Experimental Study On Impulse Coupling Coefficient During TEA CO₂ Laser Ablating Aluminum

A counteracting force can be delivered to the solid targets by the plasmaexpansion generated during the interaction between laser and solid targets. Applingthis phenomenon to propulsion field, a new type of propulsion method can generatewhich is able to replace conventional chemical propulsion. Basing on the backgroundof laser propulsion, the effect of laser flux, environment air pressure and the surfacestructure of solid targets on the impulse coupling coefficient during the interactionbetween laser and solid targets is studied in this paper.The rule of impulse coupling coefficient at different focal shift conditions isstudied by ablating aluminum targets using focused laser, with the laser flux changing.Results show that, with laser flux rising, the impulse coupling coefficient rises firstlyand then falls down. The impulse coupling coefficient reaches the maximum when thelaser flux is 2.96×10⁶W/cm². The two-dimensional model theory of laser supporteddetonation wave interacting with solid target is used to calculate the couplingcoefficient, and the reason of disagreement between theoretical results andexperimental results is given.The effect of environment air pressure on impulse coupling coefficient is studiedby ablating aluminum targets using laser at the air pressures of 100.0kPa,49.0kPa,20.0kPa,0.1kPa respectively. Results show that the relationship between laser fluxand impulse coupling coefficient are similar at air pressures of 100.0kPa,49.0kPa,20.0kPa, what's different is that the laser flux corresponding to maximal impulse coupling coefficient falls down with air pressure rising. The impulse couplingcoefficient value at air pressure of 0.1kPa is smaller than that of other pressuresclearly.To study the effect of target surface structure on the impulse coupling coefficient,the aluminum target is painted, and then both surfaces of the targets, one is paintedwhile the other is not, is ablated by laser. Results show that, for the laser flux1.31×10⁷ W/cm² and 4.99×10⁶W/cm² in this paper, the coupling coefficients ofunpainted targets are higher than the painted targets, and the differences becomelarger when laser flux becomes smaller. The thickness of the paint has little effect onthe impulse coupling coefficient at the range of 0.201mm～0.968mm.Also experiment of HF laser ablating aluminum targets is conducted in this paper,compared with TEA CO₂ laser. And the reason of different principles of impulsecoupling coefficient at the two conditions is presented.