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 power-law 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.
© 2007 Optical Society of America
Original Manuscript: October 20, 2006
Revised Manuscript: January 17, 2007
Manuscript Accepted: January 22, 2007
Published: April 17, 2007
Miaochan Zhi, Dmitry Pestov, Xi Wang, Robert K. Murawski, Yuri V. Rostovtsev, Zoe E. Sariyanni, Vladimir A. Sautenkov, Nikolai G. Kalugin, and Alexei V. Sokolov, "Concentration dependence of femtosecond coherent anti-Stokes Raman scattering in the presence of strong absorption," J. Opt. Soc. Am. B 24, 1181-1186 (2007)