Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA.
Rapid Commun Mass Spectrom. 2012 Sep 30;26(18):2145-50. doi: 10.1002/rcm.6331.
Laser ablation is widely used in conjunction with ambient ionization techniques, and a fundamental understanding of the mechanism of material removal is important to its optimal use in mass spectrometry. Finite element analysis simulates the laser material interaction on larger time and distance scales than atomistic approaches. Here, a two-dimensional finite element model was developed to simulate infrared laser irradiation of glycerol using a wavelength-tunable infrared (IR) laser.
The laser fluence used for the simulations was varied from 1000 to 6000 J/m(2), the wavelength was varied from 2.7 to 3.7 µm, and both flat-top and Gaussian shape laser profiles were studied.
Phase explosion conditions were found for laser wavelengths near 3 µm (which corresponds to the OH stretch absorption of glycerol) and fluences above 2000 J/m(2). This suggests that laser ablation of glycerol is driven by phase explosion in the OH stretch region. The Gaussian profile generated regions of higher glycerol temperature, whereas the flat-top profile heated a larger volume of material above the phase explosion temperature.
These results suggest that the best performance for pulsed IR laser sample irradiation is in the wavelength range from 2.9 to 3.1 µm for materials with a strong OH stretch absorption.
激光烧蚀广泛应用于环境电离技术，对材料去除机制的深入了解对其在质谱分析中的最佳应用至关重要。有限元分析在比原子级方法更大的时间和空间尺度上模拟激光与材料的相互作用。在此，开发了一个二维有限元模型，用于模拟使用波长可调谐红外（IR）激光的甘油的红外激光辐照。
模拟中使用的激光通量从 1000 到 6000 J/m(2) 变化，波长从 2.7 到 3.7 µm 变化，同时研究了平顶和高斯形状的激光轮廓。
在接近 3 µm 的激光波长（对应于甘油的 OH 伸缩吸收）和超过 2000 J/m(2) 的通量下，发现了相爆炸条件。这表明甘油的激光烧蚀是由 OH 伸缩区的相爆炸驱动的。高斯轮廓产生了更高的甘油温度区域，而平顶轮廓则在相爆炸温度以上加热了更大体积的材料。
这些结果表明，对于具有强 OH 伸缩吸收的材料，脉冲 IR 激光样品辐照的最佳性能在 2.9 到 3.1 µm 的波长范围内。
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