Strong Field Quantum Control. CAMOS Spring Meeting 2012 o

Transcription

1 Strong Field Quantum Control CAMOS Spring Meeting 2012 o p

2 Motivation & Outline Motivation: Want to control molecular dynamics and develop control based spectroscopy 1. Controlling Molecular Dissociation Closed loop control Phase dependent dissociation 2. Controlling Molecular Ionization Electronic hole wave packets Pulse shape dependent ionization 3. Control for Discrimination Combine control & stimulated emission for perfect discrimination Quantum Control Spectroscopy

3 Molecular Fragmentation & Ionization Apparatus

4 Ultrafast Optical Pulse Shaping Programmable mask which shapes E( ) = E( ) e i Grating Lens In Out

5 Closed Loop Molecular Control Results CH 3 COCF 3 CHBr 2 COCF 3 Shaped Pulse CF 3 + /CHBr2 + Unshaped Pulse CH 2 IBr GA results: shaped unshaped J. Chem. Phys. 123, (2005) Ion Signal CH 2 I + CH 2 IBr + J. Chem. Phys. 127, (2007)

6 Optimal Control Pulses I(t) (t) First sub-pulse pumps (launches) wave packet Second sub-pulse dumps the wave packet J. PhotoChem.& PhotoBio. A 180, 277 (2006)

7 Pump-Probe Measurements: CH 2 I 2 Bond breaking CH 2 I 2 Note phase difference Bond formation J. Chem. Phys (2007)

8 Strong Field Ionization (Pump) Keldysh parameter: V e (r) laser tunnel 1 V N (R) r R Electron can tunnel out in a fraction of laser cycle quasi static Ionic equilibrium doesn t overlap with neutral launch wave packet

9 Resonant Dissociation (probe) Small molecules with many electrons can have 1-2 ev resonances in molecular ion Low excitation energy moving hole around in the ion Wave packet moves (and spreads) Can be transferred to dissociative excited state by probe pulse J. Chem. Phys. 127, (2007)

10 Interpreting The Dynamics CH 2 I 2 2D Bending, Stretching Potential Energy Surface PES calculated by Tamás Rozgonyi, Hungarian Academy of Sciences

11 Wave Packet Dynamics

12 Comparing Experiment with Calculated Dynamics 290 fs 292 fs Wave packet calculations Pump-probe measurements

13 What Happens if we Break the Symmetry of the Molecule?: CH 2 IBr Ion Signal [arb] Ion Signal [arb] Time Delay [ps] Time Delay [ps] Note two (unequal) oscillations per vibrational period!

14 Potential Energy Curves for CH 2 IBr + V 3 ion is dissociative Energy [ev] Probe Displacement along other coordinates is very small Pump I I Br Br

15 Wave Packet Calculations for CH 2 IBr Transfer is not Symmetric!

16 Does Dissociation Depend on Phase or Amplitude? (u B ) 2 Left and right going wave packets have the same amplitude

17 Intensity Dependence Calculation Experiment Molecule is transparent for left going wave packet in large fields! Accounting for intensity volume averaging leads to excellent agreement between experiment and theory

18 Picturing the Dynamics Physical Review A (2009)

19 Understanding the Dynamics: Dressed States Diagonalize: V ion 3 ( R) h 03 E probe probe 03E probe ion V ( ) 0 R Energy [ev] Laser molecule interaction 2GV/m 5 GV/m Dissociation depends on: Strong laser field dressing the potentials Spatially varying phase of the wave function

20 Revisiting Molecular Ionization (CH 2 I 2 ) V e (r) r Molecule with many electrons Lots of electrons to choose from Multiple low lying electronic states with comparable tunneling rates

21 Comparing Weak and Strong Field Ionization Multiphoton laser ~ 10 UV tunnel E IR laser ~ 1 IR tunnel Tunnel + Multiphoton hν = 4.74 ev I p = 9.46 ev 2h = 9.48 ev Strong Field IR Ionization (Tunneling) Weak Field UV Ionization ( Multiphoton )

22 Strong vs Weak Field Ionization CH 2 I 2 + Pump Probe Scan Beating, multiple frequencies = wave packets on different potentials FT Strong Field (IR pump) Weak Field (UV pump) One wavepacket moving on a single potential

23 Multiple Electronic States Controlled by Chirp 96 cm cm cm 1 CH 2 I + 2 More Positive Chirp 96 cm cm 1 Neg. Chirp Pos. Chirp

24 Different Frequencies Correspond to Different Ionic States Excited by Pump Wave packet can cross from V 2 to V 1 here Wave Packet on V 1 starting here has ~ 98 cm -1 frequency

25 Control over Ionization Viewed with Velocity Map Imaging Variations in yield with pulse shape correlation spectroscopy V 4 V 3 V 2

26 Strong Fields - Dynamic Resonance Na energy levels 4s> 777nm 3s> 1141 nm 589 nm 3p> Coupling strength and energy shifts are of the same order of magnitude -> low efficiency Absorption -> Emission P 4s> Stark shift: E (t) o o Without Stark shift E With Stark shift 2

27 Strong Fields Dynamic Resonance

28 Spontaneous vs Stimulated Emission - Na Spontaneous Emission Stimulated Emission Unshaped pulse yield Improvement over unshaped ~ 3 Improvement over unshaped ~ 10 3

29 Understanding Single Atom Strong Field Dynamics Measured Optimal Pulses Put these measured pulses into the Schrödinger equation with H given by: (t) is atom-field phase, (t) is two-photon coupling E t A t t ( t)) cos( 0 Differential Stark shift Detuning Laser Phase

30 Understanding Single Atom Strong Field Dynamics Measured Optimal Pulses E t A t t ( t)) cos( 0

31 Understanding Single Atom Strong Field Dynamics 2 P 4s (t), (t) shaped P 4s (t), (t) unshaped I(t) measured (t) is the atom-field phase P 4s Phys. Rev. Lett (2006)

32 Stimulated Emission very sensitive to excited state population Experiment Theory Note threshold at 2/3 4s 2 Stimulated emission is superfluorescence locking of atomic dipoles Modest single atom gains lead to large stimulated gains

33 Control based Discrimination T. Brixner et al Nature 414, 57 (2001)

34 Consider the Same Experiment, but now with Stimulated Emission Combine closed loop learning control with stimulated emission

35 to Achieve Perfect Discrimination Rb Na [Ru(dpb) 3 ] 2+ DCM Control ratios >10 4 (earlier work demonstrated ~2) Stimulated emission microscopy: Min et al Nature 461, 1105 (2009) S. D. Clow et al New J of Phys (2010)

36 Control based Discrimination for measuring Enzyme Binding MDH NADH NADH: nicotinamide adenine dinucleotide MDH: mitochondrial malate dehydrogenase

37 Other Implementations of Quantum Control/Pulse Shape Spectroscopy From Pulse Shaper Detection Adenine Pump Pump Probe τ T

38 Conclusions & Future Work Shaped laser pulses can be used to control dissociation and ionization Control + stimulated emission can lead to perfect control Quantum Control Spectroscopy has many applications

39 Acknowledgements Marija Kotur Dominik Gei ler Péter Sandor Oumarou Njoya Martin Cohen Chien-Hung Tseng (University of Michigan) Sarah Nichols (College of the Canyons) Stephen Clow (Northrop Grummon) Carlos Trallero (KSU) Brett Pearson (Dickinson College) Collaborators: Spiridoula Matsika (Temple U) Tamas Rozgonyi (Hungarian Academy of Sciences) Leticia Gonzalez (Universität Jena) Philipp Marquetand (Universität Jena) Jesus Gonzalez Vasquez (Universität Jena) Funding: NSF & DoE