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 m 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.