209 / 2023-04-15 20:50:01

Characteristic of Plasma Plume Generated by Laser Irradiated Target

Plasma generated by laser irradiated target is used widely in many fields, such as ion source, chip fabrication, and material analysis. The plasma plume is researched by ICCD camera and spectrometer. The laser duration is 7.5 ns at the half maximum of the full width. The spot diameter is about 0.3 mm. The laser energy is from 30 mJ to 50 mJ. So the deposition energy density is about 5×10⁴ mJ/cm². The target is a Ta foil with 10 μm thick. The images taken by ICCD camera shows that the plasma plume is conical distribution. The light luminance is approximately proportional to the plasma density, which could represent the plasma density. The maximum light luminance appears at the peak of laser energy, and with the increase of laser energy, the appearance time is more and more advanced. When the laser energy disappears, no new plasma is generated on the target surface, the light luminance decreases and the plasma plume area increases. The plasma lifetime is about 300 ns. According to the position distribution of plasma plume at different times, it can be calculated that the expansion velocity decreases from 4cm/μs at the beginning to 1 cm/μs at the later stage, which is consistent with other literatures. The plasma emission spectra are measured by spectrometer. The spectra are mainly continuous, and some discrete spectra stand on the continuous ones. The continuous spectra come from the energy released by the recombination of free electrons and ions, while the discrete spectra come from the de-excitation process of excited Ta ions and atoms. Comparing the temporal spectral lines of different particles, the results show that Ta atoms appear first, and then high-density plasma is generated, and the spectral lines are mainly continuous. Until 15ns after the end of laser ablation, the plasma density decreases, and the spectral lines of Ta ions reach the peak. These results could help to understand the properties of laser plasma and improve its application.