About

Rebecca Jensen Clem is an Associate Professor in the Astronomy & Astrophysics Department within the Physical & Biological Sciences Division at UC Santa Cruz. Her research focuses on extreme adaptive optics technology development and observational exoplanet science. She studies the atmospheres of gas giant exoplanets and brown dwarfs using near-infrared polarimetry, while also advancing the state of the art in wavefront sensing and control to discover new exoplanets. Her educational background includes a B.S. from MIT obtained between 2008 and 2012, followed by an M.S. and Ph.D. from Caltech completed between 2012 and 2017. She was a Miller Fellow at UC Berkeley from 2017 to 2019 and has been serving as an Assistant Professor at UC Santa Cruz since 2020. Her office is located at the Center for Adaptive Optics, and she can be contacted via email at rjensenc@ucsc.edu.

Selected publications

• On-sky Demonstration of Second-stage Wave-front Control with a Photonic Lantern

  The Astronomical Journal · 2026-01-05

  articleOpen access

  Abstract 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) that are 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 wave-front control architecture, in which the first-stage wave-front 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 wave-front errors using a nondispersed PL after first-stage AO correction on the Shane 3 m telescope at Lick Observatory. Our results show that nondispersed PLs can be used for second-stage wave-front sensing, enabling performance improvements via minimally invasive retrofits to existing AO systems.

  PublisherDOI

• Exploring the capabilities of astrophotonics for the precise alignment of segmented telescopes

  2025-09-18

  article
  PublisherDOI

• Technical description and performance of the phase II version of the Keck Planet Imager and Characterizer

  arXiv (Cornell University) · 2025-02-03

  preprintOpen access

  The Keck Planet Imager and Characterizer (KPIC) is a series of upgrades for the Keck II Adaptive Optics (AO) system and the NIRSPEC spectrograph to enable diffraction limited, high resolution (R>30000) spectroscopy of exoplanets and low mass companions in the K and L bands. Phase I consisted of single mode fiber injection/extraction units (FIU/FEU) used in conjunction with a H band pyramid wavefront sensor. The use of single mode fibers provides a gain in stellar rejection, a substantial reduction in sky background, and an extremely stable line spread function in the spectrograph. Phase II, deployed and commissioned in 2022, brought a 1000 actuator deformable mirror, beam shaping optics, a vortex mask, and other upgrades to the FIU/FEU. An additional service mission in 2024 extended operations down to y band, delivered an atmospheric dispersion corrector, and provided access to two laser frequency combs. KPIC phase II brings higher planet throughput, lower stellar leakage and many new observing modes which extend its ability to characterize exoplanets at high spectral resolution, building on the success of phase I. In this paper we present a description of the final phase II version of KPIC, along with results of system level laboratory testing and characterization showing the instrument's phase II throughput, stability, repeatability, and other key performance metrics prior to delivery and during installation at Keck. We outlined the capabilities of the various observing modes enabled by the new modules as well as efforts to compensate for static aberrations and non common path errors at Keck, which were issues that plagued phase I. Finally, we show results from commissioning.

  PublisherOA PDFDOI

• Technical description and performance of the phase II version of the Keck Planet Imager and Characterizer

  Journal of Astronomical Telescopes Instruments and Systems · 2025-02-27 · 9 citations

  articleOpen access

  The Keck Planet Imager and Characterizer (KPIC) is a series of upgrades for the Keck II Adaptive Optics (AO) system and the NIRSPEC spectrograph to enable diffraction-limited, high-resolution (R>30,000) spectroscopy of exoplanets and low-mass companions in the K and L bands. Phase I consisted of single-mode fiber injection/extraction units (FIU/FEU) used in conjunction with an H band pyramid wavefront sensor. The use of single-mode fibers provides a gain in stellar rejection, a substantial reduction in sky background, and an extremely stable line-spread function in the spectrograph. Phase II, deployed and commissioned in 2022, brought a 1000-actuator deformable mirror, beam-shaping optics, a vortex mask, and other upgrades to the FIU/FEU. An additional service mission in 2024 extended operations down to the y band, delivered an atmospheric dispersion corrector, and provided access to two laser frequency combs. KPIC phase II brings higher planet throughput, lower stellar leakage, and many new observing modes which extend its ability to characterize exoplanets at high spectral resolution, building on the successes of phase I. We present a description of the final phase II version of KPIC, along with results of system-level laboratory testing and characterization showing the instrument’s phase II throughput, stability, repeatability, and other key performance metrics prior to delivery and during installation at Keck. We outline the capabilities of the various observing modes enabled by the new modules as well as efforts to compensate for static aberrations and non-common path errors at Keck, which were issues that plagued phase I. Finally, we show results from commissioning.

  PublisherOA PDFDOI

• Developments on LLNL’s high contrast testbed and Lick/ShaneAO

  2025-09-18

  article

  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.

  PublisherDOI

• ORCAS Keck instrument demonstrator

  Journal of Astronomical Telescopes Instruments and Systems · 2025-03-28

  article

  The Orbiting Configurable Artificial Star (ORCAS) mission in collaboration with the W. M. Keck Observatory has designed, assembled, built, and delivered, within 180 days, ORCAS Keck Instrument Demonstrator (ORKID) (ORCAS Keck Instrument Demonstrator), an early visible-wavelength performance demonstration with the Keck II Adaptive Optics (AO) system. The optical performance of ORKID meets the technical requirements derived from the scientific goals of having a Nyquist-sampled point spread function at 650 nm. This is achieved by diffraction-limited as-built performance with a root mean square internal wavefront error below 50 nm, which is key for the advancement of the ORCAS mission. ORKID has acquired, with a closed AO loop, no frame selection, while shifting and adding, the sharpest-ever on-sky image captured at Keck II. With a full width at half maximum of ∼15 mas, this is the equivalent of a 9-m diffraction-limited telescope. By doing so, the immense potential and viability of the proposed Hybrid Observatory ORCAS mission are demonstrated.

  PublisherDOI

• Optimization of sequential phase diversity

  2025-09-18

  article
  PublisherDOI

• Experimental validation of photonic lantern imaging and wavefront sensing performance

  2025-09-18 · 2 citations

  article

  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.

  PublisherDOI

• High-contrast exoplanet imaging at Keck Observatory with SCALES and next generation adaptive optics

  2025-09-18

  article

  The Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy (SCALES) is a 2–5 micron integral field spectrograph designed to directly image and characterize exoplanets. Around the time of SCALES’ commissioning, Keck Observatory will also receive a nearly 3000-actuator deformable mirror upgrade as part of the High-Order All Sky Keck Adaptive Optics (HAKA) project. HAKA, along with other adaptive optics (AO) improvements—such as predictive wavefront control, speckle nulling, and infrared pyramid wavefront sensing—will enhance contrast and image quality, improving exoplanet detection. Using simulations, we estimate SCALES’ achievable contrast before and after these AO improvements. From simulated Gaia and Roman planet populations, we predicted the number of planets SCALES can directly image. Our results suggest that these AO upgrades significantly increase the number of detectable planets. With Gaia data expected in 2026 and Roman data in the 2030s, SCALES will play a key role in exoplanet research while demonstrating the impact of AO advancements.

  PublisherDOI

• The Santa Cruz Extreme AO Lab (SEAL) 2.0: a reflective, multiwavelength rebuild

  2025-09-18

  article1st authorCorresponding
  PublisherDOI