The photodamage in coherent anti-Stokes Raman scattering (CARS) imaging of spinal tissues is featured by plasma-induced myelin splitting and shockwaves. When the excitation is tuned on resonance with the symmetric stretch vibration, the average point-scanning time to cause the photodamage is reduced by half. Similar Raman resonance-enhanced photodamage is also observed for a polymer film. The light–matter energy transfer in coherent Raman processes with both plane waves and focused excitation beams is analyzed to interpret this phenomenon. Our calculation indicates that at Raman resonance, a significant vibrational absorption in the material can be stimulated by the concomitant Raman gain and Raman loss processes due to high incident-field intensities under a tight-focusing condition. As a result, while the nonlinear damage induced by multiphoton absorption can be diminished in CARS microscopy owing to the use of near-infrared picosecond pulses, the coherent Raman-induced vibrational pumping is able to enhance the photodamage by assisting plasma generation in the material.
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