Using a single-beam-CARS setup for the full characterization of the third-order susceptibility and elimination of strong two-photon excited fluorescence

Single-beam-CARS microspectroscopy exploits coherent control concepts for chemo-selective imaging[1]. One way to obtain vibrational information is the introduction of a narrowband phase gate by means of femtosecond laser pulse shaping [2-3]. This narrowband probing creates a weak multiplex CARS field that is amplified by an intrinsically generated local oscillator field (LO) by the rest of the spectrum. The interference between these two fields and the ability to control the phase of the narrowband gate (Fig. 1(a)) allows for the extraction of amplitude and phase of the multiplex CARS field [4]. Key in this process is the application of double quadrature spectral interferometry (DQSI) [5], which requires measurements of four different phases of the gate and is based on the sinusoidal dependence of the measured signal on the phase of the gate.