27 research outputs found
Outgassing, Temperature Gradients and the Radiometer Effect in LISA: A Torsion Pendulum Investigation
Thermal modeling of the LISA gravitational reference sensor (GRS) includes
such effects as outgassing from the proof mass and its housing and the
radiometer effect. Experimental data in conditions emulating the LISA GRS are
required to confidently predict the GRS performance. Outgassing and the
radiometer effect are similar in characteristics and are difficult to decouple
experimentally.
The design of our torsion balance allows us to investigate differential
radiation pressure, the radiometer effect, and outgassing on closely separated
conducting surfaces with high sensitivity. A thermally controlled split copper
plate is brought near a freely hanging plate-torsion pendulum.We have varied
the temperature on each half of the copper plate and have measured the
resulting forces on the pendulum.
We have determined that to first order the current GRS model for the
radiometer effect, outgassing, and radiation pressure are mostly consistent
with our torsion balance measurements and therefore these thermal effects do
not appear to be a large hindrance to the LISA noise budget. However, there
remain discrepancies between the predicted dependence of these effects on the
temperature of our apparatus.Comment: 6th International LISA Symposiu
Closed form expressions for gravitational multipole moments of elementary solids
Perhaps the most powerful method for deriving the Newtonian gravitational
interaction between two masses is the multipole expansion. Once inner
multipoles are calculated for a particular shape this shape can be rotated,
translated, and even converted to an outer multipole with well established
methods. The most difficult stage of the multipole expansion is generating the
initial inner multipole moments without resorting to three dimensional
numerical integration of complex functions. Previous work has produced
expressions for the low degree inner multipoles for certain elementary solids.
This work goes further by presenting closed form expressions for all degrees
and orders. A combination of these solids, combined with the aforementioned
multipole transformations, can be used to model the complex structures often
used in precision gravitation experiments.Comment: 9 pages 2 figure
Picoradian deflection measurement with an interferometric quasi-autocollimator using weak value amplification
We present an "interferometric quasi-autocollimator" that employs weak value
amplification to measure angular deflections of a target mirror. The device has
been designed to be insensitive to all translations of the target. We present a
conceptual explanation of the amplification effect used by the device. An
implementation of the device demonstrates sensitivities better than 10
picoradians per root hertz between 10 and 200 hertz.Comment: To be published in Optics Letter
Design of an electrostatic balance mechanism to measure optical power of 100 kW
A new instrument is required to accommodate the need for increased
portability and accuracy in laser power measurement above 100 W. Reflection and
absorption of laser light provide a measurable force from photon momentum
exchange that is directly proportional to laser power, which can be measured
with an electrostatic balance traceable to the SI. We aim for a relative
uncertainty of with coverage factor . For this purpose, we have
designed a monolithic parallelogram 4-bar linkage incorporating elastic
circular notch flexure hinges. The design is optimized to address the main
factors driving force measurement uncertainty from the balance mechanism:
corner loading errors, balance stiffness, stress in the flexure hinges,
sensitivity to vibration, and sensitivity to thermal gradients. Parasitic
rotations in the free end of the 4-bar linkage during arcuate motion are
constrained by machining tolerances. An analytical model shows this affects the
force measurement less than 0.01 percent. Incorporating an inverted pendulum
reduces the stiffness of the system without unduly increasing tilt sensitivity.
Finite element modeling of the flexures is used to determine the hinge
orientation that minimizes stress which is therefore expected to minimize
hysteresis. Thermal effects are mitigated using an external enclosure to
minimize temperature gradients, although a quantitative analysis of this effect
is not carried out. These analyses show the optimized mechanism is expected to
contribute less than relative uncertainty in the final laser power
measurement.Comment: 11 pages, 9 figures, accepted for publication in IEEE Transactions on
Instrumentation and Measuremen