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Laser Ablation/Inductively Coupled Plasma/Atomic Emission Spectroscopy (LA-ICP-AES) Using a High-Resolution Fiber-Optic Interferometer

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Tech ID: 430
Project Overview
A high-resolution, compact, and portable interferometer system has been developed to provide isotopic and isobaric resolution and higher sensitivities for samples in complex matrices where detection limits are typically limited by low-level interferences. This system will be used in conjunction with solution nebulization and laser ablation (LA) inductively coupled plasma-atomic emission spectroscopy (ICP-AES) for analysis of environmental and process samples. The technology involves the use of an acousto-optic tunable filter (AOTF) and a high-finesse fiber-optic Fabry-Perot interferometer (FFP), two devices developed by the communications industry for high bandwidth laser communications. The small size, extreme ruggedness, and spectral ability of these devices make them well-suited for use in a fieldable spectrometer system at a fraction of the cost, size, and weight of grating-based spectrometer systems. The AOTF is used as a low resolution filter to select spectral regions to be resolved by multiple FFP filters. The AOTF is capable of switching between spectral regions in microseconds with no mechanical moving parts, and is also capable of simultaneous selection of several spectral regions.
Technology Description
The AOTF-FFP is a compact, solid-state, high-resolution spectrometer system that is capable of resolving isotopic and isobaric emission features in ICP-AES. Commercial ICP-AES spectrometer systems lack sufficient resolution to distinguish isotopes of actinide elements such as uranium, thorium, and plutonium. Commercial ICP-MS systems are subject to isobaric interferences, i.e., the inability to distinguish isotopes having the same atomic mass number. The compact size and stability of the AOTF-FFP system make it particularly well-suited for use in remote and field analytical applications. The AOTF-FFP spectrometer system may be used in LA - ICP-AES analyses of contaminated soil samples to provide rapid, on-site quantitative determinations. The AOTF-FFP may also be used for spectrometric measurements in on-line process environments where high resolution is required.

A single AOTF accesses a 200 nm range of emission features. The bandwidth of the AOTF (~1,000 GHz) and the desired spectral resolution (~5 GHz) determined the specifications for the FFP (finesse=200) that was developed to scan the spectral window defined by the AOTF. The optical coatings used in the FFP do not cover the entire region accessed by the AOTF. Therefore, a system with full access at high resolution must utilize several FFPs, with a single AOTF for prefiltering and low-resolution survey scanning. The FFP technology had previously been developed for red and near infrared wavelengths. For this project, an FFP for use in the 400 nm (blue) wavelength region has been developed in collaboration with Micron Optics, Inc. (Atlanta, GA). The AOTF-FFP system has been used to resolve uranium isotope emission features.

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