Ground-Based Interferometers

FIGURE 2 Schematic cf an interferometric gravitationai wave detectcr. 

Currently operating kilometer-scale interferometers include the Laser Interferometer Gravitational-wave Observatories (LIGO) with sites located in Hanford, Washington, and Livingston, Louisiana the GEO-600 interferometer in Hannover, Germany and the TAMA-300 interferometer in Tokyo, Japan. In addition, the VIRGO observatory is under construction near Pisa, Italy. 

---

The main problem of Far-Infrared ground based interferometers is the atmospheric attenuation at these frequencies. This effect can only be removed if the interferometer is space-based. However, water lines can be useful as a first instrument approach to calibrate the test-bed. Figure3.4 (left) shows the atmospheric attenuation and the Winston cone filtering in the 0-40 cm wavenumber range. 

Ground-based interferometers and resonant-mass detectors operate in this band. The most promising sources of gravitational waves are inspiral and coalescence of compact stellar-mass black holes and... 

For ground-based interferometers, the ground motion (seismic noise) is several orders of magnitude above the expected path difference induced by the gravitational wave. The optical elements must be isolated with special isolation systems. The main goal of isolation systems is the reduction of horizontal motions along the laser direction. The seismic noise is described by the linear spectral density ... 

The major planned ground-based interferometers are LIGO, VIRGO, GE0600, TAMA, and AIGO. The sensitivity is shown in the top part of Fig. 6. 

FIGURE 6 Strain noise sensitivity of the interferometric detectors. Top figure ground-based interferometers VIRGO (solid line), LIGO (dashed line), GE0600 (dotted line), and TAMA (dot-dash line). Bottom figure the space interferometer LISA. 

VLT Very Large Telescope, the combination of four 8m diameter ground-based telescopes and a set of 1.8 m auxiliary telescopes at Paranal Observatory of the European Southern Observatory. The telescopes can be used individually or as an interferometer (VLTI) providing very high spatial resolution. 

To achieve such angular resolution there are two options a very large aperture single dish telescope, or an array of telescopes, this is, an interferometer. It is possible for ground based systems to consist of very large apertures, but for space observatories there are launch requirements that limit both the size and the weight of the telescopes. In order to improve on the existing resolution in space, interferometry is therefore the most plausible solution. 

The problem of ground based interferometry is that although the MV-coverage can be increased by making use of the Earth rotation, the fixed position of the antennas will always limit the performance capabilities of such a system. This will not be a problem for space based interferometry, because even if operating a boom-based interferometer one will have the freedom to move the full spacecraft and sample the MV-map according to the target requirements. 

In the Introduction of this thesis the potential science cases that could be assessed by a Far-Infrared Spectro-Spatial Space Interferometer were introduced. This chapter focuses on one of these science cases, the Circumstellar Disks, because it is one of the major areas of focus in ground-based infrared interferometry observations. 

Fig. 2.8 Sketches of planned or proposed future telescopes. From left to right, top row. the space telescopes JWST (James Webb Space Telescope, currently in construction, image credit NASA) and SPICA (JAXA project, image credit JAXA) bottom row. the ground based telescopes ALMA (in construction, image credit ESO/NOAJ/NRAO), Extremely Large Telescope (ELT, ESO project). Plateau de Bure Interferometer (PdBI) (in operation, proposal for extension as NOEMA, image credit IRAM)...

A cross section of a post-dispersion grating, mounted in a slightly taller, but otherwise conventional detector dewar, is shown in Fig. 5.8.13. This dewar fits directly into the detector position of a ground-based, astronomical interferometer. Ground-based infrared observations with warm telescopes and residual emission from the warm Earth atmosphere benefit equally from the post-dispersion use of an array. Such a system has been successfully used by G. Wiedemann et al. (1989) in the 750-1250 cm atmospheric window, although with only a small number... 

We present here a summary of recent work with light-pulse interferometer based inertial sensors. We first outline the general principles of operation of light-pulse interferometers. This atomic interferometer (Borde et al., 1992 Borde et al., 1989) uses two-photon velocity selective Raman transitions (Kasevich et al., 1991), to manipulate atoms while keeping them in long-lived ground states. 

---