Optical microscopy at cryogenic temperatures and high magnetic fields

Many materials exhibit interesting physical transformations when placed under strong magnetic fields. Investigations in condensed matter physics, quantum materials research, and even biological tissue studies can benefit from observations made in extreme conditions. However, operating optical microscopes in powerful magnetic fields can be challenging.

Han et al. developed an optical microscopy probe capable of operating in magnetic fields as strong as 42 Tesla and at temperatures as low as 1.8 K.

“Water-cooled magnets have a large overall footprint but a very small bore,” said author Zhaosheng Wang. “This means the [imaging sensor] must be placed far away from the sample, which sits at the magnet’s center — in our setup, a distance of 1500 mm. Achieving stable imaging at this separation while maximizing resolution is a major challenge.”

The imaging equipment itself also must be shielded from the magnetic fields, which can disrupt their sensitive electronics. Operating at cryogenic temperatures poses an additional challenge, as the equipment expands and contracts across the temperature range.

To overcome these obstacles, the researchers built their microscope out of stainless steel, with fixed lenses placed at strategic locations to extend the imaging distance. They shielded their sensor using a shell made of permalloy foil, and the entire microscope can be repositioned for focusing.

The result is an instrument that researchers can use to study a wide range of material phenomena.

“The probe can be used to observe mesoscale materials and microorganisms under high magnetic fields at room or cryogenic temperatures, including magnetic transitions, magnetic domain motion, twin formation and annihilation, gas condensation and evaporation, and microbial behavior,” said Wang.

Source: “The world’s highest field optical microscopy probe compatible with 42 T steady magnetic field and down to 1.8 K,” by Yongqi Han, Minjie Zhang, Ke Shi, Yu Zhao, Chuanying Xi, Li Pi, and Zhaosheng Wang, Review of Scientific Instruments (2026). The article can be accessed at https://doi.org/10.1063/5.0354529 .