Conference on Lasers and Electro-Optics

Atomic fluorescence emitted into an optical nanofiber: Coupling efficiency and spectrum

Daniel Gleeson, Vladimir G. Minogin, Michael Morrissey, Kieran Deasy, Thejesh Bandi, Síle Nic Chormaic

Published May 1, 2008• 0 citations

Abstract

We present an analysis of the lineshape and strength of the fluorescence emitted by optically excited atoms and coupled to an optical fiber. We show the frequency-position selectivity and asymmetry of the spectral emission line. The theoretical analysis is compared with experimental data.

DOI: 10.1109/cleo.2008.4552000

Related papers

Atomic ∞uorescence emitted into an optical nanoflber: coupling e-ciency and spectrum

Daniel Gleeson, Vladimir G. Minogin, Michael M. Morrissey +2 more

We present an analysis of the lineshape and strength of the ∞uorescence emitted by optically excited atoms and coupled to an optical flber. We show the frequency-position selectivity and asymmetry of the spectral emission line. The theoretical analysis is compared with experimental data. @2008 Optical Society of America OCIS codes: 270.0270; 300.0300 In recent years there has been considerable interest in the problem of the interaction between optically excited atoms and dielectric nanobodies. The basic aspects of such an interaction are the modiflcation of the spontaneous emission rate near nanobodies [1-4] and the dependence of the coupling of atomic ∞uorescence to the nanobody on the strength of the interaction between the atoms and the surface of the nanobody. A study of these problems is of importance for developing both new spectroscopic techniques to measure interactions between atoms and nanobodies, and new experimental schemes to control internal and translational atomic states near optical nanobodies [5-7]. In this paper, we report on the spectrum of ∞uorescence emitted by optically excited atoms into the fundamental guided mode of an optical nanoflber and present a comparison with experimental data. We consider an ensemble of two-level atoms located in the vicinity of an optical nanoflber as shown in Fig. 1a. The atoms are excited by a laser fleld near-resonant to the atomic dipole transition and emit ∞uorescent light which can generally propagate into the guided flber modes. We speciflcally consider the practically important case when the frequency of the ∞uorescent light is chosen to be below the cut-ofi frequencies of all the guided modes except the fundamental mode HE11, so that the ∞uorescent light contributes into the fundamental guided mode only. In the simple case of two-level atoms excited by an external laser fleld near-resonant to the dipole optical transition, the power of the ∞uorescent light coupled to the guided flber mode at weak optical saturation can be shown to be

Jan 1, 20080 citations

Spectral distribution of atomic fluorescence coupled into an optical nanofibre

L Russell, Daniel Gleeson, Vladimir G. Minogin +1 more

We analyse the lineshape of the fluorescence emitted by a cloud of optically excited cold atoms and coupled into an optical nanofibre. We examine the efficiency of the fluorescence coupling and describe the asymmetry of the lineshape caused by the redshifts arising from both the van der Waals and Casimir–Polder interaction of the atoms with the surface of the optical nanofibre. We compare the contributions of the van der Waals and Casimir–Polder redshifts and show that the lineshape of the fluorescence coupled into an optical nanofibre is, basically, influenced by the van der Waals redshift and is characterized by a long tail on the red side of the spectrum. We conclude that a measurement of the lineshape of the coupled fluorescence could be used to characterize the strength of the interaction of atoms with dielectric surfaces and for the detection of atoms using nanofibres.

Journal of Physics B Atomic Molecular and Optical PhysicsSep 8, 200930 citations

Optical nanofiber as an efficient tool for manipulating and probing atomic Fluorescence

K. P. Nayak, Павел Николаевич Мелентьев, M. Morinaga +3 more

We experimentally demonstrate efficient coupling of atomic fluorescence to the guided mode of a subwavelength-diameter silica fiber, an optical nanofiber. We show that fluorescence of a very small number of atoms, around the nanofiber can be readily observed through a single-mode optical fiber. We also show that such a technique enables us to probe the van der Waals interaction between atoms and surface with high precision by observing the fluorescence excitation spectrum through the nanofiber.

Optics ExpressJan 1, 2007266 citations

Study of laser induced fluorescence spectrum of atoms using optical nanofibers

Manoj Das

Fluorescence of atoms has been the subject of interest in quantum optical measurementsfor many years. The atomic fluorescence is routinely used as a tool to detectatoms, to generate photons and to generate non-classical states of light. One of thewidely used methods to investigate the atomic fluorescence is laser-induced fluorescencespectroscopy. This thesis presents the development of optical nanofibers as atool for the measurement of fluorescence spectrum of atoms.Optical nanofibers are ultrathin optical fibers, with diameters less than the propagationwavelength of the fiber, with a silica core and a vacuum clad. Such opticalnanofibers can support only the single propagating guided-mode. The guided-modesof the nanofiber is confined in the transverse direction of the nanofiber and a partof the propagating field lies outside the fiber, in the evanescent region of the fiber.The mode density of the electromagnetic field is modified by the nanofiber. Due tothe modification of mode density, the spontaneous emission of atoms is modified bythe optical nanofibers and the confinement of the guided-modes results in a strongchanneling of spontaneous emission of atoms into the guided-modes of the nanofiber.Such a property of nanofibers can be used to study fluorescence of atoms around thenanofiber.Optical nanofibers are prepared by the adiabatic tapering of single-mode opticalfibers. Our experiments are performed by overlapping cold Cesium atoms, from amagneto-optical trap (MOT), with the optical nanofiber and observing the fluorescencethrough the guided-modes of the nanofiber. The nanofiber suppresses with highprobability any coupling of scattering light from the excitation laser into the guidedmodesand high coupling efficiency of fluorescence into the guided-modes enables us tomeasure the fluorescence spectrum of atoms present around the nanofiber with a goodsignal-to-noise ratio. In this thesis, we demonstrate the measurement of laser inducedfluorescence (LIF) emission spectra of strongly driven atoms using optical nanofibers.For the fluorescence emission spectrum measurements, we develop and demonstrate anew sensitive and high resolution method consisting of optical heterodyne techniqueand photon correlation spectroscopy. The key point of the method is to extract theinformation of first-order field correlation function from the measured second-orderintensity correlation function. The Fourier transform of the field correlation functionthen gives the fluorescence emission spectrum.The atoms emitting fluorescence in the guided-modes of the nanofiber lie very closeto the nanofiber surface and are subjected to atom-surface interactions. It has beenreported in earlier experiments on nanofiber, that such surface interactions can bemodified by irradiating the MOT-atoms overlapped with the nanofiber with UV lasers.After such irradiations, MOT-atoms are kept from falling into the surface-potentialand behave almost like free-space atoms around the nanofiber. We first perform ourfluorescence spectra measurements under this free-atom conditions. The observedexcitation spectrum lineshape shows a free-atom like Lorentzian behavior, with avery small tail in the red-detuned side (red-tail). The red-tail has been attributedto photoassociation process, due to atoms making transition from free ground statesto bound excited states of the surface potential. Under this conditions, the emissionspectra measured for on-resonant and off-resonant excitations show the well-knownthree-peak Mollow-triplet spectrum of free-space two-level atoms. The observationconfirms that the near surface atoms behave like free-space atoms. Also, the quantitativeagreement between the observed spectra with the theoretical calculationsdemonstrates the validity of the optical nanofiber method for measuring fluorescenceemission spectrum of atoms.As mentioned above, since we are observing near-surface atoms, fluorescence measurementsbased on optical nanofibers may become a unique tool to probe atomsurfaceinteractions. In earlier experiments using nanofiber, signatures of atomsurfaceinteraction have been observed in the excitation spectrum of atoms, in theform of a broad red-tail. The lineshape of the excitation spectrum is understood as aresult of a process where atoms approaching the nanofiber surface fall into the shallowsurface potential, forming long-range atom-surface bound states. In this thesis,we have systematically investigated the evolution of the lineshape of the excitationspectrum from a Lorentzian shape to a broad red-tail condition. The evolution of thespectrum lineshape has been attributed to the changing nanofiber surface condition.The spectrum shape is found to depend on the flux of background Cs-atoms. Wespeculate that this might be due to the adsorption of hot background atoms ontothe nanofiber surface, which changes the surface condition of the nanofiber locallyand helps in loading of cold MOT-atoms into the shallow surface potential. We havefound that the effect of UV laser irradiation is to photoionize the MOT-atoms, andthe generated photoelectrons might help in the desorption of adsorbed atoms on thesurface. We discuss the roles of adsorption and desorption of atoms on the surfaceconditions. We have shown that such changing surface condition can be controlledby adjusting the hot background atom flux and the UV laser intensity. Under suchcontrolled surface condition, we have measured the emission spectrum. The observedemission spectrum under the broad red-tail condition can be explained only by includingthe surface interactions. We also discuss qualitatively the phonon-mode densityfor nanofiber at room temperature and the phonon-mediated decay of atoms in thesurface potential.This work may open up the way for using optical nanofibers as a tool to investigatethe laser-induced fluorescence spectrum of strongly driven atoms, and to study atomsurfaceinteractions. In the future, we hope to create optical dipole traps around thenanofibers by introducing trap laser lights through the guided-modes and performfluorescence measurements of these trapped atoms.

Jan 1, 20110 citations

Measurement of fluorescence emission spectrum of few strongly driven atoms using an optical nanofiber

Manoj Das, A. Shirasaki, K. P. Nayak +3 more

We show that the fluorescence emission spectrum of few atoms can be measured by using an optical nanofiber combined with the optical heterodyne and photon correlation spectroscopy. The observed fluorescence spectrum of the atoms near the nanofiber shows negligible effects of the atom-surface interaction and agrees well with the Mollow triplet spectrum of free-space atoms at high excitation intensity.

Optics ExpressJul 28, 201028 citations

Manifestation of the van der Waals surface interaction in the spontaneous emission of atoms into an optical nanofiber

Vladimir G. Minogin, Síle Nic Chormaic

We study the spontaneous emission of atoms near an optical nanofiber and analyze the coupling efficiency of the spontaneous emission into a nanofiber. We also investigate the influence of the van der Waals interaction of atoms with the surface of the optical nanofiber on the spectrum of coupled light. Using, as an example, 85 Rb atoms we show that the van der Waals interaction may considerably extend the red wing of the spontaneous emission line and, accordingly, produce a well-defined asymmetry of the spontaneous emission spectrum coupled into an optical nanofiber.

Laser PhysicsJul 29, 200939 citations