Summary form only given. Fundamental processes in atoms, molecules, as well as condensed matter are triggered or mediated by the motion of electrons inside or between atoms. Electronic dynamics on atomic length scales tends to unfold within tens to thousands of attoseconds (1 attosecond [as] = 10-18 s). Recent breakthroughs in laser science are now opening the door to watching and controlling these hitherto inaccessible microscopic dynamics. The key to accessing the attosecond time domain is the control of the electric field of (visible) light, which varies its strength and direction within less than a femtosecond (1 femtosecond = 1000 attoseconds). Atoms exposed to a few oscillations cycles of intense laser light are able to emit a single extreme ultraviolet (XUV) burst lasting less than one femtosecond. Full control of the evolution of the electromagnetic field in laser pulses comprising a few wave cycles have recently allowed the reproducible generation and measurement of isolated sub-femtosecond XUV pulses, demonstrating the control of microscopic processes (electron motion and photon emission) on an attosecond time scale. These tools have enabled us to visualize the oscillating electric field of visible light with an attosecond "oscilloscope", to control single-electron and probe multi-electron dynamics in atoms, molecules and solids. Recent experiments hold promise for the development of an attosecond X-ray source, which may pave the way towards 4D electron imaging with sub-atomic resolution in space and time.

Attosecond Physics

Semiconducting carbon nanotube transistors with channel lengths exceeding 300 microns have been fabricated. In these long transistors, carrier transport is diffusive and the channel resistance dominates the transport. Transport characteristics are used to extract the field-effect mobility (79 000 cm2/Vs) and estimate the intrinsic mobility (>100 000 cm2/Vs) at room temperature. These values exceed those for all known semiconductors, which bodes well for application of nanotubes in high-speed transistors, single- and few-electron memories, and chemical/biochemical sensors.

Extraordinary Mobility in Semiconducting Carbon Nanotubes

Carbon nanotubes have unique properties that make them a most promising system on which to base molecular electronics. We briefly review the electrical characteristics of carbon nanotubes, and then focus on carbon nanotube field-effect transistors (CNTFETs). Procedures by which hole-transport, electron-transport and ambipolar CNTFETs can be fabricated are presented, and their electrical characteristics are discussed and compared with those of Si MOSFETs. Ways to fabricate arrays of CNTFETs are also demonstrated, and electron and hole CNTFETs are integrated to form complementary logic circuits.

Molecular Electronics with Carbon Nanotubes

Coherent light sources have been widely used in control schemes that exploit quantum interference effects to direct the outcome of photochemical processes. The adaptive shaping of laser pulses is a particularly powerful tool in this context: experimental output as feedback in an iterative learning loop refines the applied laser field to render it best suited to constraints set by the experimenter. This approach has been experimentally implemented to control a variety of processes, but the extent to which coherent excitation can also be used to direct the dynamics of complex molecular systems in a condensed-phase environment remains unclear. Here we report feedback-optimized coherent control over the energy-flow pathways in the light-harvesting antenna complex LH2 from Rhodopseudomonas acidophila, a photosynthetic purple bacterium. We show that phases imprinted by the light field mediate the branching ratio of energy transfer between intra- and intermolecular channels in the complex's donor acceptor system. This result illustrates that molecular complexity need not prevent coherent control, which can thus be extended to probe and affect biological functions.

Quantum control of energy flow in light harvesting.

https://engineering.purdue.edu/~fsoptics/articles/Ultrafast_optical_pulse_shaping_tutorial-Weiner.pdf

Ultrafast optical pulse shaping: A tutorial review

We used strong-field laser pulses that were tailored with closed-loop optimal control to govern specified chemical dissociation and reactivity channels in a series of organic molecules. Selective cleavage and rearrangement of chemical bonds having dissociation energies up to approximately 100 kilocalories per mole (about 4 electron volts) are reported for polyatomic molecules, including (CH 3 ) 2 CO (acetone), CH 3 COCF 3 (trifluoroacetone), and C 6 H 5 COCH 3 (acetophenone). Control over the formation of CH 3 CO from (CH 3 ) 2 CO, CF 3 (or CH 3 ) from CH 3 COCF 3 , and C 6 H 5 CH 3 (toluene) from C 6 H 5 COCH 3 was observed with high selectivity. Strong-field control appears to have generic applicability for manipulating molecular reactivity because the tailored intense laser fields (about 10 13 watts per square centimeter) can dynamically Stark shift many excited states into resonance, and consequently, the method is not confined by resonant spectral restrictions found in the perturbative (weak-field) regime.

https://science.sciencemag.org/content/sci/292/5517/709.full.pdf

Selective Bond Dissociation and Rearrangement with Optimally Tailored, Strong-Field Laser Pulses

In intense laser fields, fragment ions can be produced from CH3COX (X = CH3, CF3, and C6H5) either by absorption and dissociation followed by ionization (ADI) or absorption and ionization followed by dissociation (AID). Electronic structure calculations were carried out using Hartree−Fock, density functional, and correlated levels of theory to understand the possible fragmentation pathways. The calculated ionization potentials are in very good agreement with the available experimental data. For acetone, the acetyl ion is predicted to be the most preferred dissociation product and can be produced by either mechanism. The very low C−CF3 bond energy in the parent ion of trifluoroacetone provides a clear reason for the absence of CF3COCH3+ and CF3CO+ ion peaks from the mass spectrum of CF3COCH3 after intense laser excitation and indicates that fragmentation occurs by AID. For acetophenone, both CH3CO+ and C6H5CO+ are stable fragments, with the latter being produced by an AID mechanism.

Fragmentation Pathways in a Series of CH3COX Molecules in the Strong Field Regime

An investigation of the effects of experimental parameters on the closed-loop control of photoionization/dissociation processes in acetophenone

Control of chemical photoionization, dissociation, and rearrangement is demonstrated using tailored intense (10 W cm) laser pulses. The laser pulses are created using a closedloop learning algorithm with the product distribution guiding the shape of the laser pulses. Control is demonstrated for the production of the acetone parent ion ((CH3)2CO ), the competition of the products CH3CO + vs. CH3 + during CH3COCF3 laser induced dissociation, and the rearrangement acetophenone (C6H5COCH3) to produce C6H5CH3 vs. C6H5 + CH3CO. The generic nature of the technique is demonstrated and the fundamental underlying principles of such strong-field control experiments are considered.

The mechanisms of strong-field control of chemical reactivity using tailored laser pulses

The control of chemical reactivity is possible using tailored laser pulses in the strong field regime. We show that intense laser pulses induce sufficient transient shifting, lifetime broadening and multiphoton excitation to allow manipulation of complex organic molecules.

Getahun Menkir

Papers

Selective Bond Dissociation and Rearrangement with Optimally Tailored, Strong-Field Laser Pulses

Fragmentation Pathways in a Series of CH3COX Molecules in the Strong Field Regime

An investigation of the effects of experimental parameters on the closed-loop control of photoionization/dissociation processes in acetophenone

The mechanisms of strong-field control of chemical reactivity using tailored laser pulses

Strong Field Control of Photochemistry Using Tailored Laser Pulses