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首页> 外文会议>High-Power Laser Ablation VI pt.1 >Absorption Waves Produced by CO_2 Laser Ablation
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Absorption Waves Produced by CO_2 Laser Ablation

机译：CO_2激光烧蚀产生的吸收波

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A requirement for efficient pulsed laser propulsion from ground to LEO is the achievement of a specific impulse of up to 800 s at a jet efficiency of at least 50%. With CO_2 laser radiation at pulse lengths in the range of 10 microseconds and polymers as propellant these numbers cannot be attained by classical laser ablation because the impulse formation by laser ablation is limited by the premature absorption of the incident laser radiation in the initially produced cloud of ablation products. The power fraction of a CO_2 laser pulse transmitted through a small hole in a POM sample has been compared with the incident power. It was found that the transmitted power fraction is directly proportional to the inverse of the pulse energy. The plasma formation in vacuum and in air of 3500 Pa and the spread of the shock wave with velocities of 1.6 to 2.4 km/s in the low pressure air was observed by Schlieren photography. A sharp edged dark zone with a maximum extension of 10 to 12 mm away from the target surface develops within 5 μs independently of the pressure and is assumed to be a plasma. In order to find out, if this is also the zone where the majority of the incident laser radiation is absorbed, a CO_2 probe laser beam was directed through the expansion cloud parallel to and at various distances from the sample surface. The front of the absorption zone is found to move rapidly away from the target surface with increasing speed. The absorption lasts twice as long as the laser pulse. It is not associated with a pressure rise that would increase the mechanical impulse. The radial motion of the absorption wave turned out to be faster than the shock wave seen in the Schlieren pictures.
机译：从地面到LEO的有效脉冲激光推进的要求是，在至少50％的喷射效率下，实现高达800 s的比脉冲。在脉冲长度在10微秒范围内的CO_2激光辐射和聚合物作为推进剂的情况下，经典的激光烧蚀无法获得这些数字，因为通过激光烧蚀形成的脉冲受到初始产生的云雾中入射激光辐射过早吸收的限制。消融产品。已将通过POM样品中小孔传输的CO_2激光脉冲的功率分数与入射功率进行了比较。已经发现，发射功率分数与脉冲能量的倒数成正比。通过Schlieren摄影观察到在3500 Pa的真空和空气中的等离子体形成以及低压空气中1.6至2.4 km / s的冲击波传播。与目标表面的最大延伸距离为10至12 mm的尖锐边缘暗区在5 s内独立于压力而发展，并被认为是等离子体。为了找出，如果这也是大部分入射激光辐射被吸收的区域，则将CO_2探针激光束平行于样品表面并以不同距离引导通过膨胀云。发现吸收区的前部以增加的速度迅速远离目标表面移动。吸收持续时间是激光脉冲的两倍。它与会增加机械脉冲的压力上升无关。事实证明，吸收波的径向运动要比在Schlieren图片中看到的冲击波快。

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