Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1995-07-17
1997-07-08
Turner, Samuel A.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
356348, 356357, G01B 902
Patent
active
056467281
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a device for detecting micro-vibrations of very small amplitude, which is susceptible, due to its extraordinary sensitiveness, to detect vibrations of an amplitude of 10.sup.-20 m and less.
The theory of general relativity provides that gravity propagates in waves caused by enormous moving masses. If a gravitational wave arrives on earth, it causes changes in the geometry of each object, such as dilatation in one direction and contraction in another direction. The theoretical estimation of these changes in size situates them in the order of magnitude of 10.sup.-20 m and less. The best vibration measurement instruments which are nowadays available are optical interferometers or systems of cryogenic transducers which are able to detect displacements up to 10.sup.-18 m, which is insufficient for the measurements mentioned above. An american project named LIGO (Laser Interferometer for Gravitational Waves Observatory) is known, which uses a Michelson interferometer, each branch of which has a length of 6 km. This project will probably be in working condition by 1998, and a resolution of 10.sup.-21 m is prognosticated.
It is the aim of the present invention to supply a device for detecting micro-vibrations which is notably less bulky than the LIGO project and less expensive, and which is equally capable to detect micro-movements of an amplitude of 10.sup.-20 and even less.
According to the invention, this aim is achieved by the fact that the device comprises
an optical cavity composed of a glass plate disposed between two three-dimensional interferometric networks, said plate being in contact with a body the micro-vibrations of which are to be detected, and the two interferometric networks resting by gravity on supports which are integral with said body,
a source of coherent light illuminating a first one of said two networks of said optical cavity,
and a display screen receiving the light reflected from this optical cavity.
Characteristics of a preferred embodiment of the invention are referred to in the secondary claims.
The invention will now be described in more detail by means of an embodiment and of four figures, which relate to a laboratory size realisation.
FIG. 1 shows from above an optical table on which the device according to the invention is mounted.
FIG. 2 shows the same device seen from the side.
FIG. 3 shows the optical cavity of the same device in a front view.
FIG. 4 shows an exploded view of the optical cavity which is part of the device according to the invention.
FIGS. 1 to 3 show three orthogonal views of the device according to the invention. It has been conceived in order to detect gravitational waves and with this aim it has been mounted onto an optical table 1, the legs 2 and 3 of which are supplied with attenuation means (not shown) for ground vibrations in order to isolate the table from vibrations coming from the earth. Such means are well known for optical tables and need not be described in detail.
The table 1 is made of steel and has a weight without feet of for example 360 kg.
Two socles 4 and 5 are disposed on this table which adhere to the table by magnetic forces and which are conventional in the field of optical laboratory tests. Each of these socles presents a support rod 6 and 7 which extends parallelly to the surface of the table and which supports an optical cavity 8.
This optical cavity is represented in more detail in FIG. 4 and comprises two glass substrates 9 and 10, which confine between them a glass plate 11. The dimensions of the substrates are for example 30 to 40 cm, whereas the glass plate 11 is a square plate of 10 cm length and 1 mm thickness. Each substrate carries on one surface (outside or inside) a photographic emulsion on which an interferometric network has been registered beforehand. Such networks are known and are realised by illuminating the emulsion by two spherical waves coming from a source of coherent light.
The glass plate 11, the major part of which is confined between the substrates 9 and 10, extends by one end beyond
REFERENCES:
patent: 3744909 (1973-07-01), Bruce
patent: 4188096 (1980-02-01), Shajenko
Journal of Physics E. Scientific Insstruments, vol. 12, No. 11, Nov. 1979, Bristol, GB, pp. 1043-1050, Billing et al. `AN Argon Laser Interferometer for the Detection of Gravitational Radiation`.
European Economic Community (EEC)
Turner Samuel A.
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