Gravitational Waves Detector
Development of an Active Double-Resonator Interferometric Detector of Gravitationally Induced Laser Frequency Shift
Tech Area / Field
- PHY-OPL/Optics and Lasers/Physics
- INS-DET/Detection Devices/Instrumentation
- INS-MEA/Measuring Instruments/Instrumentation
3 Approved without Funding
Science and Production Center "State Institute of Applied Optics", Russia, Tatarstan, Kazan
- Scientific center for Gravitational Wave Research “Dulkyn”, Russia, Tatarstan, Kazan
- [Individual specialist]
The purpose of this project is twofold. The first and most important objective is to use a new design of laser interferometer to conduct a series of experiments that will test important and as yet unproven parts of Einstein’s general theory of relativity. The second objective is to exploit the technology developed for this work as a basis for new and vastly improved methods of conducting gravimetric surveys. This second objective will eventually have wide ranging applications both for geological exploration and for space borne instrumentation for very sensitive planetary gravity surveys. However, the scope of work within this second objective will be limited to investigation.
Objective one; Detection of relativistic gravitational waves
This objective will be achieved by:
- further theoretical development of new methods of gravitational field measurement that are based on interferometric detection of the influence of gravitational fields directly on the phase of a light wave as well as on its frequency.
- development of a stationary precision laser interferometer complex (LIC) based on the dual-resonator laser system (DLS) for test of Einstein’s equivalence principle.
- elaboration of experimental and theoretical preconditions to develop a compact gravitational wave detector.
The existence of gravitational waves is the consequence of the general Einstein theory of relativity (1917), but it was corroborated only indirectly by Taylor and Hulse from the precision observations of irregularities in the radio emissions of the pulsar PSR 1913 + 16, which is one of two neutron stars in a well studied binary system (1994). The direct observation of gravitational waves is complicated since their influence on physical objects is very weak. Today, the main thrust of experimental research in this sphere is through the creation and use of passive laser interferometers. Terrestrial versions of these instruments have base lengths ranging from a few hundred meters to a few kilometers (increased to several hundred kilometers by multiple reflections). These compare with a base length of several million kilometers in the LISA Project, a space-based version proposed by the European Space Agency (ESA). Such a large base length is necessary in order to increase to a physically measurable level the amplitude of the signal associated with change in space-time metrics caused by gravitational waves.
The authors of this project propose instead to use the idea of the accumulation of the signal over time by means of an active laser interferometer. This idea was formulated by M.O. Scully (1986) and independently by Z.G. Murzakhanov and A.B. Balakin (1989). The problem which limits the sensitivity of this approach is the spontaneous radiation in the laser's active medium, which leads to phase diffusion of the laser radiation. M.O. Scully proposed to solve this problem by means of a correlated laser. In this laser, the photons are simultaneously emitted into two laser resonant cavities with a common active medium so that phase variations are synchronized. The effect of gravitational waves is then measured by the effect on the interference pattern between light passing around the two cavities. This may be done in several ways.
The correlated laser technique was experimentally developed by P. Toschek (2000) using a helium-neon laser. However two correlated modes in the scheme of P. Toschek were combined in space. That’s why his scheme is useless in its direct form for gravitational wave detection. Furthermore the question of the correlation effect's influence on the useful signal in the active interferometer was left open. Another important and incompletely solved problem is the development of a correct covariant elastodynamic theory. Such a theory is necessary to calculate the gravitationally-induced shift in laser system's radiation frequency using physically bound resonator mirrors. It was shown in 1994 in the paper of A.B. Balakin, Z.G. Murzakhanov and A.F. Scochilov (“Optics and Spectroscopy”, 1994) that different alternative elastodynamic theories lead to different predictions of the value for gravitationally induced frequency shift of laser radiation in a Newtonian gravitational field. Based on this work it will now be possible to determine the correct covariant generalization of the elastodynamics by using the DLS to measure the lunar-solar induced variations of geo-potential.
In the framework of this project, an investigation will be carried out for the operation of an active interferometer possibly based on the correlated laser. Its realization, the laser interferometer complex (LIC), will be built to detect the predicted gravitationally-induced frequency shift in the electromagnetic radiation and to test Einstein’s equivalence principle. The frequency shift will yield the design specifications to build a compact LIC optimized to detect gravitational waves.
The theoretical foundation of project rests on the solution of elastodynamic equation system and electrodynamic equations on the background of known gravitational field. That lies within the sphere of competence of SC GWR “Dulkyn”. The collaboration with the scientists and specialists of NPO GIPO who were engaged in the research and production of munitions and who had the wide experience in the field of precision optical instruments will provide high quality scientific and technical resources for research and will contribute to construction of the LIC experimental sample.
It is proposed to carry out this project in three stages
The first stage involves further refinement of the theory for the gravitationally induced frequency shift of correlated laser radiation and design of the optical and functional schemes for the LIC based on a dual-resonator laser system (DLS). The DLS has a common He-Ne active medium that generates optical radiation in two spatially nonequivalent resonators with mutually orthogonal polarizations. The spatially nonequivalent resonators of DLS sense in different ways the gravitational wave field and therefore the information about periodical gravitational radiation is contained in their difference frequency. Mounting, adjusting, tuning and achieving successful operation of the DLS generation are the main tasks of the first stage.
The second stage includes coupling of the DLS optics with the frequency-phase auto-tuning (FPAT) system that tunes the frequency for one of the DLS resonators to the narrow nonlinear methane absorption resonance, and completes the prototype LIC. During this stage, the team will also conduct some preliminary experiments. The theoretical feasibility analysis for incorporating a correlated laser with the DLS will also be carried out.
The third stage involves the long-term experiment with the LIC to test Einstein’s equivalence principle. During this stage the team will analyze the results of this experiment and, by factoring in theoretical preconditions (from the first and second stages), the design of compact gravitational wave detector based on correlated laser technology.
The realization of this project will enable weapons scientists to take part in fundamental investigations and transition to the civil instrument design and manufacturing industry. The role of foreign collaborators is in methodological and technological aid to develop the LIC.
The LIC is designated for:
- measuring the characteristics of continuous periodic relativistic gravitational radiation from the rotation of binary astrophysical objects;
- testing one of main principles part of the theory of relativity, namely Einstein’s equivalence principle, that predicts a gravitational “red shift” in the frequency of electromagnetic radiation.
Main characteristics of LIC:
- theoretical sensitivity to dimensionless amplitude of gravitational radiation of h10-22 with observation time 107 sec (a correlated laser can reduce the time required for detection),
- maximal dimension of apparatus 2x2 m2.
The proposed measuring complex is innovative. Its essential difference from other methods is in the way the optical radiation of the laser is used as a sensing element.
A patent search over the leading countries (USA, Great Britain, France, Germany, Japan; the subject of search is methods and devices for gravimetric measurements) has determined that the new development has no analogs in the world practice.
The results of preliminary theoretical investigation will lay the foundation of the research by defining more precisely the course of necessary experiments conduction.
Objective two: Spinoff applications for mineralogical and planetary gravity surveys
In addition to designing laser-interferometric measuring devices to detect gravitational waves, the team will also design instrumentation based on the same concepts to measure potential gradients in the Earth’s gravitational field and their temporal variations. Because of their very high sensitivity, these instruments will be capable of detecting hitherto unknown physical phenomena and, moreover, will make gravity surveying from space a more accessible and realistic option. The methodology employed will also be able to overcome the serious problems that arise when conducting such gravity surveys from aircraft. In summary, the theoretical and experimental research conducted during this project will lead to the development of new gravimetric instrumentation with many important advantages including:
- universal compatibility of measurements;
- absence of zero-point shift; and
- automatic processing of measurement results.
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