Enhanced laser-induced plasma spectroscopy (LIPS) by second-pulse selective wavelength excitation

工业中总是非常需要能够在可能的情况下以低成本进行快速、快速和原位化学分析的技术。近年来，激光诱导等离子体光谱（LIPS）技术已成为对各种材料进行实时光谱化学分析的重要工具。在传统的LIPS中，中等强度的激光脉冲聚焦在目标材料上，从撞击点排出少量的热明亮物质（等离子体）。然后用光谱仪对等离子体发出的辐射进行定性和定量分析。与其他现有技术相比，LIPS技术具有许多显著的优势，因为不需要样品制备，并且它允许远程和现场实时分析。然而，这些优点目前被较差的灵敏度所抵消，而不是用于检测微量元素的更繁琐的传统分析技术。该项目的目标是大幅度提高LIPS技术的灵敏度。为此，我们建议基本上使用两个激光脉冲，而不是像传统的LIPS那样只有一个。第一个脉冲产生等离子体，第二个脉冲共振激发等离子体内给定原子种类的特定量子水平。第二个激光脉冲的作用是增加感兴趣的原子种类的发射，以便于检测。在这个一般方案的框架内，我们还建议研究使用非常短的激励脉冲，以便使检测到的信号与背景辐射有更好的对比。该项目涉及来自一所大学（INRS）和一个政府实验室（NRC-IMI）的合作者，他们已经在LIPS上积极合作了几年，以及三家具有广泛工业兴趣的加拿大公司（INCO， Pharma Laser和Scintrex Trace）。由于这些公司已经与NRC-IMI合作参与了LIPS的短期实施，因此对它们来说，这个项目似乎是一个机会，可以比最初预期的规模更大地应用LIPS技术。

There is always a great need in industry for technologies that allow rapid, fast and in-situ chemical analysis at, if possible, low cost. Over recent years, the Laser-Induced Plasma Spectroscopy (LIPS) technique has become an important tool for real-time spectrochemical analysis of a wide variety of materials. In conventional LIPS, a moderately powerful laser pulse is focused onto a target material to expel a small amount of hot and bright matter (a plasma) from the impact site. The radiation emitted from this plasma is then analyzed by means of a spectrometer for qualitative and quantitative purposes. The LIPS technique has many striking advantages over the other existing techniques, since no sample preparation is required, and it allows remote and in-situ real time analysis. However, these advantages are currently outweighed by a poorer sensitivity than for the more cumbersome conventional analytical techniques for the detection of trace elements. The objective of this project is to increase substantially the sensitivity of the LIPS technique. For that purpose, we propose to use basically two laser pulses instead of only one as in conventional LIPS. The first pulse generates the plasma and the second pulse resonantly excites a specific quantum level of a given atomic species inside the plasma. The effect of this second laser pulse is to increase the emission of the atomic species of interest for an easier detection. In the framework of this general scheme we also propose to investigate the use of very short excitation pulses in order to allow a better contrast of the detected signal with the background radiation. The project involves collaborators from a university (INRS) and a government laboratory (NRC-IMI) who have been working actively on LIPS together for several years, as well as three Canadian companies (INCO, Pharma Laser, and Scintrex Trace) of wide industrial interest. Since these companies are already involved in short-term implementation of LIPS, in collaboration with NRC-IMI, this project appear to them as an opportunity to apply the LIPS technique on a much larger scale than expected initially.