Abstract
In this paper, we experimentally study the selective excitation of two-pulse femtosecond coherent anti-Stokes Raman scattering (CARS) in a mixture of dibromomethane (CH2Br2) and chloroform (CHCl3) by adaptive pulse shaping based on genetic algorithm. Second harmonic generation frequency-resolved optical gating (SHG-FROG) traces indicate that the spectral amplitude and phase of the optimal pulse are both modulated. Finally, we discuss the physical mechanism for the selective excitation of femtosecond CARS based on the retrieved information from SHG-FROG traces.
Highlights
Coherent anti-Stokes Raman scattering (CARS), a nonlinear four-wave-mixing (FWM) process, is one of the most important nonlinear spectroscopic techniques, [1,2,3,4,5] and has been widely employed to investigate the molecular dynamical process
We experimentally study the selective excitation of two-pulse femtosecond coherent anti-Stokes Raman scattering (CARS) in a mixture of dibromomethane (CH2Br2) and chloroform (CHCl3) by adaptive pulse shaping based on genetic algorithm
Coherent control by shaping the femtosecond pulse has been widely utilized to realize the selective excitation of femtosecond CARS. [6,7,8,9,10,11,12,13,14,15,16,17,18,19] Such as, the shaped femtosecond pulse with the simple spectral phase pattern of -step, sinusoidal, chirped or binary function has been employed to realize the selective excitation of the femtosecond CARS. [8,9,10,11,12,13,14] the use of adaptive feed- back control based on genetic algorithm or evolution strategy to selectively excite the femtosecond CARS has been reported.[15,16,17,18,19]
Summary
Coherent anti-Stokes Raman scattering (CARS), a nonlinear four-wave-mixing (FWM) process, is one of the most important nonlinear spectroscopic techniques, [1,2,3,4,5] and has been widely employed to investigate the molecular dynamical process. A promising method for the mode-selective excitation is coherent control by the femtosecond pulse shaping technique. Coherent control by shaping the femtosecond pulse has been widely utilized to realize the selective excitation of femtosecond CARS. In our previous study on the selective excitation of one or more Raman modes in the benzene (C6H6) solution by the optimal control of two-pulse femtosecond CARS,[19]. We experimentally study the selective excitation of two-pulse femtosecond coherent anti-Stokes Raman scattering (CARS) in a mixture of dibromomethane (CH2Br2) and chloroform (CHCl3) by shaping femtosecond laser pulse based on genetic algorithm, the CARS signal from chloroform can be enhanced and simultaneously the CARS signal from dibromomethane is effectively suppressed. The original and optimal laser pulses are characterized by second harmonic generation frequency-resolved optical gating (SHG-FROG) technique, and the physical control mechanisms are explicitly discussed and analyzed based on the retrieved information from SHG-FROG traces
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