198 research outputs found
Cavity optomechanics with ultra-high Q crystalline micro-resonators
We present the first observation of optomechanical coupling in ultra-high Q
crystalline whispering-gallery-mode (WGM) resonators. The high purity of the
crystalline material enables optical quality factors in excess of 10^{10} and
finesse exceeding 10^{6}. Simultaneously, mechanical quality factors greater
than 10^{5} are obtained, still limited by clamping losses. Compared to
previously demonstrated cylindrical resonators, the effective mass of the
mechanical modes can be dramatically reduced by the fabrication of CaF2
microdisc resonators. Optical displacement monitoring at the 10^{-18}
m/sqrt{Hz}-level reveals mechanical radial modes at frequencies up to 20 MHz,
corresponding to unprecedented sideband factors (>100). Together with the weak
intrinsic mechanical damping in crystalline materials, such high sindeband
factors render crystalline WGM micro-resonators promising for backaction
evading measurements, resolved sideband cooling or optomechanical normal mode
splitting. Moreover, these resonators can operate in a regime where
optomechanical Brillouin lasing can become accessible
Determination of the vacuum optomechanical coupling rate using frequency noise calibration
The strength of optomechanical interactions in a cavity optomechanical system
can be quantified by a vacuum coupling rate \vcr analogous to cavity quantum
electrodynamics. This single figure of merit removes the ambiguity in the
frequently quoted coupling parameter defining the frequency shift for a given
mechanical displacement, and the effective mass of the mechanical mode. Here we
demonstrate and verify a straightforward experimental technique to derive the
vacuum optomechanical coupling rate. It only requires applying a known
frequency modulation of the employed electromagnetic probe field and knowledge
of the mechanical oscillator's occupation. The method is experimentally
verified for a micromechanical mode in a toroidal whispering-gallery-resonator
and a nanomechanical oscillator coupled to a toroidal cavity via its near
field.Comment: 11 pages, 2 figure
Tunable pulse delay and advancement in a coupled nanomechanical resonator-superconducting microwave cavity system
We theoretically study the transmission of a weak probe field under the
influence of a strong pump field in a coupled nanomechanical
resonator-superconducting microwave cavity system. Using the standard
input-output theory, we find that both pulse delay (slow light effect) and
advancement (fast light effect) of the probe field can appear in this coupled
system provided that we choose the suitable detuning of the pump field from
cavity resonance. The magnitude of the delay (advancement) can be tuned
continuously by adjusting the power of the pump field. This technique
demonstrates great potential in applications including microwave phase shifter
and delay line.Comment: 12pages, 3 figure
Cryogenic properties of optomechanical silica microcavities
We present the optical and mechanical properties of high-Q fused silica
microtoroidal resonators at cryogenic temperatures (down to 1.6 K). A thermally
induced optical multistability is observed and theoretically described; it
serves to characterize quantitatively the static heating induced by light
absorption. Moreover the influence of structural defect states in glass on the
toroid mechanical properties is observed and the resulting implications of
cavity optomechanical systems on the study of mechanical dissipation discussed.Comment: 4 pages, 3 figure
Prophylaxie de la septicémie des veaux, par colonisation artificielle avec des microbes
L’efficacité d’une colonisation artificielle de microbes non patho gènes dans le naso pharynx, en tant que prophylaxie anti-infectieuse chez le veau nouveau-né, a été étudiée dans les conditions de la pra tique. La colonisation microbienne a été réalisée immédiatement après la naissance, grâce à l’administration intranasale d’un mélange de bactéries, contenant environ 107 microbes vivants appartenant à 3 souches non pathogènes de bactéries des genres Micrococcus, Streptococcus et Corynebacterium. Les résultats suivants ont été notés : 1. — La suspension microbienne est dénuée de toute nocivité et elle est bien tolérée par les veaux nouveau-nés même mis au monde par césarienne. 2. — Dans 38 élevages où sévit la septicémie, 12 (= 7 p. 100) des 171 veaux traités prophylactiquement ont été malades et 2 sont morts. Parmi les 319 veaux-contrôles non traités des mêmes éleva ges et de la même période de vêlage, 114 (= 35,7 p. 100) sont deve nus malades, et 24 sont morts. 3. — Dans 5 élevages infectés, le taux de morbidité chez les ani maux traités a été comparé avec les pertes survenues au cours de périodes de vêlage précédentes. Sur 107 veaux traités, 5 (4,6 p. 100) ont été malades et 2 sont morts. Parmi les 232 animaux non traités, 78 (= 33,8 p. 100) ont été malades et 27 sont morts. La colonisation microbienne artificielle du naso pharynx de veau nouveau-né est donc considérée comme une mesure prophylactique efficace contre les maladies infectieuses de la période néonatale
Mid-infrared frequency comb spanning an octave based on an Er fiber laser and difference-frequency generation
We describe a coherent mid-infrared continuum source with 700 cm-1 usable
bandwidth, readily tuned within 600 - 2500 cm-1 (4 - 17 \mum) and thus covering
much of the infrared "fingerprint" molecular vibration region. It is based on
nonlinear frequency conversion in GaSe using a compact commercial 100-fs-pulsed
Er fiber laser system providing two amplified near-infrared beams, one of them
broadened by a nonlinear optical fiber. The resulting collimated mid-infrared
continuum beam of 1 mW quasi-cw power represents a coherent infrared frequency
comb with zero carrier-envelope phase, containing about 500,000 modes that are
exact multiples of the pulse repetition rate of 40 MHz. The beam's
diffraction-limited performance enables long-distance spectroscopic probing as
well as maximal focusability for classical and ultraresolving near-field
microscopies. Applications are foreseen also in studies of transient chemical
phenomena even at ultrafast pump-probe scale, and in high-resolution gas
spectroscopy for e.g. breath analysis.Comment: 8 pages, 2 figures revised version, added reference
High-sensitivity monitoring of micromechanical vibration using optical whispering gallery mode resonators
The inherent coupling of optical and mechanical modes in high finesse optical
microresonators provide a natural, highly sensitive transduction mechanism for
micromechanical vibrations. Using homodyne and polarization spectroscopy
techniques, we achieve shot-noise limited displacement sensitivities of
10^(-19) m Hz^(-1/2). In an unprecedented manner, this enables the detection
and study of a variety of mechanical modes, which are identified as radial
breathing, flexural and torsional modes using 3-dimensional finite element
modelling. Furthermore, a broadband equivalent displacement noise is measured
and found to agree well with models for thermorefractive noise in silica
dielectric cavities. Implications for ground-state cooling, displacement
sensing and Kerr squeezing are discussed.Comment: 25 pages, 8 figure
Transgenic expression of human glial cell line-derived neurotrophic factor (hGDNF) from integration-deficient lentiviral vectors is neuroprotective in a rodent model of Parkinson's disease
Standard integration-proficient lentiviral vectors (IPLVs) are effective at much lower doses than other vector systems and have shown promise for gene therapy of Parkinson's disease (PD). Their main drawback is the risk of insertional mutagenesis. The novel biosafety-enhanced integration-deficient lentiviral vectors (IDLVs) may offer a significant enhancement in biosafety, but have not been previously tested in a model of a major disease. We have assessed biosafety and transduction efficiency of IDLVs in a rat model of PD, using IPLVs as a reference. Genomic insertion of lentivectors injected into the lesioned striatum was studied by linear amplification-mediated polymerase chain reaction (PCR), followed by deep sequencing and insertion site analysis, demonstrating lack of significant IDLV integration. Reporter gene expression studies showed efficient, long-lived, and transcriptionally targeted expression from IDLVs injected ahead of lesioning in the rat striatum, although at somewhat lower expression levels than from IPLVs. Transgenic human glial cell line-derived neurotrophic factor (hGDNF) expression from IDLVs was used for a long-term investigation of lentivector-mediated, transcriptionally targeted neuroprotection in this PD rat model. Vectors were injected before striatal lesioning, and the results showed improvements in nigral dopaminergic neuron survival and behavioral tests regardless of lentiviral integration proficiency, although they confirmed lower expression levels of hGDNF from IDLVs. These data demonstrate the effectiveness of IDLVs in a model of a major disease and indicate that these vectors could provide long-term PD treatment at low dose, combining efficacy and biosafety for targeted central nervous system applications
Strong and Tunable Nonlinear Optomechanical Coupling in a Low-Loss System
A major goal in optomechanics is to observe and control quantum behavior in a
system consisting of a mechanical resonator coupled to an optical cavity. Work
towards this goal has focused on increasing the strength of the coupling
between the mechanical and optical degrees of freedom; however, the form of
this coupling is crucial in determining which phenomena can be observed in such
a system. Here we demonstrate that avoided crossings in the spectrum of an
optical cavity containing a flexible dielectric membrane allow us to realize
several different forms of the optomechanical coupling. These include cavity
detunings that are (to lowest order) linear, quadratic, or quartic in the
membrane's displacement, and a cavity finesse that is linear in (or independent
of) the membrane's displacement. All these couplings are realized in a single
device with extremely low optical loss and can be tuned over a wide range in
situ; in particular, we find that the quadratic coupling can be increased three
orders of magnitude beyond previous devices. As a result of these advances, the
device presented here should be capable of demonstrating the quantization of
the membrane's mechanical energy.Comment: 12 pages, 4 figures, 1 tabl
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