Asgard/NOTT: Status of laboratory nulling performance
This paper presents the first ambient performance assessment of the Asgard/NOTT nulling instrument's test bench with spectrally dispersed light, revealing a contrast degradation to ~10⁻¹ compared to previous results and outlining necessary pipeline revisions and future experimental adjustments to achieve the target 10⁻⁵ contrast.
Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Deep in the heart of astronomy lies a persistent challenge: seeing the faint, dim companions of stars. Young giant planets and swirling clouds of dust often hide in the glare of their parent stars, much like trying to spot a firefly next to a spotlight. To solve this, astronomers use a technique called nulling interferometry. Instead of trying to block the star's light with a physical shield, they combine light from multiple telescopes in a way that causes the starlight waves to cancel each other out. Imagine two waves of water meeting; if one is pushed up while the other is pushed down at the exact same moment, they flatten into a calm surface. By creating this "dark" zone for the star, the instrument can reveal the much fainter light coming from nearby planets or dust rings that would otherwise be lost in the glare. This method is crucial for finding worlds near the "snowline"—a region around a star where it is cold enough for ice to form, a key location for understanding how planets are born.
A team of researchers has been working on a new instrument called Asgard/NOTT, designed to perform this delicate cancellation in a specific range of infrared light known as the L' band. This band is particularly useful because the contrast between a star and a young planet is more favorable here, and the background heat from the atmosphere is lower than at longer wavelengths. The instrument relies on a tiny, specialized chip made of a glass-like material called Gallium Lanthanum Sulfide. Inside this chip, light travels through microscopic channels that act like roads for photons. When light from different telescopes enters these channels, they merge and interfere with one another. The chip is engineered to ensure that the light from the star cancels out perfectly while the light from a companion planet passes through to the detector. Before this instrument can be installed on the Very Large Telescope Interferometer in Chile, it must be tested thoroughly on a laboratory bench to ensure it works as intended.
In this recent work, the researchers took a significant step by testing the instrument's performance in normal room-temperature conditions, but with a new twist: they used light that was spread out into its component colors, or dispersed. Previous tests had either used a broad mix of colors or were done in freezing cold conditions, but this new test aimed to see how the chip performed when looking at specific colors of light while still in the lab. The team built a sophisticated test setup that mimics the light coming from the telescopes, using mirrors and lenses to guide four beams of light into the photonic chip. They carefully adjusted the position of these beams and scanned them back and forth to find the exact point where the starlight cancels out. To make sense of the data, they developed a new computer pipeline to clean up the images, removing background noise and correcting for uneven lighting on the camera sensor.
The results of this test revealed a mix of success and unexpected hurdles. The researchers confirmed that the tiny channels inside the chip split the light in the way they had hoped, with the different colors of light behaving consistently across the target wavelength range. This was an important verification that the chip itself was functioning correctly. However, when they tried to measure how well the instrument could cancel out the starlight, the performance was not as good as they had seen in earlier, simpler tests. Instead of achieving the extremely high level of darkness they were aiming for, the "null" was about ten times brighter than expected. The team discovered that this was not because the chip was broken, but because the light entering the chip was not perfectly balanced. The internal channels split the light unevenly, and because the researchers had previously tried to feed equal amounts of light into the system, the cancellation was less effective.
To fix this, the researchers realized they need to change their approach. In future tests, they plan to deliberately feed slightly different amounts of light into the different channels to compensate for the uneven splitting inside the chip. They also identified that their current method of removing background noise from the camera was not perfect, as the background light drifts over time. They intend to install a mechanical chopper wheel that can rapidly switch the light on and off, allowing them to subtract the background noise in real-time. With these adjustments, along with the installation of a final, more sensitive camera and a cryostat to cool the system, the team expects to re-test the instrument and achieve the high-performance cancellation needed for real astronomical observations. This work serves as a vital checkpoint, proving that while the core technology is sound, the path to perfecting the instrument requires careful tuning of the light entering the system and better management of the background noise.
Drowning in papers in your field?
Get daily digests of the most novel papers matching your research keywords — with technical summaries, in your language.