Highly Sensitive Vibrational Imaging by Femtosecond Pulse Stimulated Raman Loss.

Nonlinear vibrational imaging of live cells and organisms is demonstrated by detecting femtosecond pulse stimulated Raman loss. Femtosecond pulse excitation produced a 12 times larger stimulated Raman loss signal than picosecond pulse excitation. The large signal allowed real-time imaging of the conversion of deuterated palmitic acid into lipid droplets inside live cells, and three-dimensional sectioning of fat storage in live C. elegans. With the majority of the excitation power contributed by the Stokes beam in the 1.0 to 1.2 μm wavelength range, photodamage of biological samples was not observed.