Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session H8: Focus Session: Molecular Control and ImagingFocus
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Chair: Robert Lewis, Temple University Room: 555AB |
Wednesday, May 25, 2016 10:30AM - 10:42AM |
H8.00001: Coherent control of quantum dynamics in laser kicked molecular rotors Martin Bitter, Valery Milner We investigate experimentally the dynamics of true quantum kicked rotors - oxygen and nitrogen molecules subject to a sequence of more than 20 ultrashort laser pulses with peak intensities exceeding $10^{13}$ W/cm$^2$ per pulse. Using state-resolved rotational Raman spectroscopy, we show that the centrifugal distortion is the main obstacle in reaching high rotational states, as it results in the coherent oscillations of rotational population similar to Bloch oscillations in condensed matter. We demonstrate that the timing of the individual pulses can be optimized to partially mitigate the centrifugal limit and produce broader rotational wave packets with higher degrees of rotational coherence. Progress towards the experimental observation of Anderson localization in laser-kicked molecular rotors will be discussed. [Preview Abstract] |
Wednesday, May 25, 2016 10:42AM - 10:54AM |
H8.00002: Adiabatic field-free alignment of asymmetric top molecules with an optical centrifuge Aleksey Korobenko, Valery Milner We use an optical centrifuge to align asymmetric top $\mathrm{SO_2}$ molecules by adiabatically spinning their most polarizable O-O axis. The effective centrifugal potential in the rotating frame confines sulfur atoms to the plane of the laser-induced rotation, leading to the planar molecular alignment which persists after the molecules are released from the centrifuge. Periodic appearance of the full three-dimensional alignment, typically observed only with linear and symmetric top molecules, is also detected. Together with strong in-plane centrifugal forces, which bend the molecules by up to 10 degrees, permanent field-free alignment offers new ways of controlling molecules with laser light. [Preview Abstract] |
Wednesday, May 25, 2016 10:54AM - 11:06AM |
H8.00003: Capture into resonance and phase space dynamics in optical centrifuge Tsafrir Armon, Lazar Friedland The process of capture of a molecular enesemble into rotational resonance in the optical centrifuge is investigated. The adiabaticity and phase space incompressibility are used to find the resonant capture probability in terms of two dimensionless parameters $P_{1,2}$ characterising the driving strength and the nonlinearity, and related to three characteristic time scales in the problem. The analysis is based on the transformation to action-angle variables and the single resonance approximation, yielding reduction of the\ three-dimensional rotation problem to one degree of freedom. The analytic results for capture probability are in a good agreement with simulations. The existing experiments satisfy the validity conditions of the theory. [Preview Abstract] |
Wednesday, May 25, 2016 11:06AM - 11:36AM |
H8.00004: Quantum Localization in Laser-Driven Molecular Rotation Invited Speaker: Ilya Averbukh Recently we predicted that several celebrated solid state quantum localization phenomena -- Anderson localization, Bloch oscillations, and Tamm-Shockley surface states -- may manifest themselves in the rotational dynamics of laser-kicked molecules. In this talk, I will present these new rotational effects in a gas of linear molecules subject to a moderately long periodic train of femtosecond laser pulses. A small detuning of the train period from the rotational revival time causes Anderson localization in the angular momentum space above some critical value of J -- the Anderson wall. This wall marks an impenetrable border stopping any further rotational excitation. Below the Anderson wall, the rotational excitation oscillates with the number of pulses due to a mechanism similar to Bloch oscillations in crystalline solids. I will present the results of the first experimental observation of the laser-induced rotational Bloch oscillations in molecular nitrogen at ambient conditions (Stanford {\&} Weizmann, 2015). We will also discuss the prospects of observing the rotational analogues of the Tamm surface states in a similar experimental setup. Our results offer laser-driven molecular rotation as a new platform for studies on the localization phenomena in quantum transport. These effects are important for many processes involving highly excited rotational states, including coherent optical manipulations in molecular mixtures, and propagation of powerful laser pulses in atmosphere. [Preview Abstract] |
Wednesday, May 25, 2016 11:36AM - 11:48AM |
H8.00005: Coherent control of wavepacket launch and evolution in molecular cations in strong-field regime Dmitri Romanov(1,3), Katharine Moore Tibbetts(2,3), Maryam Tarazkar(2,3), Timothy Bohinsky(2,3), Spiridoula Matsika(2,3), Robert Levis(2,3) The time-resolved dissociative ionization dynamics for a family of acetophenone radical cations has been studied in pump-probe experiments. Modifications of the relative fragment yield have been measured as a function of the pump laser wavelength from 790 nm to 1500 nm. In the case of tunnel ionization (1150$-$1500 nm pump), the time-resolved transients of the parent and fragment ions probed with a weak 790 nm pulse reveal an order-of-magnitude enhancement of the peak-to-peak amplitude oscillations, $\sim $ 100 fs longer coherence time, and an order-of-magnitude increase in the ratio of parent to fragment ions, as compared to the case of multiphoton ionization (790 nm pump). The results are quantitatively explained with a model of wavepacket evolution on the ground (D0) and excited (D1 and D2) ionic potential energy surfaces, with the probe-induced and conical-intersection-related transitions between the surfaces. The theory predicts the periods of fragment-ratio oscillations, thus confirming the ability to prepare and manipulate multiple wavepackets in the vicinity of a conical intersection for polyatomic molecules on the time scale of picoseconds. [Preview Abstract] |
Wednesday, May 25, 2016 11:48AM - 12:00PM |
H8.00006: Separation of \textit{cis} and \textit{trans} geometric isomers by Coulomb explosion imaging Utuq Ablikim, B. Kaderiya, V. Kumarapan, A. Rudenko, D. Rolles, C. Bomme, E. Savelyev, H. Xiong, N. Berrah, D. Kilcoyne Isomers, i.e. molecules with the same chemical formula but different chemical structure, play an important role in many biological processes [1]. Recently, it was shown that it is possible to identify different isomers of a chiral molecule by Coulomb explosion imaging [2]. Here, we show that by imaging the Coulomb explosion of C$_{\mathrm{2}}$H$_{\mathrm{2}}$Br$_{\mathrm{2}}$ molecules after inner-shell photoionization, we are able to separate a mixture of \textit{cis} and \textit{trans} structures using the momentum correlation between ionic fragments measured in coincidence. Furthermore, we used this capability to investigate the isomer-selective photoionization and fragmentation dynamics of C$_{\mathrm{2}}$H$_{\mathrm{2}}$Br$_{\mathrm{2}}$ after Br (3d) ionization. Coulomb explosion simulation results for momentum correlation as well as kinetic energies match closely the experimental results. [1] B. Levine \textit{et al, }Annu. Rev. Phys. Chem. \textbf{58}:613--34 (\textit{2007}) [2] M. Pitzer \textit{et al}, Science \textbf{341}, 1096-1100 (2013). [Preview Abstract] |
Wednesday, May 25, 2016 12:00PM - 12:30PM |
H8.00007: Molecular Control and Imaging Invited Speaker: Vinod Kumarappan |
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