Aims. The detection and measurement of acoustic modes on the giant planets of the solar system is of great interest for the study of the internal structure and evolution of the giant planets, as well as the study of the solar system formation. Such observations require a dedicated instrument and observing procedure. Methods. We describe the principle and the performance of an instrument dedicated to seismology of giant planets. In this first paper, we describe the principle and the optical scheme, and derive the theoretical performances. As for the Sun, it is possible to measure modes with spatial resolution, but a larger collecting area is necessary. As for asteroseismology in general, continuity in the observation is also required. Results. From results obtained at the laboratory, we derive the actual performance of the instrument and estimate its capabilities in network observations. Conclusions. We demonstrate that the proposed instrument and strategy is adapted for the seismology of giant planets. In a second paper, we will present the first data set obtained with it, explain the data reduction procedure, and present preliminary results.

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Abstract. We report laboratory results from a monochromatic prototype of the Phase Knife Coronagraph which validate our previous theoretical and numerical simulations, prove the physical principle of it and set realistic limitations to the nulling properties of the coronagraph. The optical set-up, phase knife manufacturing technique and different aspects of the instrumental limitations are given. The first results attain easily a 3000 nulling effect obtained both on single and simulated double stars. Optical and mechanical stabilities are discussed and future steps to be carried out for a wide band version of this coronagraph are outlined.