Depth Analysis of Semi-Transparent Media by a Time-Correlated CMOS SPAD Line Sensor-Based Depth-Resolving Raman Spectrometer

Raman spectroscopy has proved to have potential in deep surface analytical applications. We present here, to the best of our knowledge, the first time depth analysis of semi-transparent media by a depth-resolving Raman spectrometer based on an adjustable time-correlated CMOS SPAD (single-photon avalanche diode) line sensor that can measure the depth of target samples embedded in a centimeter-scale semi-transparent medium simultaneously with a normal Raman depth profiling operation and suppress the fluorescence background by means of adjustable picosecond time gating. The variability of the depth derivation was measured to be ± 0.43 cm at depths ranging from 2 to 9 cm. In addition, the advantages of the adjustable picosecond time gating in terms of depth derivation and fluorescence background suppression performance were shown by comparing gate widths ranging from 100 ps to 13 ns. We believe that the technology concerned could pave the way for a new kind of compact, practical depth-resolving Raman spectrometer for deep subsurface analytical applications.