Interferometric apodization by homothety – I. Optimization of the device parameters

Abstract

This study is focused on the very high dynamic imaging field, specifically the direct observation of exoplanetary systems. The coronagraph is an essential technique for suppressing the star’s light, making it possible to detect an exoplanet with a very weak luminosity compared to its host star. Apodization improves the rejection of the coronagraph, thereby increasing its sensitivity. This work presents the apodization method by interferometry using homothety, with either a rectangular or circular aperture. We discuss the principle method, the proposed experimental setup, and present the obtained results by optimizing the free parameters of the system while concentrating the maximum of the light energy in the central diffraction lobe, with a concentration rate of 93.6% for the circular aperture and 91.5% for the rectangular geometry. The obtained results enabled scaling the various elements of the experiment in accordance with practical constraints. Simulation results are presented for both circular and rectangular apertures. We performed simulations on a hexagonal aperture, both with and without a central obstruction, as well as a segmented aperture similar to the one used in the Thirty Meter Telescope (TMT). This approach enables the attainment of a contrast of approximately 10−4 at small angular separations, specifically around 1.8λ/D. When integrated with a coronagraph, this technique exhibits great promise. These findings confirm that our proposed technique can effectively enhance the performance of a coronagraph.

Interferometric apodization by homothety – II. Experimental validation

“…Before presenting the experimental results of rectangular apertures, let us recapitulate some steps involved in optimizing the design of the experimental set-up. These steps have been detailed elsewhere in a previous article (Chafi et al 2023 ).…”

“…The ef fecti veness of the apodization greatly depends on the values assigned to the parameters γ and η. In a recent work (Chafi et al 2023 ), we determined the optimal values for these two parameters to concentrate the maximum energy in the central lobe of the PSF. The optimal values are γ = 1.928 and η = 1.657.…”

“…Additionally, significant attenuation is observed in the diagonal regions, indicating that the IAH technique with a rectangular geometry offers a general and precise idea of the possibility of applying the IAH technique to any geometric shape of a telescope. For example, segmented apertures are similar to those used in large observatories like the TMT telescope that we used in the simulations shown in our previous article (Chafi et al 2023 ). 2008) performed an experimental validation of this apodization in the laboratory using a MZI, with converging and diverging lenses placed in the arms of the interferometer.…”

“…Following the mathematical formalism presented in our previous article (Chafi et al 2023 ), we have extensively examined the theory associated with circular apertures, both unapodized and apodized, in the image plane. As a reminder, we introduced mathematical expressions for the transmission using a circularly symmetric top-hat function r R , where represents the circularly symmetric tophat function with a radius R .…”

“…In our previous article (Chafi et al 2023 ), we presented simulation results for various aperture shapes, such as circular , rectangular , hexagonal, and apertures similar to those used in the TMT telescope. These results demonstrated promising performance in enhancing coronagraph capabilities by increasing contrast at low-angular separations, making the IAH technique even more attractive for use in major observatories.…”