Development of an underwater combined Raman-fluorescence detection system and preliminary test

A variety of chemosynthetic micro-organisms inhabit the deep sea hydrothermal vent environments. Steep chemical and thermal gradient, rapid and turbulent mixing and biological processes produce a multitude of diverse mineral phases. Raman spectrometer system is well suited to mineral speciation measurements and has been successfully used for the detection in deep sea hydrothermal environments so far. However, to further understand the interaction of mineral and microbial processes, a Raman system optimized for mineral identification that incorporates a fluorescence for microbial processes is needed. In order to meet the requirement of deep sea hydrothermal research, a new compact spectroscopy Raman-fluorescence combined system prototype was presented. The combined system was composed of a double wavelength laser which can emit both 532 nm and 266 nm wavelength, the 532 nm wavelength was used for Raman spectroscopy excitation, and the 266 nm wavelength was used for fluorescence excitation, and two miniature optical fiber spectrometer. The double wavelength laser beam was split into two paths according to the wavelength and entered into the seawater or liquid solution by different quartz window. The produced Raman and fluorescence signals were collected by a back-scattering optical set-up and coupled into Raman spectrometer and fluorescence spectrometer separately. The whole system was housed in a L790 mm270 mm capsule with an optical window on the end, and the computer, power were also contained into it. The power supply, system control, and signal delivery were provided through an 8 pins cable. Systematic experiments had been carried out with seawater and pseudo-nitzschia samples in laboratory. The results show that the Raman and fluorescence spectra could be obtained simultaneously with moderate sensitivity. Some experiment results ware acquired at Qingdao coast. It is hoped this prototype could be fully developed in hydrothermal area detection in the near future.