arXiv subjects

Lukas Novotny

Publications and source records attributed to Lukas Novotny.

100 records · Page 6Linked to original sources

arXiv2013

Observation of nitrogen vacancy photoluminescence from an optically levitated nanodiamond

We present the first evidence of nitrogen vacancy (NV) photoluminescence from a nanodiamond suspended in a free-space optical dipole trap at atmospheric pressure. The photoluminescence rates are shown to decrease with increasing trap laser power, but are inconsistent with a thermal quenching process. For a continuous-wave trap, the neutral charge state (NV$^0$) appears to be suppressed. Chopping the trap laser yields higher total count rates and results in a mixture of both NV$^0$ and the negative charge state (NV$^-$).

physics.optics↗

arXiv2013

Thermal nonlinearities in a nanomechanical oscillator

Nano- and micromechanical oscillators with high quality (Q) factors have gained much attention for their potential application as ultrasensitive detectors. In contrast to micro-fabricated devices, optically trapped nanoparticles in vacuum do not suffer from clamping losses, hence leading to much larger Q-factors. We find that for a levitated nanoparticle the thermal energy suffices to drive the motion of the nanoparticle into the nonlinear regime. First, we experimentally measure and fully characterize the frequency fluctuations originating from thermal motion and nonlinearities. Second, we demonstrate that feedback cooling can be used to mitigate these fluctuations. The high level of control allows us to fully exploit the force sensing capabilities of the nanoresonator. Our approach offers a force sensitivity of 20 zN $Hz^{-1/2}$, which is the highest value reported to date at room temperature, sufficient to sense ultra-weak interactions, such as non-Newtonian gravity-like forces.

cond-mat.mes-hall↗

arXiv2013

Nanoscale fluorescence lifetime imaging with a single diamond NV center

Solid-state quantum emitters, such as artificially engineered quantum dots or naturally occurring defects in solids, are being investigated for applications ranging from quantum information science and optoelectronics to biomedical imaging. Recently, these same systems have also been studied from the perspective of nanoscale metrology. In this letter we study the near-field optical properties of a diamond nanocrystal hosting a single nitrogen vacancy center. We find that the nitrogen vacancy center is a sensitive probe of the surrounding electromagnetic mode structure. We exploit this sensitivity to demonstrate nanoscale fluorescence lifetime imaging microscopy (FLIM) with a single nitrogen vacancy center by imaging the local density of states of an optical antenna.

quant-ph↗

arXiv2013

Graphene Transfer with Reduced Residue

We present a new transfer procedure for graphene using acetic acid, which removes the residue that is common in standard acetone treatments. Post-transfer samples cleaned with acetic acid and acetone were characterized using Raman spectroscopy and atomic force microscopy for comparison. We further illustrate the quality of our transfer process by using fluorescence quenching to create an optical map of surface contaminants.

cond-mat.mes-hall↗

arXiv2012

Demonstration of zero optical backscattering from single nanoparticles

We present the first experimental demonstration of zero backscattering from nanoparticles at op- tical frequencies as originally discussed by Kerker et. al. [M. Kerker, D. Wang, and C. Giles, J. Opt. Soc. A 73, 765 (1983)]. GaAs pillars were fabricated on a fused silica substrate and the spectrum of the backscattered radiation was measured in the wavelength range 600-1000 nm. Suppression of backscattering occurred at ~725 nm, agreeing with calculations based on the discrete dipole approximation. Particles with zero backscattering provide new functionality for metamaterials and optical antennas.

physics.optics↗

arXiv2012

Controllable Optical Negative Refraction and Phase Conjugation in Graphene

The development of optical metamaterials has resulted in the demonstration of remarkable physical properties, including cloaking, optical magnetism, and negative refraction. The latter has attracted particular interest, mainly because of its promise for super-resolution imaging. In recent years, negative refraction has been demonstrated with plasmonic materials and nonlinear discrete elements. However, the widespread use of negative refraction at optical frequencies is limited by high losses and strong dispersion effects, which typically limits operation to narrow frequency bands. Here we use degenerate four-wave mixing (d-4WM) to demonstrate controllable negative refraction at a graphene interface, which acts as a highly efficient phase-conjugating surface. The scheme has very low loss because of the very small thickness of the nonlinear material and it ensures broadband operation due to the linear bandstructure of graphene.

cond-mat.mes-hall↗

arXiv2012

Sub-Kelvin Parametric Feedback Cooling of a Laser-Trapped Nanoparticle

Recent experiments have demonstrated the ability to optically cool a macroscopic mechanical oscillator to its quantum ground state by means of dynamic backaction. Such experiments allow quantum mechanics to be tested with mesoscopic objects, and represent an essential step toward quantum optical memories, transducers, and amplifiers. Most oscillators considered so far are rigidly connected to their thermal environment, fundamentally limiting their mechanical Q-factors and requiring cryogenic precooling to liquid helium temperatures. Here we demonstrate parametric feedback cooling of a laser-trapped nanoparticle which is entirely isolated from the thermal bath. The lack of a clamping mechanism provides robust decoupling from internal vibrations and makes it possible to cool the nanoparticle in all degrees of freedom by means of a single laser beam. Compared to laser-trapped microspheres, nanoparticles have the advantage of higher resonance frequencies and lower recoil heating, which are favorable conditions for quantum ground state cooling

cond-mat.mes-hall↗

arXiv2011

Electrical excitation of surface plasmons

We exploit a plasmon mediated two-step momentum downconversion scheme to convert low-energy tunneling electrons into propagating photons. Surface plasmon polaritons (SPPs) propagating along an extended gold nanowire are excited on one end by low-energy electron tunneling and are then converted to free-propagating photons at the other end. The separation of excitation and outcoupling proofs that tunneling electrons excite gap plasmons that subsequently couple to propagating plasmons. Our work shows that electron tunneling provides a non-optical, voltage-controlled and low-energy pathway for launching SPPs in nanostructures, such as plasmonic waveguides

cond-mat.mes-hall↗

arXiv2010

Optical Measurement of the Phase-Breaking Length in Graphene

In mesoscopic physics, interference effects play a central role on the transport properties of conduction electrons, giving rise to exotic phenomena such as weak localization, Aharonov-Bohm effect, and universal conduction fluctuations. Mesoscopic objects have a size on the order of the {\em phase-breaking length} $L_ϕ$, the length conduction electrons travel while keeping phase coherence. In this letter, we use vibrational spectroscopy in combination with a novel optical defocusing method to measure $L_ϕ$ of photo-excited electrons in graphene which undergo inelastic scattering by optical phonons. We extract $L_ϕ$ from the spatial confinement of the defect-induced Raman D band near the edges of graphene. Temperature dependent measurements in the range of 1.55\,K to 300\,K yield $L_ϕ \propto 1/\sqrt{T}$, in agreement with previous magneto-transport measurements.

cond-mat.mes-hall↗

arXiv2008

Optical Measurement of the Phase-Breaking Length in Graphene

This paper reports the experimental determination of the phase-breaking length L of conduction electrons in graphene using Raman spectroscopy. Based on the double-resonance model, we extract L from the spatial dependence of the D band susceptibility near the graphene edge. By using prior knowledge of sample properties and the excitation point-spread function we are able to determine the spatial variation of the Raman susceptibilities with high accuracy, and the results reveal a phase-breaking length L~40nm near the graphene edge.

cond-mat.mtrl-sci↗