Spectral Characteristics of Ge Plasma Induced by Femtosecond Pulsed Laser Ablation
YAN Ming-liang1, ZHANG Chen-long2, ZHAO Lian-xiang3, ZHAO Hua-he4, GAO Xun2*
1. Non-Commissioned Officer School of Army Academy of Armored Forces, Changchun 130017, China
2. School of Physics, Changchun University of Science and Technology, Changchun 130022，China
3. The Second Military Representative Office of the Military Representative Bureau of the Army Equipment Department in Shenyang, Shenyang 110020，China
4. School of Opto-electronic Engineering, Changchun University of Science and Technology, Changchun 130022，China
Abstract：For the pulse width of a femtosecond laser is shorter than the electron-lattice thermal relaxation time of the medium, and the processes of femtosecond laser ablation and the dynamic process of plasma expansion are different from that of a nanosecond pulse laser, it is very important to study the emission spectrum characteristics of femtosecond laser-induced plasma for studying the femtosecond laser ablation mechanism and the femtosecond laser-induced plasma expansion dynamics. Ge material is commonly used for mid-far infrared detectors and optical components. In this paper, the processes of the temporal and spatial evolution of plasma emission spectroscopy intensity produced by femtosecond pulsed laser ablated Ge material with center wavelength of 800 nm and pulse width of 50 fs are studied in air, and the effect of laser pulse energy on plasma emission spectral intensity is discussed. The experimental results show thatthe Ge plasma emission spectrum induced by the femtosecond pulsed laser is mainly composed of line spectrum and continuous spectrum at the early stage of plasma plume expansion, and the continuous spectrum weakens gradually. In contrast,the line spectrum becomes dominating within the delay time of 200ns. With the rapid expansion of the plasma plume, the plasma emission spectral intensity increases first and then decreases with the delay time increasing, and plasma emission spectral intensity reaches the maximum at a delay time of 335 ns. With the distance increasingto the Ge target surface at the delay time of 335 ns, the plasma emission spectral intensity increases first and then decreases and reaches the maximum at a distance of 0.8 mm to the Ge target surface. In the process of plume expansion, the existence time of the ion spectrum line is shorter than that of the atom spectrum line. Due to the existence of the self-absorption mechanism of the plasma plume, the plasma emission spectral intensity increases with the increasing of femtosecond pulse energy. When the pulse energy is 0.627 mJ, femtosecond laser-induced Ge plasma has a self-absorption phenomenon, which decreasesthe plasma emission spectral intensity.
Key words：Femtosecond pulse laser; Ge plasma; Spectral characteristics; Self-absorption
[1] LIU Ze-jin, YANG Wei-qiang, HAN Kai, et al(刘泽金，杨未强，韩 凯，等). Chinese Journal of Laser（中国激光），2021, 48（12）：1201001.
[2] Chen J K, Tzou D Y, Beraun J E. International Journal of Heat and Mass Transfer, 2005, 48（3-4）: 501.
[3] PandeyP K, Thareja R K. Journal of Applied Physics，2011, 109：074901.
[4] Yang J J, Zhu X N, Liu W W. Chinese Physics B，2007, 16(7): 2003.
[5] ZHANG Xing-de, ZHAO Xiu-li, CHENG Yu-feng(张兴德，赵秀丽，程玉峰). Chinese Journal of Rare Metals（稀有金属），1988, (6): 447.
[6] Aragon C, Aguilera J A. Spectrochimica Acta Part B，2008, 63: 893.
[7] Wang Y, Chen A M, Zhang D, et al. Physics of Plasma，2020, 27: 023507.
[8] Yamagata Y, Sharma A, Narayan J, et al. Journal of Applied Physics，1999, 86(8): 4154.
[9] Harilal S S, Kautz E J, Jones R J, et al. Plasma Sources Science and Technology，2021, 30(4): 045007.
[10] Verhoff B, Harilal S S, Freeman J R, et al. Journal of Applied Physics，2012, 112：093303.
[11] DENG Fan, HU Zhen-lin, CUI Hao-hao, et al(邓 凡，胡桢麟，崔灏灏，等). Spectroscopy and Spectral Analysis(光谱学与光谱分析)，2021, 41（10）：2989.
