Implementation of vibrational phase contrast coherent anti-Stokes Raman scattering microscopy.

Detection of molecules using vibrational resonances in the fingerprint region for narrowband coherent anti-Stokes Raman scattering (CARS) is challenging. The spectrum is highly congested resulting in a large background and a reduced specificity. Recently we introduced vibrational phase contrast CARS (VPC-CARS) microscopy as a technique capable of detecting both the amplitude and phase of the CARS signal, providing background-free images and high specificity. In this paper we present a new implementation of VPC-CARS based on a third-order cascaded phase-preserving chain, where the CARS signal is generated at a single (constant) wavelength independent of the vibrational frequency that is addressed. This implementation will simplify the detection side considerably.