A photoelectron-photoion coincidence imaging apparatus for femtosecond time-resolved molecular dynamics with electron time-of-flight resolution of σ=18ps and energy resolution ΔE∕E=3.5%

Abstract

We report on the construction and performance of a novel photoelectron-photoion coincidence machine in our laboratory in Amsterdam to measure the full three-dimensional momentum distribution of correlated electrons and ions in femtosecond time-resolved molecular beam experiments. We implemented sets of open electron and ion lenses to time stretch and velocity map the charged particles. Time switched voltages are operated on the particle lenses to enable optimal electric field strengths for velocity map focusing conditions of electrons and ions separately. The position and time sensitive detectors employ microchannel plates (MCPs) in front of delay line detectors. A special effort was made to obtain the time-of-flight (TOF) of the electrons at high temporal resolution using small pore (5 microm) MCPs and implementing fast timing electronics. We measured the TOF distribution of the electrons under our typical coincidence field strengths with a temporal resolution down to sigma=18 ps. We observed that our electron coincidence detector has a timing resolution better than sigma=16 ps, which is mainly determined by the residual transit time spread of the MCPs. The typical electron energy resolution appears to be nearly laser bandwidth limited with a relative resolution of DeltaE(FWHM)/E=3.5% for electrons with kinetic energy near 2 eV. The mass resolution of the ion detector for ions measured in coincidence with electrons is about Deltam(FWHM)/m=14150. The velocity map focusing of our extended source volume of particles, due to the overlap of the molecular beam with the laser beams, results in a parent ion spot on our detector focused down to sigma=115 microm.

Probing chirality with a femtosecond reaction microscope

“…The detection setup consists of a state of the art coincidence imaging setup for photoelectrons and photoions using the velocity map imaging technique. Both the electron and the coincident ion were detected on a single Micro-Channel-Plate delay-line detector, by switching the High-Voltages (HV) on the ion optics of the Velocity-Map-Ion (VMI) lenses [5][6][7]. Initial experiments were done on the two enantiomers of camphor that were obtained commercially (Sigma-Aldrich, purity 98% (R) and 99% (S)) and were contained in two separate tubes in vacuum lines outside the coincidence imaging setup.…”

“…This chiral asymmetry in the photoelectron angular distribution using This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. [5][6][7] can be used to detect mass-selected chiral molecules with high selectivity and sensitivity with our results on the chiral molecule camphor.…”

Incorporating real time velocity map image reconstruction into closed-loop coherent control

“…Three-dimensional image-based feedback should make identifying the exit pathways 72,73 from the conical intersection plausible. Continuing advances in VMI and related techniques 74,75 might also suggest future possibilities for more refined feedback for adaptive control.…”

Toward elucidating the mechanism of femtosecond pulse shaping control in photodynamics of molecules by velocity map photoelectron and ion imaging

“…This leads to an enhanced fragmentation with near statistical ͑low͒ kinetic energy of the fragments and an isotropic angular distribution. At present we are performing full photoelectron-photoion coincidence experiments of CH 2 BrCl in our newly developed apparatus in Amsterdam 26,27,55 with full adaptive LCD-pulse shaping. We hope that such more advanced coincidence experiments will provide additional information that in combination with theoretical dynamics calculations will reveal the definite mechanism of the pulse shaping control in the multiphoton photodynamics of CH 2 BrCl.…”

“…[14][15][16][17][18][19][20][21][22][23] Especially, the combination of photoelectron-photoion coincidence imaging with femtosecond time-resolved spectroscopy has been shown to provide extremely insightful information on multiphoton multichannel dynamics. [24][25][26][27] In this paper, we report our first results combining velocity map ͑noncoincidence͒ electron and ion imaging techniques with ultrafast pulse shaping to study the control of molecular ionization and fragmentation processes in polyatomic molecules. We have chosen a relatively small molecule, CH 2 BrCl, as a target system to make ͑future͒ comparison with theoretical calculations more tractable.…”