Remote analysis of deep sea objects by LIBS

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  • Published: Mar 4, 2015
  • Author: Steve Down
  • Channels: Atomic
thumbnail image: Remote analysis of deep sea objects by LIBS

A system for the remote analysis of submerged objects in the sea by laser-induced breakdown spectroscopy has been designed by scientists in Spain. In the proof-of-principle studies, they analysed objects which were positioned 80 cm from the sensor and claim that this setup would work at depths of 3500-4000 m as described in Journal of Analytical Atomic Spectrometry.

The system builds on an earlier LIBS system which the same team designed for deployment on a submarine for the characterisation of underwater objects at shallow depths. It was controlled from a vessel on the surface while a professional diver operated the LIBS probe. The main target field of work is archaeological exploration and it was demonstrated for objects consisting of bronze, ceramics, meals and precious alloys as well as bones.

In the novel stand-off LIBS system, the aim is to analyse objects at greater distances using a remotely operated vehicle. This was achieved with the dual pulse laser to deliver focused pulses through the water towards the target before detecting the reflected light after focusing by a quartz lens. The first laser pulse interacts with the submerged object to remove small amounts of matter, forming a cavitation bubble which begins to expand. The arrival of the second laser pulse after an optimised delay expands the plasma inside the bubble to give intense and well-resolved emission signals that were detected by a spectrometer.

The signal intensity falls as the temperature of the sea drops at greater depths but the researchers calculated that it would still be operable down to 3500-4000 m, equivalent to a temperature of 2°C. At lower temperatures, the signal would fail. At these depths, the path length of the laser would need to be between 10 and 80 cm, the shorter the better to give higher resolution.  

Due to the highly challenging nature of this application, the research team declared that this work could be regarded as a new LIBS frontier. It holds promise for other areas of underwater exploration apart from archaeology, such as geology, mineralogy and inspecting pipelines on the sea floor.

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