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Asgard/NOTT: L-band nulling interferometry at the VLTI. II. Warm optical design and injection system
Stray light represents a major performance limitation for optical instruments. Analyses are done with ray-tracing software to evaluate the stray light performances of a design and, if necessary, improve it before manufacturing. Accurate simulations, however, require sending a sufficient number of rays. Hence, the process can be very time-consuming. We introduce the concept of stray light entrance pupil (SLEP) and demonstrate how it can be an efficient tool for simulating stray light for point sources. The SLEP defines a pupil over which light entering the optical system generates stray light reaching the detector. When that pupil is smaller than the first lens of the system, rays can be sent only through that pupil instead of the full lens aperture. Therefore, the time required to perform the simulation is reduced. Moreover, the efficiency can be further improved by defining a source with nonuniform ray density. The SLEP method is demonstrated on a wide-angle Earth observation camera and a time reduction up to about 20 is obtained. The SLEP concept can also be used to facilitate experimental characterization.
The objective of these filters is to select the scientific waveband between 160 and 180 nm. The combined four mirrors have to give an out-of-band rejection ratio as high as possible to reject light from solar diffusion, dayglow and unwanted atomic lines in a range of 10-8 – 10-9. Different multilayer coatings are considered and optimized according to the π- multilayer equation for different H/L ratio and for different angles of incidence.
Our theoretical evaluation shows a least a modification of the reflectance spectrum as a function of the angle of incidence, so that the optical beams hitting the different mirrors can have different optical properties depending on the optical fields and the distribution of the rays on the pupil. In this paper the effect of fields and coating homogeneity on the spectral throughput of the UVI instrument will be assessed and described.
The low number of photons to be gathered from the planets, high contrast with the star and small angular resolution are the major difficulties for a direct detection. However, nulling interferometry seems to be a solution to tackle these challenges. By combining the light of two or more telescopes, we would considerably increase the angular resolution, and thus could potentially lead to the detection of Earth-size rocky exoplanets around Solar-type stars. Moreover, with a π- phase shift between the two interferometer arms, the starlight is reduced which allows the detection of much fainter objects around the star. In this paper it will be presented the development of a new mission based on nulling interferometry and dedicated to the Alpha Centauri system. As our nearest stellar system, it is a prime target to investigate for the research of new worlds. Monte-Carlo simulations about potential exoplanet yield of such an interferometer will be described, for different assumptions such as the detection wavelength and telescope size. Single-mode fibers and integrated optics will also be investigated for this mission. This could lead to low-cost type missions with a high potential of scientific return.
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