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An experiment is proposed to measure the post-Maxwellian parameters of the nonlinear electrodynamics of a vacuum. It is shown that the system for recording small differences of optical paths used in the Laser Interferometer Gravitational-Wave Observatory ͑LIGO͒ and in other laser interferometers for gravitational wave detectors permits us to measure the nonlinear electrodynamics corrections predicted by quantum electrodynamics. However, the use of LIGO or other full-scale laser interferometers of the gravitational wave detectors for this purpose does not seem sensible. Therefore it is suggested to perform this experiment on one of the laboratory prototypes used to develop interferometry for gravitational wave detection. The sensitivity of these laboratory prototypes is about the same as the sensitivity of the full-scale instruments, and the other parameters are most similar to the optimal values allowing us to observe the considered effect: the arm length l 0 of these prototypes is about several meters and in the Fabry-Perot interferometer about Nϳ2ϫ10 5 bounces can be realized. A further increase in the detector sensitivity is noted to offer also an opportunity of experimentally studying the nonlinearly electrodynamic corrections predicted by the Born-Infeld theory.

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The aim of this paper is to investigate the relative influence of geometrical and order parameters on diffuse -ED intensities. In most diffuse LEED studies relative to molecules adsorbed at single crystal surfaces, there are probably several chemisorption sites or several adsorbedspecies. Forthisreason, thissituation isexamined indetail here. Theelasticdiffuse LEED intensity from a single crystal surface Pt(ll1) partially covered with CO molecules is calculated for different valuesof the parameters which characterize the adsorbatelsubstrate model. These parameters are separated into: geometrical parameters related to the local arrangement of atoms near chemisorption sites, and order parameters related to the statistical distribution of the occupied chemisorption sites. In the present case, the geometrical parameters are the C-Pt and the C-0 bond lengths and the location in the 2D unit cell of the surface lattice (bridge and top sites). The order parameters are the site occupancy pair correlation functions or the quantities which determine them: surface coverage. surface temperature, pair interaction potential between adsorbates. etc. Even in thecaseof ashortrangeorder, thesensitivitiesofdiffuseintensitiesto bothkindsofparametersarefoundvery similar. On the other hand, in thesituation where several kinds ofchemisorption sitesexist, the diffuse LEED intensity is not the product of a form factor and a structure factor. So the use ofthe Yfunctionmethod,which avoidsthestructure factor determination, is not possible.Thus, a determination of the statistical distribution of adsorbates at the substrate surface cannot be circumvented,