Effects of the inhomogeneity of the time resolving CMOS single-photon avalanche diode array on time-gated Raman spectroscopy

The effects of the inhomogeneity of a time resolving CMOS single-photon avalanche diode array on the fluorescence-suppressed, time-gated, Raman spectroscopy device was experimentally studied here. Raman spectroscopy device using a 532 nm pulsed laser and a single time resolving single-photon avalanche diode (SPAD) with a micro step motor was developed to study these effects. A single SPAD with a step motor allows us to test the performance which could be achieved with an ideal line detector without any nonlinearities and inhomogeneities because the same SPAD and time interval measurement unit is used in every spectral point. Additionally, the single element can be replaced by a SPAD array with an on-chip time-to-digital converter (TDC) to make comparison measurements to clarify the effects of inhomogeneity. These comparison measurements were made by using an array of 256 elements with an on-chip 100 ps TDC and showed that the deterioration of Raman spectra is larger when fluorescence lifetimes and levels are shorter and higher, respectively.