Virgos

Figure 2. Right figure amplitude of the Miju coefficients of a real mirror. If the mirror were perfect, then only diagonal elements would be non-null. Left figure surface figure map of a Virgo mirror.

At 10Hz in a typical Nd-YAG laser 1000Hz/- /Hz, and the typical finesse asymmetry is of the order of one percent. In order to detect a gw signal the laser frequency noise has to be lowered by six orders of magnitudes (compared to the noise of a free running laser), and the two arms made as identical as possible. In order to achieve this complex frequency stabilization methods are employed in all interferometric detectors, and in order to insure the perfect symmetry of the interferometer, all pairs of Virgo optical components are coated during the same run (both Fabry-Perot input mirrors then both end mirrors are coated simultaneously). 

Figure 3. Virgo sensitivity curve with contribution from all identified noise sources...

Abstract The principles of coatings to either enhance reflectivity of mirrors or to enhance transmission of glass optics are described. Then the ion assisted deposition and ion beam sputtering techniques are addressed. Performances of these technique-sand their limitations are illustrated with the characteristics of the VIRGO mirrors coated at LMA. The importance of metrology is emphasized. 

In this lecture we recall the basic principles of the two main coating families dielectric and metallic coatings. In a second part, we describe the coatings deposition techniques and we address their performances and limitation. Most of the examples given in this lecture have been developed for the gravitational waves interferometers VIRGO and LJGO (see Ch. 18). 

Figure 21 shows the large coater for the VIRGO optics at LMA (Lyon). The technology is DIBS. Its size is 2x2.2x2.2 m. The inner pressure is 2 x 10 mBar. The coater is located in a 150 m class 1 room whith metrology and control. In a class 1 room, tolerance is <10 particles of 0.1 jum and <1 particle of 0.5 /xm xfoot xs l. 

Scattering and transmission. Figure 28 shows the layout of the seattering measurement bench. Scattering is measured over almost Ttt steradians, with two 1 dead angles, in the direetion of the source and of the deteetor. A typieal value of the amount of seattered light is 4 10 over 150 mm. On the baek side, one measures the transmission. A t5 ical value of the transmission obtained at LMA for VIRGO is 42.9 0.210 over a diameter of 50 mm. 

Wavefront. A critieal parameter of eoatings, for VIRGO or other instruments, is the wavefront rms error. It is measured with the bench in Fig. 29,... 

Figure 27. The relative reflexion bench for VIRGO coatings.

Figure 28. Layout of the bench for scattered light measurements (right), and a VIRGO bulk being measured (left).

Finally, microroughness and defects are micromapped, down to a threshold of 0.3 /rm. Table 1 summarizes the LMA-VIRGO measurements of optics for the VIRGO end mirror, and compares them with VIRGO requirements. For all parameters, average values are significantly better than the specifications. 

Table 1. Summary of measurements of the parameters of VIRGO optics at LMA, compared with VIRGO specifications.

Wavefront accuracies of < A/1000 are a target within the 4-5 coming years, in particular for relatively gravitationally faint sources observed with VIRGO. Extremely large telescopes (see Ch. 7) are also a big challenge for researchers... 

Polygynax (Innothera)-comb. wfm Polygynax Virgo (Innothera)-comb. wfm Pyorex (Bailly-Speab)-comb. wfm... 

Since cryogenics is not involved in interferometer detector (but the proposal of cooling mirrors has been done for VIRGO), we no longer deal with this type of detector. 

A type II Cepheid variable is observed in the elliptical galaxy M49 in the Virgo cluster of galaxies with a period of 30 days. Calculate the absolute magnitude of this star. If the total flux on the Earth from the star is 4.2 x 10 22 W m-2, estimate the distance to the Virgo cluster. 

Local group The collection of galaxies, including the Milky Way and Andromeda, that form part of the Virgo cluster as part of the local supercluster of galaxies. 

Cid N, Ibanez C, Prat N (2008) Life history and production of the burrowing mayfly Ephoron virgo (Olivier, 1791) (Ephemeroptera Polymitarcyidae) in the lower Ebro river a comparison after 18 years. Aquatic Insects 30 163-178... 

Koskimaki, J. et al., Immunocompetence and resource holding potential in the damselfly, Calopteryx virgo, Behavioural Ecol., 15, 169, 2004. 

Leo Digestion, the tribe of Judah, Strength Virgo Distillation, the tribe of Naphtali, The Hermit Libra Sublimation, the tribe of Asher, Justice Scorpio Putrefaction, the tribe of Dan, Death Sagittarius Incineration, the tribe of Benjamin, Temperance Capricorn Fermentation, the tribe of Issachar, The Devil Aquarius Dissolution, the tribe of Manasseh, The Star Pisces Multiplication, the tribe of Reuben, The Moon... 

In natural melts, the presence of high field strength ions such as Fe , TF, and P, which, like silicon, preferentially assume a tetrahedral coordination with oxygen, complicates the structure, and the constitution of the anion matrix may not be deduced on the basis of the equations in section 6.1.2. Structural parameters valid for compositionally complex melts were proposed by Mysen et al. (1980) and Virgo et al. (1980) on the basis of the results of Raman spectroscopy. These parameters are NBO/Si and NBO/T (NBO = Non-Bridging Oxygen T groups all tetrahedrally coordinated cations—i.e., Fe ", TF, P ", ... 

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