CMOS and CCD detection in Raman spectroscopy: a comparison using spontaneous and multiplex coherent anti-Stokes Raman scattering (CARS)

Cooled CCD cameras are used widely in spectroscopy, mainly due to their sensitivity and low noise operating under low light conditions, and relatively high image and spectral readout rates. Despite their many advantages, CCD cameras have limitations. Particularly under bright light conditions, such as those encountered with coherent Raman spectroscopies, where the finite readout time of CCD chips is limiting. Furthermore, where weak signals need to be observed close to intense signals, blooming and smearing limit the signal to noise ratios achievable. Scientific complementary mixed oxide (sCMOS) based sensors are relatively new. Although they still show much higher readout noise than cooled CCDs, their application to spectroscopy is certainly of interest given the higher readout rates, and dynamic ranges possible. Here, we evaluate sCMOS sensors for specific spectroscopic applications, including multiplex (50 picosecond) CARS and spontaneous Raman spectroscopy. We compare the performance of a sCMOS based camera to a state-of-the-art (EM)CCD detector for these applications. The EMCCD camera outperforms the sCMOS camera in terms of limits of detection, while the sCMOS camera performs better than the CCD in terms of dynamic range and readout rate. Importantly, sCMOS camera does not suffer from interference due to blooming and smearing seen with CCD cameras, which enables observation of weak bands (e.g., Raman overtones) close to much more intense signals. Here we show that, at moderate readout rates, the relative performances of the two detector types are not substantially different. We anticipate that sCMOS based cameras will find application for bright spectroscopies, such as multiplex CARS, as well as spontaneous Raman spectroscopy, and Raman spectral imaging.