After years of dedicated research, the solar photospheric magnetic and velocity field measurement system developed by the Nanjing Institute of Astronomical Optics and Technology (NIAOT), Chinese Academy of Sciences, successfully completed the acceptance review conducted by the Yunnan Observatories on July 4, 2025.

The system integrates a dual-band (617.334 nm/630.251 nm) liquid-crystal tunable birefringent filter with a liquid-crystal vector magnetograph.

Featuring a 40 mm effective aperture and full width at half maximum (FWHM) below 0.0085 nm, this filter demonstrates the narrowest spectral resolution among domestic equivalent instruments.

Its wavelength-switching and spectral line-shifting durations both under 50 milliseconds represent a 2-3 order of magnitude enhancement compared to conventional systems, establishing global leadership in switching speed.

Its wavelength-switching and spectral line-shifting durations both under 50 milliseconds represent a 2-3 order of magnitude enhancement compared to conventional systems, establishing global leadership in switching speed.

The thermal regulation subsystem achieves temperature control precision surpassing 0.01°C.

Upon operational deployment, the 617.334/630.251 nm dual-band system will be exclusively dedicated to photospheric magnetic field and Doppler velocity measurements for the 2-meter Ring Solar Telescope at Yunnan Observatories.

Fig. 1. External view of the instrument

Fig. 2. Spectral line calibration at 617.334 nm

Fig. 3. Spectral line calibration at 630.251 nm

Note: Dr. Xiqun Wang from Yunnan Observatories of the Chinese Academy of Sciences contributed to the development of this system.