Browsing by Author "Hello, P."

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    Radiation pressure induced instabilities in laser interferometric detectors of gravitational waves
    (2015-03-13) Pai, A.; Dhurandhar, S.V.; Hello, P.; Vinet, J.Y.
    The large scale interferometric gravitational wave detectors consist of Fabry-Perot cavities operating at very high powers ranging from tens of kW to MW. The high powers may result in several nonlinear effects which would affect the performance of the detector. In this paper, we investigate the effects of radiation pressure, which tend to displace the mirrors from their resonant position resulting in the detuning of the cavity. We observe a remarkable effect, namely, that the freely hanging mirrors gain energy continuously and swing with increasing amplitude. It is found that the 'time delay', that is, the time taken for the field to adjust to its instantaneous equilibrium value, when the mirrors are in motion, is responsible for this effect. This effect is likely to be important in the optimal functioning of the full-scale interferometers such as the VIRGO and LIGO.
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    The thermo-optical coupling in optical resonators
    (2015-02-07) Dhurandhar, S.V.; Hello, P.; Sathyaprakash, B.S.
    Interferometric detectors of gravitational waves employ long baseline FabryPerot cavities with stored power of the order of 10 kW. The mirrors have a high reflectivity with absorption coefficient of a few parts in a million. The laser beam therefore acts as a source of heat creating a thermal gradient in the substrate and the consequent deformation in the mirror which in turn modifies the intra-cavity light field. The problem is thus coupled and nonlinear. Though the effect is expected to be negligible in the case of initial interferometers future interferometers are expected to employ much higher powers and it is necessary to ascertain thermo-elastic deformations and their effect on the stability of the laser field in the cavity. In this paper, which is first in a series to study instabilities in giant high power laser cavities, we have analytically solved the coupled problem of thermo-elastic deformations and their effect on the laser field, perturbatively and we show that within the realm of our (physically reasonable) assumptions there are no instabilities in the frequency range of 1 Hz-1 kHz.