Xie has significantly improved the use of coherent anti-Stokes Raman scattering (CARS) for microscopy of living cells. This technique utilized vibrational spectroscopy as the contrast mechanism, concurrently allowing identification of chemical species with the imaging. The new CARS microscope utilizes simultaneous forward and epidetection of the scattering enabling fast data acquisition and high sensitivity. Xie has exploited these improvements to image cells undergoing apoptosis, or programmed death. For example, he is able to visualize the formation of lipid vesicles in the cytoplasm when the CARS microscope is tuned to the C-H stretching vibration.