89 research outputs found
Quantum noise of white light cavity using double-pumped gain medium
Laser interferometric gravitational-wave detectors implement Fabry-Perot
cavities to increase their peak sensitivity. However, this is at cost of
reducing their detection bandwidth, which origins from the propagation phase
delay of the light. The "white-light-cavity" idea, first proposed by Wicht et
al. [Optics Communications 134, 431 (1997)], is to circumvent this limitation
by introducing anomalous dispersion, using double-pumped gain medium, to
compensate for such phase delay. In this article, starting from the Hamiltonian
of atom-light interaction, we apply the input-output formalism to evaluate the
quantum noise of the system. We find that apart from the additional noise
associated with the parametric amplification process noticed by others, the
stability condition for the entire system poses an additional constraint.
Through surveying the parameter regimes where the gain medium remains stable
(not lasing) and stationary, we find that there is no net enhancement of the
shot-noise limited sensitivity. Therefore, other gain mediums or different
parameter regimes shall be explored for realizing the white light cavity.Comment: 12 pages, 7 figure
Extraction of energy from gravitational waves by laser interferometer detectors
In this paper we discuss the energy interaction between gravitational waves
and laser interferom- eter gravitational wave detectors. We show that the
widely held view that the laser interferometer gravitational wave detector
absorbs no energy from gravitational waves is only valid under the
approximation of a frequency-independent optomechanical coupling strength and a
pump laser without detuning with respect to the resonance of the
interferometer. For a strongly detuned interferometer, the optical-damping
dynamics dissipates gravitational wave energy through the interaction between
the test masses and the optical field. For a non-detuned interferometer, the
frequency-dependence of the optomechanical coupling strength causes a tiny
energy dissipation, which is proved to be equivalent to the Doppler friction
raised by Braginsky et.al.Comment: 20 pages, 7 figure
Enhancing the bandwidth of gravitational-wave detectors with unstable optomechanical filters
For gravitational-wave interferometric detectors, there is a tradeoff between
the detector bandwidth and peak sensitivity when focusing on the shot noise
level. This has to do with the frequency-dependent propagation phase lag
(positive dispersion) of the signal. We consider embedding an active unstable
filter---a cavity-assisted optomechanical device operating in the instability
regime---inside the interferometer to compensate the phase, and using feedback
control to stabilize the entire system. We show that this scheme in principle
can enhance the bandwidth without sacrificing the peak sensitivity. However,
there is one practical difficulty for implementing it due to the thermal
fluctuation of the mechanical oscillator in the optomechanical filter, which
puts a very stringent requirement on the environmental temperature and the
mechanical quality factor.Comment: 5 pages and 6 figures. Comments are welcom
Quantum ground-state cooling and tripartite entanglement with three-mode optoacoustic interactions
We present a quantum analysis of three-mode optoacoustic parametric
interactions in an optical cavity, in which two orthogonal transverse
optical-cavity modes are coupled to one acoustic mode through radiation
pressure. Due to the optimal frequency matching -- the frequency separation of
two cavity modes is equal to the acoustic-mode frequency -- the carrier and
sideband fields simultaneously resonate and coherently build up. This mechanism
significantly enhances the optoacoustic couplings in the quantum regime. It
allows exploration of quantum behavior of optoacoustic interactions in
small-scale table-top experiments. We show explicitly that given an
experimentally achievable parameter, three-mode scheme can realize quantum
ground-state cooling of milligram scale mechanical oscillators and create
robust stationary tripartite optoacoustic quantum entanglements.Comment: 20 pages, 5 figure
Parametric Instability in Long Optical Cavities and Suppression by Dynamic Transverse Mode Frequency Modulation
Three mode parametric instability has been predicted in Advanced
gravitational wave detectors. Here we present the first observation of this
phenomenon in a large scale suspended optical cavity designed to be comparable
to those of advanced gravitational wave detectors. Our results show that
previous modelling assumptions that transverse optical modes are stable in
frequency except for frequency drifts on a thermal deformation time scale is
unlikely to be valid for suspended mass optical cavities. We demonstrate that
mirror figure errors cause a dependence of transverse mode offset frequency on
spot position. Combined with low frequency residual motion of suspended
mirrors, this leads to transverse mode frequency modulation which suppresses
the effective parametric gain. We show that this gain suppression mechanism can
be enhanced by laser spot dithering or fast thermal modulation. Using Advanced
LIGO test mass data and thermal modelling we show that gain suppression factors
of 10-20 could be achieved for individual modes, sufficient to greatly
ameliorate the parametric instability problem
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