Photoelectron diffraction from small molecules: Structure and Dynamics of Atoms, Ions, Molecules and Surfaces: Atomic Physics with Ion Beams, Lasers and Synchrotron Radiation 2004 Research Meeting of the BES AMOS Program C.L.Cocke, Physics Department, J.R. Macdonald Laboratory, Kansas State University, Manhattan, KS 66506 Current Projects: Multiple electron removal from neutral systems studied with COLTRIMS (Cocke, Lin, Tong, Chang..) Photoelectron diffraction from small molecules: a) ALS: Synchrotron radiation (Many..) b) KSU: Harmonic generation source, time-resolved studies (Cocke,Chang,Shan…) 3) Picopulsing the Tandem (Chang,Carnes,Cocke,Needham,Richard,DePaola,Ben Itzhak, ..) Konza prairie just outside Manhattan

Mechanisms for Double Electron Removal from Light Molecules by Intense Laser Pulses: Fast Clocks The time line in seconds: 10-12 10-18 10-15 10-9 Phase transitions Electronic motion Heavy particle motion Radiative lifetimes Collisions: integrated trajectories Attosecond pulses Pulsed Lasers: real time movies

Electron rescattering from molecules in intense laser fields Ali Alnaser, S.Voss, T.Osipov, M.Benis, B.Ulrich, C.Maharjan, X.-M.Tong, C.D.Lin, Z.Chang, B.Shan,P.Ranitovic,C.L.Cocke D2/H2 Old and new mechanisms for double electron removal and fs clocks N2/O2 Mechanisms for double electron removal: Does the orbital structure play a role and how? Tuttle creek reservoir just outside Manhattan

Experimental setup: COLTRIMS Laser supersonic Jet X Y Z E-Field Recoil Detector Spectrometer Time resolution: <1 ns Position resolution: 0.3 mm Multihit: 16 events/pulse Pulse pair resolution: 15 ns B field 10-20 gauss E field 1-10 V/cm Flight distances 10-50 cm Vacuum < 10 -10 torr Ion detection only Intensity : 0.9 -8 x1014 Watt/cm2 800 nm Wavelength 1-2 kHz Repetition Rate 8-35 fs

The COLTRIMS apparatus with an operator…. Predrag Ranitovic

The other apparatus with operators M.Zamkov C.Wang M.Benis S.Voss L.Cocke A.Alnaser T.Osipov B.Shan C.Maharjan

Electron rescattering from molecules in intense laser fields Ali Alnaser, S.Voss, T.Osipov, M.Benis, B.Ulrich, C.Maharjan, X.-M.Tong, C.D.Lin, Z.Chang, B.Shan, C.L.Cocke D2/H2 Old and new mechanisms for double electron removal and fs clocks N2/O2 Mechanisms for double electron removal: How do you get the electronic energy into the system? Does the orbital structure play a role and how?

The hydrogen (deuterium) molecule The Kinetic Energy Release spectra Background Dissociation Double ionization: enhanced ionization Rescattering Sequential Ionization Clocking the wave packet on a fs time scale using all three processes Konza prairie just outside Manhattan

d+ time of flight spectrum along laser polarization

The data: p+ or d+ spectra Frazinski et al, PRL 83, 3625 A.Zavriyev et al.,PRA 42, 5500 (1990). H+ + H+ BS CREI ATD H+ + H H + H

d+ time of flight spectrum along laser polarization

Rescattering:the electron returns with energy -Maximum return energy 3.17 Up at phase of 17 degrees -If circularly polarize the light, electron does not return

Staudte et al.:the energy distributions of coincident ion pairs d+/d+ ??? A.Staudte, C.L.Cocke, M.H.Prior et al., Phys.Rev.A 65, 020703 (R) (2002) CREI

Niikura et al., Nature 417,917 (2002)

Mechanisms for doubly ionizing H2 Rescattering Enhanced H. Niikura, et. al., Nature 417, 917 (2002); Nature 421, 826 (2003). Seideman et al., PRL 75, 2819 (1995);Zuo and Bandrauk, PRA 52, R2511 (1995). Increasing intensity Increasing intensity

How we identify rescattering in the double ionization channel: linear/circular polarization Linear Polarization Circular Polarization |p1+p2| A. Staudte et al, , PRA 65,020703 R (2002) A. Alnaser, et al., PRL 91, 163002 (2003) Magnitude of vector sum of momentum of two fragments

General character of results cos(q) Ion sum energy (eV) 1 -1 20 1.1 2.5 1.6 1.3 1.2 1.5 Spectra at various peak laser intensities (in units of 10 14 w/cm2 ) CREI Rescattering q e

The model X.M.Tong, Z.X.Zhao and C.D.Lin, PRA 68, 043412 (2003) ADK Classical electrons Theoretical differential excitation cross sections Vibrational wave packet propagation ADK

Multiple returns: the 2.7 fs clock A. Alnaser, et al., PRL 91, 163002 (2003) Return Time ( fs) <R>( a.u.) H2+ D2+ t1 1.9 1.8 1.6 t3 4.3 2.5 2.1 t5 7.0 3.0 2.6 t7 9.6 3.2 35 fs, 2.8 x 10 14 w/cm2 * Model by X.M.Tong, Z.X.Zhao and C.D.Lin, PRA 68, 043412 (2003)

The short pulse: 8 fs In rescattering regime, can isolate first return.

The short pulse: only the first return The short pulse: 8 fs, 1.5 x 10 14 W/cm2

The hydrogen (deuterium) molecule The Kinetic Energy Release spectra Background Dissociation Double ionization: enhanced ionization Rescattering Sequential Ionization Clocking the wave packet on a fs time scale using all three processes

Sequential ionization in non-coincident data with short pulse Légaré et al., PRL 91, 093002 (2003)

Mechanisms for doubly ionizing H2 Rescattering Enhanced Sequential H. Niikura, et. al., Nature 417, 917 (2002); Nature 421, 826 (2003). Seideman et al., PRL 75, 2819 (1995);Zuo and Bandrauk, PRA 52, R2511 (1995). Légaré et al., PRL 91, 093002 (2003) Increasing intensity Increasing intensity

The hydrogen (deuterium) molecule The Kinetic Energy Release spectra Background Dissociation Double ionization: enhanced ionization Rescattering Sequential Ionization Clocking the wave packet on a fs time scale using all three processes

The shortish pulse spectrum: all three processes time direction Momentum slice in plane containing polarization vector of internal motion of proton pair 12 fs, 2 x 10 14 w/cm2

Model and Experiment Model: Expt: Alnaser et al. Tong, Lin and Zhao 10 fs, 4 x 10 14 w/cm2 12 fs, 2 x 10 14 w/cm2

Overview of ionization and vibrational wave packet center Model: Tong, Lin and Zhao 10 fs, 4 x 10 14 w/cm2

Electron rescattering from molecules in intense laser fields Ali Alnaser, S.Voss, T.Osipov, M.Benis, B.Ulrich, C.Maharjan, X.-M.Tong, C.D.Lin, Z.Chang, B.Shan, P.Ranitovic, C.L.Cocke D2/H2 Old and new mechanisms for double electron removal and fs clocks N2/O2 Mechanisms for double electron removal: How do you get the electronic energy into the system? Does the orbital structure play a role and how?

Coulomb imaging used to take snapshots of molecule? How does snapshot really go and how long does it last? O2+4 O2+3 O2+2 O2+ O2

N2 and O2 :Are there similar mechanisms for heavier molecules? Rescattering Enhanced Sequential/MP O2 O2+ O2+2 TI TI TI O2+2 O2+2 O2+2 O2+2 MP MP O2+ O2+ O2+ O2+ TI TI O2 O2 O2 O2 Yes, but not with Short pulses Not without MP step Yes Low intensity, < 2x 10 14 w/cm2 High intensity, >5x10 14 w/cm2

Time of flight spectra for oxygen

Rescattering region (below 2 x 10 14 w/cm2): the momentum spheres have fine structure: oxygen z e q

O22+ 3sg -1pg-1 O2 pu -1pg-1 ..3sg2 pu4 pg2 The states populated are the same as are known from electron scattering pu -1pg-1 3sg -1pg-1 O22+ O2 ..3sg2 pu4 pg2 M. Lundqvist et al., J.Phys.B 29 499 (1996) Electrons Kinetic Energy Release (eV) Laser Kinetic Energy Release(eV)

The process… O2 O2+ O2+2 TI e- P1(q) P3(q) P2(q)

Angular distributions of N2 and O2 Can the alignment dependence of the first step , the production of the singly charged molecule, be seen? For H2, this distribution was isotropic; for other molecules, it is predicted by molecular ADK to reflect orbital structure. O+ - N+ + + e N2 .. pu4 3sg2 O2 ..3sg2 pu4 pg2

Momentum slices of N2 and O2 in rescattering region (short pulse) Pairs of singly charged ions only

The polar plots… pu -1pg-1

Molecular ADK Model 1.5 x 1014 watt/cm2, 8fs Model Experiment X. M. Tong, Z. X. Zhao, and C. D. Lin, Phys.Rev.A, 66, 033402 (2002)

Summary : For the hydrogen molecule, the vibrational molecule wave packet can be tracked on fs time scale using the optical cycle (2.7 fs) as a clock. This works when the double ionization is driven by rescattering or sequential ionization (not enhanced ionization). For nitrogen and oxygen, in the rescattering region, the expansion is initiated through population of well defined states of the dication (Coulomb potentials are irrelevant). The structure of the outermost orbitals is seen in the alignment dependence of the double ionization and supports the molecular ADK prediction.

Other issues: The dynamic alignment (a posteriori) of molecules/fragments Bond-softening couplings which peak at 90 degrees The short pulse “freezes” the nuclear motion

p g removal : short pulse 1.5 3 Intensities in 10 14 w/cm2 8 fs pulse 7 8

O2 short pulse KER vs angle KER (eV) q O+ Cos (q)

Future plans Do the orbital mappings apply to other systems?

Other systems.. C2H2 CO2 CO pu pg s Theory Preliminary experiment (lowest intensity)

Future plans Do the orbital mappings apply to other systems? Pump-probe experiments: Can the vibrational wave function be mapped out as a function of time?

Future plans: pump-probe Oscillation of wave packet in 1sg potential Sequential D+ + D+ Field Ionization probe, strong D2+ Time delay t Field Ionization pump, weak D 2 Enhanced ionization First results for molecular hydrogen Increasing intensity

Future plans Do the orbital mappings apply to other systems? Pump-probe experiments: Can the vibrational wave function be mapped out as a function of time? Use of electrons as “second hand” of clock

THE END