REPORTS 22. A simple calculation indicates that the magnitudes of V 24. R F. Pierret, Semiconductor Device Fundamental Projects Agency. We thank X Wang, W. L. Hughes, 1. Zhou, and ] Liu for their help 5. W. I. Park, G. C Yi, ]. W. Kim, S. M. Park, Appl Phys. Lett. dielectric screening in the calculation, the local potential 82,4358(2003) Supporting Online Material here. An accurate calculation of the potential distribution 27. A. Bachtold, P. Hadley, T. Nakanishi, C. Dekker, Science wwsciencemag. org/cgi/content/ull312/5771/242/D as a result of the ionic charges introduced by the Pz 294, 1317(2001): published online 4 October 2001 24) igs. SI to must be solved numerically and self-consistently. In 28. ) Chen et aL, Science 310, 1171 (2005 able 51 9. U.S. patent pending Movies s1 and 52 Supported by NSF grant DMR 9733160, the NASA Vehicle 23. 5. Hasegawa, S Nishida, T. Yamashita, H. Asahi, Ceramic Systems Program and Department of Defense Researd 19 December 2005: accepted 10 March 2006 PoC.Res6,245(2005) and Engineering and the Defense Advanced Research 10 1126/science. 1124005 Control of electron localization in curs via a two-step mechanism(Fig. 1A)in which initially the molecule is ionized by the laser field Molecular dissociation Fig. 1A, red arrow) and a vibrational wave packet is launched in the lso+state. Breakup M E. King,Ch. Siedschlag, 1 A ) Verhoef, 2]. L Khan, M. Schultze Th. Uphues, Y Ni, 1 of the D, ion is triggered by excitation to a repulsive state or after double ionization. M. Uiberacker, M Drescher, F Krausz, 2.4M.]. ] Vrakking' In the single-ionization pathways, excitation of We demonstrated how the subcycle evolution of the electric field of light can be used to control the bound D,(such as to the 2pa,t state in Fig. 1A) motion of bound electrons. Results are presented for the dissociative ionization of deuterium by recollision of the first electron [recollision molecules(D,-D++D), where asymmetric ejection of the ionic fragment reveals that light excitation(RCE) green line] or directly by the laser driven intramolecular electronic motion before dissociation localizes the electron on one of the tw eld [sequential excitation( SE), blue line) leads to D+ ions in a controlled way. The results extend subfemtosecond electron control to molecules and dissociation and the formation of a dt ion and a d provide evidence of its usefulness in controlling reaction dynamics atom. For example, in recent molecular clock studies, vibrational motion in D, was time- F ew-cycle laser light with a controlled evo- classical computations reveal that light-field resolved by exploiting RCE (10, ID). Additional lution of the electric field E(=anx control of molecular electron dynamics is re- dissociation mechanisms can be understood by s((f+o), with amplitude a(n), frequen- sponsible for the observed phenomeno considering that molecular potentials are modi y o, and carrier envelope The dynamics of molecules in intense laser fied by strong laser fields. Bond softening(Bs ly allowed the steering of the motion of fields typically inchudes ionization and dissocia- purple line)(2)occurs when energy gaps open electrons in and around atoms on a subfemto- tion. The dissociation of D, in intense laser fields up at avoided crossings between adiabatic field- second time scale. Manifestations of this control is known to involve several pathways whose dressed potential energy curves include the reproducible generation and mea- relative importance depends on intensity and pulse In double-ionization pathways, the forma- surement of single subfemtosecond pulses(2, 3) duration(6). The formation of fragment ions oc- tion of D,+ is followed by a second ionization and controlled electron emission from atom (4, 5). Here we address the question of whether this control can be extended to electron wave packets in molecules and, if so, can light-field- driven electronic motion affect reaction dynamics? Many of the processes in terms of which rong-field molecular interactions are present LP 8.0 fs interpreted( such as bond softening and enhanced ionization) were discovered in experimental and theoretical work on H, and its isotopes HD and 2po D++D+ D2 [see(6)and references therein]. The role of LP 6.5 fs phase control in the dissociation of hydrogen has recently been addressed in a few theoretical studies(7-9). We present experiments on the LP 5.0 fs dissociation of D,+ into D+ + d by intense few-cycle laser pulses with controlled field D++ D evolution and report a pronounced dependence CP 5.0 fs of the direction of the D+ ejection(a of the localization of the electron in the system) D+D on the waveform driving the reaction. Quantum- energy /ev FOM Instituut voor Atoom en Molecul Fysica (AMOLF Planck-lnstitut fur Quantenoptik, Hans-Kopfermann-Strasse bond distance ny. Fakultat fur Physik, Fig. 1.(A)Pathways for the production of D+ ions from D, by Universitat Bielefeld, Universitatsstrasse 25, D-33615 (through BS, SE, or RCE)or by Coulomb explosion (through RCl,SI ossing between diabatic potentials that are dressed by the las D-85748 Garching, Germany. institut for Experimen- vibrational levels that were originally bound (12).(B)D+ kinetic energy spectra talphysik, Universitat Hamburg, Luruper Chaussee 149, by 5-to 8-fs linearly polarized (LP)and 5fs circularly polarized (CP)laser D-22761 Hamburg, Germany stabilization,atl=12±0.2×1014Wcm2andl=24±0.2×1014Wcm 246 14ApriL2006Vol312ScieNcewww.sciencemag.org22. A simple calculation indicates that the magnitudes of Vs þ and Vs – are on the order of a few tens to hundreds of volts. In practice, if we consider the polarization and dielectric screening in the calculation, the local potential is much smaller than the numbers given by the equations here. An accurate calculation of the potential distribution as a result of the ionic charges introduced by the PZ effect and the surface charges caused by boundaries must be solved numerically and self-consistently. In our analysis, a correct magnitude and sign of the potential is sufficient for illustrating the physical model. 23. S. Hasegawa, S. Nishida, T. Yamashita, H. Asahi, J. Ceramic Proc. Res. 6, 245 (2005). 24. R. F. Pierret, Semiconductor Device Fundamentals (Addison-Wesley, Reading, MA, 1996), chapter 14. 25. W. I. Park, G. C. Yi, J. W. Kim, S. M. Park, Appl. Phys. Lett. 82, 4358 (2003). 26. Y. Huang et al., Science 294, 1313 (2001). 27. A. Bachtold, P. Hadley, T. Nakanishi, C. Dekker, Science 294, 1317 (2001); published online 4 October 2001 (10.1126/science.1065824). 28. J. Chen et al., Science 310, 1171 (2005). 29. U.S. patent pending. 30. Supported by NSF grant DMR 9733160, the NASA Vehicle Systems Program and Department of Defense Research and Engineering, and the Defense Advanced Research Projects Agency. We thank X. Wang, W. L. Hughes, J. Zhou, and J. Liu for their help. Supporting Online Material www.sciencemag.org/cgi/content/full/312/5771/242/DC1 SOM Text Figs. S1 to S6 Table S1 Movies S1 and S2 19 December 2005; accepted 10 March 2006 10.1126/science.1124005 Control of Electron Localization in Molecular Dissociation M. F. Kling,1 Ch. Siedschlag,1 A. J. Verhoef,2 J. I. Khan,1 M. Schultze,2 Th. Uphues,3 Y. Ni,1 M. Uiberacker,4 M. Drescher,3,5 F. Krausz,2,4 M. J. J. Vrakking1 We demonstrated how the subcycle evolution of the electric field of light can be used to control the motion of bound electrons. Results are presented for the dissociative ionization of deuterium molecules (D2 Y Dþ þ D), where asymmetric ejection of the ionic fragment reveals that light￾driven intramolecular electronic motion before dissociation localizes the electron on one of the two Dþ ions in a controlled way. The results extend subfemtosecond electron control to molecules and provide evidence of its usefulness in controlling reaction dynamics. F ew-cycle laser light with a controlled evo￾lution of the electric field E(t) 0 a(t)
cos(wt þ 8), with amplitude a(t), frequen￾cy w, and carrier envelope phase 8 (1), has recently allowed the steering of the motion of electrons in and around atoms on a subfemto￾second time scale. Manifestations of this control include the reproducible generation and mea￾surement of single subfemtosecond pulses (2, 3) and controlled electron emission from atoms (4, 5). Here we address the question of whether this control can be extended to electron wave packets in molecules and, if so, can light-field– driven electronic motion affect reaction dynamics? Many of the processes in terms of which strong-field molecular interactions are presently interpreted (such as bond softening and enhanced ionization) were discovered in experimental and theoretical work on H2 and its isotopes HD and D2 Esee (6) and references therein^. The role of phase control in the dissociation of hydrogen has recently been addressed in a few theoretical studies (7–9). We present experiments on the dissociation of D2 þ into Dþ þ D by intense few-cycle laser pulses with controlled field evolution and report a pronounced dependence of the direction of the Dþ ejection (and hence of the localization of the electron in the system) on the waveform driving the reaction. Quantum￾classical computations reveal that light-field control of molecular electron dynamics is re￾sponsible for the observed phenomenon. The dynamics of molecules in intense laser fields typically includes ionization and dissocia￾tion. The dissociation of D2 in intense laser fields is known to involve several pathways whose relative importance depends on intensity and pulse duration (6). The formation of fragment ions oc￾curs via a two-step mechanism (Fig. 1A) in which initially the molecule is ionized by the laser field (Fig. 1A, red arrow) and a vibrational wave packet is launched in the 1ssg þ state. Breakup of the D2 þ ion is triggered by excitation to a repulsive state or after double ionization. In the single-ionization pathways, excitation of bound D2 þ (such as to the 2psu þ state in Fig. 1A) by recollision of the first electron Erecollision excitation (RCE), green line^ or directly by the laser field Esequential excitation (SE), blue line^ leads to dissociation and the formation of a Dþ ion and a D atom. For example, in recent molecular clock studies, vibrational motion in D2 þ was time￾resolved by exploiting RCE (10, 11). Additional dissociation mechanisms can be understood by considering that molecular potentials are modi￾fied by strong laser fields. Bond softening (BS, purple line) (12) occurs when energy gaps open up at avoided crossings between adiabatic field￾dressed potential energy curves. In double-ionization pathways, the forma￾tion of D2 þ is followed by a second ionization 1 FOM Instituut voor Atoom en Molecuul Fysica (AMOLF), Kruislaan 407, 1098 SJ Amsterdam, Netherlands. 2 Max￾Planck-Institut fu¨r Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany. 3 Fakulta¨t fu¨r Physik, Universita¨t Bielefeld, Universita¨tsstrasse 25, D-33615 Bielefeld, Germany. 4 Department fu¨r Physik, Ludwig￾Maximilians-Universita¨t Mu¨ nchen, Am Coulombwall 1, D-85748 Garching, Germany. 5 Institut fu¨r Experimen￾talphysik, Universita¨t Hamburg, Luruper Chaussee 149, D-22761 Hamburg, Germany. Fig. 1. (A) Pathways for the production of Dþ ions from D2 by dissociation of the molecular ion (through BS, SE, or RCE) or by Coulomb explosion (through RCI, SI, or EI). BS occurs when the avoided crossing between diabatic potentials that are dressed by the laser field gives rise to dissociation from vibrational levels that were originally bound (12). (B) Dþ kinetic energy spectra for dissociation of D2 by 5- to 8-fs linearly polarized (LP) and 5-fs circularly polarized (CP) laser pulses without phase stabilization, at I 0 1.2 T 0.2
1014 W cm–2 and I 0 2.4 T 0.2
1014 W cm–2, respectively. REPORTS 246 14 APRIL 2006 VOL 312 SCIENCE www.sciencemag.org