Large telescope receiver optics confirmed in lab ahead of installation at Simons Observatory – ScienceDaily

Some of the largest and most advanced telescopes ever built are being built at the Simons Observatory in northern Chile. They were designed to measure the cosmic microwave background – electromagnetic radiation left over from the formation of the universe – with unprecedented sensitivity. In a new study, researchers describe an analysis method that could improve these telescopes by evaluating their performance before installation.

“We have developed a way to use radio holography to characterize a fully integrated cryogenic telescope instrument prior to deployment,” said Grace Chesmore, a research team member from the University of Chicago. “In the lab, it’s much easier to spot problems before they become problematic and manipulate the components inside the telescope to optimize performance.”

Although it is common to wait until after installation to characterize a telescope’s optical performance, it is difficult to make adjustments once everything is in place. However, a full analysis cannot usually be performed prior to installation, as laboratory-based techniques are designed for analysis at room temperature while the telescope components are kept at cryogenic temperatures to improve sensitivity.

In the magazine of the Optica Publishing Group Applied opticsresearchers led by University of Chicago’s Jeff McMahon describe how they applied their new measurement approach to the Simons Observatory Large Aperture Telescope’s receiver optics, which includes lenses, filters, baffles and other components. This is the first time such parameters have been confirmed in the laboratory prior to deployment of a new receiver.

“The Simons Observatory will produce unprecedented maps of the Big Bang afterglow that will provide an understanding of the first moments and the inner workings of our Universe,” said Chesmore, first author of the publication. “The observatory will help enable these highly sensitive cosmic microwave background maps.”

Look back in time

The cosmic microwave background maps being produced by the Simons Observatory will provide a window into our Universe at such an early point in its history that tiny signals from quantum gravity could be detectable, says Chesmore. However, to study space with such sensitivity requires a better understanding of how electromagnetic radiation propagates through the telescope’s optical system and eliminating as much scattering as possible.

In the new work, the researchers used a technique known as near-field radioholography, which can be used to reconstruct how electromagnetic radiation travels through a system such as a telescope. To do this at cryogenic temperatures, they installed a detector that can image a very bright coherent source while operating at the extremely cold temperature of 4 Kelvin. This allowed them to create maps with a very high signal-to-noise ratio, which they used to ensure that the Large Aperture Telescope’s receiver optics worked as expected.

“All objects, including lenses, shrink and exhibit changes in optical properties as they cool,” Chesmore explained. “By operating the holographic detector at 4 Kelvin, we were able to measure the optics in the shapes they will have when observed in Chile.”

From laboratory to space observations

After those measurements were complete, the researchers developed software to predict how the telescope would perform using photons from space rather than the near-field source used in the lab.

“The software uses the near-field maps we measured to determine the behavior of a far-field microwave source,” Chesmore said. “This is only possible with radio holography because it measures both the amplitude and the phase of the microwaves and there is a well-known relationship between the properties in the near and far field.”

Using their new approach, the researchers found that the telescope’s optics matched predictions. They were also able to identify and mitigate a source of scatter before deploying the telescope.

The optical system of the Large Aperture Telescope they characterized is now on its way to Chile for installation. The Simons Observatory will include the Large Aperture Telescope and three Small Aperture Telescopes that will be used together for precise and detailed observations of the cosmic microwave background. The University of Chicago researchers will continue to characterize components for the Simons Observatory telescopes and say they look forward to using these telescopes to better understand our universe.

Other members of the University of Chicago team include postdoctoral researchers Katie Harrington and Patricio Gallardo, and graduate students Carlos Sierra, Shreya Sutariya, and Tommy Alford. Also cCooperating institutions around the world are working to make the Simons Observatory a success.

story source:

Materials provided by optics. Note: Content can be edited for style and length.

Leave a Reply

Your email address will not be published. Required fields are marked *