Swayambunathan V, Singh G, Sausa R C
Appl Opt. 1999 Oct 20;38(30):6447-54. doi: 10.1364/ao.38.006447.
Trace concentrations of energetic materials such as 2, 4, 6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), and hexahydro-1, 3, 5-trinitro-s-triazine (RDX) are detected by laser photofragmentation-fragment detection (PF-FD) spectrometry. In this technique, a single laser operating near 227 nm photofragments the parent molecule and facilitates the detection of the characteristic NO fragment by means of its A (2)Sigma(+)-X (2)Sigma (0, 0) transitions near 227 nm. Fragment detection is accomplished by resonance-enhanced multiphoton ionization with miniature electrodes and by laser-induced fluorescence (LIF) with a photodetector. Experiments are also conducted in the visible region by use of 453.85-nm radiation for photofragmentation and fragment detection. Sand samples contaminated with PETN and RDX are analyzed by a pyrolysis-LIF technique, which involves pyrolysis of the energetic material with subsequent detection of the pyrolysis products NO and NO(2) by LIF and PF-LIF, respectively, near 227 nm. The application of these techniques to the trace analysis of TNT, PETN, and RDX at ambient pressure in room air is demonstrated with limits of detection (signal-to-noise ratio, 3) in the low parts-in-10(9) to parts-in-10(6) range for a 20-s integration time and 10-120 microJ of laser energy at 226.8 nm and approximately 5 mJ at 453.85 nm. An increase in detection sensitivity is projected with an increase in laser energy and an improved system design. The analytical merits of these techniques are discussed and compared with those of other laser-based techniques.
通过激光光致碎裂-碎片检测（PF-FD）光谱法可检测到痕量浓度的高能材料，如2,4,6-三硝基甲苯（TNT）、季戊四醇四硝酸酯（PETN）和六氢-1,3,5-三硝基-s-三嗪（RDX）。在该技术中，一台工作在227 nm附近的单激光将母体分子光致碎裂，并通过其在227 nm附近的A(2)Σ⁺-X(2)Σ(0,0)跃迁来促进对特征性NO碎片的检测。碎片检测通过使用微型电极的共振增强多光子电离以及利用光电探测器的激光诱导荧光（LIF）来完成。还利用453.85 nm辐射在可见光区域进行光致碎裂和碎片检测实验。对受PETN和RDX污染的沙子样品采用热解-LIF技术进行分析，该技术包括对高能材料进行热解，随后分别通过LIF和PF-LIF在227 nm附近检测热解产物NO和NO₂。在室温空气中，将这些技术应用于TNT、PETN和RDX的痕量分析，在226.8 nm处激光能量为10 - 120 μJ、453.85 nm处约为5 mJ、积分时间为20 s的情况下，检测限（信噪比为3）在10⁻⁹至10⁻⁶范围内。预计随着激光能量的增加和系统设计的改进，检测灵敏度会提高。讨论了这些技术的分析优点，并与其他基于激光的技术进行了比较。
