14,527 research outputs found
Using gravitational-wave standard sirens
Gravitational waves (GWs) from supermassive binary black hole (BBH) inspirals
are potentially powerful standard sirens (the GW analog to standard candles)
(Schutz 1986, 2002). Because these systems are well-modeled, the space-based GW
observatory LISA will be able to measure the luminosity distance (but not the
redshift) to some distant massive BBH systems with 1-10% accuracy. This
accuracy is largely limited by pointing error: GW sources generally are poorly
localized on the sky. Localizing the binary independently (e.g., through
association with an electromagnetic counterpart) greatly reduces this
positional error. An electromagnetic counterpart may also allow determination
of the event's redshift. In this case, BBH coalescence would constitute an
extremely precise (better than 1%) standard candle visible to high redshift. In
practice, gravitational lensing degrades this precision, though the candle
remains precise enough to provide useful information about the
distance-redshift relation. Even if very rare, these GW standard sirens would
complement, and increase confidence in, other standard candles.Comment: 10 pages, 8 figures. ApJ, in pres
Soliton crystals in Kerr resonators
Strongly interacting solitons confined to an optical resonator would offer
unique capabilities for experiments in communication, computation, and sensing
with light. Here we report on the discovery of soliton crystals in monolithic
Kerr microresonators-spontaneously and collectively ordered ensembles of
co-propagating solitons whose interactions discretize their allowed temporal
separations. We unambiguously identify and characterize soliton crystals
through analysis of their 'fingerprint' optical spectra, which arise from
spectral interference between the solitons. We identify a rich space of soliton
crystals exhibiting crystallographic defects, and time-domain measurements
directly confirm our inference of their crystal structure. The crystallization
we observe is explained by long-range soliton interactions mediated by
resonator mode degeneracies, and we probe the qualitative difference between
soliton crystals and a soliton liquid that forms in the absence of these
interactions. Our work explores the rich physics of monolithic Kerr resonators
in a new regime of dense soliton occupation and offers a way to greatly
increase the efficiency of Kerr combs; further, the extreme degeneracy of the
configuration space of soliton crystals suggests an implementation for a robust
on-chip optical buffer
Self-referencing a continuous-wave laser with electro-optic modulation
We phase-coherently measure the frequency of continuous-wave (CW) laser light
by use of optical-phase modulation and f-2f nonlinear interferometry. Periodic
electro-optic modulation (EOM) transforms the CW laser into a continuous train
of picosecond optical pulses. Subsequent nonlinear-fiber broadening of this EOM
frequency comb produces a supercontinuum with 160 THz of bandwidth. A critical
intermediate step is optical filtering of the EOM comb to reduce
electronic-noise-induced decoherence of the supercontinuum. Applying f-2f
self-referencing with the supercontinuum yields the carrier-envelope offset
frequency of the EOM comb, which is precisely the difference of the CW laser
frequency and an exact integer multiple of the EOM pulse repetition rate. Here
we demonstrate absolute optical frequency metrology and synthesis applications
of the self-referenced CW laser with <5E-14 fractional accuracy and stability.Comment: 8 pages, 4 figure
Overview of MultiLayer Metal Insulation Development for Small Stirling Convertors at NASA Glenn Research Center
A small Stirling convertor is currently under development at the NASA Glenn Research Center to produce one watt of electrical power from eight watts of heat. Previous radioisotope power systems made use of the General-Purpose Heat Source (GPHS) which produces 250 watts of heat but is unsuitable for a one-watt Stirling convertor. The only other qualified heat source available is the Light-Weight Radioisotope Heating Unit (LWRHU), which produces one watt of heat and is primarily used to provide heat to electronics and instrumentation to maintain their appropriate operating temperature. Unfortunately, the LWRHU has a heat flux of 272 W/meters squared compared to the GPHS heat flux of 6000 W/m2 which greatly increases the demands on the insulation to ensure that enough of the heat produced is available to the convertor and not lost to the environment. An analysis was performed that showed that the insulation must have an effective thermal conductivity of 0.005 W/mK or better for the system to function. A multi-layer metal insulation package was designed and a prototype was fabricated and tested to investigate the feasibility of this design. While the prototype did not meet the requirements perfectly, the lessons learned are being used to generate an improved thermal model using the test data so that a second iteration can developed that will meet the performance requirements with a much higher confidence
A microrod-resonator Brillouin laser with 240 Hz absolute linewidth
We demonstrate an ultralow-noise microrod-resonator based laser that
oscillates on the gain supplied by the stimulated Brillouin scattering optical
nonlinearity. Microresonator Brillouin lasers are known to offer an outstanding
frequency noise floor, which is limited by fundamental thermal fluctuations.
Here, we show experimental evidence that thermal effects also dominate the
close-to-carrier frequency fluctuations. The 6-mm diameter microrod resonator
used in our experiments has a large optical mode area of ~100 {\mu}m, and
hence its 10 ms thermal time constant filters the close-to-carrier optical
frequency noise. The result is an absolute laser linewidth of 240 Hz with a
corresponding white-frequency noise floor of 0.1 Hz/Hz. We explain the
steady-state performance of this laser by measurements of its operation state
and of its mode detuning and lineshape. Our results highlight a mechanism for
noise that is common to many microresonator devices due to the inherent
coupling between intracavity power and mode frequency. We demonstrate the
ability to reduce this noise through a feedback loop that stabilizes the
intracavity power.Comment: 11 pages, 5 figure
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