arXiv subjects

Aditya R. Sengupta

Publications and source records attributed to Aditya R. Sengupta.

15 recordsLinked to original sources

arXiv2026

On-sky results from REDWOODS, a platform at Lick/ShaneAO for testing second stage AO technologies

REDWOODS is a new sub-testbed within the Shane Adaptive Optics (AO) system at Lick observatory, developed to test second stage AO wavefront sensing and control technologies, including a Self-Coherent Camera with optional broadband Wynne corrector, two different three-sided fully reflective highly broadband pyramid wavefront sensor modes, and multi-wavefront sensor single conjugate AO control. We present project results to date, including on-sky data.

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arXiv2026

Demonstrating the integration of a photonic lantern with an all-fiber-based nulling interferometer

High-contrast imaging of Solar System scale exoplanets and protoplanets demands advancements in instrumentation to access deeper starlight suppression at smaller angular separations than today's state-of-the-art. The multi-mode to single-mode conversion capabilities of photonic lanterns (PLs) provide new avenues to implement techniques such as nulling interferometry due to the inherent spatial filtering of single-mode waveguides. In this work, we present laboratory results on an all-fiber-based focal plane nulling interferometer using off-the-shelf components operating at 1550 nm. We demonstrate the implementation of a PL for coupling light into the instrument, and compare it to the case when laser light is directly fed into the interferometer. The integration of a PL with the interferometer evidences their potential for feeding photonic-based science instruments. Additionally, we discuss expanding the concept of the instrument for the detection of accreting protoplanets.

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arXiv2026

Experimentally-determined performance limits for joint imaging and wavefront sensing with a photonic lantern

The photonic lantern (PL) is a focal-plane wavefront sensor (WFS) that can be used for second-stage control of extreme adaptive optics (AO) systems. While the number of sensed modes and the dynamic range with respect to each mode have been relatively well characterized, little attention has been paid to the PL's sensitivity, i.e. how measurement noise impacts the accuracy of PL wavefront reconstruction. We compute the PL's sensitivity to photon noise as a function of spatial frequency, and compare it to existing WFSs, using simulations as well as experiments on the muirSEAL testbed. We further assess these metrics in the case where only a subset of PL ports are available for wavefront sensing. In this configuration, the remaining ports are used to spatially and spectrally reconstruct the observed scene using algorithms such as SPADE. Using more ports for wavefront sensing enables greater aberration sensitivity but leaves less spatial information for image reconstruction. This allows us to trade off between fewer samples with smaller aberrations and more samples with larger aberrations. This work sets the stage for AO system design incorporating the PL as a joint WFS and imager.

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arXiv2026

Laboratory characterization of a multi-photonic lantern optical waveguide using off-axis holography

Photonic lanterns (PLs) are waveguides that convert multi-mode input light to single-mode outputs. Wavefront sensing (WFS) and spectroscopy using a PL have been demonstrated, but PL simulations and experiments show significant mismatches. For the WaveDriver project, a proposed Habitable Worlds Observatory pathfinder that uses a PL for WFS as well as for integral field spectroscopy, we manufactured an optical waveguide consisting of an array of seven 19-port PLs in one device. We present laboratory characterization of the individual PLs, consisting of measurements of the principal modes at each PL input using digital off-axis holography. We compare our mode measurements to simulations to assess the variation in the PL manufacturing process. We discuss expected WFS performance in the WaveDriver configuration.

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arXiv2026

WaveDriver: a Laser Guide Star AO System for HWO

Habitable Worlds Observatory (HWO) presents a key challenge for technology development in the coming years, requiring a $>$ $100\times$ more stable system than \textit{JWST}. WaveDriver is a concept for a laser guide star spacecraft coupled to an adaptive optics (AO) system onboard HWO that would enable HWO to reach its picometer-level wavefront stability requirements while relaxing other HWO subsystem requirements. At LLNL and UCSC we are revisiting the concept initially proposed by Douglas et al.\ (2019). We present key results key initial results from the first phase of our project, including (1) AO control developments, including with Linear Quadratic Gaussian control and machine learning, (2) AO wavefront sensor (WFS) trade study simulations, and (3) simulations of a photonic lantern natural guide star WFS. A key finding from our work is that WaveDriver could be needed to enable HWO's primary mirror segment stability and/or low order wavefront stability requirements.

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arXiv2026

WaveDriver: a Laser Guide Star AO System for HWO

HWO's Tier 1 Contrast Stability Technology Gap presents a key challenge for technology development in the coming years, requiring to a >100x more stable system than JWST. WaveDriver is a concept for a laser guide star spacecraft coupled to an adaptive optics (AO) system onboard HWO that would enable HWO to reach its picometer-level wavefront stability requirements while relaxing other HWO subsystem requirements. At LLNL and UCSC we are revisiting the concept initially proposed by Douglas et al. (2019). We present results from our project's first year, including (1) AO control developments, including with Linear Quadratic Gaussian control and machine learning, (2) AO wavefront sensor (WFS) trade study simulations, and (3) simulations, fabrication, and testing of a 133-port photonic lantern WFS/spectrograph. A key finding from our work is that WaveDriver could be needed to enable HWO's primary mirror segment stability and/or low order wavefront stability requirements.

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arXiv2026

Control algorithms for dual-wavefront sensor single-conjugate adaptive optics

High-contrast imaging systems using active control with adaptive optics (AO) are often limited by non-common path (NCP) aberrations that are seen only at the final science image. AO systems employing focal-plane wavefront sensors (FP-WFSs) are able to simultaneously correct NCP aberrations and measure science images, but they typically require a second stage of control that adds system cost and complexity. We present control algorithms to augment AO systems with FP-WFSs within their existing control setup. We demonstrate inter-arm NCP aberration transfer can be mitigated through temporal filtering, present frequency- and time-domain validation of controller stability and performance, and discuss the optimality of the chosen controllers. This work will enable the development, testing, and installation of FP-WFS technologies for direct imaging of exoplanets.

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arXiv2025

On-sky demonstration of second-stage wavefront control with a photonic lantern

Ground-based direct imaging of exoplanets at high contrast requires precise correction of atmospheric turbulence using adaptive optics (AO). The planet-to-star contrast ratio at small angular separations from the host star is often limited by non-common-path aberrations (NCPAs) seen only in the science plane. The photonic lantern (PL) can be used to sense aberrations at the final science imaging plane. This enables a two-stage wavefront control architecture, in which the first-stage wavefront sensor senses atmospheric turbulence and the PL senses NCPAs and other aberrations not seen by the first stage. We demonstrate closed-loop control of residual wavefront errors using a non-dispersed PL after first-stage AO correction on the Shane 3m telescope at Lick Observatory. Our results show that non-dispersed PLs can be used for second-stage wavefront sensing, enabling performance improvements via minimally invasive retrofits to existing AO systems.

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arXiv2025

The Santa Cruz Extreme AO Lab (SEAL) 2.0: A reflective, multi-wavelength rebuild

The Santa cruz Extreme Adaptive optics Lab (SEAL) is a visible/near-infrared wavelength testbed designed to support technology development for high contrast imaging on large, segmented, ground-based telescopes. SEAL saw first light in 2021 as a transmissive, visible-wavelength AO testbed. In this paper, we present four major upgrades to SEAL: (1) the testbed has been rebuilt with custom off-axis parabolic mirrors, enabling operation in both near-infrared and visible wavelengths; (2) the suite of wavefront sensors now includes a Shack-Hartmann, transmissive four-sided pyramid, vector-Zernike, and, in the muirSEAL testbed, a photonic lantern; (3) the testbed includes a vector-vortex coronagraph and will soon include a hybrid astrophotonic coronagraph; (4) in addition to its original Keck-heritage RTC, SEAL now includes two additional control software packages: Catkit, originally developed for the HiCAT testbed at the Space Telescope Science Institute, and the RTC Compute And Control for Adaptive Optics (CACAO), originally designed for Subaru/SCExAO. We discuss the performance of the testbed after the reflective rebuild and on-going technology development work at SEAL.

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arXiv2025

Exploring the Capabilities of Astrophotonics for the Precise Alignment of Segmented Telescopes

The next generation of large telescopes for direct imaging of exoplanets will require segmented primary mirrors. Over both long and short timescales, these telescopes experience segment misalignments which degrade the final science image. Adaptive optics (AO) systems can be used to correct these aberrations in real time. AO systems require wavefront sensors (WFSs) that measure the phase of the incoming light in order to reconstruct optical aberrations. However, most WFSs used for sensing atmospheric turbulence cannot correctly detect aberrations induced by misalignments in segmented telescopes, as they show poor sensitivity to phase discontinuities. We investigate the potential of photonic lanterns (PLs), which are waveguides that allow for the low-loss transmission from multi-mode to multiple single-mode optical signals, for sensing segment misalignments at the focal plane. We assess the ability of PLs to measure piston offsets in segmented mirrors through both simulations and laboratory experiments. We simulate the photonic lantern and demonstrate linear reconstruction on segment pistons. Further, we train a neural network to reconstruct aberrations outside of the linear regime. We experimentally validate reconstruction of segment piston offsets on the Miniature Infrared SEAL (muirSEAL) testbed, which includes a segmented deformable mirror, a PSF imaging branch, and a PL. This work demonstrates the potential of the PL as a compact WFS for future space- and ground-based segmented-mirror telescopes.

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arXiv2025

Experimental validation of photonic lantern imaging and wavefront sensing performance

Photonic lanterns (PLs) are fiber-based waveguides that are capable of focal-plane wavefront sensing while simultaneously directing light to downstream science instruments. The optimal choice of wavefront reconstruction algorithm has yet to be determined, and likely depends on the particular observing scenario under consideration. Previous work in simulation suggests that PLs can be used for nonlinear wavefront sensing for several applications, including sensing the low-wind effect and correcting large-amplitude aberrations. We present the design of muirSEAL (miniature IR SEAL), a testbed designed to test PL wavefront reconstruction over Zernike modes and segmented-mirror offsets. We demonstrate throughput and linear wavefront reconstruction at multiple f-numbers. We further present initial laboratory imaging of a new photonic lantern fabricated at Lawrence Livermore National Laboratory.

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arXiv2025

Condensation Clouds in Substellar Atmospheres with Virga

Here we present an open-source cloud model for substellar atmospheres, called Virga. The Virga-v0 series has already been widely adopted in the literature. It is written in Python and has heritage from the Ackerman & Marley (2001) model (often referred to as eddysed), used to study clouds on both exoplanets and brown dwarfs. In the development of the official Virga-v1 we have retained all the original functionality of eddysed and updated/expanded several components including the back-end optical constants data, calculations of the Mie properties, available condensate species, saturation vapor pressure curves and formalism for fall speeds calculations. Here we benchmark Virga by reproducing key results in the literature, including the SiO2 cloud detection in WASP-17 b and the brown dwarf Diamondback-Sonora model series. Development of Virga is ongoing, with future versions already planned and ready for release. We encourage community feedback and collaborations within the GitHub code repository.

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arXiv2025

Developments on LLNL's high contrast testbed and Lick/ShaneAO

LLNL has recently setup a High Contrast Testbed (HCT) for AO and exoplanet imaging technology development. We present the various HCT technologies currently under development, including (1) a Wynne corrector, (2) multi-wavefront sensor (WFS) single conjugate AO (SCAO) control. We present HCT testing results of a first Wynne corrector prototype with a self-coherent camera. We present updates on development efforts to design and apply multi-WFS SCAO control to our HCT setup. We also present ongoing HCT deformable mirror and WFS upgrades. Lastly, we present developments for REDWOODS, a project to deploy many of these technologies on-sky on a sub-bench of the Shane AO system at Lick Observatory.

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arXiv2024

Photonic lantern wavefront reconstruction in a multi-wavefront sensor single-conjugate adaptive optics system

Exoplanet direct imaging using adaptive optics (AO) is often limited by non-common path aberrations (NCPAs) and aberrations that are invisible to traditional pupil-plane wavefront sensors (WFSs). This can be remedied by focal-plane (FP) WFSs that characterize aberrations directly from a final science image. Photonic lanterns (PLs) can act as low-order FPWFSs with the ability to direct some light to downstream science instruments. Using a PL on the SEAL (Santa Cruz Extreme AO Laboratory) high-contrast imaging testbed, we demonstrate (1) linear ranges and (2) closed-loop control. Additionally, we simulate the use of the PL in a multi-wavefront sensor AO system, in which multiple WFSs feed back to the same common-path deformable mirror. Building on previous multi-WFS AO demonstrations on SEAL, we simulate a modulated pyramid WFS to sense aberrations of high spatial order and large amplitude, and the PL to sense low order aberrations including NCPAs. We assess adaptive optics performance in this setting using three different PL wavefront reconstruction algorithms. We also provide a new method to experimentally identify the propagation matrix of a PL, making advanced model-based algorithms practical. This work demonstrates the role of photonic technologies and multi-stage wavefront sensing in the context of extreme AO and high contrast imaging.

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arXiv2022

Laboratory Demonstration of Optimal Identification and Control of Tip-Tilt Systems

We present the results of testing optimal linear-quadratic-Gaussian (LQG) control for tip and tilt Zernike wavefront modes on the SEAL (Santa cruz Extreme AO Lab) testbed. The controller employs a physics model conditioned by the expected tip/tilt power spectrum and vibration peaks. The model builds on similar implementations, such as that of the Gemini Planet Imager, by considering the effects of loop delays and the response of the control hardware. Tests are being performed on SEAL using the Fast Atmospheric Self-coherent camera Technique (FAST), and being executed using a custom Python library to align optics, generate interaction matrices, and perform real-time control by combining controllers with simulated disturbance signals to be corrected. We have carried out open-loop data collection, characterizing the natural bench dynamics, and have shown a reduction in RMS wavefront error due to integrator control and LQG control.

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