In the present work, laser-induced plasma (LIP) of Mo is studied using both time and space resolved laser-induced breakdown spectroscopy (LIBS) in air as a function of incident laser energy. For this a second harmonic Q-switched Nd:YAG laser having pulse width of 7 ns and repetition rate of 1 Hz is used. The Boltzmann plot method is employed to estimate the plasma temperature of LIP using MoI and MoII lines separately. The stark-broadened profile of MoI-313.2 nm is exploited to measure the electron density. The temporal study in the time delay range of 0.5–5.0 μs shows that both the parameters, decay with the increase in delay time but increases with the increase in laser energy. It is observed that the plasma temperature estimated for MoII lines is higher than that of the MoI lines during the initial stage of plasma formation, delay time of 0.5–1.0 μs, but at a later time scale, both these species are found to possess nearly the same values of the temperature, indicating the coexistence of thermal equilibrium among the Mo atoms and ions in LIP. Therefore, in the second part of the experiment, time-integrated spatial evolution of the LIP of Mo is studied at a fixed delay of 2 μs as a function of axial distance normal to the target. It is found that emission intensity (MoI and MoII both), plasma temperature, and electron density initially increase with the increase in distance from the target, attains maximum value and then falls down. The Mc-Whirter criteria is applied to test the validity of local thermodynamic equilibrium (LTE). The relaxation time and diffusion length are estimated in time and space resolved studies respectively to take care of the transient and inhomogeneous nature of the LIP. The optical thin condition of LIP is verified by employing the branching ratio method. From these studies, a suitable spatio-temporal is identified where the LTE and optically thin plasma condition hold along with a high signal to noise ratio.

在当前的工作中，使用时间和空间分辨的激光诱导击穿光谱法（LIBS）在空气中作为入射激光能量的函数研究了Mo的激光诱导等离子体（LIP）。为此，使用脉冲宽度为7 ns，重复频率为1 Hz的二次谐波Q开关Nd：YAG激光器。分别使用MoI和MoII谱线，采用Boltzmann绘图法估算LIP的血浆温度。利用MoI-313.2 nm的明显增宽的轮廓来测量电子密度。在0.5–5.0μs的时间延迟范围内的时间研究表明，两个参数均随延迟时间的增加而衰减，但随激光能量的增加而增加。可以观察到，在等离子形成的初始阶段，MoII谱线的估计血浆温度高于MoI谱线的温度，延迟时间为0.5-1。0μs，但在较晚的时间尺度上，发现这两种物质都具有几乎相同的温度值，这表明LIP中Mo原子和离子之间存在热平衡。因此，在实验的第二部分中，研究了Mo的LIP的时间积分空间演化，其固定延迟为2μs，是垂直于目标的轴向距离的函数。可以发现，发射强度（MoI和MoII都），等离子体温度和电子密度最初随着与靶材距离的增加而增加，达到最大值，然后下降。Mc-Whirter标准适用于测试局部热力学平衡（LTE）的有效性。分别在时间和空间分辨的研究中估计了弛豫时间和扩散长度，以照顾到LIP的瞬态和非均质性。LIP的光学稀薄条件通过采用支化比方法来验证。从这些研究中，可以确定出合适的时空，其中LTE和光学上稀薄的等离子体条件以及较高的信噪比都可以保持。