[Water Raman spectrum suppression with low-pass filter in underwater in-situ Raman spectroscopy]

As a powerful tool for studying chemical structures, Raman spectroscopy has been used in aquatic environments in-situ measurement widely, and has been used in deep sea research recently. For underwater in-situ detection, O-H vibration Raman peak of water is inherent and strong compared with other dissolved matter's Raman signals. When the authors want to get a good SNR Raman signal of dissolved matter by increasing detection time, O-H vibration Raman peak of water will get to saturation easily, which influences other Raman signal's detection. In the present paper, a specially designed short-pass optical filter was used for suppression of water's O-H vibration Raman peak. The authors calculated the suppression effect of short-pass optical filter with linear and exponential edges. The simulation shows that exponential edge filter has better performance and can suppress water's O-H vibration Raman peak effectively. The experiment also proves the calculation results. With the suppression optical filter, the intensity of water's O-H vibration Raman signal and other dissolved matters' become similar. And the influence of suppression optical filter on other dissolved matters' Raman signal is little. So the suppression optical filter is feasible for in-situ underwater Raman spectroscopy.