Nuller

A nuller is an optical instrument, e.g., a beam combiner for nulling interferometry[1], used to block or cancel out a strong source so that fainter signals near that source can be observed. This is typically useful to detect off-axis exoplanet or exozodiacal dust by interferometrically nulling out the on-axis parent star.

The VLT interferometer’s visiting instrument Asgard's[2] submodule NOTT (Nulling Observations of exoplaneTs and dusT) contains such a nuller to combine four telescope signals to perform nulling interferometry[3].

## Contents

* 1 Nulling interferometry
* 2 See also
* 3 References
* 4 External links

## Nulling interferometry

Nulling interferometry evolved from traditional stellar interferometry. The key difference is that it induces a 180-degree phase shift, for example, in one beam of a two-telescope interferometer. This creates destructive interference on the optical axis (where the star is) and constructive interference for off-axis objects (like planets). A technique initially proposed by Australian-American astronomer Ronald N. Bracewell in 1978 [4].

A different technique is called a coronagraph, using a physical obstacle to block the unwanted signals.

## See also

* Coronagraph
* Interferometry

## References

1. ↑ Bracewell, R. N. (1978). "Detecting nonsolar planets by spinning infrared interferometer" (in en). Nature 274 (5673): 780–781. doi:10.1038/274780a0. ISSN 1476-4687. https://www.nature.com/articles/274780a0.
2. ↑ Martinod, Marc-Antoine; Defrère, Denis; Ireland, Michael; Kraus, Stefan; Martinache, Frantz; Tuthill, Peter; Bigioli, Azzurra; Bouzerand, Emilie et al. (2023-06-27). "High-angular resolution and high contrast observations from Y to L band at the Very Large Telescope Interferometer with the Asgard Instrumental suite". Journal of Astronomical Telescopes, Instruments, and Systems 9 (02). doi:10.1117/1.JATIS.9.2.025007. ISSN 2329-4124. https://www.spiedigitallibrary.org/journals/Journal-of-Astronomical-Telescopes-Instruments-and-Systems/volume-9/issue-02/025007/High-angular-resolution-and-high-contrast-observations-from-Y-to/10.1117/1.JATIS.9.2.025007.full.
3. ↑ Sanny, Ahmed; Labadie, Lucas; Gross, Simon; Barjot, Kévin; Laugier, Romain; Garreau, Germain; Martinod, Marc-Antoine; Defrère, Denis et al. (2026-01-01). "Asgard/NOTT: L-band nulling interferometry at the VLTI - III. The mid-infrared integrated optics beam combiner for NOTT" (in en). Astronomy & Astrophysics 705: A37. doi:10.1051/0004-6361/202555865. ISSN 0004-6361. https://www.aanda.org/articles/aa/abs/2026/01/aa55865-25/aa55865-25.html.
4. ↑ Bracewell, R. N. (1978). "Detecting nonsolar planets by spinning infrared interferometer" (in en). Nature 274 (5673): 780–781. doi:10.1038/274780a0. ISSN 1476-4687. https://www.nature.com/articles/274780a0.

## External links

* Interferometric Nulling at TNO
* Nulling interferometer basics
* Tutorial on nulling interferometry
* Progress Toward Astronomical Nulling (Criteria governing efficacy of nulling interferometry), Chapter 10 of the Terrestrial Planet Finder (TPF): A NASA Origins Program to Search for Habitable Planets - JPL Publication 99-003, May 1999
* Interactive "virtual" interferometer

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