2017-2018 AMOP Seminar Abstracts

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Friday, Aug. 18, 2017

Spatial-Temporal Engineering of Few-Cycle Laser Pulses

James Strohaber, Department of Physics, Florida Agricultural and Mechanical University

James Strohaber, a former Ph.D. student who worked with Kees Uiterwaal, will give an AMO seminar TODAY, August 18 at 2:00-3:00 p.m. in room JH 247. After working at Texas A&M and Qatar, he become a tenure track professor in AMO at FAMU. Since 2013, he has more than 15 published papers in refereed journals. The topics he published on are frequency combs, broad band light generation, molecular alignment, optical vortices, and even frame dragging with optical vortices. The first part of the talk will be also focused on his career after earning his Ph.D. at UNL and aimed towards graduate students.

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Friday, Sept. 8, 2017

Picosecond Infrared Laser (PIRL) Scalpel: Achieving Fundamental Limits to Minimally Invasive Surgery and Biodiagnostics

R. J. Dwayne Miller, Max Planck Institute for the Structure and Dynamics of Matter

The first atomic view of strongly driven phase transitions (Siwick et al, Science 2003) illustrated the mechanism to control nucleation growth to nm scales (nucleation as small as 10 molecules). To take advantage of this new insight, a laser concept was developed based on a seeded Optical Parametric Amplifier and microchip laser technology to provide a compact robust source engineered to excite the OH stretch of water in biological tissue for use in laser surgery. The laser ablation process is driven within resonant 1-photon transitions in which the strong localization of the laser energy is provided by the extremely strong absorption of water in the 3 micron range. The strong absorption of water provides intrinsic confinement of the ablation process to the micron dimensions of a single cell in the longitudinal direction with lateral confinement defined by the laser focus conditions. Lasers currently in clinical use involve either massive tissue damage due to shock wave and thermal transport resulting in burning and tissue necrosis or is highly ionizing. The PIRL scalpel was found to readily cuts all tissues types and most importantly, the damage to surrounding tissue was negligible, with no discernable scar tissue formation (Amini-Nik et al, PLoS 2010). The reduced damage to surrounding tissue was correlated to reduced expression levels of signaling proteins involved in fibroblast formation that causes scar tissue formation to reinforce this conclusion. This is the first method, by any means, capable of surgery without scar tissue formation. In this respect, the long held promise of the laser for achieving the fundamental (cell) limit to surgery has now been realized. In the process, it was also discovered that entire proteins, even protein complexes, are ejected into the gas phase intact (Ren et al., Nanotechnology 2015). This observation has been rationalized on the basis that the whole process of vibrational excitation and coupling to translational motion driving ablation occurs faster than even collisional exchange of the excited water with the constituent proteins (see Miller, Ann. Rev. Phys. Chem. 1989) and the ensuing ablation occurs on time scales much faster than thermal fragmentation of the protein signatures. This new laser ablation mechanism referred to as Desorption by Impulsive Vibrational Excitation (DIVE) provides a new means for in situ spatial mapping with mass spectroscopy in which preliminary results show very detailed molecular fingerprints of different tissue types. An imaging mass spectrometer is being designed, based on lessons from the high brightness electron source development in the group, that should be capable of near unit ion and detection efficiency, to provide significant gains in sensitivity in mass spectroscopy. Preliminary results for ambient injection conditions relevant for laser surgery show that this method is capable of near attomolar sensitivity, which is near theoretical limits in terms of the collection and detector efficiency. The applications of basic research have turned full circle in which the technology developed for medical applications is now making the scientific case for Making a Molecular Map of the Cell – to reveal the essential nonlinear physics/biochemistry breathing life into otherwise inanimate matter.

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Wednesday, Sept. 27, 2017

Plasmonic metasurfaces and nanoantennas: an ideal platform to boost nanoscale light-matter interactions

Christos Argyropoulos, Department of Electrical and Computer Engineering, UNL

Plasmonic metasurfaces and nanoantennas can enhance, control, and manipulate the electromagnetic radiation in unprecedented ways and at nanoscale regions. They are poised to have fundamental implications at nanoscale light-matter interactions, especially in the nonlinear and quantum regimes. The large field enhancement in the vicinity of these systems due to localized or collective resonances ensures a significant boosting of optical nonlinear effects, chemical processes, collective and coherent spontaneous emission (superradiance), and other quantum effects in the weak and strong coupling regimes. In my talk, I will present recent theoretical and experimental advances towards demonstrating new nonlinear and quantum plasmonic systems. Several future integrated nanophotonic devices are envisioned based on the proposed nanostructures, such as nonlinear optical wave mixers and low-THz sources, nanolasers, all-optical switches, and efficient optical modulators with compact footprints.

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Wednesday, Feb. 28, 2018

Control of Electron Motion on an Attosecond Timescale

Jean Marcel Ngoko Djiokap, Department of Physics and Astronomy, UNL

Technological advances 17 years ago in producing new extreme ultraviolet coherent light sources with attosecond (1 as=10-18s) duration have created a new research field, namely, attosecond physics. A main goal of attosecond physics is to control electron motion on its natural (attosecond) timescale, in order to probe bond formation and breaking in molecules during chemical reactions. A milestone toward achieving such goal is the experimental realization of isolated, few-cycle, linearly-polarized attosecond pulses with stable and tunable carrier-envelope phase (CEP). However, the low intensity of these existing sources is a major obstacle towards inducing and controlling electron motion via nonlinear effects. Use of circularly or elliptically polarized attosecond light opens the possibility of investigating effects that are not accessible with linearly-polarized pulses.

In this talk, after briefly introducing the physical mechanisms at the basis of attosecond pulse generation, I will focus on our numerical and analytical methods for the investigation of ultrafast ionization processes in atoms and molecules of astrophysical interest, with emphasis on two-electron processes in which electron correlations play a key role. Enabled by the broad bandwidth of attosecond pulses, the first unusual effect we predicted in double ionization of helium by an intense few-cycle elliptically polarized attosecond pulse is the nonlinear dichroism [1]. The other effect is the novel electron phenomenon of electron vortices [2] in attosecond photoionization of atoms and molecules (cf. Fig.1), which provides a dramatic example of wave-particle duality. Our predictions of electron matter-wave vortices [2,3], which have now been observed experimentally [4], have already opened a new interdisciplinary area in physics.

References: [1] J.M. Ngoko Djiokap, N.L. Manakov, A.V. Meremianin, S.X. Hu, L.B. Madsen, and A.F. Starace, Phys. Rev. Lett. 113, 223002 (2014). [2] J.M. Ngoko Djiokap, S.X. Hu, L.B. Madsen, N.L. Manakov, A.V. Meremianin, and A.F. Starace, Phys. Rev. Lett. 115, 113004 (2015). [3] J.M. Ngoko Djiokap, A.V. Meremianin, N.L. Manakov, S.X. Hu, L.B. Madsen, and A.F. Starace, Phys. Rev. A 94, 013408 (2016). [4] D. Pengel, S. Kerbstadt, D. Johannmeyer, L. Englert, T. Bayer, and M. Wollenhaupt, Phys. Rev. Lett. 118, 053003 (2017).

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