Roman Barankov - Academia.edu (original) (raw)

Papers by Roman Barankov

Journal of the Optical Society of America A, 2015

An optically transparent thin sample is characterized by a distribution of pathlengths and a weak... more An optically transparent thin sample is characterized by a distribution of pathlengths and a weak attenuation parameter. The phase shifts imparted by the sample can be measured using a partitioned detection aperture [Opt. Lett. 37, 4062 (2012)]. In this work, we analyze the system using paraxial wave optics and derive three-dimensional spread functions for phase and intensity. Using these functions we discuss methods of phase reconstruction for in-and out-of-focus samples, insensitive to weak attenuations of light. Our approach provides a strategy for detection-limited lateral resolution with extended depth of field, and is applicable to imaging smooth and rough samples.

Optica, 2015

ABSTRACT Adaptive optics is a strategy to compensate for sample-induced aberrations in microscopy... more ABSTRACT Adaptive optics is a strategy to compensate for sample-induced aberrations in microscopy applications. Generally, it requires the presence of "guide stars" in the sample to serve as localized reference targets. We describe an implementation of conjugate adaptive optics that is amenable to widefield (i.e. non-scanning) microscopy, and can provide aberration corrections over potentially large fields of view without the use of guide stars. A unique feature of our implementation is that it is based on wavefront sensing with a single-shot partitioned-aperture sensor that provides large dynamic range compatible with extended samples. Combined information provided by this sensor and the imaging camera enable robust image de-blurring based on a rapid estimation of sample and aberrations obtained by closed-loop feedback. We present the theoretical principle of our technique and proof of concept experimental demonstrations.

Optics in the Life Sciences, 2015

ABSTRACT We demonstrate the possibility of image transmission through a single optical fiber, whe... more ABSTRACT We demonstrate the possibility of image transmission through a single optical fiber, where spatial positions are converted to spectral codes that span the full bandwidth of the object spectrum.

Recent experiments on strongly-interacting bosons in optical lattices [1,2] have revealed the co-... more Recent experiments on strongly-interacting bosons in optical lattices [1,2] have revealed the co-existence of spatially-separated Mott-insulating and number-fluctuating phases in the presence of an external trapping potential. Employing a simple theoretical model [3], we obtain an effective description of the superfluid state trapped between the Mott states. We calculate the collective excitation spectrum of such a superfluid and its critical temperature, and discuss the crossover between two- and three-dimensional behavior of its thermal properties as a function of the lattice parameters. [1] S. F"olling, A. Widera, T. M"uller, F. Gerbier, and I. Bloch, Phys. Rev. Lett. 97, 060403 (2006). [2] G. K. Campbell, J. Mun, M. Boyd, P. Medley, A. E. Leanhardt, L. Marcassa, D. E. Pritchard, and W. Ketterle, Science 313, 649 (2006). [3] R. A. Barankov, C. Lannert, and S. Vishveshwara, cond-mat/0611126.

The dynamical atom/molecule projection, recently used to probe fermion pairing, is fast compared ... more The dynamical atom/molecule projection, recently used to probe fermion pairing, is fast compared to collective fermion times, but slow on the Feshbach resonance width scale. Theory of detuning-induced dynamics of molecules coupled to resonantly associating atom pairs, employing a time-dependent many-body Green's function approach, is presented. An exact solution is found, predicting a 1/3 power law for molecule production efficiency at fast sweep. The results for sss- and p-wave resonances are obtained and compared. The predicted production efficiency agrees with experimental observations for both condensed and incoherent molecules away from saturation.

We study a time-dependent sine-Gordon model in the range of the coupling costant (Luttinger param... more We study a time-dependent sine-Gordon model in the range of the coupling costant (Luttinger parameter) where the quasiparticles excitations change from massive bosons to free fermions. We find that, if we include the effects of finite temperature, the non-adiabatic response to slow perturbations is enhanced for the bosonic case and reduced for the fermionic one with respect to zero temperature. The signature of this bunching (anti-bunching) behaviour can also be seen at zero temperature by analyzing the second order corrections of a perturbative approach in the number of quasiparticles created. This suggests the existence of a crossover (for the Luttinger parameter) that separates systems with bose-like statistics from systems with fermi-like statistics, and therefore time-dependent perturbations to the system can be used to probe the statistics of the quasiparticles. We show how this model is relevant for cold atoms experiments that realize splitting and merging of two one-dimensio...

Journal of Lightwave Technology, 2015

We demonstrate a radiation mode coupler based on a tilted fiber Bragg grating that spatially demu... more We demonstrate a radiation mode coupler based on a tilted fiber Bragg grating that spatially demultiplexes different modes in a few-mode fiber. The observed radiation patterns match well with those theoretically predicted using the volume current method. The correlations in measured relative modal weights obtained from this device and an accurate interferometric measurement used as a reference, suggest that this technique has potential applications in providing real-time, nondestructive modal power measurement for mode division-multiplexed communications systems or monitoring the modal content in fiber lasers.

Physical Review A, 2007

Recent experiments on strongly-interacting bosons in optical lattices have revealed the coexisten... more Recent experiments on strongly-interacting bosons in optical lattices have revealed the coexistence of spatially-separated Mott-insulating and number-fluctuating phases. The description of this inhomogeneous situation is the topic of this Letter. We establish that the number-fluctuating phase forms a superfluid trapped between the Mott-insulating regions and derive the associated collective mode structure. We discuss the interlayer's crossover between two-and three-dimensional behavior as a function of the lattice parameters and estimate the critical temperatures for the transition of the superfluid phase to a normal phase.

Nature communications, 2014

Imaging through a single optical fibre offers attractive possibilities in many applications such ... more Imaging through a single optical fibre offers attractive possibilities in many applications such as micro-endoscopy or remote sensing. However, the direct transmission of an image through an optical fibre is difficult because spatial information is scrambled upon propagation. We demonstrate an image transmission strategy where spatial information is first converted to spectral information. Our strategy is based on a principle of spread-spectrum encoding, borrowed from wireless communications, wherein object pixels are converted into distinct spectral codes that span the full bandwidth of the object spectrum. Image recovery is performed by numerical inversion of the detected spectrum at the fibre output. We provide a simple demonstration of spread-spectrum encoding using Fabry-Perot etalons. Our technique enables the two-dimensional imaging of self-luminous (that is, incoherent) objects with high throughput in principle independent of pixel number. Moreover, it is insensitive to fibr...

2014 United States National Committee of URSI National Radio Science Meeting (USNC-URSI NRSM), 2014

Fiber Lasers X: Technology, Systems, and Applications, 2013

We analyze the modal properties of an 85μm core distributed mode filtering rod fiber using cross-... more We analyze the modal properties of an 85μm core distributed mode filtering rod fiber using cross-correlated (C 2 ) imaging. We evaluate suppression of higher-order modes (HOMs) under severely misaligned mode excitation and identify a single-mode regime where HOMs are suppressed by more than 20dB. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 01/29/2015 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 8601 86010K-2 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 01/29/2015 Terms of Use: http://spiedl.org/terms

In response to recent experiments by the Berkeley group, we construct a model of superflow throug... more In response to recent experiments by the Berkeley group, we construct a model of superflow through an array of nanosize apertures that incorporates two basic ingredients:(1) disorder associated with each aperture having its own random critical velocity, and (2) effective ...

Motivated by recent experiments on degenerate Fermi gases with time-dependent interaction~[1, 2],... more Motivated by recent experiments on degenerate Fermi gases with time-dependent interaction~[1, 2], we consider the time dynamics of BCS-paired fermions with switchable interaction. Several new regimes [3] of dissipationless coupled dynamics of the collective ...

Two coupled 3D Bose-Einstein condensates with a large population imbalance exhibit macroscopic qu... more Two coupled 3D Bose-Einstein condensates with a large population imbalance exhibit macroscopic quantum self-trapping if the ratio of interaction energy to the coupling energy between the two gases is above a critical value. Above the self trapping transition, one ...

The amplitude mode of a fermionic superfluid, analogous to the Higgs Boson, becomes undamped in t... more The amplitude mode of a fermionic superfluid, analogous to the Higgs Boson, becomes undamped in the strong coupling regime when its frequency is pushed inside the BCS energy gap. We argue that this is the case in cold gases due to the energy dispersion and nonlocality of the pairing interaction, and propose to use the Feshbach resonance regime for parametric excitation of this mode. The results presented for the BCS pairing dynamics indicate that even weak dispersion suppresses dephasing and gives rise to persistent oscillations. The frequency of oscillations extracted from our simulation of the BCS dynamics agrees with the prediction of the many-body theory.