Abstract

With Coherent anti-Stokes Raman scattering (CARS) microscopy and its ability to reflect the characteristic vibrational spectrum, three-dimensional images can be taken from unstained samples with chemical contrast. Due to the interference of CARS emission, the signal has a dependence on the squared number of Raman scatterers. While beneficial for majority chemical species, this poses difficulties for the detection of low concentrations. However, interfering the CARS signal with an auxiliary local oscillator (LO) field allows a more sensitive heterodyne detection with linear concentration dependence. The drawback commonly is a complex experimental setup, requiring that several laser beams be overlaid with wavelength precision.

© 2007 IEEE