ESA (European Space Agency) scientific missions like GAIA (Global Astrometric Interferometer for Astrophysics) and LISA (Laser Interferometer Space Antenna) require laser interferometry as driving technology. A frequency-stable light radiation is employed as a dimensional standard for very accurate (below 10pm) distance measurements. The wavelength of the light radiation, emitted by a monolithic laser source, must be stabilized against a frequency standard, which should be provided by a Fabry-Perot cavity which is dimensionally stable better than one part over 10{sup}12. A cavity of this kind, although made by a thermally stable material, must be thermally stabilized better than 0.1 mK. Moreover, construction must absolutely guarantee the only cause of deformation to be thermo-elastic, in order to make decisive and effective thermal control. The paper presents thermal design of the cavity as well as the digital control guaranteeing thermal stability. Simulated results are encouraging. Cavity construction is under way.
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