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, low noise 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, the finite readout time of CCD chips becomes limiting. Furthermore, when 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 of interest given the higher readout rates and dynamic ranges possible. Here, we evaluate sCMOS sensors for multiplex (50 ps) CARS and spontaneous Raman spectroscopy, making a direct comparison with a state-of-the-art EM-CCD detector. The EM-CCD 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, an 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 readout rates > 20-50 Hz, the 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.