Joanna M. Atkin

University of Colorado at Boulder, Boulder, Colorado, United States

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Publications (18)102.34 Total impact

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    ABSTRACT: With nanosecond radiative lifetimes, quenching dominates over enhancement for conventional fluorescence emitters near metal interfaces. We explore the fundamentally distinct behavior of photoluminescence (PL) with few-femtosecond radiative lifetimes of a coupled plasmonic emitter. Controlling the emitter-surface distance with sub-nanometer precision by combining atomic force and scanning tunneling distance control, we explore the unique behavior of plasmon dynamics at the transition from long range classical resonant energy transfer to quantum coupling. Because of the ultrafast radiative plasmon emission, classical quenching is completely suppressed. Field-enhanced behavior dominates until the onset of quantum coupling dramatically reduces emission intensity and field enhancement, as verified in concomitant tip-enhanced Raman measurements. The entire distance behavior from 10's nm to sub-nm can accurately be described using a phenomenological rate equation model and highlights the new degrees of freedom in radiation control enabled by an ultrafast emitter near surfaces.
    Nano letters. 08/2014;
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    ABSTRACT: We demonstrate ultrafast infrared vibrational free-induction decay probing in scattering-scanning near-field microscopy. We observe long-lived few picosecond vibrational coherences, far in excess of the far-field ensemble response.
    CLEO: QELS_Fundamental Science; 06/2014
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    ABSTRACT: a * Since its first experimental realization, tip-enhanced Raman spectroscopy (TERS) has emerged as a potentially powerful nanochemical analysis tool. However, questions about the comparability and reproducibility of TERS data have emerged. This interlaboratory comparison study addresses these issues by bringing together different TERS groups to perform TERS mea-surements on nominally identical samples. Based on the spectra obtained, the absolute and relative peak positions, number of bands, peak intensity ratios, and comparability to reference Raman and surface-enhanced Raman spectroscopy (SERS) data are discussed. Our general findings are that all research groups obtained similar spectral patterns, irrespective of the setup or tip that was used. The TERS (and SERS) spectra consistently showed fewer bands than the conventional Raman spectrum. When comparing these three methods, the spectral pattern match and substance identification is readily possible. Absolute and relative peak positions of the three major signals of thiophenol scattered by 19 and 9 cm À1 , respectively, which can prob-ably be attributed to different spectrometer calibrations. However, within the same group (but between different tips), the signals only scattered by 3 cm À1 on average. This study demonstrated the suitability of TERS as an analytical tool and brings TERS a big step forward to becoming a routine technique.
    · 2.68 Impact Factor
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    ABSTRACT: We demonstrate broadband slow light through adiabatic nanofocusing of surface plasmon polaritons (SPPs) on a conical tip. A few femtosecond group delay for nanofocused pulses is found, corresponding to an SPP velocity of less than 0.2c at the apex of the tip.
    CLEO: QELS_Fundamental Science; 06/2013
  • Joanna M Atkin, Markus B Raschke
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    ABSTRACT: Optical spectroscopic imaging has taken a leap into the intramolecular regime with an approach that achieves subnanometre spatial resolution. The technique should find applications in photochemistry and nanotechnology. See Letter p.82
    Nature 06/2013; 498(7452):44-5. · 38.60 Impact Factor
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    ABSTRACT: We study the decrease in group velocity of broadband surface plasmon polariton propagation on a conical tip, using femtosecond time-domain interferometry. The group delay of (9±3) fs measured corresponds to a group velocity at the apex of less than 0.2c. The result agrees in general with the prediction from adiabatic plasmonic nanofocusing theory, yet is sensitive with respect to the exact taper geometry near the apex. This, together with the sub 25 fs<sup>2</sup> second-order dispersion observed, provides the fundamental basis for the use of plasmons for broadband slow-light applications.
    Optics Letters 04/2013; 38(8):1322-4. · 3.39 Impact Factor
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    ABSTRACT: We demonstrate a generalized route to generate nanometer spatially confined ultrafast optical pulses with arbitrary deterministic femtosecond waveform control using surface plasmon polarition nanofocusing in 3D tapered noble metal tips.
    03/2013;
  • Advances In Physics 12/2012; 61(6):745-842. · 34.29 Impact Factor
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    ABSTRACT: The efficiency of plasmonic nanostructures as optical antennas to concentrate optical fields to the nanoscale has been limited by intrinsically short dephasing times and small absorption cross sections. We discuss a new optical antenna concept based on surface plasmon polariton (SPP) nanofocusing on conical noble metal tips to achieve efficient far- to near-field transformation of light from the micro- to the nanoscale. The spatial separation of the launching of propagating SPPs from their subsequent apex confinement with high energy concentration enables background-free near-field imaging, tip-enhanced Raman scattering, and nonlinear nanospectroscopy. The broad bandwidth and spectral tunability of the nanofocusing mechanism in combination with frequency domain pulse shaping uniquely allow for the spatial confinement of ultrashort laser pulses and few-femtosecond spatiotemporal optical control on the nanoscale. This technique not only extends powerful nonlinear and ultrafast spectroscopies to the nanoscale but can also generate fields of sufficient intensity for electron emission and higher harmonic generation.
    Journal of Physical Chemistry Letters 03/2012; 3(7):945–952. · 6.59 Impact Factor
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    ABSTRACT: The simultaneous control of optical fields on both nanometer spatial and femtosecond time scales would enable direct spectroscopic access to the elementary electronic and vibrational excitations in matter. Here, we utilize adiabatic surface plasmon polariton (SPP) nanofocusing on free-standing 3D tapered metal tips in order to generate nanometer confined field localization at the tip apex. Using the second harmonic generation (SHG) at the tip apex we perform MIIPS pulse optimization and frequency-resolved optical gating (FROG) characterization of the nanofocused pulses. With the combination of high bandwidth coupling using a chirped grating, pulse-shaping, and low-dispersion nanofocusing, we can achieve full optical control on the nanoscale, from < 16 fs pulse duration to arbitrary optical waveforms. This technique enables linear and non-linear plasmon-enhanced spectroscopy, with the simultaneous temporal control over ultrashort pulses opening the possibility for true time-resolved scanning-probe imaging. We demonstrate this capability for background-free probing of individual molecular and nanocrystalline systems.
    02/2012;
  • Molly May, Joanna Atkin, Markus Raschke
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    ABSTRACT: Strongly correlated electron materials display diverse complex phenomena such as metal-insulator transitions and ferroelectric and ferromagnetic ordering, with characteristic lengths on the nanometer scale. In order to directly access and study the associated nano-phase behavior and domains for a wide range of materials, we have developed a low temperature tip-enhanced scattering-type scanning near-field optical microscope (s-SNOM). A microscopy flow cryostat reservoir is coupled to a shear-force atomic force microscope, with illumination of electrochemically etched Au tips provided by an on-axis high numerical aperture parabolic mirror. We will discuss the use of this system for the study and imaging of ferroic ordering in multiferroic and ferroelectric materials through the symmetry selectivity provided by tip-enhanced second harmonic generation (SHG) and nano-Raman crystallography via the tensor based selection rules.
    02/2012;
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    ABSTRACT: In addition to its metal-insulator transition (MIT), VO2 exhibits a rich phase behavior of insulating monoclinic (M1,M2) and triclinic (T) phases. By using micro-Raman spectroscopy and independent control of temperature and uniaxial strain in individual single-crystal microbeams, we map these insulating phases with their associated structural changes as represented by their respective phonon frequencies. The competition between these structural forms is dictated by the internal strain due to differing lattice constants, the experimentally applied external strain, and the temperature-dependent phase stability. We identify the nature of the triclinic phase as a continuously distorted variant of the M1 monoclinic phase, while a discontinuous transition into the M2 phase occurs from both the M1 and T phases. The results suggest that understanding the driving forces that determine the interplay between M1, M2, and T phases near the MIT could be critical for the identification of the underlying mechanism behind the MIT itself.
    Physical review. B, Condensed matter 01/2012; 85(2). · 3.77 Impact Factor
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    ABSTRACT: We demonstrate the simultaneous and independent nanometer-femtosecond spatiotemporal control of optical fields through the intrinsic adiabatic surface plasmon polariton nanofocusing ability of tapered Au tips combined with femtosecond pulse shaping.
    Frontiers in Optics; 10/2011
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    ABSTRACT: The simultaneous nanometer spatial confinement and femtosecond temporal control of an optical excitation has been a long-standing challenge in optics. Previous approaches using surface plasmon polariton (SPP) resonant nanostructures or SPP waveguides have suffered from, for example, mode mismatch, or possible dependence on the phase of the driving laser field to achieve spatial localization. Here we take advantage of the intrinsic phase- and amplitude-independent nanofocusing ability of a conical noble metal tip with weak wavelength dependence over a broad bandwidth to achieve a 10 nm spatially and few-femtosecond temporally confined excitation. In combination with spectral pulse shaping and feedback on the second-harmonic response of the tip apex, we demonstrate deterministic arbitrary optical waveform control. In addition, the high efficiency of the nanofocusing tip provided by the continuous micro- to nanoscale mode transformation opens the door for spectroscopy of elementary optical excitations in matter on their natural length and time scales and enables applications from ultrafast nano-opto-electronics to single molecule quantum coherent control.
    Nano Letters 08/2011; 11(10):4309-13. · 13.03 Impact Factor
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    ABSTRACT: The spatial confinement and temporal control of an optical excitation on nanometer length scales and femtosecond time scales has been a long-standing challenge in optics. It would provide spectroscopic access to the elementary optical excitations in matter on their natural length and time scales and enable applications from ultrafast nano-opto-electronics to single molecule quantum coherent control. Previous approaches have largely focused on using surface plasmon polariton (SPP) resonant nanostructures or SPP waveguides to generate nanometer localized excitations. However, these implementations generally suffer from mode mismatch between the far-field propagating light and the near-field confinement. In addition, the spatial localization in itself may depend on the spectral phase and amplitude of the driving laser pulse thus limiting the degrees of freedom available to independently control the nano-optical waveform. Here we utilize femtosecond broadband SPP coupling, by laterally chirped fan gratings, onto the shaft of a monolithic noble metal tip, leading to adiabatic SPP compression and localization at the tip apex. In combination with spectral pulse shaping with feedback on the intrinsic nonlinear response of the tip apex, we demonstrate the continuous micro- to nano-scale self-similar mode matched transformation of the propagating femtosecond SPP field into a 20 nm spatially and 16 fs temporally confined light pulse at the tip apex. Furthermore, with the essentially wavelength and phase independent 3D focusing mechanism we show the generation of arbitrary optical waveforms nanofocused at the tip. This unique femtosecond nano-torch with high nano-scale power delivery in free space and full spectral and temporal control opens the door for the extension of the powerful nonlinear and ultrafast vibrational and electronic spectroscopies to the nanoscale.
    06/2011;
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    ABSTRACT: We demonstrate independent spatiotemporal control of optical fields on nanometer and femtosecond scales, enabled by the adiabatic and mode-matched surface plasmon polariton nanofocusing ability of 3D Au tips, combined with femtosecond pulse-shaping.
    04/2011;
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    ABSTRACT: The metal-insulator transition (MIT) of VO2 exhibits a rich phase behavior involving two monoclinic (M1, M2), triclinic, and tetragonal phases that can form a complex domain structure and accompany the electronic transition. The interplay between these structural variants arises from strain due to differing lattice constants, temperature-dependent phase stability, and possible external strain from the substrate; the coupling between these effects renders a systematic study of the phase behavior difficult. We report on phase mapping of the structural changes through independent control of temperature and uniaxial strain in individual single-crystal nanorods, using Raman spectroscopy and near-field imaging. This allows us to investigate the transformation between the various insulating phases, elucidating the nature of the triclinic phase as a continuously distorted variant of the M1 monoclinic phase, intermediate in the first-order transformation into the monoclinic M2 phase.
    03/2011;
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    ABSTRACT: True nanoscale optical spectroscopy requires the efficient delivery of light for a spatially nanoconfined excitation. We utilize adiabatic plasmon focusing to concentrate an optical field into the apex of a scanning probe tip of 10 nm in radius. The conical tips with the ability for two-stage optical mode matching of the surface plasmon polariton (SPP) grating-coupling and the adiabatic propagating SPP conversion into a localized SPP at the tip apex represent a special optical antenna concept for far-field transduction into nanoscale excitation. The resulting high nanofocusing efficiency and the spatial separation of the plasmonic grating-coupling element on the tip shaft from the near-field apex probe region allows for true background-free nanospectroscopy. As an application, we demonstrate tip-enhanced Raman spectroscopy (TERS) of surface molecules with enhanced contrast and its extension into the near-IR with 800 nm excitation.Keywords: tip-enhanced Raman; TERS; plasmon; adiabatic nanofocusing; scanning near-field optical microscopy; grating coupling
    Journal of Physical Chemistry Letters - J PHYS CHEM LETT. 11/2010;