Coherent vibrational dynamics of polydiacetylenes in their electronic ground stateDedicated to Professor F. Dörr on the occasion of his 80th birthday.

Optimal control of ground-state dynamics in polymers

“…With a constant time delay of ⌬ between pump and Stokes pulse, the time delay between Stokes and probe pulses was varied. According to the discussion in a previous paper, 22 the relative intensities of the three Gaussian-like peaks, which are centered at about 1400, 1200, and 960 cm Ϫ1 , reflect the relative population of the three coherently excited modes. Cuts of the anti-Stokes signal along the time axis result in the transient behavior of the three spectral features: 23…”

“…Polydiacetelyne has been studied in detail with femtosecond time-and frequency-resolved coherent anti-Stokes Raman scattering ͑fs-CARS͒. [20][21][22] In those experiments, several normal modes were excited in a stimulated Raman process and the vibrational dynamics in the electronic ground and excited state were studied by analyzing the anti-Stokes signal. Additionally, two strategies to excite selectively vibrational motion of the 2 / 2 Ј modes in the electronic ground state of the PDAs were demonstrated.…”

Evolutionary algorithms and their application to optimal control studies

“…With a constant time delay of τ 1 between pump and Stokes pulse, the time delay τ 2 between Stokes and probe pulses was varied. According to a previous article [145], the relative intensities of the three Gaussian-like peaks, which are centered at about 1480 cm −1 , 1200 cm −1 , and 960 cm −1 , reflect the relative population of the three coherently excited modes. The time-and frequency-resolved anti-Stokes signal I(ω, τ 2 ) can be written as [155]:…”

“…where Q i (ω) is the spectral amplitude distribution of mode i, given by the product of a mode intensity with a frequency-dependent function reflecting the spectral contribution of this mode to the anti-Stokes signal [145], T 2i the coherent dephasing time, and ω ij = |ω i − ω j |, where ω i and ω j are the carrier angular frequencies of modes i and j, respectively. Since the probe was wobbled over several beating periods, the CARS signal has to be integrated over several oscillations of the second term in eqn.…”

“…The process is optimized in a feedback loop using the anti-Stokes Raman signal of a four-wave-mixing (FWM) process as feedback. Polydiacetylene (PDA) has been studied in detail with femtosecond time-and frequencyresolved coherent anti-Stokes Raman Scattering (fs-CARS) [143][144][145]. In those experiments, several normal modes were excited in a stimulated Raman process and the vibrational dynamics in the electronic ground and self-trapped exciton state were studied by analyzing the anti-Stokes signal.…”