Femtosecond time-resolved spectroscopy of elementary molecular dynamics

Abstract

Femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) is applied in order to prepare and monitor laser-induced vibrational coherences (wave packets) of different samples mainly in its electronic ground state but also in excited states. The time evolution of these wave packets gives information on the dynamics of molecular vibrations. In a first example the femtosecond (fs) CARS transients of iodine are investigated. By changing the relative delay between the applied laser pulses of this non-degenerated four-wave mixing technique, both the wavepacket motion on the electronically excited and the ground states can be detected as oscillations in the coherent anti-Stokes signal. Second we report on selective excitation of the vibrational modes in the electronic ground state of polymers of diacetylene by means of a femtosecond time-resolved CARS scheme. This selectivity is achieved by varying the phase shape (chirp) and the relative delay between the exciting laser pulses.

Quantum Control of Population Transfer and Vibrational States via Chirped Pulses in Four Level Density Matrix Equations

“…Closed-loop learning algorithms are exploited in CC to generate complex optical phases in order to optimize specific reaction pathways. CC has been used as a tool in the control of dynamic processes [17][18][19][20][21], and it explains how a specific state can be selectively populated, for example, to attain 100% population transfer [22][23][24][25], and recent studies have shown the possibility of having enhancements even higher than 100% [26][27][28][29][30][31][32][33][34][35]. QCS also exploits tailored excitation but differs from CC in its applications [30,36].…”

Ultra-Broadband Time-Resolved Coherent Anti-Stokes Raman Scattering Spectroscopy and Microscopy with Photonic Crystal Fiber Generated Supercontinuum

“…With the improvement of temporalspectral distribution of the SC, the simultaneously detectable spectral range of system can be further extended, which is called the ultra-broadband T-CARS and will be discussed in detail in the next section. [84,96] With a broadband T-CARS spectroscopy, we can obtain more specificities of the sample, not only the vibrational spectra reflecting the molecular structure and compositions, but also the dephasing time of various molecular vibrational modes reflecting the molecular responses to the external micro-environment, which are especially favorable for the study of the complicated interaction processes between molecules and their micro-environment such as solute-solvent interactions [108,109] , molecular dynamics [110][111][112][113][114] , supramolecular structures [115] and excess energy dissipations in the fields of biology, chemistry and material science [64,[116][117][118] .…”

Communication: Tracking molecular structure deformation and relaxation in real time

“…Ro-vibrational Raman spectroscopy enables researchers to directly prepare and monitor the molecular vibrational and rotational behaviors in the molecular ground and excited states. 1,2 In this communication, we demonstrate that the transient stimulated Raman scattering (SRS) induced by intense laser pulse enables the tracking of the molecular structural deformation and relaxation. Under the intense offresonance pump pulse excitation (10 11 -10 12 W/cm 2 ), molecules can experience large torques to drive molecular alignment and deformation within a time scale of ∼100 fs.…”