Interferometric apodization of rectangular aperture – Laboratory Experiments

Azhari, Y. El; Azagrouze, O.; Martin, F.; Soummer, Rémi; Aime, Claude

doi:10.1017/s1743921306009744

Cited by 3 publications

(1 citation statement)

References 2 publications

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“…Unlike Guyon's proposal, because of the linearity of the process, the apodized output cannot be brighter than what could be obtained with an absorbing apodizer, the complementary energy being transferred to the second output of the MZI. The first experiments using a Michelson interferometer were conducted by Soummer (2002) and Azhari et al (2005) to test this idea. A cosine apodization was obtained by introducing a thin wedge-shaped air film by slightly tilting a mirror.…”

Section: Introductionmentioning

confidence: 99%

Interferometric apodization of telescope apertures

Carlotti

Ricort

Aime

et al. 2007

A&A

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Aims. We seek to produce apodized apertures for application in stellar coronagraphy to help in direct detections of exoplanets. We show that chromatic apodized apertures of any shape in transmission can be obtained with a specific MZI and we demonstrate this capability in two cases. Methods. The method takes advantage of the capabilities of the MZI, in which the two outputs correspond to the addition and subtraction of the two wave amplitudes in both arms. The result is obtained by re-imaging the entrance aperture of the telescope in the arms of the MZI where two complementary phase masks ± ϕ(x, y) are set. At the two outputs of the MZI, the re-imaged apertures interfere, and their transmissions are multiplied respectively by a factor of the form cos[ϕ(x, y)] and i sin[ϕ(x, y)]. They correspond to the apodized and anti-apodized complementary outputs. Results. We present the results obtained for two types of apodization. A 1D cosine apodization for a square aperture is obtained by introducing a thin wedge-shaped air film, slightly tilting one of the mirrors of the MZI. A 2D circular symmetric apodization of the form cos[x 2 + y 2 ] is obtained for a circular aperture using two complementary convergent and divergent lenses as phase masks. Aperture transmissions (in intensity) and corresponding point spread functions (PSFs) are given in each case and compared to the theoretical expectations. Conclusions. We have demonstrated the capability of the MZI to produce an apodized aperture. This result is obtained with no loss of photons, considering the fact that there are two complementary outputs. Considerations are given on the wavelength dependence of this technique.

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Section: Introductionmentioning

confidence: 99%

Interferometric apodization of telescope apertures

Carlotti

Ricort

Aime

et al. 2007

A&A

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

Chafi

Azhari

Azagrouze

et al. 2023

Monthly Notices of the Royal Astronomical Society

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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.

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Interferometric apodization by homothety – II. Experimental validation

Chafi,

El Azhari,

Azagrouze

et al. 2023

Monthly Notices of the Royal Astronomical Society

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This work presents the results of experimental laboratory tests on the apodization of circular and rectangular apertures using the Interferometric Apodization by Homothety (IAH) technique. The IAH approach involves splitting the amplitude of the instrumental PSF into two equal parts. One of the two produced PSFs undergoes homothety to change its transverse dimensions while its amplitude is properly controlled. The two PSFs are then combined to produce an apodized image. The diffraction wings of the resulting PSF are subsequently reduced by some variable reduction factor, depending on an amplitude parameter γ and a spread parameter η. This apodization approach was implemented in the laboratory using an interferometric set-up based on the Mach–Zehnder Interferometer (MZI). The experimental results exhibit a strong agreement between theory and experiment. For instance, the average experimental contrast obtained at a low angular separation of 2.4λ/D does not exceed 5 × 10−4. This work also allowed us to study the influence on the apodizer’s performance of some parameters, such as the wavelength and the density of the neutral filters.

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Interferometric apodization of rectangular aperture – Laboratory Experiments

Cited by 3 publications

References 2 publications

Interferometric apodization of telescope apertures

Interferometric apodization of telescope apertures

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

Interferometric apodization by homothety – II. Experimental validation

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