Elimination of Strong Two-photon Excited Fluorescence Using a Single-beam-cars Setup[1]

Nonlinear microscopy techniques are highly appreciated for imaging applications. Second harmonic generation (SHG), two-photon fluorescence (2PEF) and coherent anti-Stokes Raman scattering (CARS) are examples that show well known advantages like intrinsic sectioning capability and chemical selectivity. However, often different contributions, especially 2PEF and CARS, spectrally overlap which makes the interpretation of each of them difficult. We present in our contribution two schemes to eliminate 2PEF contributions from CARS measurements using single-beam -setup, where only one broadband laser pulse is used that is shaped by means of a dispersion-free 4f-line and a spatial light modulator in its Fourier plane. [2] The single-beam-CARS approach we use here is multiplexing[3-4], where a narrowband feature is introduced in the excitation spectrum acting as probe, creating a conventional CARS spectrum that is amplified by an intrinsically created local oscillator.[5] This local oscillator is coherent to the CARS signal but not to the 2PEF contribution, which is the basis for an elimination of it. Our contribution includes a theoretical analysis of the signal generation, simulations and measurements on a model system consisting of acetonitrile and the laser dye DCM.