1,080 research outputs found
High-sensitivity optical measurement of mechanical Brownian motion
We describe an experiment in which a laser beam is sent into a high-finesse
optical cavity with a mirror coated on a mechanical resonator. We show that the
reflected light is very sensitive to small mirror displacements. We have
observed the Brownian motion of the resonator with a very high sensitivity.Comment: 4 pages, 4 figures, RevTe
Numerical investigation of the quantum fluctuations of optical fields transmitted through an atomic medium
We have numerically solved the Heisenberg-Langevin equations describing the
propagation of quantized fields through an optically thick sample of atoms. Two
orthogonal polarization components are considered for the field and the
complete Zeeman sublevel structure of the atomic transition is taken into
account. Quantum fluctuations of atomic operators are included through
appropriate Langevin forces. We have considered an incident field in a linearly
polarized coherent state (driving field) and vacuum in the perpendicular
polarization and calculated the noise spectra of the amplitude and phase
quadratures of the output field for two orthogonal polarizations. We analyze
different configurations depending on the total angular momentum of the ground
and excited atomic states. We examine the generation of squeezing for the
driving field polarization component and vacuum squeezing of the orthogonal
polarization. Entanglement of orthogonally polarized modes is predicted. Noise
spectral features specific of (Zeeman) multi-level configurations are
identified.Comment: 12 pages 9 figures. Submitted to Physical Review
A micropillar for cavity optomechanics
We present a new micromechanical resonator designed for cavity optomechanics.
We have used a micropillar geometry to obtain a high-frequency mechanical
resonance with a low effective mass and a very high quality factor. We have
coated a 60-m diameter low-loss dielectric mirror on top of the pillar and
are planning to use this micromirror as part of a high-finesse Fabry-Perot
cavity, to laser cool the resonator down to its quantum ground state and to
monitor its quantum position fluctuations by quantum-limited optical
interferometry
Radiation-pressure cooling and optomechanical instability of a micro-mirror
Recent experimental progress in table-top experiments or gravitational-wave
interferometers has enlightened the unique displacement sensitivity offered by
optical interferometry. As the mirrors move in response to radiation pressure,
higher power operation, though crucial for further sensitivity enhancement,
will however increase quantum effects of radiation pressure, or even jeopardize
the stable operation of the detuned cavities proposed for next-generation
interferometers. The appearance of such optomechanical instabilities is the
result of the nonlinear interplay between the motion of the mirrors and the
optical field dynamics. In a detuned cavity indeed, the displacements of the
mirror are coupled to intensity fluctuations, which modifies the effective
dynamics of the mirror. Such "optical spring" effects have already been
demonstrated on the mechanical damping of an electromagnetic waveguide with a
moving wall, on the resonance frequency of a specially designed flexure
oscillator, and through the optomechanical instability of a silica
micro-toroidal resonator. We present here an experiment where a
micro-mechanical resonator is used as a mirror in a very high-finesse optical
cavity and its displacements monitored with an unprecedented sensitivity. By
detuning the cavity, we have observed a drastic cooling of the micro-resonator
by intracavity radiation pressure, down to an effective temperature of 10 K. We
have also obtained an efficient heating for an opposite detuning, up to the
observation of a radiation-pressure induced instability of the resonator.
Further experimental progress and cryogenic operation may lead to the
experimental observation of the quantum ground state of a mechanical resonator,
either by passive or active cooling techniques
High-sensitivity optical monitoring of a micro-mechanical resonator with a quantum-limited optomechanical sensor
We experimentally demonstrate the high-sensitivity optical monitoring of a
micro-mechanical resonator and its cooling by active control. Coating a
low-loss mirror upon the resonator, we have built an optomechanical sensor
based on a very high-finesse cavity (30000). We have measured the thermal noise
of the resonator with a quantum-limited sensitivity at the 10^-19 m/rootHz
level, and cooled the resonator down to 5K by a cold-damping technique.
Applications of our setup range from quantum optics experiments to the
experimental demonstration of the quantum ground state of a macroscopic
mechanical resonator.Comment: 4 pages, 5 figure
Noise reduction in gravitational wave interferometers using feedback
We show that the quantum locking scheme recently proposed by Courty {\it et
al.} [Phys. Rev. Lett. {\bf 90}, 083601 (2003)] for the reduction of back
action noise is able to significantly improve the sensitivity of the next
generation of gravitational wave interferometers.Comment: 12 pages, 2 figures, in print in the Special Issue of J. Opt. B on
Fluctuations and Noise in Photonics and Quantum Optic
2D photonic-crystal optomechanical nanoresonator
We present the optical optimization of an optomechanical device based on a
suspended InP membrane patterned with a 2D near-wavelength grating (NWG) based
on a 2D photonic-crystal geometry. We first identify by numerical simulation a
set of geometrical parameters providing a reflectivity higher than 99.8 % over
a 50-nm span. We then study the limitations induced by the finite value of the
optical waist and lateral size of the NWG pattern using different numerical
approaches. The NWG grating, pierced in a suspended InP 265 nm-thick membrane,
is used to form a compact microcavity involving the suspended nano-membrane as
end mirror. The resulting cavity has a waist size smaller than 10 m and a
finesse in the 200 range. It is used to probe the Brownian motion of the
mechanical modes of the nanomembrane
Cooling of a mirror by radiation pressure
We describe an experiment in which a mirror is cooled by the radiation
pressure of light. A high-finesse optical cavity with a mirror coated on a
mechanical resonator is used as an optomechanical sensor of the Brownian motion
of the mirror. A feedback mechanism controls this motion via the radiation
pressure of a laser beam reflected on the mirror. We have observed either a
cooling or a heating of the mirror, depending on the gain of the feedback loop.Comment: 4 pages, 6 figures, RevTe
Quantum noise in the position measurement of a cavity mirror undergoing Brownian motion
We perform a quantum theoretical calculation of the noise power spectrum for
a phase measurement of the light output from a coherently driven optical cavity
with a freely moving rear mirror. We examine how the noise resulting from the
quantum back action appears among the various contributions from other noise
sources. We do not assume an ideal (homodyne) phase measurement, but rather
consider phase modulation detection, which we show has a different shot noise
level. We also take into account the effects of thermal damping of the mirror,
losses within the cavity, and classical laser noise. We relate our theoretical
results to experimental parameters, so as to make direct comparisons with
current experiments simple. We also show that in this situation, the standard
Brownian motion master equation is inadequate for describing the thermal
damping of the mirror, as it produces a spurious term in the steady-state phase
fluctuation spectrum. The corrected Brownian motion master equation [L. Diosi,
Europhys. Lett. {\bf 22}, 1 (1993)] rectifies this inadequacy.Comment: 12 pages revtex, 2 figure
Growth and shape of indium islands on molybdenum at micro-roughened spots created by femtosecond laser pulses
Indium islands on molybdenum coated glass can be grown in ordered arrays by surface structuring using a femtosecond laser. The effect of varying the molybdenum coated glass substrate temperature and the indium deposition rate on island areal density, volume and geometry is investigated and evaluated in a physical vapor deposition (PVD) process. The joined impact of growth conditions and spacing of the femtosecond laser structured spots on the arrangement and morphology of indium islands is demonstrated. The results yield a deeper understanding of the island growth and its precise adjustment to industrial requirements, which is indispensable for a technological application of such structures at a high throughput, for instance as precursors for the preparation of Cu(In,Ga)Se2 micro concentrator solar cells
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