The combination of computer simulations and two powerful experimental methods for following molecular change on femtosecond timescales offers an unprecedented view of how a photoexcited molecule breaks apart.
The structural dynamics of photoexcited gas-phase carbon disulfide (CS2) molecules are investigated using ultrafast electron diffraction. The dynamics were triggered by excitation of the optically bright 1B2(1Σu+) state by an ultraviolet femtosecond laser pulse centred at 200 nm. In accordance with previous studies, rapid vibrational motion facilitates a combination of internal conversion and intersystem crossing to lower-lying electronic states. Photodissociation via these electronic manifolds results in the production of CS fragments in the electronic ground state and dissociated singlet and triplet sulphur atoms. The structural dynamics are extracted from the experiment using a trajectory-fitting filtering approach, revealing the main characteristics of the singlet and triplet dissociation pathways. Finally, the effect of the time-resolution on the experimental signal is considered and an outlook to future experiments provided.
We demonstrate an enhancement in the formation of D 2 O 3+ as a consequence of field-free molecular dynamics following the strong-field multiple ionization of deuterated water via 6-fs 800-nm pulse pairs.
We present a bichromatic prism pair interferometer (BPPI) for controlling the delay between laser pulses of two different frequencies propagating collinearly in a single beam. The BPPI is especially useful when working with ultrafast laser pulses because it intrinsically allows for independent control over the second-order dispersion experienced by the differently colored pulses. We use this control to demonstrate successful precompensation for blue (lambda approximately 390 nm) and UV (lambda approximately 260 nm) pulses that pass through 2.2 cm of dispersive material after the interferometer. The BPPI is extremely flexible and works with all frequencies from the UV to the near-infrared. We demonstrate this by describing measurements made with BPPIs configured for three different combinations of central frequencies.
This paper provides a detailed description of how to construct a pulsed atomic beam source [including a fast ionization gauge (FIG) for characterization] with a unique combination of characteristics. We include technical drawings for a real-time adjustable piezo electric actuated pulsed valve capable of generating a 11 μs duration pulse of gas at a repetition rate of >5 KHz, with a shot-to-shot stability of 0.6%, and maximum densities of 1015 particles/cm3. We also include details on how to construct a FIG, with a 4 μs rise time, to measure the pulse. We report a 3D density map of a supersonic expansion of helium gas with a speed ratio S = 46 and a calculated longitudinal temperature of 0.3 K. Finally, the results of a laser ionization test are provided in order to verify the performance of the pulsed valve in a typical experimental configuration.
Control over CF 3 +/CHBr 2 + in laser driven fragmentation of CHBr 2 COCF 3 , is observed. Pump-probe spectroscopy reveals a charge transfer mechanism. This mechanism may allow for a measurement of the wave function for a dissociating polyatomic molecule.
This talk will focus on uncovering mechanism in closed loop coherent control experiments. The experiments, which use shaped ultrafast laser pulses, range from strong field population transfer in atoms to fragmentation of polyatomic molecules.
