Charles Hagedorn

A high-precision mechanical absolute-rotation sensor

We have developed a mechanical absolute-rotation sensor capable of resolving ground rotation angle of less than 1 nrad/√Hz above 30 mHz and 0.2 nrad/√Hz above 100 mHz about a single horizontal axis. The device consists of a meter-scale beam balance, suspended by a pair of flexures, with a resonance frequency of 10.8 mHz. The center of mass is located 3 μm above the pivot, giving an excellent horizontal displacement rejection of better than 3 × 10(-5) rad/m. The angle of the beam is read out optically using a high-sensitivity autocollimator. We have also built a tiltmeter with better than 1 nrad/√Hz sensitivity above 30 mHz. Co-located measurements using the two instruments allowed us to distinguish between background rotation signal at low frequencies and intrinsic instrument noise. The rotation sensor is useful for rotational seismology and for rejecting background rotation signal from seismometers in experiments demanding high levels of seismic isolation, such as Advanced Laser Interferometer Gravitational-wave Observatory.

A reference-beam autocollimator with nanoradian sensitivity from mHz to kHz and dynamic range of 10^7

We describe an autocollimating optical angle sensor with a dynamic range of 9 mrad and nrad/√Hz sensitivity at frequencies from 5 mHz to 3 kHz. This work improves the standard multi-slit autocollimator design by adding two optical components, a reference mirror and a condensing lens. This autocollimator makes a differential measurement between a reference mirror and a target mirror, suppressing common-mode noise sources. The condensing lens reduces optical aberrations, increases intensity, and improves image quality. To further improve the stability of the device at low frequencies the body of the autocollimator is designed to reduce temperature variations and their effects. A new data processing technique was developed in order to suppress the effects of imperfections in the CCD.

Charge management for gravitational-wave observatories using UV LEDs

Accumulation of electrical charge on the end mirrors of gravitational-wave observatories can become a source of noise limiting the sensitivity of such detectors through electronic couplings to nearby surfaces. Torsion balances provide an ideal means for testing gravitational-wave technologies due to their high sensitivity to small forces. Our torsion pendulum apparatus consists of a movable plate brought near a plate pendulum suspended from a nonconducting quartz fiber. A UV LED located near the pendulum photoejects electrons from the surface, and a UV LED driven electron gun directs photoelectrons towards the pendulum surface. We have demonstrated both charging and discharging of the pendulum with equivalent charging rates of

High Sensitivity Torsion Balance Tests for LISA Proof Mass Modeling

\ensuremath{\sim}{10}^{5}e/\mathrm{s}

Quality Factors of Bare and Metal‐Coated Quartz and Fused Silica Torsion Fibers

, as well as spectral measurements of the pendulum charge resulting in a white noise level equivalent to

Low‐Frequency Tilt Seismology with a Precision Ground‐Rotation Sensor

3\ifmmode\times\else\texttimes\fi{}{10}^{5}e/\sqrt{\mathrm{Hz}}

Picoradian deflection measurement with an interferometric quasi-autocollimator using weak value amplification

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Subtracting Tilt from a Horizontal Seismometer Using a Ground‐Rotation Sensor

We have built a highly sensitive torsion balance to investigate small forces between closely spaced gold coated surfaces. Such forces will occur between the LISA proof mass and its housing. These forces are not well understood and experimental investigations are imperative. We describe our torsion balance and present the noise of the system. A significant contribution to the LISA noise budget at low frequencies is the fluctuation in the surface potential difference between the proof mass and its housing. We present first results of these measurements with our apparatus.

Indirect evidence for Levy walks in squeeze film damping

The thermal noise of a torsion balance is determined by the mechanical quality factor Q of its fiber, where higher‐Q fibers are less noisy. We report here on the fabrication and characterization of fused quartz and fused silica torsion fibers with Qs as high as 3.6 × 105 at frequencies below 0.1 Hz. Fibers as small as 10 μm in diameter were made conducting with thin metal coatings while retaining Qs larger than 104. Pressure‐dependent damping was discerned at pressures lower than 10−5 Pa, suggesting residual gas damping may limit experiments using these higher‐Q fibers.

INTERFEROMETRIC QUASI-AUTOCOLLIMATOR

We describe measurements of the rotational component of teleseismic surface waves using an inertial high-precision ground-rotation-sensor installed at the LIGO Hanford Observatory (LHO). The sensor has a noise floor of 0.4 nrad