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

Abstract

The effects of the inhomogeneity of a time resolving CMOS single-photon avalanche diode array on the fluorescencesuppressed, 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.

Single-photon avalanche diode imagers in biophotonics: review and outlook

“…Further nonhomogeneity studies have been carried out by the same group, including by means of a 256×16 SPAD test array with two on-chip TDCs, leading to a detailed investigation of the effect of DCR and PDE as well as gate length variations and temporal skews. The latter can indeed play an increasing role, with growing design complexity, on the derivation of the Raman spectrum when targeting 100 ps accuracy levels [134,135]. In general, the spectra have been found to be subject to a larger deterioration, as could be expected, when the fluorescence lifetimes and levels get shorter and higher, respectively.…”