China unveils world's first mid-infrared solar magnetic-field telescope

Photo shows the AIMS telescope.

China has launched the world's first mid-infrared solar magnetic-field telescope, the Accurate Infrared Magnetic Field Measurements of the Sun (AIMS), marking a major breakthrough in solar observation and sharpening humanity's ability to study the Sun.

Located atop Mount Saishiteng in Lenghu township, northwest China's Qinghai province at an elevation of over 4,000 meters, the AIMS telescope fills a global gap in mid-infrared magnetic-field observations. Its deployment also establishes a benchmark for building advanced astronomical facilities in high-altitude regions.

Advancing solar science

Magnetic fields are fundamental to solar atmospheric activity, which occurs within a vast plasma environment. Improving the precision of magnetic-field measurements is crucial both for advancing solar physics and for enhancing space weather forecasting, said Deng Yuanyong, researcher at the National Astronomical Observatories of China (NAOC) and principal investigator of the AIMS project.

For a long time, solar magnetic-field observations have focused primarily on spatial resolution, often at the expense of measurement precision. Most large-aperture solar telescopes worldwide achieve accuracy only at the 100-gauss level. However, as scientific understanding has progressed, there is a growing consensus that investigating weak magnetic fields is equally critical and that high resolution alone is insufficient for advancing solar physics.

"Just as a standard photograph and an X-ray expose different aspects of the human body, observations at different wavelengths uncover distinct physical processes on the Sun," explained Wang Dongguang, a researcher at NAOC and technical director of the AIMS project. "AIMS is specifically designed to address the long-standing gap in mid-infrared solar magnetic-field observations."

Breakthrough technologies

Since its launch in 2015, the AIMS project has achieved a series of landmark breakthroughs. Most notably, it has enhanced magnetic-field measurement precision to below the 10-gauss level and developed the world's first mid-infrared Fourier spectrometer with both ultra-high spectral resolution and imaging capability, improving spectral-resolution performance to 156 times the previous domestic benchmark.

These achievements were the result of overcoming significant technical challenges. A prime example is polarization measurement. Although the NAOC team had more than four decades of experience in polarization detection within the visible spectrum, transitioning to mid-infrared polarization required building entirely new capabilities from the ground up.

"At the time, there were no instruments for mid-infrared polarization measurement anywhere in the world -- no detectors, no established techniques," Wang recalled. "We had to independently select materials, experiment with processing methods, and design testing equipment. Through extensive research, we ultimately succeeded in producing the world's largest cadmium selenide mid-infrared wave plate."

National collaboration and local support

The development of AIMS was a nationally coordinated, multidisciplinary effort led by NAOC, with collaboration from the Shanghai Institute of Technical Physics, the Xi'an Institute of Optics and Precision Mechanics, the Yunnan Observatories, the Kunming Institute of Physics, Nanjing Astronomical Instruments Co., Ltd., and other institutions.

"From the outset, we emphasized top-level design, breaking down technical specifications and functions with clearly defined technical interfaces. This approach ensured smooth progress and minimized rework during development," Wang noted.

Thanks to this collaboration, all core components of the AIMS telescope were developed and manufactured domestically, achieving full independent control over critical technologies and demonstrating China's growing strength in astronomical instrumentation.

Site selection for solar observatories is highly demanding, requiring long hours of sunlight, dry atmospheric conditions to minimize water-vapor interference in infrared observations, and high altitudes to improve detection sensitivity. After evaluating five potential sites, the team selected Mount Saishiteng in Lenghu, Qinghai province.

Deng expressed strong appreciation for local government support: "Because the telescope equipment was too large to transport by road, the local authorities provided helicopter assistance. Within two years of confirming the site, all necessary infrastructure was completed."

During testing and initial scientific observations, AIMS successfully captured multiple mid-infrared datasets of solar flares, providing valuable insights into the transfer of mass and energy during eruptions, as well as the accumulation and release of magnetic energy. "Our next priority is to ensure stable operation of the telescope and advance frontier research using the new data it provides," Deng added.

A technician debugs the AIMS telescope.

(Photos provided by the National Astronomical Observatories of China)