空气中激光支持爆轰波实验及理论分析

为了研究激光击穿空气产生的等离子体爆轰波形成机制和传播规律,利用高能量CO2激光器产生强激光,进行了空气中产生激光支持等离子体爆轰波实验。实验中:设置了诱导靶板,用于诱发和定位空气中的激光支持爆轰波;以激光器升压过程球隙放电产生的光信号作为触发源,触发高时间分辨率(纳秒级)的高速相机,记录了激光支持爆轰波的成长和传播全过程。分析了激光支持爆轰波的形成机理和传播规律。采用C-J爆轰理论,计算了激光支持爆轰波的压力和温度。研究结果表明:激光支持等离子体爆轰波形成初期,等离子体爆轰波发光体为球形;随着时间增加,等离子体爆轰波发光体的形状类似流星,且头部为等离子体前沿吸收层,亮度较高,而尾部等离子体温度较低,亮度较弱。等离子体爆轰波高速向激光源的方向移动,爆轰波速度高达18 km/s,温度约为107K。随着激光强度的减弱,爆轰波速度迅速按指数规律衰减,当爆轰波吸收的激光能量不能有效支持爆轰波传播时,爆轰波转变为冲击波。

Experimental and Theoretical Investigation on Laser Supported Detonation Waves in Air

For investigating the formation mechanism and propagation characteristics of the laser supported detonation waves, an experiment was designed and conducted. The laser supported detonation waves were generated in air atmosphere by focusing a 10.6 μm microsecond pulse from a CO₂ laser. In the experiment, a solid target was set to make the laser supported detonation wave ignition more easily and locate the laser supported detonation wave. The optical emission from the gap switch of the laser discharge tube was used to trigger the shutter of the high-time resolution (ns) camera, which was used to visualize the growing and propagation of the laser supported detonation regime spark. Formation mechanism and propagation characteristics of the laser supported detonation waves were analyzed, meanwhile the pressure and temperature behind the detonation front were calculated employing C-J detonation theory. In the initial stage of the breakdown, the detonation spark is spherical and transforms into meteoric shape in later time. The head of the meteoric body is the high-brightness and high-temperature plasma absorption layer, and the tail is low-brightness and low-temperature plasma. The laser supported detonation wave travels along the laser light channel toward the laser source. The temperature of the laser supported detonation waves was estimated to be 10⁷ K. The propagation speed was estimated to exceed 18 km/s in the initial stage of breakdown, and then exponential decays with time. The analysis indicated that laser supported detonation waves will transform into shock waves as the energy absorbed by the detonation front cannot sustain the propagation of the detonation waves.