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Laboratory demonstration of single-camera PPPP wavefront sensing using neural networks (2024)
Journal Article
Gonzalez-Gutierrez, C., Bharmal, N. A., Rodriguez-Muro, J., Buendia-Roca, A., Yang, H., Fitzpatrick, L. W., Morris, T. J., & de Cos Juez, F. J. (2024). Laboratory demonstration of single-camera PPPP wavefront sensing using neural networks. International Journal of Optomechatronics, 18(1), Article 2386985. https://doi.org/10.1080/15599612.2024.2386985

Laser guide stars in astronomical adaptive optics systems have the focus anisoplanatism problem, especially for telescopes larger than 4 m in diameter. The Projected Pupil Plane Pattern (PPPP) offers an alternative solution by projecting a collimated... Read More about Laboratory demonstration of single-camera PPPP wavefront sensing using neural networks.

WIVERN: a laboratory experiment for testing novel laser-based wavefront sensing techniques (2022)
Presentation / Conference Contribution
Bharmal, N. A., Bramall, D., Calcines Rosario, A. Z., Morris, T. J., Schmoll, J., & Staykov, L. (2022, December). WIVERN: a laboratory experiment for testing novel laser-based wavefront sensing techniques. Presented at Adaptive Optics Systems VIII

WIVERN is a testbed for laboratory experiments in laser-based wavefront sensing. It emulates laser uplink from a 4m telescope with 1.6 arcsec seeing and laser back-scattering from up to 20 km. Currently there are three current wavefront sensing capab... Read More about WIVERN: a laboratory experiment for testing novel laser-based wavefront sensing techniques.

Concept validation of a high dynamic range point-diffraction interferometer for wavefront sensing in adaptive optics (2022)
Journal Article
Dubost, N., Bharmal, N. A., Dubbeldam, M., & Myers, R. M. (2022). Concept validation of a high dynamic range point-diffraction interferometer for wavefront sensing in adaptive optics. Applied Optics, 61(14), 4160-4167. https://doi.org/10.1364/ao.439569

The direct detection and imaging of exoplanets requires the use of high-contrast adaptive optics (AO). In these systems quasi-static aberrations need to be highly corrected and calibrated. To achieve this, the pupil-modulated point-diffraction interf... Read More about Concept validation of a high dynamic range point-diffraction interferometer for wavefront sensing in adaptive optics.

On-sky results for the integrated microlens ring tip-tilt sensor (2021)
Journal Article
Hottinger, P., Harris, R. J., Crass, J., Dietrich, P.-I., Blaicher, M., Bechter, A., Sands, B., Morris, T., Basden, A. G., Bharmal, N. A., Heidt, J., Anagnos, T., Neureuther, P. L., Glück, M., Power, J., Pott, J.-U., Koos, C., Sawodny, O., & Quirrenbach, A. (2021). On-sky results for the integrated microlens ring tip-tilt sensor. Journal of the Optical Society of America B, 38(9), https://doi.org/10.1364/josab.421459

We present the first on-sky results of the microlens ring tip-tilt sensor. This sensor uses a 3D printed microlens ring feeding six multimode fibers to sense misaligned light, allowing centroid reconstruction. A tip-tilt mirror allows the beam to be... Read More about On-sky results for the integrated microlens ring tip-tilt sensor.

First stellar photons for an integrated optics discrete beam combiner at the William Herschel Telescope (2021)
Journal Article
Nayak, A. S., Labadie, L., Sharma, T. K., Piacentini, S., Corrielli, G., Osellame, R., Gendron, É., Buey, J.-T. M., Chemla, F., Cohen, M., Bharmal, N. A., Bardou, L. F., Staykov, L., Osborn, J., Morris, T. J., Pedretti, E., Dinkelaker, A. N., Madhav, K. V., & Roth, M. M. (2021). First stellar photons for an integrated optics discrete beam combiner at the William Herschel Telescope. Applied Optics, 60(19), D129-D142. https://doi.org/10.1364/ao.423881

We present the first on-sky results of a four-telescope integrated optics discrete beam combiner (DBC) tested at the 4.2 m William Herschel Telescope. The device consists of a four-input pupil remapper followed by a DBC and a 23-output reformatter. T... Read More about First stellar photons for an integrated optics discrete beam combiner at the William Herschel Telescope.

Global tip-tilt and high-order aberration correction with plenoptic wavefront sensors in closed-loop AO systems (2021)
Journal Article
Zhang, Z., Morris, T., Bharmal, N., & Liang, Y. (2021). Global tip-tilt and high-order aberration correction with plenoptic wavefront sensors in closed-loop AO systems. Applied Optics, 60(14), 4208 - 4216. https://doi.org/10.1364/ao.420729

The plenoptic wavefront sensor (PlWFS) has been proposed as being suitable for operating on extended objects in adaptive optics (AO) systems. We propose a new self-referencing method that uses the cell image of PlWFS as a correlation reference and en... Read More about Global tip-tilt and high-order aberration correction with plenoptic wavefront sensors in closed-loop AO systems.

On-sky results for adaptive optics control with data-driven models on low-order modes (2020)
Journal Article
Sinquin, B., Prengere, L., Kulcsár, C., Raynaud, H.-F., Gendron, E., Osborn, J., Basden, A., Conan, J.-M., Bharmal, N., Bardou, L., Staykov, L., Morris, T., Buey, T., Chemla, F., & Cohen, M. (2020). On-sky results for adaptive optics control with data-driven models on low-order modes. Monthly Notices of the Royal Astronomical Society, 498(3), 3228-3240. https://doi.org/10.1093/mnras/staa2562

Dedicated tip-tilt loops are commonly implemented on adaptive optics (AO) systems. In addition, a number of recent high-performance systems feature tip-tilt controllers which are more efficient than the integral action controller. In this context, Li... Read More about On-sky results for adaptive optics control with data-driven models on low-order modes.

Wind-driven halo in high-contrast images (2020)
Journal Article
Cantalloube, F., Farley, O., Milli, J., Bharmal, N., Brandner, W., Correia, C., Dohlen, K., Henning, T., Osborn, J., Por, E., Suárez Valles, M., & Vigan, A. (2020). Wind-driven halo in high-contrast images. Astronomy & Astrophysics, 638, Article A98. https://doi.org/10.1051/0004-6361/201937397

Context. The wind-driven halo is a feature that is observed in images that were delivered by the latest generation of ground-based instruments that are equipped with an extreme adaptive optics system and a coronagraphic device, such as SPHERE at the... Read More about Wind-driven halo in high-contrast images.

Projected Pupil Plane Pattern (PPPP) with artificial Neural Networks (2019)
Journal Article
Yang, H., Gonzalez, C., Bharmal, N., & de Cos, F. (2019). Projected Pupil Plane Pattern (PPPP) with artificial Neural Networks. Monthly Notices of the Royal Astronomical Society, 487(1), 1480-1487. https://doi.org/10.1093/mnras/stz1362

Focus anisoplanatism is a significant measurement error when using one single laser guide star (LGS) in an Adaptive Optics (AO) system, especially for the next generation of extremely large telescopes. An alternative LGS configuration, called Project... Read More about Projected Pupil Plane Pattern (PPPP) with artificial Neural Networks.

Laboratory demonstration of an alternative laser guide stars wavefront sensing technique—projected pupil plane pattern (2019)
Journal Article
Yang, H., Bharmal, N., Myers, R., & Younger, E. (2019). Laboratory demonstration of an alternative laser guide stars wavefront sensing technique—projected pupil plane pattern. Journal of Astronomical Telescopes, Instruments, and Systems, 5(2), Article 029002. https://doi.org/10.1117/1.jatis.5.2.029002

Adaptive optics (AO) is widely used in optical/near-infrared telescopes to remove the effects of atmospheric distortion, and laser guide stars (LGSs) are commonly used to ease the requirement for a bright, natural reference source close to the scient... Read More about Laboratory demonstration of an alternative laser guide stars wavefront sensing technique—projected pupil plane pattern.

PEPITO: atmospheric Profiling from short-Exposure focal Plane Images in seeing-limiTed mOde (2019)
Journal Article
Beltramo-Martin, O., Bharmal, N. A., & Correia, C. (2019). PEPITO: atmospheric Profiling from short-Exposure focal Plane Images in seeing-limiTed mOde. Monthly Notices of the Royal Astronomical Society, 486(2), 2032-2041. https://doi.org/10.1093/mnras/stz979

Atmospheric profiling is a requirement for controlling wide-field Adaptive Optics (AO) instruments, analyzing the AO performance with respect to the observing conditions and predicting the Point Spread Function (PSF) spatial variations. We present PE... Read More about PEPITO: atmospheric Profiling from short-Exposure focal Plane Images in seeing-limiTed mOde.

Origin of the asymmetry of the wind driven halo observed in high-contrast images (2018)
Journal Article
Cantalloube, F., Por, E., Dohlen, K., Sauvage, J., Vigan, A., Kasper, M., …Fusco, T. (2018). Origin of the asymmetry of the wind driven halo observed in high-contrast images. Astronomy & Astrophysics, 620, Article L10. https://doi.org/10.1051/0004-6361/201834311

The latest generation of high-contrast instruments dedicated to exoplanets and circumstellar disk imaging are equipped with extreme adaptive optics and coronagraphs to reach contrasts of up to 10−4 at a few tenths of arcseconds in the near-infrared.... Read More about Origin of the asymmetry of the wind driven halo observed in high-contrast images.

Calibration of quasi-static aberrations in high-contrast astronomical adaptive optics with a pupil-modulated point-diffraction interferometer (2018)
Journal Article
Dubost, N., Bharmal, N., & Myers, R. M. (2018). Calibration of quasi-static aberrations in high-contrast astronomical adaptive optics with a pupil-modulated point-diffraction interferometer. Optics Express, 26(9), 11068-11083. https://doi.org/10.1364/oe.26.011068

The direct detection and imaging of exoplanets requires the use of high-contrast adaptive optics (AO). In these systems quasi-static aberrations need to be highly corrected and calibrated. In order to achieve this, a high-sensitivity wavefront sensor... Read More about Calibration of quasi-static aberrations in high-contrast astronomical adaptive optics with a pupil-modulated point-diffraction interferometer.

Projected Pupil Plane Pattern: an alternative LGS wavefront sensing technique (2018)
Journal Article
Yang, H., Bharmal, N. A., & Myers, R. M. (2018). Projected Pupil Plane Pattern: an alternative LGS wavefront sensing technique. Monthly Notices of the Royal Astronomical Society, 477(4), 4443-4453. https://doi.org/10.1093/mnras/sty926

We have analysed and simulated a novel alternative Laser Guide Star (LGS) configuration termed Projected Pupil Plane Pattern (PPPP), including wavefront sensing and the reconstruction method. A key advantage of this method is that a collimated beam i... Read More about Projected Pupil Plane Pattern: an alternative LGS wavefront sensing technique.

Estimating stochastic noise using in-situ measurements from a linear wavefront slope sensor (2016)
Journal Article
Bharmal, N., & Reeves, A. (2016). Estimating stochastic noise using in-situ measurements from a linear wavefront slope sensor. Optics Letters, 41(2), 428-431. https://doi.org/10.1364/ol.41.000428

It is shown how the solenoidal component of noise from the measurements of a wavefront slope sensor can be utilized to estimate the total noise: specifically, the ensemble noise variance. It is well known that solenoidal noise is orthogonal to the re... Read More about Estimating stochastic noise using in-situ measurements from a linear wavefront slope sensor.