Sharly Fleischer, Yan Zhou, Robert W. Field, Keith A. Nelson FRISNO 11 Orientation and Alignment of Gas Phase Molecules by Single Cycle THz Pulses

Multiphoton Ionization Self focusing & Filamentation High Harmonic Generation Ultrafast x-ray diffraction Up – Down Symmetry Conserved

DC field + - Not Field Free !

Sakai and colleagues: DC electric field + laser pulse with adiabatic turn-on and nonadiabatic turn-off. Approaches for field – free orientation A. Goban, S. Minemoto, and H. Sakai, “Laser-Field-Free Molecular Orientation,“ Phys. Rev. Lett. 101, (2008).

Vrakking and colleagues: Hexapole state selector (Producing molecules in a single quantum state) + a combination of a DC and intense fs laser field. Approaches for field – free orientation O. Ghafur, A. Rouzée, A. Gijsbertsen, W. K. Siu, S. Stolte and M. J. J. Vrakking, “Impulsive orientation and alignment of quantum-state-selected NO molecules,” Nature Phys. 5, (2009).

Approaches for field – free orientation L. Holmegaard, J. L. Hansen, L. Kalhøj, S. L. Kragh, H. Stapelfeldt, F. Filsinger, J. Küpper, G. Meijer, D. Dimitrovski, M. Abu-samha, C. P. J. Martiny and L. B. Madsen, “Photoelectron angular distributions from strong- field ionization of oriented molecules,” Nature Phys. 6, (2010). Holmegaard and colleagues: Electrostatic quantum state selector + deflector combination of a DC and femstosecond laser field.

Kling and colleagues: Approaches for field – free orientation two-color excitation scheme in which the fundamental laser frequency (800 nm) is mixed with its second harmonic with a specified relative phase. S. De, I. Znakovskaya, D. Ray, F. Anis, Nora G. Johnson, I. A. Bocharova, M. Magrakvelidze, B. D. Esry, C. L. Cocke, I.V. Litvinyuk, and M. F. Kling “Field-Free Orientation of CO Molecules by Femtosecond Two-Color Laser Fields,” Phys. Rev. Lett. 103, (2009).

Optical Pulse vs. Half Cycle Pulse 1.3 fs

Ultrashort optical pulse Half cycle pulse AlignmentOrientation

Population Transfer Coherences Alignment Density matrix – non resonant

Population Transfer Coherences Alignment x x x x x x x x x x x x x Density matrix – non resonant

Population Transfer Coherences Orientation Density matrix - resonant

Population Transfer Coherences Orientation and Alignment Density matrix - resonant

ResonantNon resonant May induce all the rotational cohernces May induce only even rotational coherences No orientation Only alignment Both orientation and alignment Short summary

Intense single cycle THz pulse K. L. Yeh, M. C. Hoffmann, J. Hebling and K. A. Nelson, “Generation of 10 μJ ultrashort THz pulses by optical rectification”, Appl. Phys. Lett. 90, (2007); LiNb

“But you don’t have a Half Cycle Pulse !!!” Time (ps) Amplitude (a.u)

Time (ps) Amplitude (a.u) Frequency (THz) Spectral Amplitude (noramlized) ResonantNon - Resonant Time(ps) J states (m=0) Amplitude (a.u) Population Transfer J,J+1 coherences J,J+2 coherences

Revival

Quantum revivals of rotational wave packets Rotational energy: Rotational wave packet: Quantum revival time: The wavefunction is periodic: - full revival Accumulated phase

O=C=S BS G LiNb Laser Pellicle BS ZnTeW PD Delay EO sampling

1 T rev 2 T rev 3 T rev Time (ps) Amplitude (a.u) EO sampling, OCS, 250torr Reflections

O=C=S BS G LiNb Laser Delay PPD Pellicle BS BS P 45 0 to THz polarization Pellicle BS ZnTeW PD Delay Detection of Molecular Alignment

Time (ps) Intensity (a.u.) Population Transferred To higher J’s Alignment of OCS, 350torr, 300K

Each molecule is forced to rotate in a plane Non thermal rotational distribution Time independent alignment

Time (ps) Intensity (a.u.) Decay of population (T 1 )

Decay of coherence (T 2 ) Time (ps) Intensity (a.u.)

Rotational state distribution (J) Intensity (a.u.)

Experimental alignment factor

Max 1T rev (x10 2 ) Max 1/2T rev (x10 4 ) Peak field amplitude (a.u.) Max Alignment=1.207x10 -4 x Peak 2 Max Orientation=1.441x10 -2 x Peak Time (ps) Amplitude (a.u) 1% orientation 5% orientation8% orientation

Summary Table top single cycle THz pulses can induce significant field-free orientation under ambient conditions Relatively high orientation is not necessarily associated Requires with high degree of alignment. With jet cold molecular samples, higher degree of orientation is expected. Combining optical and THz pulses may enable two independent handles for manipulating molecular angular distributions in 3D.

Thank you