We report on high-accuracy, high-resolut ion ( < 20mas) stellar measurements obtained in the near infra red (~ 2.2 microns) at the P alomar 200 inch telescope using two elliptical (3 m x 1.5 m) sub-a pertures located 3.4 m a part . Our interferometric coronagraph, known as the " Palomar Fiber Nuller" (PFN), is located downstream of the Palomar adaptive optics (AO) system and recombines t he two separate beams into a common singlemode fiber. The AO system acts as a " fr inge tracker", maintaining the optical path difference (OPD) between t he beams around an adjustable value, which is set to the central dar k interference fringe. AO correction ensures high efficiency and stable inject ion of the beams into the single-mode fi ber. A chopper wheel and a fast photometer are used to record short ( < 50ms per beam) interleaved sequences of backgro. und, individual beam and interferometric signals. In order to analyze these chopped null data sequences, we developed a new statistical method , baptized " Null Self-Calibration" (NSC), which provides astrophysical null measurements at the 0.001 level, wi th 1 a uncertainties as low as 0.0003. Such accuracy translates into a dynamic range greater than 1000:1 within the diffraction limit , demonstrating that the approach effectively bridges the tradit ional gap between regular coronagra phs, limited in angular resolution , and long baseline visibility interferometers, whose dynamic range is restricted to ~ 100:1. As our measurements are extremely sensitive to the bright ness distribution very close to t he opt ical axis, we were able to constrain the stellar diameters and amounts of circumstellar emission for a sample of very bright stars. With the improvement expected when t he PALM-3000 extreme AO system comes on-line at Palomar, the same instrument now equipped with a state of the art low noise fast read-out near IR camera, will yield 10-4 to 10-3 contrast as close as 30 mas for stars wit h K magnitude brighter than 6. Such a system will provide a unique and ideal tool for the detection of young ( < 100 Myr) self-luminous planets and hot debris disks in t he immediate vicinity (0.1 to a few A Us) of nearby ( < 50pc) stars.

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Abstract. This paper provides an overview of technology development for the Terrestrial Planet Finder Interferometer (TPF-I). TPF-I is a mid-infrared space interferometer being designed with the capability of detecting Earth-like planets in the habitable zones around nearby stars.

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