In the present work, our main focus is to find out an optical window where the plasma is optically thin and the plasma parameters can be determined more reliably. The strontium plasma was generated using the fundamental (1064 nm) and the second harmonic (532 nm) of a Q-switched Nd:YAG laser. The spectra were registered using a set of five miniature spectrometers covering the spectral range from 200 to 720 nm. The intensity ratios of some specific lines have been compared with the theoretically calculated intensities to check the validity of optically thin plasma, free from self-absorption and in local thermodynamic equilibrium. In the selected optical window, the electron number densities have been determined from the Stark broadened line profiles, and the excitation temperatures have been calculated using the Boltzmann plot method for 1064- and 532-nm laser wavelengths. The variations in the electron number density and excitation temperature have been studied as a function of laser energy (8–100 mJ), atmospheric pressure (100–600 mbar), and spatial distribution of the plasma plume (0.5–4.0 mm) for both the lasers. The electron number density is found to be higher for the 532-nm laser than the 1064-nm laser, while the excitation temperature is higher for the 1064-nm laser than the 532-nm laser. We have fitted a power law on the experimental data to analyze the varying trends of excitation temperature.

中文翻译：

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Nd：YAG激光的基本和二次谐波光谱分析激光产生的锶等离子体

在当前的工作中，我们的主要重点是找到一个光学窗口，其中等离子体在光学上很薄，并且可以更可靠地确定等离子体参数。使用调Q的Nd：YAG激光器的基波（1064 nm）和二次谐波（532 nm）生成锶等离子体。使用一组五个微型光谱仪记录光谱，光谱仪覆盖200至720 nm的光谱范围。已将某些特定谱线的强度比与理论计算的强度进行了比较，以检查无自吸收且处于局部热力学平衡状态的光学薄等离子体的有效性。在所选的光学窗口中，已从Stark加宽的线轮廓确定了电子数密度，并使用Boltzmann绘图法计算了1064和532 nm激光波长的激发温度。研究了电子数密度和激发温度随激光能量（8–100 mJ），大气压力（100–600 mbar）和等离子羽流的空间分布（0.5–4.0 mm）的函数。激光。发现532-nm激光器的电子数密度高于1064-nm激光器，而1064-nm激光器的激发温度高于532-nm激光器。我们在实验数据上拟合了幂定律，以分析激发温度的变化趋势。两种激光器的等离子羽流（0.5-4.0 mm）的空间分布。发现532-nm激光器的电子数密度高于1064-nm激光器，而1064-nm激光器的激发温度高于532-nm激光器。我们在实验数据上拟合了幂定律，以分析激发温度的变化趋势。两种激光器的等离子羽流（0.5-4.0 mm）的空间分布。发现532-nm激光器的电子数密度高于1064-nm激光器，而1064-nm激光器的激发温度高于532-nm激光器。我们在实验数据上拟合了幂定律，以分析激发温度的变化趋势。