Dieter Hils

Laser stabilization at the millihertz level

The main task of this paper is to identify a number of physical problems that must be successfully addressed to achieve stabilized laser linewidths well below 1 Hz. After presentation of the basic stability characteristics of available laser sources, we show that if any of these lasers were optimally locked to a high-finesse Fabry–Perot cavity it would be theoretically possible to obtain a laser linewidth in the millihertz domain. Problems of optical feedback, modulation waveform errors, mechanical support and isolation of the reference cavity, thermal stabilization of the environment, etc. are considered, and interim solutions are discussed. Experimentally, locking accuracy to successive cavity orders of <2 × 10−5 linewidths (±1.5 Hz) was achieved; mirror birefringence pulled the lock point approximately 10-fold more. Relative phase coherence between two independent lasers locked onto adjacent cavity orders was preserved for 8 sec, corresponding to a linewidth of each optical source of ∼50 mHz.

Gravitational radiation from the Galaxy

The spectral flux of gravitational radiation incident on earth from the Galactic W UMa binaries, unevolved binaries, cataclysmic binaries, neutron star binaries, black hole-neutron star binaries, and close white dwarf binary (CWDB) systems is calculated. The peak values for the strain amplitude hv produced by the binaries are: log hv = -17.0/sq rt Hz at log v = -4.40 Hz for W UMas; log hv = -16.5/sq rt Hz at log v = -5.50 Hz for unevolved binaries; log hv = -18.2/sq rt Hz at log v = -5.15 Hz for neutron star binaries; log hv = -17.0/sq rt Hz at log v = -4.7 Hz for black hole-neutron star binaries; log hv = -18.0 /sq rt Hz at log v = -4.10 Hz for cataclysmic binaries, and log hv = -27.0/sq rt Hz at log v = -4.0 Hz for CWDBs. The gravitational flux at ultralow frequencies is emitted mainly by unevolved binaries. The integrated flux incident on earth is about 2.4 x 10 to the -9th ergs/sq cm/s. 74 refs.

Dye-Laser Frequency Stabilization Using Optical Resonators

We describe a study, performed using heterodyne techniques, of the frequency fluctuations of two completely independent ring dye lasers locked to independent reference cavities. Single laser linewidths of less than 750 Hz were achieved, the principal limitation being residual vibrations from the noisy laboratory environment. With future design and environmental improvements, ultranarrow linewidths are expected thus providing a useful tool for a great variety of high precision experiments.

Confusion noise level due to galactic and extragalactic binaries

We have revised our earlier rough estimate of the combined galactic and extragalactic binary confusion noise level curve for gravitational waves. This was done to correct some numerical errors and to allow for roughly three frequency bins worth of information about weaker sources being lost for each galactic binary signal that is removed from the data. The results are still based on the spectral amplitude estimates for different types of galactic binaries reported by Hils et al in 1990, and assume that the gravitational wave power spectral densities for other galaxies are proportional to the optical luminosities. The estimated confusion noise level drops to the LISA instrumental noise level at between roughly 3 and 8 mHz.

Response of a Fabry–Perot cavity to phase modulated light

We present a solution to the lock‐in detection method which is valid for arbitrary values of the modulation frequency. Our solutions agree with the results of the quasistatic theory, in the limit of small modulation frequency compared to the resonance linewidth.

Gravitational Radiation from Helium Cataclysmics

For a gravitational wave antenna in space, radiation from very large numbers of galactic binaries will be present in the observable frequency band from roughly 10-5 Hz to 1 Hz. At frequencies above about 3 mHz, signals from thousands of compact binaries will be resolvable in both frequency and direction. At lower frequencies, there will be confusion noise from having more than one binary per frequency resolution bin, even with a year or more of data. In this paper, we extend previous discussions of the galactic binaries to include an improved estimate of the contributions to the confusion noise from AM CVn binaries and their probable progenitors, which we refer to as helium cataclysmics. We find only a slight increase in the confusion noise below about 3 mHz, and essentially no increase at higher frequencies.

Practical sound‐reducing enclosure for laboratory use

We describe the design of a sound‐reducing laboratory enclosure. The unit fits directly over the experiment and is hoisted to the ceiling during setup and adjustment stages. The advantages of the design are its modest cost, saving of space, and the fact that no door is required. The average sound isolation achieved is 30 dB, typical for a wall mass per unit area of 35 kg/m2.

An antenna for laser gravitational-wave observations in space

Abstract Progress during the past two years on a proposed Laser Gravitational-Wave Observatory in Space (LAGOS) is discussed. Calculated performance for a 106 km sized antenna over the frequency range of 10−5 to 1 Hz is given. The sensitivity from 10−3 to 10−1 Hz is expected to be 1 × 10−21/Hz0.5. Noise sources such as accelerations of the drag-free test masses by random molecular impacts and by fluctuations in the net thermal radiation pressure will limit the sensitivity at lower frequencies. The scientific objectives are the observation of CW gravitational waves from large numbers of binary systems and the detection of pulses which may have been emitted during the period of galaxy formation.

Gravitational wave sources containing massive black holes

Abstract Types of sources containing massive black holes (MBHs) that could be observed by the Laser Interferometer Space Antenna (LISA) will be discussed. Probably the most likely type of source is compact stars or 5 to 10 M⊙ black holes (BHs) orbiting around roughly 10 5 to 10 7 M⊙ MBHs in galactic nuclei. Another perhaps observable type is the collapse of supermassive stars to form MBHs. Other possible sources are MBH-MBH binaries formed from multiple seed MBHs grown in galactic nuclei, or formed after galaxy mergers. It appears plausible, or even likely, that one or more of the above types of binaries containing MBHs can be detected and studied by LISA.

Gravitational radiation from dual neutron star elliptical binaries

General expressions are derived for the gravitational radiation incident on Earth due to elliptical binary systems in the Galaxy. These results are applied to dual neutron star elliptical binaries. The calculations show that eccentric dual neutron star binaries lead to a moderate increase in gravitational flux density compared with circular systems for frequencies above approximately 10 −4 Hz. Tables of various quantities such as average gravitational luminosity, number of sources per unit bandwidth, energy spectral flux density, and gravitational wave strain density are given