Document Type : Research Paper

Authors

• A.H Farahbod
• M Afshari
• E Agayari

Abstract

In this paper, the behavior of temperature, density, velocity and pressure of the plasma shock front produced by the interaction of a focused Nd:YAG laser beam on a copper target, with an average pulsewidth of 30ns and 140mJ laser energy, have been studied using shadowgraphy technique. For this purpose, the plasma was examined in air at the pressure from 760 to 2×10^-4 Torr by a laser probe beam of 10 ns pulsewidth at the wavelength of 532 nm. The results obtained from the measurements and by using the hydrodynamical model indicated that at atmospheric pressure the temperature and plasma pressure near the target surface increase up to 30 eV and 7×10⁴ atm, respectively. The relative plasma density during the interaction time was found to be about 6 times of the air density at the normal atmospheric pressure. By decreasing the pressure from 760 Torr to 50 Torr the shock wave gradually converts to a rarefaction wave. For the pressure less than 0.1 Torr, only a dense region with an electron density higher than ≈3.94×10²¹ cm^-3 near the target surface was observed.

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Keywords

• Laser-Target Interaction
• Shock Wave
• Rarefaction Wave
• Shadowgraphy
• Ablation Pressure
• Hydrodynamical Model