Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session B2: Focus Session: Control of Quantum Dynamics |
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Chair: Louis DiMauro, Ohio State University Room: A602 |
Tuesday, June 14, 2011 10:30AM - 11:00AM |
B2.00001: Adaptive femtosecond control using feedback from three-dimensional momentum images Invited Speaker: Shaping ultrafast laser pulses using adaptive feedback is a proven technique for manipulating dynamics in molecular systems with no readily apparent control mechanism. Commonly employed feedback signals include fluorescence or ion yield, which may not uniquely identify the final state. Raw velocity map images, which contain a two-dimensional representation of the full three-dimensional photofragment momentum vector, are a more specific feedback source. The raw images, however, are limited by an azimuthal ambiguity which is usually removed in offline processing. By implementing a rapid inversion procedure based upon the onion-peeling technique, we are able to incorporate three-dimensional momentum information directly into the adaptive control loop. This method enables more targeted control experiments. Two examples are used to demonstrate the utility of this feedback. First, double ionization of CO produces C$^{+}$ and O$^{+}$ fragments ejected both perpendicular and parallel to the laser polarization with kinetic energy release of $\sim $6 eV. Both suppression and enhancement of the perpendicular transitions relative to the parallel transitions are demonstrated. Second, double ionization of acetylene can lead to both HCCH$^{2+}$ and HHCC$^{2+}$ isomers. We select between these outcomes using the angular information contained in the CH$^{+}$ and CH$_{2}^{+}$ images. [Preview Abstract] |
Tuesday, June 14, 2011 11:00AM - 11:12AM |
B2.00002: Controlling the XUV Transparency of Helium using Two Pathway Quantum Interference Craig W. Hogle, X.M. Tong, X. Zhou, N. Toshima, P. Ranitovic, M.M. Murnane, H.C. Kapteyn Atoms irradiated with combined femtosecond laser and extreme ultraviolet (XUV) fields will ionize through multiphoton processes, even when the energy of the XUV photon is below the ionization potential. However, in the presence of two different XUV photons and an intense laser field, it is possible to induce full electromagnetic transparency in helium. The laser field modifies the electronic structure of helium, while the presence of two different XUV photons (11$^{th}$ and 13$^{th}$ harmonics) leads to two distinct ionization pathways that can interfere destructively, totally suppressing the helium ionization yield. By fine-tuning the energies of the harmonic pair across the IR-modified 2p resonance in a time-resolved fashion, we show, both experimentally and theoretically, that the maximum interference occurs when the harmonics are energetically tuned into the 2p Floquet double slit created by the IR laser. The relative amplitudes of the harmonics are controlled by changing the laser intensity, and by different coatings of the XUV mirrors. This work demonstrates a new approach for coherent control in a regime of highly-excited states and strong optical fields. [Preview Abstract] |
Tuesday, June 14, 2011 11:12AM - 11:24AM |
B2.00003: Controlling double ionization of atoms in an intense bichromatic laser pulse Adam Kamor, Francois Mauger, Cristel Chandre, Turgay Uzer We consider the classical dynamics of a two-electron system subjected to an intense bichromatic linearly polarized laser pulse. By varying the parameters of the field, such as the phase lag and the relative amplitude between the two colors of the field, we observe several trends from the statistical analysis of a large ensemble of trajectories initially in the ground state energy of the helium atom: High sensitivity of the sequential double ionization component, low sensitivity of the intensities where nonsequential double ionization occurs while the corresponding yields can vary drastically. All these trends hold irrespective of which parameter is varied: the phase lag or the relative amplitude. We rationalize these observations by an analysis of the phase space structures which drive the dynamics of this system and determine the extent of double ionization. These trends turn out to be mainly regulated by the dynamics of the inner electron. \\ Ref: A. Kamor, F. Mauger, C. Chandre, and T. Uzer, Physical Review E, in press (2011). [Preview Abstract] |
Tuesday, June 14, 2011 11:24AM - 11:36AM |
B2.00004: Coherent control of vibrational state distribution in non-polar molecules Antonio Picon, Jens Biegert, Agnieszka Jaron-Becker, Andreas Becker A novel coherent control scheme for the vibrational state distribution in nonpolar molecules is proposed. We apply the scheme to H$_2^+$ and study it theoretically and numerically. Our results reveal a two-photon selective excitation, which is robust against dissociation, and a dynamical Stark shift, which depends linearly on the laser intensity. By using a controllable spectral-phase laser pulse (or a train of pulses) a complete coherent transfer can be achieved from one vibrational state to another. [Preview Abstract] |
Tuesday, June 14, 2011 11:36AM - 11:48AM |
B2.00005: Coherent control of H$_2^+$ ionization with intense XUV+IR fields C.B. Madsen, B.D. Esry We recently developed a method to calculate how the electron and nuclei of the H$_2^+$ share the energy absorbed from an intense laser pulse. While neither the electron energy spectrum nor the nuclear energy spectrum showed much structure separately, their joint energy spectrum revealed considerable structure. It showed multiphoton absorption with the energy shared between the nuclei and the electron. A number of questions followed our initial results: Can the joint energy distribution be used to map the vibrational wave function? To what extent can we control the asymptotic energies of the ionization products? The model behind above Coulomb threshold explosion [PRL {\bf 97}, 013003 (2006)] seems to give a consistent explanation for the calculated energy distributions. We present joint energy distributions of the ionization resulting from an IR+XUV pump-probe laser scheme. In this way, we may investigate the controllability of the asymptotic energies of the ionization fragments and explore the possibility of using the joint energy distribution to map the vibrational wave function. [Preview Abstract] |
Tuesday, June 14, 2011 11:48AM - 12:00PM |
B2.00006: Carrier-envelope phase control of the dissociation of $\rm{H}_2^+$ at long infrared wavelengths ( $800 - 2000$~nm ) Shuo Zeng, Brett Esry We perform a systematic calculation for $\rm{H}_2^+$ in intense, ultrashort laser pulses with wavelength in the range $800$~nm $ \sim$ $2000$~nm. For three-cycle pulses, we found an asymmetric spatial distribution of $p+\rm{H}$ fragments as is generally anticipated for few cycle pulses. The effects of the longer wavelengths relative to the commonly used $800$~nm case are discussed. The calculated carrier-envelope phase (CEP) effects are interpreted as the interference of different multiphoton pathways whose relative phase is CEP-dependent [1,2]. The important pathways are identified and used to explain the observed wavelength dependence. \\[4pt] [1] V. Roudnev and B. D. Esry, Phys. Rev. Lett. 99, 220406 (2007)\\[0pt] [2] J. J. Hua and B. D. Esry, J. Phys. B 42, 085601 (2009) [Preview Abstract] |
Tuesday, June 14, 2011 12:00PM - 12:30PM |
B2.00007: Control of Strong Field Molecular Ionization using Shaped Ultrafast Laser Pulses Invited Speaker: This talk will focus on control over strong field molecular ionization using shaped ultrafast laser pulses. We make use of both time of flight mass spectroscopy and velocity map imaging to characterize the pulse shape dependence of the molecular ionization. Experimental measurements are interpreted with the aid of ab initio molecular structure calculations. [Preview Abstract] |
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