纳秒激光诱导空气等离子体存在从紫外、 可见、 近红外乃至射频微波的宽谱段辐射, 但目前的研究大多关注紫外到可见波段的光谱辐射。 激光等离子体作为一种新型的红外辐射源具有很多优势, 相比于红外干扰弹以及红外干扰手段而言, 空气等离子体红外辐射源可以灵活布置, 成本低廉, 因此研究空气等离子体的红外辐射特性就很有必要。 针对目前脉冲激光诱导空气等离子体的红外干扰研究需要, 对激光波长为532 nm的纳秒脉冲激光诱导空气等离子体的红外辐射特性进行实验研究, 探讨激光能量对空气等离子体红外辐射强度的影响规律, 以及空气等离子体红外辐射的角度分布特性, 分析了等离子体红外辐射的可能产生机制。 实验结果表明, 激光诱导空气等离子体在950～1 700 nm范围内的红外光谱为线状谱和连续谱的叠加。 其中线状谱主要是氮和氧的中性原子谱线, 并且氮原子红外辐射占主导。 随着激光能量的增加, 由于空气击穿产生的氧和氮原子数量增加, 导致空气等离子体红外辐射的谱线强度逐渐增大。 随着红外探测角度的变化, 在探测角度为75°时, OⅠ 1 12863 nm和NⅠ1 24696和1 36242 nm谱线强度达到最大, 在探测角度为120°时, NⅠ 1 01146和1 05396 nm谱线强度达到最大, 这是因为空气等离子体红外辐射强度随探测角度变化呈现空间非对称性, 表明空气等离子体内不同粒子的空间分布呈现非对称性。

Nanosecond laser-induced air plasma has a wide spectrum of radiation from ultraviolet, visible, near-infrared, and even radio frequency microwaves, but most people are currently concerned about spectral radiation from the ultraviolet to visible wavelength range. Laser plasma has many advantages as a new type of infrared radiation source. Compared with infrared bombs and infrared interference means, air plasma infrared radiation sources can be flexibly arranged and have low cost. Therefore, the study of the infrared radiation characteristics of air plasma is necessary. In view of the current research on the infrared interference of pulsed laser-induced air plasma, the infrared radiation characteristics of nanosecond pulsed laser-induced air plasma with a laser wavelength of 532 nm are experimentally studied. The influences of laser energy on the infrared radiation intensity of the air plasma are discussed, the angle distribution characteristics of the infrared radiation are presented, the possible mechanisms of plasma infrared radiation are analyzed. The experimental results show that the infrared spectrum of the laser-induced air plasma in the range of 950～1 700 nm is a superposition of the line spectrum and the continuous spectrum. The main spectrum is the neutral atomic lines of nitrogen and oxygen, and the infrared radiation of nitrogen atom dominates at the whole radiation. As the laser pulse energy increases, which induces the amount of oxygen and nitrogen atoms increasing produced by the air breakdown, the intensity of the infrared spectrum of the air plasma gradually increases. With the change of infrared radiation detection angle, the spectral intensity of OⅠ 1 12863 nm and NⅠ 1 24696 nm and 1 36242 nm reaches the maximum at the detection angle of 75 degrees. When the detection angle is 120 degrees, the spectral intensity of NⅠ 1 01146 nm and 1 05396 nm reaches peak. The biggest reason is that the intensity of infrared radiation in the air plasma shows a spatial asymmetry with the change of the detection angle, indicating that the spatial distribution of different particles in the air plasma is asymmetric.