About

J. Roger Angel is a Professor of Astronomy at the University of Arizona, affiliated with the Department of Astronomy and Steward Observatory. He holds additional titles as Regents Professor and Professor of Optical Sciences, with an affiliation in Arid Lands Resources Sciences - GIDP. His research focuses on astronomical telescopes and instrumentation, extrasolar planets, optical design and fabrication, geoengineering, and optics for solar energy generation. Angel has contributed to various innovative projects, including the development of large-scale telescopes, such as a 20-meter wide-field diffraction-limited telescope, and has explored concepts like cryogenic liquid-mirror telescopes on the Moon and the feasibility of cooling the Earth with spacecraft near the Lagrange point. His work encompasses both theoretical and applied aspects of optical sciences and astronomy, with numerous publications advancing the field.

Research topics

• Physics
• Optics
• Astronomy
• Computer Science
• Geology
• Geodesy
• Mechanical engineering
• Structural engineering
• Acoustics
• Ecology
• Materials science
• Environmental science
• Astrobiology
• Electrical engineering
• Engineering

Selected publications

• The large fiber array spectroscopic telescope: updates on the design, fabrication, and testing of the 20X prototype

  2025-09-17

  article
  PublisherDOI

• Print optimization for kilo-fiber experiments using micro-optics and nanostructures

  2025-09-17

  article

  The most pressing problems in modern astrophysics have often required the largest telescopes. With the cost scaling of mirror diameters, the field as a whole is faced with a challenge- how to replicate or improve on the collecting area and sensitivity of the current generation of ELTs, which already boast 30 m class apertures and are multi-billion dollar facilities. One such approach is being pursued by the Large Fiber Array Spectroscopic Telescope (LFAST) - a scalable array telescope. Each element of the array will consist of multiple mirrors each feeding to an individual fiber; with those fiber feeds feeding optical and infrared spectrometers. Coupling fiber bundle to spectrometer slit input must be optimized to take full advantage of the photon collecting ability of the telescope array, requiring precise alignment of microlenses to each fiber. Advances in two photon polymerization processes (2PP) now allow for optical quality microlenses with wavefront aberrations as small as λ/20 to be created, opening up the design parameter of bespoke optical design and custom fabricated lenses. We present our approach to tackling these coupling problems with rapid prototyping and detailed quantification of the tolerances of the lenses. Our approach leverages our access to the Nanoscribe GT2 system at Penn State, enabling tests of new optically transparent resins like IPX-Clear to explore multiple design approaches. Our goal is to share our results and enable wider use of these techniques for astronomical applications.

  PublisherDOI

• The large fiber array spectroscopic telescope: active primary mirror shape control using phase diversity

  2025-09-17

  article

  The Large Fiber Array Spectroscopic Telescope (LFAST) is a concept for a telescope with a divided, incoherent aperture to reduce the cost of fabrication and maintenance when compared with more traditional telescopes. LFAST primary mirrors are thin, with an aspect ratio of 32:1, which means it is necessary to adopt active mirror control to maintain the expected mirror shapes through changes in ambient temperature and telescope elevation angle. To realize the active mirror control, we are developing a system based on phase diversity to calculate the wavefront error using the images provided by the telescope guide camera. This will dramatically reduce hardware costs over the option of having dedicated wavefront sensors in each telescope. We have compared the result from the phase diversity system to that obtained with a Shack-Hartmann wavefront sensor. Here, we describe the implementation of our phase diversity wavefront sensing algorithm and compare its performance with that from the Shack-Hartmann ground-truth.

  PublisherDOI

• POKEMON: print optimization for kilo-fiber experiments using micro-optics and nanostructures

  ArXiv.org · 2025-08-29

  preprintOpen access

  The most pressing problems in modern astrophysics have often required the largest telescopes. With the cost scaling of mirror diameters, the field as a whole is faced with a challenge -- how to replicate or improve on the collecting area and sensitivity of the current generation of ELTs, which already boast 30 m class apertures and are multi-billion dollar facilities. One such approach is being pursued by the Large Fiber Array Spectroscopic Telescope (LFAST) -- a scalable array telescope. Each element of the array will consist of multiple mirrors each feeding to an individual fiber; with those fiber feeds feeding optical and infrared spectrometers. Coupling fiber bundle to spectrometer slit input must be optimized to take full advantage of the photon collecting ability of the telescope array, requiring precise alignment of microlenses to each fiber. Advances in two photon polymerization processes (2PP) now allow for optical quality microlenses with wavefront aberrations as small as $λ/20 to be created, opening up the design parameter of bespoke optical design and custom fabricated lenses. We present our approach to tackling these coupling problems with rapid prototyping and detailed quantification of the tolerances of the lenses. Our approach leverages our access to the Nanoscribe GT2 system at Penn State, enabling tests of new optically transparent resins like IPX-Clear to explore multiple design approaches. Our goal is to share our results and enable wider use of these techniques for astronomical applications.

  PublisherOA PDFDOI

• Technology development for a low-mass solar system and interstellar communications system

  2024-01-26 · 1 citations

  articleOpen access

  We describe the requirements and associated technology development plan for the communications data link from low mass interstellar probes. This work is motivated by several proposed deep space and interstellar missions with an emphasis on the Breakthrough Starshot project. The Starshot project is an effort to send the first low mass interstellar probes to nearby star systems and transmit back scientific data acquired during system transit within the time scale of a human lifetime. The about 104-fold increase in distance to nearby stars compared to the outer planets of our solar system requires a new form of propulsion to reach speeds of approximately 20% of the speed of light. The proposed use of a low mass sailcraft places strong constraints on the mass and power for the Starshot communications system. We compare the communications systems in current and upcoming solar system probes, New Horizons and Psyche, against the requirements for Starshot and define Figures of Merit for the communications capability in terms of data downlink rate multiplied by distance squared per unit mass. We describe current and future technology developments required for the on-board transmitter (signal generation, signal distribution, and beamforming) and for the near-Earth communications receiver (low-cost large aperture telescopes, high resolution spectrometers, and single photon counting detectors). We also describe a roadmap for technology development to meet the goals for future interstellar communications.

  PublisherOA PDFDOI

• The Large Fiber Array Spectroscopic Telescope: fiber-feed fabrication and characterization

  2024-06-14

  article

  The Large Fiber Array Spectroscopic Telescope (LFAST) project seeks to construct large arrays of small, individual fiber-fed telescopes for very high resolution spectroscopy. We are currently developing a prototype of a 20× telescope to investigate the technical requirements for LFAST. For each unit telescope, the 0.76 m primary mirror operates at f/3.5, focusing light onto our fused silica fiber with an 18 μm core, which subtends 1.4” on the sky. This receiving fiber collects and transmits light to the entrance slit of the spectrograph. We are developing a reliable fiber fabrication recipe, including fiber-end termination and polishing, to ensure consistency, efficiency, and affordability in mass manufacturing of the thousands of fibers that the future LFAST arrays require. The 18 μm core size places our optical fiber in the “few-mode” regime, which is not widely used in astronomy. Since the properties of “few-mode” fibers are not yet well characterized, extensive testing is required to gain a comprehensive understanding of their behaviors, such as focal ratio degradation, throughput and modal scrambling. We are designing optical tests to study the optical properties of the LFAST custom fibers. In this paper, we present the fiber feed design and fabrication recipe of our prototype. We also outline our optical test procedures and report results on surface flatness of our fibers.

  PublisherDOI

• Heliostats with Adjustable Shape for High Concentration throughout the Day

  2024-11-26

  reportOpen access

  Our motivation is to develop more efficient heliostats that can provide commercially viable solar thermal power at temperatures > 800°C. Such high temperatures will enable high-temperature industrial processes, as well as electrical generation after sunset with high efficiency. The importance of this research is that such heliostats have the potential to substantially expand the global use of solar energy, by adding solar thermal power as a major component. Thermal solar currently accounts for only 1% of all solar power (with PV being the rest), with heliostat fields providing just 0.25%. Our goals have been 1) to demonstrate a technical improvement for heliostats that can enable fields of them to more efficiently power receivers and reactors, and 2) to show a path to low-cost mass production. Our solution uses new opto-mechanical technology to correct a fundamental deficiency of present heliostats that limits their concentration, namely that they have fixed shape. Most of today’s heliostat research does not address this, but is directed simply toward cost reduction in an effort to make heliostats commercially viable. We are motivated to explore also improving heliostat efficiency, which can be done by continually changing their shape to maximize the concentration of sunlight throughout the day. This is not a new concept, but it has never been implemented in a practical, cost-effective way that approaches the theoretical limit to concentration while also improving mechanical performance; this is our goal. Our major accomplishments have been: 1) We have realized the planned design, construction, and test of a prototype heliostat that achieves the required shape changes in an 8 m2 single-piece glass mirror. The mirror is attached to a steel support frame that is automatically mechanically twisted by the heliostat drives that orient the mirror to direct sunlight to the tower-mounted receiver. Closed-loop tracking is done using a new beamsplitter camera that exploits the target-oriented mount configuration. Field tests of the heliostat show that the light is reflected through the day to always form a disc image of the sun, as needed to obtain the highest concentration. 2) We have developed the design for a field of 431 heliostats to deliver annual average of 1 MW of thermal power at 3,000 sun concentration, matched to a high-temperature ≥ 1000°C chemical reactor. 3) We have also developed, beyond the original stated goals of the project, a new concept for closed-loop tracking and shape-sensing for all the heliostats in the above field, using just 6 cameras around the concentrated reactor focus. Our research adds to the understanding of solar thermal energy by its demonstration of the technical effectiveness of a higher performing heliostat, and by its concept for a new powerful method for real-time tracking and shape sensing in the field, as described above. We have studied the economic feasibility of fields of our twisting heliostats to provide high- temperature heat at a price competitive with that of burning gas, to satisfy the DOE’s studied zero-emissions scenario, where the gas price has to include the cost of carbon capture. The project has the potential to greatly benefit the public if it helps limit global warming by 1) reducing carbon emission from industrial heating, which is currently a major contributor to the 40-billion-ton annual increase in atmospheric CO2. 2) Ultimately, the technology could prove to be the least expensive method to power direct air capture of CO2 on the very large scale needed to remove the 1 trillion-ton excess of CO2 already in the atmosphere.

  PublisherOA PDFDOI

• Performance of a Prototype Heliostat Having a Twisting Mechanism to Maintain Focus Throughout the Day

  SolarPACES Conference Proceedings · 2024-07-24

  articleOpen access1st authorCorresponding

  A prototype heliostat has been designed and built with a rectangular reflector whose shape is altered automatically through the day, to maximize concentration at the receiver. The shape changes needed to form solar disc images, which give the highest possible concentration, can be realized by twisting the reflector from its corners, provided that a target-oriented, dual-axis mount is used. Then a cam mechanism connected to the second (cross) axis drive, turning with the angle of incident sunlight, may be used to twist the reflector as needed. Our prototype reflector comprises a single glass mirror, 2.4 m x 3.3 m, attached to a steel frame. Four diagonal back struts extend from the central mechanism out to the rectangular frame corners. The glass mirror of the prototype is attached to the steel frame by 58 screw actuators. Before twisting the frame, the glass shape is adjusted to the biconic shape needed to form a 1 m diameter disc image on a 113 m distant target when sunlight is incident at 60°. To form disc images over the full range of angles of incidence from 0° (normal incidence) to 70°, the struts push the corners up and down by up to 17 mm. A reflectometry metrology system has been used to set the 58 adjustment screws for the initial shape to an accuracy of ≤ 0.6 mrad, and to measure the accuracy of the different twisted shapes. The prototype will be tested at NSTTF early next year.

  PublisherOA PDFDOI

• Design, performance, and field operation of twisting heliostats for 3,000-sun concentration and high temperature

  2024-10-01

  article1st authorCorresponding

  The idea is to combine the solar energy reflected from a field of many heliostats to obtain a single focus of high concentration and high power. We exploit a new type of “twisting” heliostat” in which as the mount is moved to track the sun through the day, the reflector shape is twisted to maintain a focused image of the sun’s disc on the target, through the day over a wide range of angles of incidence. By combining the light reflected by many twisting heliostats into a single focus, we are not only able to accomplish but also maintain very high concentration and temperature through the day, with higher efficiency than has previously been possible with conventional heliostats having a fixed shape. A circular field of twisting heliostats is used to power a single intense focus atop a central tower. The light from all the heliostats is relayed to an upward facing receiver at the focus via a central Cassegrain secondary reflector located above the receiver. In a specific design targeting 1 MW of power, a 100 m diameter field arrays 431 twisting heliostats, each with a 7 m² reflector. The secondary reflector ,7.2 m in diameter, is located 24 m above the heliostat field, bringing sunlight with annual average power of 1 MW to a circular focus 0.8 m in diameter, at a concentration averaging 3,000 suns.

  PublisherDOI

• A 600 m ² array of 6.5 m telescopes at the lunar pole

  Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences · 2024-03-24 · 2 citations

  articleOpen access1st authorCorresponding

  The proposed lunar telescope for optical and infrared astronomy aims at very large aperture, 600 m 2 , at a fundable cost. It comprises an array of 18 separate telescopes, each of 6.5 m aperture. The 200 m diameter array will be located within 1/2° (15 km) of a lunar pole on approximately level ground, with a perimeter screen deployed to provide shade and cooling to cryogenic temperature. The 500 m diameter screen will allow unobscured access down to 8° elevation. All 18 telescopes will reflect light into a central beam combiner to form a single image covering wavelengths from 0.4 µm to 10 µm. The initial instrument complement will include high-resolution and multi-object spectrographs to exploit the single combined field of view of two arcminute diameter, with the diffraction limited resolution of 6.5 m aperture. Scientific applications include the search for molecular biosignatures in transiting exoplanets, and the study of galaxy evolution using red-shifted spectra to beyond z = 10. The array cost, including delivery to the Moon by SpaceX Starship for installation using lunar base infrastructure, is around $10 billion, similar to that of the 25 m 2 JWST. To test the concept, first a single prototype 6.5 m unit would be operated at the lunar south pole. This article is part of a discussion meeting issue ‘Astronomy from the Moon: the next decades (part 2)’.

  PublisherOA PDFDOI

Recent grants

• The 20/20 Telescope - a new concept for the GSMT

  NSF · $1.9M · 2002–2007

Frequent coauthors

• Michael Lloyd‐Hart

  Optical Sciences (United States)

  28 shared

• Thomas Stalcup

  Process Instruments (United States)

  16 shared

• Philip M. Hinz

  University of California, Santa Cruz

  14 shared

• Matt Rademacher

  University of Arizona

  13 shared

• Brian Wheelwright

  META Health

  13 shared

• Olivier Guyon

  National Astronomical Observatory of Japan

  13 shared

• Nick Didato

  12 shared

• Blake Coughenour

  11 shared