Closed-loop learning control of isomerization using shaped ultrafast laser pulses in the deep ultraviolet

Abstract

We demonstrate the use of shaped ultrafast laser pulses in the deep ultraviolet to control the ring opening isomerization of 1,3-cyclohexadiene to form 1,3,5-hexatriene. The experiments are performed with a gas phase sample and the isomerization yield is probed with dissociative ionization driven by a time-delayed, intense infrared laser pulse. Differences in the electronic structure of the ions for the two isomers, as shown by ab initio calculations, result in very different fragmentation products following strong-field ionization. We find that a shaped pulse yields a approximately 37% increase in the isomerization over an unshaped laser pulse.

Transient X-Ray Fragmentation: Probing a Prototypical Photoinduced Ring Opening

“…This process has been extensively studied, in part because of its role in vitamin D biosynthesis. Time-resolved pump-probe techniques have been employed to understand this process [20][21][22][23][24][25]. These studies have found that the conical intersection-mediated ring-opening step in isomerization is completed in less than 200 fs [22], after which the molecule undergoes conformational changes on a range of timescales (see inset in Fig.…”

Vibrationally assisted below-threshold ionization

“…Linear interpolations in internal coordinates at the SA4-CASSCF level were used to connect cis,cis-COD to the two CIs found, and the CIs to the products. The conical intersection for CHD is taken from previous work [7]. Linear interpolations between CHD and the CI and HT and the CI were computed using CASSCF(6,6) with the cc-pVDZ basis set and averaging 3 states.…”

“…We consider the ionization of 1,3-cyclohexadiene (CHD), whose ionization potential is slightly above our photon energy of 7.94 eV. The excited state dynamics of CHD has been the subject of intense study, [3][4][5][6][7], and it's neutral excited state dynamics are well understood. Initial excitation to the first bright state (S 1 ) is followed by rapid internal conversion to the ground states, with some fraction of the molecules isomerizing to form 1,3,5-hexatriene (HT).…”

Examining resonant inelastic spontaneous scattering of classical Laguerre-Gauss beams from molecules

“…However, in all cases this angle is small enough to justify the simplifications used in Eq. (12). Using this replacement, the interaction Hamiltonian becomes,…”

“…While many researchers have investigated how changes to the spectrum of an ultrashort pulse of light can control atomic and molecular dynamics, few researchers have looked into the ability of light fields, continuous or pulsed, * arury@caltech.edu to affect the fundamental coupling of nuclear and electronic degrees of freedom that determine subsequent dynamics and behavior. [6][7][8][9][10][11][12] However, recent studies propose the possibility that tailored transverse modes of light beams control the coupling of internal degrees of freedom of a molecule. [13,14] One such tailored optical mode is a Laguerre-Guass beam.…”