。研究指出,这一显示方法对折射率突变区敏感,能清晰地显示气流界面,从而构成气流形态,判明流场性质。文中研究了气流衍射条纹的分布特征。结果表明,在气流界面上折射率较大的一侧出现亮条纹;折射率较小的一侧出现暗条纹,因而有可能判断哪一侧是什么气体。从这些原理出发,对自由喷流、冲击流和电弧冲击流的图象特征进行了分析判读。在研究拍摄距离对成象影响的基础上,提出了最佳拍摄距离一般可选1.5～2m。 The use of laser to display the welding air flow is a new display method developed in recent years. Due to the complexity of its image stripes, it is necessary to study its imaging principle. In this paper, the role of refractive index in imaging has been experimentally studied. The research indicates that this display method is sensitive to the abrupt change of refractive index and can clearly show the air flow interface, thus forming the air flow pattern and determining the flow field property. In this paper, the distribution characteristics of the gas diffraction fringes are studied. The results show that bright stripes appear on the larger refractive index side of the air flow interface, dark stripes appear on the smaller refractive index side, and it is therefore possible to determine which side is what gas. Based on these principles, the image features of free jet, impinging stream and arc impinging stream were analyzed and interpreted. Based on the study of the effect of shooting distance on the imaging, the optimal shooting distance is proposed to be 1.5 ~ 2m.