A Multitime-Gated SPAD Line Detector for Pulsed Raman Spectroscopy

A time-gated 2 × (4) × 128 single photon avalanche diode line detector for pulsed laser Raman spectroscopy has been developed and fabricated in a 0.35-μm high-voltage CMOS technology. The sample is illuminated with short laser pulses (~100 ps) at a rate of ~50 kHz and four time gates synchronized with these pulses and having selectable widths within the subnanoseconds range are used to measure the Raman photons and fluorescence background simultaneously. The fluorescence background measurement is used to suppress the residual fluorescence level to improve the quality of the Raman spectrum. The variation in the width of the time window was measured to be approximately ±17.5 ps along the spectral axis when set externally to a nominal value of 100 ps. Measurements with a reference sample demonstrate the effect of nonhomogeneities in the time gates on the quality of the recorded Raman spectrum and the residual fluorescence correction.