title: Femtosecond pulse shaping enables detection of optical Kerr-effect (OKE) dynamics for molecular imaging.
abstract: We apply femtosecond pulse shaping to generate optical pulse trains that directly access a material's nonlinear refractive index (n2) and can thus determine time-resolved optical Kerr-effect (OKE) dynamics. Two types of static pulse trains are discussed: The first uses two identical fields delayed in time, plus a pump field at a different wavelength. Time-resolved OKE dynamics are retrieved by monitoring the phase of the interference pattern produced by the two identical fields in the Fourier-domain (FD) as a function of pump-probe-time-delay (where the probe is one of the two identical fields). The second pulse train uses three fields with equal time delays, but with the center field phase shifted by π/2. In this pulse scheme, changes on a sample's nonlinear refractive index produce a new frequency in the FD signal, which in turn yields background-free intensity changes in the conjugate (time) domain and provides superior signal-to-noise ratios. The demonstrated sensitivity improvements enable, for the first time to our knowledge, molecular imaging based on OKE dynamics.
authors.forename: Francisco E
authors.initials: FE
authors.lastname: Robles
authors.forename: Martin C
authors.initials: MC
authors.lastname: Fischer
authors.forename: Warren S
authors.initials: WS
authors.lastname: Warren
mesh_terms: D000465:Algorithms; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D057054:Molecular Imaging / Q000379:methods*; D012815:Signal Processing, Computer-Assisted