Laser raman spectroscopic instrumentation for in situ geochemical analyses in the deep ocean

Abstract

Engineers and scientists at the Monterey Bay Aquarium Research Institute (MBARI) have successfully developed instrumentation for performing laser Raman spectroscopy in the deep ocean. Laser Raman spectroscopy is a form of vibrational spectroscopy that is capable of performing rapid, nondestructive, in situ geochemical analyses. The Deep Ocean Raman In Situ Spectrometer (DORISS) is based on a laboratory model laser Raman spectrometer from Kaiser optical systems, Inc. The sample is interrogated by a 532 nm laser and the Raman backscattered radiation passes through a holographic grating and is recorded on a CCD camera. Laser Raman spectroscopy is capable of analyzing a variety of solid, liquid and gaseous species. Due to the strict requirements for positioning the laser focal point when analyzing opaque samples, a Precision Underwater Positioning (PUP) system was built to position the DORISS probe head with respect to the sample. PUP is capable of translating the DORISS probe head in 0.1 mm increments with 1 mm repeatability. DORISS and PUP are deployed by MBARI's remotely operated vehicles - ROVs Tiburon and Ventana - and are controlled by a scientist aboard the surface ship. DORISS and PUP have been deployed a number of times in Monterey Bay, the Gulf of California, and Hydrate Ridge, Oregon for testing and analyses of natural targets of interest. The development of smaller, second generation systems will allow DORISS and PUP to be carried on other deep submergence vehicles for use by the wider oceanographic community.