A new way to explore the universe has potential to transform our understanding of astrophysical objects like black holes, and the College of Natural Sciences & Mathematics (NSM) has an important part to play in that research.

Imminent completion of lab renovations in the Nicholas and Lee Begovich Center for Gravitational-Wave Physics and Astronomy (GWPAC) will allow Cal State Fullerton faculty, staff, and students to play an early and critical role in research and development for the Cosmic Explorer. That project is the United States’ planned next-generation gravitational-wave observatory.

The vision for Cosmic Explorer was recently described in a Horizon Study co-authored by Josh Smith, Dan Black Director of Gravitational Wave Physics and Astronomy; Associate Professor of Physics Jocelyn Read; Associate Professor of Physics Geoffrey Lovelace; and Graduate Researcher Alexandra Gruson. The project is now moving toward its conceptual design phase, which will rely on research from research labs like the one at GWPAC.

The 1,280-square-foot lab will primarily be used for optics research for gravitational-wave interferometers, specifically looking at the optical coatings that transform the glass or silicon substrates into mirrors.

The lab now has new floors, ceilings, walls, paint, wall decals, and electrical elements in place.

“Three-phase power and recirculating water from the tri-gen plant were added to power and cool our cryogenic experiment and for our annealing oven, which will [be used to] help us understand how optics and their substrate and coating materials behave when they are very cold and very hot,” Smith says. “All of the lab’s instruments will allow us to test the optical properties of materials and coatings in consideration for future detectors including Cosmic Explorer.”

Smith’s team has already achieved excellent results using the annealing oven. He explains that glass substrates (pieces of glass) are turned into mirrors by applying thin-film coatings to their surfaces. These coatings are designed to use either constructive or destructive interference to either nearly perfectly reflect or nearly perfectly transmit the light. The coatings have optical properties, such as light absorption or scattering, and mechanical properties, such as mechanical loss, which can be improved by annealing them (baking them in an oven).

“However, if the coatings are baked to too high a temperature, they can form crystals, bubbles, cracks, or other defects,” Smith says. “We have worked with industry, specifically Sentro Tech, to develop an annealing oven with viewports machined into its exterior so that we can watch coated optics as they are heated. Using this, we have observed the formation and evolution of crystals and bubbles and are working with colleagues on ways to reduce these defects to improve the optics.”

One of Few Laboratories Equipped to Support Gravitational-Wave Science

The lab’s cryogenic vacuum chamber, funded by a National Science Foundation (NSF) grant, will allow researchers to measure the optical properties of silicon and its coatings at very low temperature. An ultra-low vibration, ultra-high vacuum ColdEdge Stinger will be used to investigate the cryogenic optical properties of crystalline silicon, a material likely to be used for future gravitational-wave detectors. Other lab equipment will help researchers to:

• Access optical properties at longer near-infrared wavelengths at which silicon is transparent
• Image scatter versus annealing to temperatures of 800°C
• Measure the total scatter from any optical sample to compare with the angle-resolved scatter measured by other instruments
• Image and quantify low levels of light scatter from high-quality optics
• Work in a stable and dust-free environment

The study of gravitational waves is still a relatively new field, with its first astrophysical discoveries having been made in only 2015. Relatively few experimental research laboratories support gravitational-wave science in the United States, and the GWPAC lab will be one of the few labs with cryogenic technologies and a broad array of optical measurement technologies.

“This lab was made possible by generous donations from Nick and Lee Begovich, and my students and I are incredibly grateful to the Begoviches for their support of gravitational-wave science in general and this laboratory in particular,” Smith says. “We are also grateful to Dan Black and family, who support many of our students and postdocs and have allowed us to increase our computing and laboratory technology. Further, Nancy Goodhue-McWilliams is supporting our master’s students through a graduate student fellowship. These incredible donations are allowing us, at Cal State Fullerton, to play an outsized role in gravitational-wave science.”

An Out-of-This-World Opportunity for Student Researchers

The Cosmic Explorer Horizon Study was supported by a collaborative NSF grant to Cal State Fullerton, MIT, Caltech, Penn State, and Syracuse, which has allowed Cal State Fullerton to play a foundational role in the development of Cosmic Explorer. This includes co-writing the Horizon Study, contributing white papers to the Astro2020 Decadal Survey, and co-authoring five Cosmic Explorer publications.

The GWPAC lab’s projects are already attracting top students.

“We currently have five physics master’s students carrying out their projects here, and we have two undergraduates working on the projects and plan to add more,” Smith says. “The students are working with optical, vacuum, and cryogenic technologies that are uncommon for research at the undergraduate and even master’s level. This lab will also help us attract excellent postdoctoral fellows.”

Smith recently submitted a proposal titled “RUI: Advancing gravitational-wave optics to further explore the cosmos” to the NSF, heavily aimed at supporting student-faculty research in the new lab. His team has requested $355,684 in funding for three years, starting in July 2022.

“Working on this program offers students the opportunity to play a foundational role in the worldwide effort to develop a future gravitational-wave observatory,” Smith says. “This observatory will detect gravitational waves from the remnants of the first stars and answer questions such as how black holes have formed and evolved and their roles in galaxy formation.”