Concentration dependence of femtosecond coherent anti-Stokes Raman scattering in the presence of strong absorption (original) (raw)
2007, Journal of The Optical Society of America B-optical Physics
We study near-resonant femtosecond coherent anti-Stokes Raman scattering (CARS) of dipicolinic acid (DPA) by exciting the molecular system with a pair of visible pump and Stokes pulses and probing the resultant molecular coherence with a time-delayed UV probe pulse. We record the generated Stokes and anti-Stokes pulse energies as functions of DPA concentration. We observe that the CARS signal has a maximum and the powerlaw dependence is steeper than the well-known quadratic one. We present a model that describes the propagation of the generated signal through the medium. From this model, we derive an analytical expression that closely agrees with our experimental data. Since DPA serves as a marker molecule for bacterial spores, our results help to establish the detectability limits for a lethal spore dosage when the present technique is applied.
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