利用无源电探针检测A304不锈钢在不同的NdYAG激光焊接条件下的光致等离子体电信号，研究了不同的激光焊接模式与激光等离子体电信号频谱分析结果之间的关系，分析了不同条件下的等离子体电信号波形图和频谱图，阐述了不同激光焊接模式下的焊缝横截面成形特征与等离子体电信号波形、频谱特征的关系。结果表明,在试验设定条件下，不同的激光焊接模式具有不同的等离子体电信号频谱特征。利用在500~1000 Hz范围内等离子体电信号频谱的谱强度E的大小可判别激光焊接过程是否为深熔焊，当E较大或超过一定值时，激光焊接模式为深熔焊。

The electrical signals of laser induced plasma from NdYAG laser welding of A304 stainless steels are detected by a passive electrical probe. The relationship between different laser welding modes and the spectral analysis results of plasma electrical signals are investigated. The waveforms and spectra of plasma electrical signals are analyzed. The relationship between the formation characteristic of laser welds under different laser welding modes and the waveforms and spectra of the plasma electrical signals is illustrated. The results indicate that, under the specified conditions in the experiments, different laser welding modes correspond to different spectral characteristics of plasma electrical signals. Moreover, whether the welding mode is a deep penetration one or not can be identified by the spectral intensity E of plasma electrical signals within the scope of 500～1000 Hz. When E is large enough or exceeds a certain value, the laser welding mode is a deep penetration welding.