Improved Ar(II) transition probabilities

Precise Ar(II) branching ratios have been measured on a high current hollow cathode with a 1-m Fourier transform spectrometer. Absolute transition probabilities for 11 Ar(II) lines were calculated from these branching ratios and lifetime measurements published by Mohamed et al. For the prominent 4806 Å line, the present result is Aik = 7.12×107s-1 ±2.8%, which is in excellent agreement with recent literature data derived from pure argon diagnostics, two-wavelength-interferometry, and Hβ-diagnostics when using the theoretical data of Vidal et al

Oscillator strengths of Ti II from combined hook and emission measurements

It is demonstrated that a large set of accurate oscillator strengths of Ti II can be determined from a combination of hook and emission measurements without any assumption concerning the plasma state. Modified cascaded arcs and hollow cathode discharges have been used as plasma light sources for both hook and emission measurements. The relative f values have been converted to an absolute scale by means of literature data. The overall uncertainties of the f values are about 13-25%. Comparisons with other experimental and theoretical data are made which indicate excellent to fair agreement. Only for one of the published data sets has a wavelength-dependent discrepancy of up to a factor of two been found

First stage of LISA data processing II: Alternative filtering dynamic models for LISA

Space-borne gravitational wave detectors, such as (e)LISA, are designed to operate in the low-frequency band (mHz to Hz), where there is a variety of gravitational wave sources of great scientific value. To achieve the extraordinary sensitivity of these detector, the precise synchronization of the clocks on the separate spacecraft and the accurate determination of the interspacecraft distances are important ingredients. In our previous paper (Phys. Rev. D 90, 064016 [2014]), we have described a hybrid-extend Kalman filter with a full state vector to do this job. In this paper, we explore several different state vectors and their corresponding (phenomenological) dynamic models, to reduce the redundancy in the full state vector, to accelerate the algorithm, and to make the algorithm easily extendable to more complicated scenarios.Comment: 12 page

First stage of LISA data processing: Clock synchronization and arm-length determination via a hybrid-extended Kalman filter

In this paper, we describe a hybrid-extended Kalman filter algorithm to synchronize the clocks and to precisely determine the inter-spacecraft distances for space-based gravitational wave detectors, such as (e)LISA. According to the simulation, the algorithm has significantly improved the ranging accuracy and synchronized the clocks, making the phase-meter raw measurements qualified for time- delay interferometry algorithms.Comment: 14 pages, Phys. Rev. D 90, 064016 (2014

Coherent control of broadband vacuum squeezing

We present the observation of optical fields carrying squeezed vacuum states at sideband frequencies from 10Hz to above 35MHz. The field was generated with type-I optical parametric oscillation below threshold at 1064nm. A coherent, unbalanced classical modulation field at 40MHz enabled the generation of error signals for stable phase control of the squeezed vacuum field with respect to a strong local oscillator. Broadband squeezing of approximately -4dB was measured with balanced homodyne detection. The spectrum of the squeezed field allows a quantum noise reduction of ground-based gravitational wave detectors over their full detection band, regardless of whether homodyne readout or radio-frequency heterodyne readout is used.Comment: 9 pages, 8 figure

The finite mass beamsplitter in high power interferometers

The beamplitter in high-power interferometers is subject to significant radiation-pressure fluctuations. As a consequence, the phase relations which appear in the beamsplitter coupling equations oscillate and phase modulation fields are generated which add to the reflected fields. In this paper, the transfer function of the various input fields impinging on the beamsplitter from all four ports onto the output field is presented including radiation-pressure effects. We apply the general solution of the coupling equations to evaluate the input-output relations of the dual-recycled laser-interferometer topology of the gravitational-wave detector GEO600 and the power-recycling, signal-extraction topology of advanced LIGO. We show that the input-output relation exhibits a bright-port dark-port coupling. This mechanism is responsible for bright-port contributions to the noise density of the output field and technical laser noise is expected to decrease the interferometer's sensitivity at low frequencies. It is shown quantitatively that the issue of technical laser noise is unimportant in this context if the interferometer contains arm cavities.Comment: 10 pages, 7 figure

Inversion of the Coupling Absorption at the Two-Photon Resonance in a Coupling-Probe-Spectroscopy Experiment

Using probe and coupling lasers, a system characterized by electromagnetically induced absorption was investigated. A switch of the EIA peak of the coupling laser to a dip was measured as function of the laser intensities

New design of electrostatic mirror actuators for application in high-precision interferometry

We describe a new geometry for electrostatic actuators to be used in sensitive laser interferometers, suited for prototype and table top experiments related to gravitational wave detection with mirrors of 100 g or less. The arrangement consists of two plates at the sides of the mirror (test mass), and therefore does not reduce its clear aperture as a conventional electrostatic drive (ESD) would do. Using the sample case of the AEI-10 m prototype interferometer, we investigate the actuation range and the influence of the relative misalignment of the ESD plates with respect to the test mass. We find that in the case of the AEI-10 m prototype interferometer, this new kind of ESD could provide a range of 0.28 μm when operated at a voltage of 1 kV. In addition, the geometry presented is shown to provide a reduction factor of about 100 in the magnitude of the actuator motion coupling to the test mass displacement. We show that therefore in the specific case of the AEI-10 m interferometer, it is possible to mount the ESD actuators directly on the optical table without spoiling the seismic isolation performance of the triple stage suspension of the main test masses

Laser power stabilization for second-generation gravitational wave detectors

We present results on the power stabilization of a Nd:YAG laser in the frequency band from 1 Hz to 100 kHz. High-power, low-noise photodetectors are used in a dc-coupled control loop to achieve relative power fluctuations down to 5×10−9 Hz−1/2 at 10 Hz and 3.5×10−9 Hz−1/2 up to several kHz, which is very close to the shot-noise limit for 80 mA of detected photocurrent on each detector. We investigated and eliminated several noise sources such as ground loops and beam pointing. The achieved stability level is close to the requirements for the Advanced LIGO gravitational wave detector