The Study On The Temporal And Spatial Evolution Characteristics Of Femtosecond Laser-Induced Zn Plasma Emission Spectroscopy

The laser-induced plasma is generated by focusing a high power density pulsed laser beam on a sample surface. It has its unique advantages in application, such as it does not need contact with the sample directly, and the samples need not pretreatment, and it can be used to analyze the various elements at the same time, and it has low limit of detection, and minimal damage to the samples. With its unique advantages, it is widely used in biology, chemistry, plasma physics and atomic and molecular physics and so on. Its dynamics is very complex. So in order to have better application of this technology, it is necessary to carry out more in-depth study. The laser induced plasma is produced by laser ablation target material, so the laser characteristics(such as wavelength, frequency, energy density), the physical characteristics of the target(such as species and temperature) and the buffer gas environment(such as ingredient and pressure and temperature)have an impact on the process of the plasma generation. Electron temperature, electron density and the spectral shifts are important physics parameters. We can use these parameters to describe the dynamic characteristics of plasma. For have a better study to the kinetics, we used the technology of laser-induced plasma emission spectrometry in our experiments.In this paper, the laser-induced Zn plasma are produced respectively by using a femtosecond laser beam at 800 nm wavelength and 1000 Hz repetition rate and 100 fs pulse duration. 1. By observing the time evolution of plasma, we can find in initial time the continuous spectra appear, and disappear within 100 ns. Then the characteristic spectrum is generated in 30 ns with the continuous spectra, and at 150 ns reaches to its maximum intensity, and finally disappear at 1500 ns. Owing to the different upper energy level transition probability of the corresponding spectra, the line intensity of Zn 481.0nm is maximum, the line 472.2nm is second and the 468.0nm minimum. The electron density is at the 1016cm-3 orders of magnitude and the temperature is within the range of 4990K-6769K; the red shift of 481.0nm can be observed until 300 ns with a maximum of 0.23nm; through making the relation curves between line shift and the electron density, as well as between line shift and electron temperature, it is found that line red shift is approximately in linear relationship with electron density, and is positively correlated with temperature electron. 2. Meanwhile the spectra special evolutions were measured. The plasma is symmetric diffusion in parallel direction of the target within the range of 1.2mm and is in the range of 1.8mm at the laser beam direction, the diffusion range at the laser beam direction is larger than in parallel direction. The spatial distribution of the plasma can be regarded as an ellipse approximately. 3. Changing the laser pulse energy, the plasma spectra were acquired at 1.10 mJ, 1.35 mJ and 1.70 mJ respectively. The experimental results showed that with the energy increases, the plasma intensity increases, the corresponding maximum intensity of Zn 481.0nm is 10663 a.u, 7534 a.u, 8417 a.u respectively at 1.10 mJ, 1.35 mJ and 1.70 mJ,respectively. At this time the gap of the spectral intensity is the largest. The gap of intensity is decreases with time delay, and then the intensity are almost equal under three energy at 850 ns. They are 278 a.u, 137 a.u, and 143 a.u. respectively. The electron temperature and density are all increasing with the laser energy increasing. Plasma parameters(electron temperature and electron density) are positively correlated with the laser energy. In space, the intensities corresponding to the same position also increase with the energy increases, but distributing characteristics of the plasma intensities are invariant and can be regarded as an ellipse approximately. 4. Changing the background pressure ranging from 10 Pa to 1.0 * 105 Pa, the experimental results showed that the plasma intensity increased with the pressure increasing. The intensity at 105 Pa is nearly 6 times larger than that at 10 Pa,. So the pressure has a great influence on the laser induced plasma. The plasma rapidly disappear without environmental obstacles at 10 Pa. Meanwhile, the electron temperature and density are increase with the pressure increasing.