Abstract

In recent years, Raman spectroscopy techniques have been successfully applied to the area of deep-sea exploration. However, there are still some problems impeding the further application of Raman systems. For example, the large size of an underwater Raman system makes it difficult to deploy on the underwater vehicle. Meanwhile, the sensitivity is often a disadvantage, requiring improvement for detecting more trace components. To solve these problems, a new compact deep-sea in situ Raman spectroscopy system is presented in this paper. The whole system weighs 60 kg and is housed in an L$800\mathrm{mm}\times \mathrm{\varphi }258\mathrm{mm}$ pressure vessel with an optical window on the front end cap. The main components include a 532 nm Nd:YAG laser, an optics module, a high-throughput spectrograph with $0\sim 4900{\mathrm{cm}}^{-1}$ spectral range and $8{\mathrm{cm}}^{-1}$ spectral resolution, a TEC-cooled $2000\text{pixel}\times 256\text{pixel}$ CCD detector, a PC104 embedded computer, and an electronics module. To evaluate the performance of the newly developed Raman system, systematic experiments have been carried out with solutions in laboratory, and the results have shown that the system limit of detection of ${\mathrm{SO}}_4^{2-}$ is 0.4 mmol/L. The Raman system has been successfully deployed on a remote-operated vehicle on the Kexue research vessel in June 2015. The typical in situ detection results are presented in this paper, and it is shown that the Raman system is capable of detecting the Raman signal of ${\mathrm{SO}}_4^{2-}$ and fluorescence of chlorophyll a (chl-a) and chromophoric dissolved organic matter (CDOM) in seawater. With 500 spectra accumulations and some data processing, the Raman signal of ${\mathrm{HCO}}_3^{-}$ is obtained. This is the first report of direct measurement of ${\mathrm{HCO}}_3^{-}$ by Raman system in in situ experiments. After further optimization, it is hoped to apply the Raman system in seafloor observation networks for long-time carbon cycling research.

© 2019 Optical Society of America

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