Atomic Physics

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Doppler-free saturation of the cascade fluorescence that follows excitation of the transition in atomic rubidium (1906.07114v1)

J. E. Navarro-Navarrete, A. Díaz-Calderón, L. M. Hoyos-Campo, F. Ponciano-Ojeda, J. Flores-Mijangos, F. Ramírez-Martínez, J. Jiménez-Mier

2019-06-17

We present an experimental scheme that produces Doppler-free spectra of the second resonance transition in atomic rubidium. The experiment uses the saturation of the cascade fluorescence that occurs when thermal rubidium atoms interact with two counterpropagating nm laser beams of comparable intensity. Part of the excited atomic population goes through the level which then decays by emission of nm photons. Narrow dips appear in this otherwise broad nm fluorescence, which allows resolution of the hyperfine structure. A rate equation model is used to interpret the spectra. It is also shown that these narrow peaks can be used to lock the frequency of the nm laser. Using a second beam modulated in frequency produces three sets of spectra with known frequency spacings that can be used to perform an all-optical measurement of the hyperfine splittings of the manifold in rubidium.

Tracking Attosecond Electronic Coherences using Phase-Manipulated Extreme Ultraviolet Pulses (1906.07112v1)

Andreas Wituschek, Lukas Bruder, Enrico Allaria, Ulrich Bangert, Marcel Binz, Carlo Callegari, Giulio Cerullo, Paolo Cinquegrana, Luca Gianessi, Miltcho Danailov, Alexander Demidovich, Michele Di Fraia, Marcel Drabbels, Raimund Feifel, Tim Laarmann, Rupert Michiels, Najmeh Sadat Mirian, Marcel Mudrich, Ivaylo Nikolov, Finn H. O'Shea, Giuseppe Penco, Paolo Piseri, Oksana Plekan, Kevin Charles Prince, Andreas Przystawik, Primož Rebernik Ribič, Giuseppe Sansone, Paolo Sigalotti, Simone Spampinati, Carlo Spezzani, Richard James Squibb, Stefano Stranges, Daniel Uhl, Frank Stienkemeier

2019-06-17

The recent development of novel extreme ultraviolet (XUV) coherent light sources bears great potential for a better understanding of the structure and dynamics of matter. Promising routes are advanced coherent control and nonlinear spectroscopy schemes in the XUV energy range, yielding unprecedented spatial and temporal resolution. However, their implementation has been hampered by the experimental challenge of generating XUV pulse sequences with precisely controlled timing and phase properties. In particular, direct control and manipulation of the phase of individual pulses within a XUV pulse sequence opens exciting new possibilities for coherent control and multidimensional spectroscopy schemes, but has not been accomplished. Here, we overcome these constraints in a highly time-stabilized and phase-modulated XUV-pump, XUV-probe experiment which directly probes the evolution and dephasing of an inner subshell electronic coherence. This new approach, avoiding any XUV optics for direct pulse manipulation, opens up extensive applications of advanced nonlinear optics and spectroscopy at XUV wavelengths.

Nonlinear magneto-optical rotation with parametric resonance (1906.07082v1)

Piotr Put, Piotr Wcisło, Wojciech Gawlik, Szymon Pustelny

2019-06-17

We report on investigations of nonlinear magneto-optical rotation (NMOR) in rubidium vapor subjected to a modulated magnetic field and continuous-wave (CW) laser-light illumination. By superimposing modulation and a static (DC) magnetic fields, we demonstrate the appearance of resonances at both small and large (compared to the ground-state relaxation rate) values of the static field. Since in conventional NMOR, there is no rotation at high fields, this suggests an existence of a novel mechanism generating anisotropy in the considered case, which we identify as parametric resonance. The experiments are performed using light of small ellipticity and rotation signals are significantly enhanced by combining atom-induced polarization rotation with a passive rotation induced with a wave plate. All the experimental observations are supported with theoretical simulations. The density-matrix formalism and angular-momentum probability surfaces are used to provide intuitive explanation of the observed signals.

Reconstruction of attosecond pulses in the presence of interfering dressing fields using the 100 kHz ELI-ALPS HR-1 laser system (1906.07059v1)

D. Hammerland, P. Zhang, S. Kuehn, P. Jojart, I. Seres, V. Zuba, Z. Varallyay, K. Osvay, T. T. Luu, H. J. Woerner

2019-06-17

Attosecond Pulse Trains (APT) generated by high-harmonic generation (HHG) of high-intensity near-infrared (IR) laser pulses have proven valuable for studying the electronic dynamics of atomic and molecular species. However, the high intensities required for high-photon-energy, high-flux HHG usually limit the class of adequate laser systems to repetition rates below 10~kHz. Here, APT's generated from the 100 kHz, 160 W, 40 fs laser system (HR1) of the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI-ALPS) are reconstructed using the Reconstruction of Attosecond Beating By Interference of two-photon Transitions (RABBIT) technique. These experiments constitute the first attosecond time-resolved photoelectron spectroscopy measurements performed at 100 kHz repetition rate and the first attosecond experiments performed at ELI-ALPS. These RABBIT measurements were taken with an additional IR field temporally locked to the extreme-ultraviolet APT, resulting in an atypical omega beating. We show that the phase of the 2-omega beating recorded under these conditions is strictly identical to that observed in standard RABBIT measurements within second-order perturbation theory. This work highlights an experimental simplification for future experiments based on attosecond interferometry (or RABBIT), which is particularly useful when lasers with high average powers are used.

Roles of cooperative effects and disorder in photon localization: The case of a vector radiation field (1906.06966v1)

L. Bellando, A. Gero, E. Akkermans, R. Kaiser

2019-06-17

We numerically study photon escape rates from three-dimensional atomic gases and investigate the roles of cooperative effects and disorder in photon localization, while taking into account the vectorial nature of light. A scaling behavior is observed for the escape rates, and photons undergo a crossover from delocalization toward localization as the optical thickness of the cloud is increased. This result indicates that photon localization is dominated by cooperative effects rather than disorder. We compare our results with those obtained in the case of a scalar radiation field and find no significant differences. We conclude that the scalar model constitutes an excellent approximation when considering photon escape rates from atomic gases.

Complex collisions of ultracold molecules: a toy model (1906.06960v1)

Jia K. Yao, Nirav P. Mehta, Kaden R. A. Hazzard

2019-06-17

We introduce a model to study the collisions of two ultracold diatomic molecules in one dimension interacting via pairwise potentials. We present results for this system, and argue that it offers lessons for real molecular collisions in three dimensions. We analyze the distribution of the adiabatic potentials in the hyperspherical coordinate representation as well as the distribution of the four-body bound states in the adiabatic approximation (i.e. no coupling between adiabatic channels). It is found that while the adiabatic potential distribution transitions from chaotic to non-chaotic as the two molecules are separated, the four-body bound states show no visible chaos in the distribution of nearest-neighbor energy level spacing. We also study the effects of molecular properties, such as interaction strength, interaction range, and atomic mass, on the resonance density and degree of chaos in the adiabatic potentials. We numerically find that the dependence of the four-body bound state density on these parameters is captured by simple scaling laws, in agreement with previous analytic arguments, even though these arguments relied on uncontrolled approximations. This agreement suggests that similar scaling laws may also govern real molecular collisions in three dimensions.

Laser Cooling of Radium Ions (1901.09882v2)

M. Fan, C. A. Holliman, A. L. Wang, A. M. Jayich

2019-01-28

The unstable radium nucleus is appealing for probing new physics due to its high mass, octupole deformation and energy level structure. Ion traps, with long hold times and low particle numbers, are excellent for work with radioactive species, such as radium and radium-based molecular ions, where low activity, and hence low total numbers, is desirable. We address the challenges associated with the lack of stable isotopes in a tabletop experiment with a low-activity () source where we laser-cool trapped radium ions. With a laser-cooled radium ion we measured the state's branching fractions to the ground state, , and a metastable excited state, , to be and , respectively. With a nearby tellurium reference line we measured the transition frequency, 640.09663(6) THz.

Observing zero-field spin dynamics with spin noise in a pi-pulse modulated field (1901.00714v3)

Guiying Zhang, Ya Wen, Jian Qiu, Kaifeng Zhao

2019-01-03

Spin noise spectroscopic study of spin dynamics in a zero magnetic field is commonly frustrated by the dominating 1/f noise. We show that in a pi-pulse modulated magnetic field, spin noise spectrum centered one-half of the field modulation frequency reveals spin dynamics in zero-fields, free of any low-frequency noises.

Gaseous He Nuclear Magnetic Resonance Probe for Cryogenic Environments (1904.04804v2)

X. Fan, S. E. Fayer, G. Gabrielse

2019-04-09

Normal nuclear magnetic resonance (NMR) probes cannot be used to make high frequency resolution measurements in a cryogenic environment because they lose their frequency resolution when the liquid sample in the probe freezes. A gaseous He NMR probe, designed and constructed to work naturally in such cryogenic environments, is demonstrated at 4.2 K and 5.3 Tesla to have a frequency resolution better than 0.4 part per billion. As a demonstration of its usefulness, the cryogenic probe is used to shim a superconducting solenoid with a cryogenic interior to produce a magnetic field with a high spatial homogeneity, and to measure the magnetic field stability.

Optical Quenching of Metastable Helium Atoms using Excitation to the State (1906.06731v1)

Jiwen Guan, Vivien Behrendt, Pinrui Shen, Simon Hofsäss, Thilina Muthu-Arachchige, Jonas Grzesiak, Frank Stienkemeier, Katrin Dulitz

2019-06-16

Discharge and electron-impact excitation lead to the production of metastable helium atoms in two metastable states, 2S and 2S. However, many applications require pure beams of one of these species or at least a detailed knowledge of the relative state populations. In this paper, we present the characterization of an original experimental scheme for the optical depletion of He(2S) in a supersonic beam which is based on the optical excitation of the 4PS transition at 397 nm using a diode laser. From our experimental results and from a comparison with numerical calculations, we infer a near unit depletion efficiency at all beam velocities under study (1070 m/s 1750 m/s). Since the technique provides a direct means to determine the singlet-to-triplet ratio in a pulsed supersonic helium beam, our results show that the intrabeam singlet-to-triplet ratio is different at the trailing edges of the gas pulse.

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