Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session B32: Strong Field and Ultrafast Physics |
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Sponsoring Units: DAMOP Chair: Marc Vrakking, Institute for Atomic and Molecular Physics Room: Colorado Convention Center 402 |
Monday, March 5, 2007 11:15AM - 11:27AM |
B32.00001: Spatial Dependence of High Harmonic Generation in Hydrogen Atom Seth Ross, G.P. Zhang We used the hydrogen atom as a model and computed the continuum mavefunction and the transition matrix elements. The total quantum number used is 200 and the number of plane waves is 100. We have done dynamical simulations to mimic the laser and electron interaction. Fianlly we compute the power spectrum by Fourier transformation of the dipole matrix. This gives us the opportunity to see the spatial dependence of high harmonic generations in the hydrogen atom. References: H. Niikura {\it et al}, Nature {\bf 417}, 917 (2002); {\bf 421}, 826 (2003); G. P. Zhang, Phys. Rev. Lett. {\bf 95}, 047401 (2005); G. P. Zhang and T. F. George, Phys. Rev. A {\bf 74}, 023811 (2006) [Preview Abstract] |
Monday, March 5, 2007 11:27AM - 11:39AM |
B32.00002: Demonstration of a high brightness injection-seeded soft x-ray laser amplifier using a dense plasma Eduardo Granados, Yong Wang, Miguel A. Larotonda, Mark Berrill, Brad M. Luther, Dinesh Patel, Carmen S. Menoni, Jorge J. Rocca There is a great interest in the generation of high brightness beams of soft x-ray light. We have conducted a table-top experiment in which we have demonstrated the generation of an intense soft x-ray laser beam by saturated amplification of high harmonic seed pulses in a dense transient collisional soft x-ray laser plasma amplifier created by heating a solid titanium target. Amplification of the seed pulses in the 32.6 nm line of Ne-like Ti generates laser pulses of sub-picosecond duration that are measured to approach full spatial coherence. The peak spectral brightness is estimated to be $\sim $ 2$\times $10$^{26}$ photons/( s mm$^{2}$ mrad$^{2}$ 0.01{\%} bandwidth). The scheme is scalable to produce extremely bright lasers at very short wavelength with full temporal and spatial coherence for applications. [Preview Abstract] |
Monday, March 5, 2007 11:39AM - 11:51AM |
B32.00003: ABSTRACT WITHDRAWN |
Monday, March 5, 2007 11:51AM - 12:03PM |
B32.00004: Quasi Phase Matching and Quantum Path Control of High Harmonic Generation using Counterpropagating Light Xiaoshi Zhang, Amy Lytle, Oren Cohen, Henry Kapteyn, Margaret Murnane We demonstrate the first use of a 3-pulse train of counterpropagating pulses to enhance the coherent upconversion of an intense ultrashort laser pulse into the extreme ultraviolet region of the spectrum. This all-optical quasi-phase-matching technique uses interfering beams to scramble the quantum phase of the generated high-order harmonics, to suppress emission from out-of-phase regions. A wavelength selective enhancement in the flux of up to $\approx $ 300x is observed at photon energies around 70 eV in Argon, that cannot otherwise be phase matched. We also show that further very large enhancements are possible, presenting a real prospect for orders-of-magnitude improvement in coherent upconversion of lasers into the soft x-ray region of the spectrum. Finally we show that by adjusting the intensity of the counterpropagating light, we can selectively enhance different electron quantum path trajectories, demonstrating attosecond time-scale coherent control of the radiating electron wavefunction. [Preview Abstract] |
Monday, March 5, 2007 12:03PM - 12:15PM |
B32.00005: ABSTRACT WITHDRAWN |
Monday, March 5, 2007 12:15PM - 12:27PM |
B32.00006: Controlling rotational revivals in asymmetric tops Vinod Kumarappan, Lotte Holmegaard, Simon Viftrup, Christer Bisgaard, Henrik Stapelfeldt, Edward Hamilton, Tamar Seideman We use improved experimental and theoretical tools to demonstrate a novel method for controlling the revival structure of strong-field alignment of asymmetric top molecules. Experimentally, iodobenzene molecules (which is a near-prolate top) are cooled to 1 K using an Even-Lavie supersonic valve and non-adiabatically aligned using 800 nm pulses of durations ranging from 200 fs to 2 ps. The alignment is probed by velocity map imaging of I$^{+}$ fragments produced by Coulomb explosion of the molecules using a 25 fs pulse focused tightly to restrict the volume probed. We show that as the fluence of aligning pulse is increased, the revival structure is simplified to a nearly period pattern reminiscent of symmetric tops. Theoretically, non-perturbative solution of the Schrodinger equation demonstrates the generality of the effect, and emphasizes the importance of this new control scheme for the alignment and revival dynamics of asymmetric tops. Classically, the simplified motion at high fluence corresponds to stable rotations about the slowest principal axis (the C-axis) of the molecule. [Preview Abstract] |
Monday, March 5, 2007 12:27PM - 12:39PM |
B32.00007: Heterodyne control of attosecond pulse generation Thomas Pfeifer, Lukas Gallmann, Mark J. Abel, Phillip M. Nagel, Aurelie Jullien, Daniel M. Neumark, Stephen R. Leone Adding a weak laser field at a different color to the fundamental in high-order harmonic generation results in a new type of heterodyne mixing in the kinetic energy term of the active electron. Analytical calculations and quantum simulations show that the effect of the weak field is amplified by the strong fundamental laser field that acts as the local oscillator [1]. The photon energy of different attosecond pulses within the produced pulse trains can thus be significantly modified. Two important applications for this phenomenon are the generation of isolated attosecond pulses with multi-cycle driving fields and the shaping of attosecond pulse trains. \newline \newline Ref.: [1] T. Pfeifer et al., Phys. Rev. Lett. 97, 163901 (2006) [Preview Abstract] |
Monday, March 5, 2007 12:39PM - 12:51PM |
B32.00008: Measurement of higher-order moments of a rotational wave packet dynamics and alignment Klaus Hartinger, Randy Bartels Field free molecular alignment, attributed to the revivals of a rotational wave packet, has been an area of very active research recently, with numerable potential applications$^1$. While there is very rich structure and temporal dynamics in the quantum rotational wave packet, so far, measurements have been restricted to just the first moment of the wave packet, i.e., a measurement of $\langle\langle\cos^2\theta\rangle\rangle$. This measure probes the transient alignment of the molecules, but does not reveal the complete dynamics of the quantum wave packet. A measurement of the rotational wave packet dynamics with a linear optical technique depends only on $\langle\langle\cos^2\theta\rangle\rangle$ and does not provide information on higher order moments of the alignment. Third-order nonlinear interactions provide information on the $\langle\langle\cos^4\theta\rangle\rangle$ moment and provide additional information about rotational wave packet dynamics. We present third harmonic generation experiments measuring the transient THG susceptibility, which includes the $\langle\langle\cos^4\theta\rangle\rangle$ dynamics.\\ $^1$T. Seideman, Adv. in At., Mol. and Opt. Phys., 52 (2006) [Preview Abstract] |
Monday, March 5, 2007 12:51PM - 1:03PM |
B32.00009: In-situ probe of ionization and coherent buildup for high-order harmonic generation in hollow waveguides using counterpropagating light Amy Lytle, Xiaoshi Zhang, Margaret Murnane, Henry Kapteyn, Oren Cohen We use counterpropagating light to directly observe, in-situ, the coherent buildup of high harmonic generation in a hollow waveguide. We measure, for the first time, the phase mismatch, (i.e. coherence lengths) for high photon energies that cannot be phase matched using conventional approaches. We also probe the transition through phase matching, the ionization level at which different harmonic orders are generated, and the change in the coherence length as the intensity of the guided mode evolves along the fiber. These results demonstrate that the hollow waveguide geometry possesses exceptional coherence and a ``quasi-one-dimensional'' plane wave geometry, in analogy to conventional fiber optics in the visible. This in-situ information also directly prescribes the optimal structures or pulsetrains required for implementing quasi phase matching. [Preview Abstract] |
Monday, March 5, 2007 1:03PM - 1:15PM |
B32.00010: High harmonic generation from ions in a capillary discharge Tenio Popmintchev, David M. Gaudiosi, Oren Cohen, Margaret M. Murnane, Henry C. Kapteyn, Michael Grisham, Brendan Reagan, Mark Berrill, Jorge J. Rocca, Barry C. Walker We demonstrated a significant extension of the high harmonic spectra from noble gases by generating harmonics from ions in a capillary discharge plasma. The discharge plasma eliminates ionization-induced defocusing and ionization loss, allowing photon energies of 160 eV, 170 eV and 275 eV to be generated from xenon, krypton and argon ions, respectively. In addition to extending the spectra, harmonic generation in a capillary discharge results in an enhancement of the flux of up to two orders of magnitude near the harmonic cutoff observed in a hollow waveguide. The use of a capillary discharge plasma as a new medium for high harmonic generation shows great promise for extending efficient harmonic generation to shorter wavelengths. [Preview Abstract] |
Monday, March 5, 2007 1:15PM - 1:27PM |
B32.00011: Computational Study of Orientation-dependent Molecular High Harmonic Spectra Anthony Dutoi, Tamar Seideman Recently, there has been much interest in high harmonic generation (HHG) by aligned molecules [{\it Phys. Rev. A} {\bf 67} 023819, {\it Nature} {\bf 432} 867, {\it Nature} {\bf 435} 470]. During HHG, an electron is ionized and driven back to the cation by a strong, low-frequency field, and radiation is emitted at harmonics of this driving pulse. Because this process is sensitive to the orientation of a molecule, rotational dynamics can be probed on very short time scales. We are working to predict the time-dependent HHG spectra for aligned rotational wavepackets. In conjunction with experiment, these simulations should be valuable for studying the loss of rotational coherence in media such as dense gases. Within the presented formalism, Born-Oppenheimer rotational dynamics are handled exactly, while HHG at any given orientation is estimated by numerical time integration of a one-electron Schr\"{o}dinger equation. Propagation outside of the integration grid can be handled using an analytical Volkov propagator at the expense of ignoring the cation field at this distance. [Preview Abstract] |
Monday, March 5, 2007 1:27PM - 1:39PM |
B32.00012: Effect of nuclear motion on the absorption spectrum of dipicolinic acid Petra Sauer, Yuri Rostovtsev, Roland Allen A current scientific challenge is the rapid detection of chemical and biological substances, including bacterial spores. A significant component of spores is the molecule dipicolinic acid (DPA or 2,6-pyridinedicarboxylic acid) and its salts. A variety of spectroscopic detection schemes are being explored, including fluorescence spectroscopy, ultraviolet and visible resonant Raman spectroscopy, and FAST CARS. Using semiclassical electron-radiation-ion dynamics (SERID), we have examined the effect of nuclear motion, resulting from both finite temperature and the response to a radiation field, on the line broadening of the excitation profile of DPA. With nuclei fixed, we find a relatively small broadening associated with the finite time duration of an applied laser pulse. When the nuclei are allowed to move, the excitation spectrum exhibits a much larger broadening, and is also reduced in height and shifted toward lower frequencies. In both cases, the excitation is due to well-defined $\pi$ to $\pi*$ transitions. The further inclusion of thermal motion at room temperature broadens the linewidth considerably because of variations in the molecular geometry: Transitions that had zero or negligible transition probabilities in the ground state geometry are weakly excited at room temperature. [Preview Abstract] |
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