Dr. Marko Gacesa,
BAER Institute / NASA Ames Research Center

Photoassociation of ultracold molecular ions and controlling atom-ion charge exchange using magnetic Feshbach resonances

Feshbach resonances offer a way to control the strength and sign of particle-particle interactions in ultracold atomic and molecular gases by tuning external magnetic or electric fields. This discovery led to a number of experimental applications in ultracold AMO physics, in particular in preparation and production of dense samples of ultracold molecules. Because of their importance, Feshbach resonances have been measured and characterized in numerous of neutral diatomic mixtures. A natural generalization of studies of neutral ultracold gases includes atom-ion mixtures, which remain much less investigated than neutral systems. Atom-ion interactions are, generally, more difficult to investigate due to their long-range nature and presence of the charge. Nevertheless, the same properties also offer a window to investigate different physical regimes than the ones accessible by the neutral systems.

In this talk, I will present recent results, obtained in collaboration with the group of Prof. Robin Cote, related to using external magnetic and electric fields in controlling charge-exchange in atom-ion collisions. Specifically, I will present our theoretical investigation of magnetic Feshbach resonances and their application to controlled charge transfer in \({}^{9,10}\)Be + \({}^{9,10}\)Be+, and \({}^{40}\)Ca+\({}^{43}\)Ca+ both of which are good model systems for heavier and more complex elements. I will also present the results of first theoretical study of photoassociative formation of cold molecular ions, where we estimated the production rates of NaCa+ molecular ions from trapped cold Na+ ions and Ca atoms. This study is based on experiments conducted in the group of Prof. W. Smith at UConn.

Dr. Thomas Allison
Stony Brook University


Cavity-enhanced ultrafast spectroscopy: ultrafast meets ultrasensitive


Ultrafast optical spectroscopy methods, such as transient absorption spectroscopy and 2D spectroscopy, are widely used across many disciplines. However, these techniques are typically restricted to optically thick samples, such as solids and liquid solutions. Using a frequency comb laser and optical cavities, we present a technique for performing ultrafast optical spectroscopy with high sensitivity, enabling work in dilute gas-phase molecular beams. Resonantly enhancing the probe pulses, we demonstrate transient absorption measurements with a detection limit of \(\Delta OD = 2 \times 10^{−10}\) (\(1 \times 10^{-9} / \sqrt{Hz}\)). Resonantly enhancing the pump pulses allows us to produce a high excitation fraction at a high repetition rate, so that signals can be recorded from samples with optical densities as low as \(OD ≈ 10^{−8}\), or column densities \( < 10^{10}\) molecules∕cm\(^2\). In this talk, I will discuss initial demonstration experiments, methods for cavity-enhancing multidimensional spectroscopy signals using multiple frequency combs, and progress towards widely tunable cavity-enhanced ultrafast spectrometers operating from the ultraviolet to the infrared.

Dr. Nora Kling
Department of Physics,
University of Connecticut

Ultrafast Nuclear Motion: Resolving Hydrogen Migration(s) in Time

Intramolecular hydrogen migration is a natural process that plays a crucial role in many biological, chemical, and physical phenomena, and is the object of current research efforts in fuel cells, proteomics, and combustion chemistry. Using ultrafast, intense lasers and sophisticated pump-probe ion imaging techniques, we can explore the rich dynamics of hydrogen migration reactions, including what timescale they occur on. In my talk, I will present two studies. The first study is on acetylene, a small hydrocarbon, where a hydrogen can migrate across the carbon atoms to form its vinylidene isomer [1,2]. The second study is on ethanol, a complex molecule where both single and double hydrogen migrations occur, and the timescale for each is individually determined [3]. These experimental results, in combination with state-of-the art quantum chemical trajectory calculations, give us new insight into the complex nuclear motions in complex polyatomic molecules.



[1] C. Burger et al. Faraday Discussions 194, 495 (2016).

[2] M. Kübel et al. Phys. Rev. Lett. 116, 193001 (2016).

[3] N. G. Kling et al. submitted for publication

Dr. Aaron LaForge, Department of Physics, University of Connecticut

Excitation dynamics in helium nanodroplets induced by XUV radiation

As opposed to purely molecular systems where electron dynamics proceed only through intramolecular processes, weakly-bound complexes like helium nanodroplets offer an environment where local excitations can interact with neighboring molecules leading to new intermolecular relaxation mechanisms. Here, we present a systematic, time-resolved study of the excitation dynamics when helium nanodroplets are resonantly excited by XUV free electron laser radiation. At low pulse energy, a single atom is excited leading to the formation of a bubble state which relaxes to the droplet surface on a femtosecond timescale. At high pulse energy, a network of excited atoms is formed within a nanodroplets which then collectively autoionizes with high efficiency. Using the pump-probe technique, we were able to time resolve this process.

Dr. Shimshon Kallush, Physics and Optical Engineering Department, ORT Braude College, Karmiel, and The Fritz Haber Center for Molecular Dynamics, The Hebrew University, Jerusalem, Israel

Molecular alignment in hot and cold regimes, and its relationship to quantum coherence

The phenomena of field-free instantaneous quantum revivals of molecular alignment and orientation driven by optical and/or terahertz fields will be introduced. A brief survey over a few applications of the phenomena will be presented within this context:

1. Ultracold photoassociation will be shown to intrinsically contain molecular alignment. Its characteristics and the feasibility to detect directional preferences for the photoassociated species will be discussed.

2. Rotational echoes of alignment under multiple pulses will be shown to lead to unique spatial-temporal structures of the refractive index. Several applications of this feature will be suggested.

3. The quantum picture of alignment raises questions that relate to the ability to embed quantum coherences into thermal quantum systems. The problem of quantification of coherences is defined and some results that predict the ability to induce field-driven coherences will be presented

Dr. Peter Walter, SLAC National Accelerator Laboratory

The TMO Instrument: Opportunities and Plans for Time-resolved Atomic, Molecular, and Optical Science at LCLS-II

The unique capabilities of LCLS, the world's first hard X-ray FEL, have had significant impact on
advancing our understanding across a broad range of science, from fundamental atomic and molecular
physics, to condensed matter, to catalysis and to structural biology.

A major upgrade of the LCLS facility, the LCLS-II project, is now underway. LCLS-II is being developed
as a high-repetition rate X-ray laser with two simultaneously operating, independently tunable
FELs. It features a 4 GeV continuous wave superconducting linac that is capable of producing
uniformly spaced (or programmable) ultrafast X-ray laser pulses at a repetition rate up to 1 MHz spanning the energy range from 0.25 to 5 keV.

The Time resolved AMO (TMO) instrument, one of the four new LCLS-II instruments, will support AMO science, strong-field and nonlinear science, and a new dynamic reaction microscope. TMO will support
many experimental techniques not currently available at LCLS and will locate two experimental endstations. A new reaction microscope endstation will house a COLTRIMS type spectrometer to accommodate extreme vacuum, sub-micron focus spot size, and target purity requirements as dictated by coincidence experiments. The accumulation of data will be performed on an event-by-event basis using the the 1MHz full repetition rate of LCLS-II. A second TMO
endstation will be optimized for performing high energy, high resolution, time- but also angular-resolved
photoelectron spectroscopic measurements. By leveraging its existing suite of spectrometers (i.e. high
resolution iTOF, eTOF, LAMP double-sided VMIs, Kaesdorf spectrometers) a high resolution, high throughput, hemispherical electron analyzer will also be available. The photon fluence at TMO should reach up to 10^22 photons/cm^2, thus allowing to be tailored to specific experimental needs.

This talk will present some of the important science opportunities, new capabilities and instrumentation being planned for NEH 1.1 (TMO) at LCSL-II.

Dr. Robert R. Jones, Department of Physics, University of Virginia

Controlled Transfer of Electronic Wavepacket Motion Between Distant Atoms

The establishment, observation, and potential control of correlated multi-electron dynamics is a complex problem of interest across disciplines with numerous applications in a variety of contexts, from femtosecond interatomic Coulomb decay and attosecond charge migration within small molecules, to energy transfer in photosynthetic systems, to quantum control of few- and many-body systems, and quantum information processing. The extreme sensitivity of Rydberg atoms to electric fields, including those produced by neighboring atoms, makes them superb candidates for studying such phenomena. In a quantum analogy to classical far-field radio transmission from a source to receiver antenna, we have transferred electronic wavepacket motion established within Rydberg atoms in a dilute nearly-frozen gas to neighboring Rydberg atoms. The transfer is enabled by electron correlations resulting from electric field-controlled, atom-atom couplings and relies on the use of both cold atom and ultrafast techniques.

Prof. Dominik Schneble, Department of Physics and Astronomy, Stony Brook University

Exploring the Physics of Spontaneous Emission in a Matter-Wave Open Quantum System

The question how irreversibility can emerge in quantum mechanics is central to the study of open quantum systems. A simple example is the exponential decay of an excited two-level atom as described by the Wigner-Weisskopf model of quantum optics, in which spontaneous photon emission is sometimes viewed as being driven by fluctuations of the surrounding vacuum. However, the Markov approximation underlying this model can be violated under certain conditions, and recent experiments on optical decay in photonic bandgap materials have indeed started to find deviations from its predictions.

We have recently realized an "artificial atom" in which the excited-state energy and the vacuum coupling can be controlled at will, thus allowing for a systematic exploration of spontaneous emission beyond the Markov approximation. Naively, a two-level atom may be viewed as a photon trap that is empty or full; we instead realize a microscopic trap for a single atom that can decay, under coherent external driving, by emitting the atom into the surrounding vacuum. The experiments are performed using an optical lattice geometry that provides arrays of such artificial atoms coupled to a one-dimensional matter waveguide. In my talk I will present experimental results on Markovian and strongly non-Markovian dynamics, including exponential and partly reversible oscillatory decay, atom reabsorption, as well as a bound state for emission below the edge of the mode continuum that features an evanescent matter wave and which is the direct analog of the long-predicted atom-photon bound state in photonic bandgap materials. I will conclude with an outlook on future applications of our system in open-system many-body quantum physics.

Sadiq Rangwala, Raman Research Institute, India

Refrigeration of ions with atoms

Advances in cooling and trapping for several distinct species of atoms, ions and molecules have gone hand-in-hand for a long time now. Cold dilute gas ensembles to single particle realization of these have led to investigations of diverse problems in many body physics and exotic physics on one hand to unprecedented spectroscopic precision on the other. In most cases, it is the interaction between trapped particles and the confining fields which is used to realize the system of interest. In these systems, it is typical to know the initial position and motional state with precision. Most experiments though are performed with either atoms or ions or molecules.

Combining cold ions, atoms and molecules for experiments has been gaining traction in recent times. Such combined hybrid traps [1] pose very specific challenges for simultaneous trapping and cooling of the multiple species. In addition the interactions between different species become paramount and it is imperative to understand how the combined systems evolve, how energy is exchanged, what is the final state mediated by these interactions, etc. Of course very important work on this topic has been pioneered at U. Conn. In this talk I shall present our experimental system which can simultaneously cool and trap, within a cavity mode, atoms, ion and molecules in any combination [2]. In this experiment interactions between co-trapped species whose long range interaction range from 1/r to 1/r6 can be probed. I shall then present results of how an ion in a Paul trap is cooled by a MOT of atoms. The details of the cooling hold several surprises such that the ultimate temperature of the trapped ions can be decided by the spatial size of the MOT [3,4], the process of resonant charge exchange is very effective of ion cooling [5], etc. I shall conclude with the prospects of experiments in the future, with such ion-atom systems at ultracold temperatures.

References:

[1] K. Ravi, S. Lee, A. Sharma, G. Werth, and S. A. Rangwala, Appl. Phys. B 107, 971 (2012).

[2] S. Jyothi, T. Ray, N. B. Ram, and S. A. Rangwala, in Ion Traps Tomorrow's Applications (IOS Press, 2015), 189, 269--278.

[3] K. Ravi, S. Lee, A. Sharma, G. Werth, and S. A. Rangwala, Nat. Commun. 3, 1126 (2012).

[4] S. Dutta, R. Sawant, and S. A. Rangwala, Phys. Rev. Lett. 118, 113401 (2017).

[5] S. Dutta and S. A. Rangwala, arXiv:1705.07572

Niloy Dutta, Department of Physics, University of Connecticut

Optical Transmission and Fiber Lasers

This talk will describe our research over the last few years in the area of fiber lasers, supercontinuum generation, optical correlation and optical transmission studies. Future directions in these areas will be discussed

Derrek Wilson, Department of Physics, Kansas State University

The scaling of strong field interactions with wavelength

An important aspect of light-matter interactions is their dependence on the frequency of the light. In the ultrafast, strong-field regime, the wavelength can be responsible for how matter responds to an intense field, governing phenomena related to the dynamics of accelerating free (or quasi-free) electrons. In this presentation, I will discuss two studies whose aims are to answer questions on the role wavelength in strong field interactions.

In the first study, we will look into strong field absorption in solid state materials, which have been shown to depend on the density of states. We consider the role of wavelength on this process by scanning across an octave of central wavelengths, covering two photon and three photon absorption for Gallium Arsenide. When varying the density of states, we see that the response changes with wavelength. Our current explanation is based on the dynamics of the electron in the conduction band, with longer wavelengths capable of inducing Bragg reflections more readily.

The second project shows progress on a light source suitable of studying strong field science in the long wave infrared (LWIR). The source, which is based on difference frequency generation of an optical parametric amplifier, is capable of generating few-cycle pulses with central wavelengths spanning 5-9 microns, and peak intensities in the 100 TW/cm^2 region. As a proof of principle for this sources ability to extend strong field science into the LWIR, we perform strong field ionization of Xenon gas across this wavelength range.

Soroush Khosravi-Dehaghi, Department of Physics, University of Connecticut

Femtosecond nonlinear optical spectroscopy of carotenoids and single wall carbon nanotubes

Nonlinear optical spectroscopy can provide the most comprehensive picture of the optical response of any quantum system. The energy structure and excited state dynamics of the system can be revealed unambiguously, using such a comprehensive time- and frequency- resolved (both detection and excitation frequencies) optical response. My research has been focused on the measurement and interpretation of the optical responses of different samples using two of the most advanced ultrafast nonlinear optical spectroscopy techniques including Transient Absorption (TA) and Transient Grating (TG) spectroscopies. Transient absorption spectroscopy measures the time- and frequency- resolved (detection) amplitude of the optical response of the system after an initial excitation to a specific energy state. Heterodyne transient grating spectroscopy, which employs a more sophisticated light-matter interaction geometry, measures the phase of the optical response in addition to its time- and frequency- resolved (detection) amplitude. The latest results of the measurements on carotenoids and single wall carbon nanotubes (SWNTs) will be presented.