Active magnetic field diagnosis based on the Faraday rotation effect is widely used in experimental studies on magnetized plasmas. The Faraday rotation angle is correlated with both magnetic field strength and electron density, and magnetic field information can be obtained through simultaneous measurement of interferometric and polarization information. Conventional designs introduce the diagnostic beam into an interferometer and a polarimeter, respectively, which require multiple back-end recording devices. As a result, the complexity of the optical path is increased, and inter-device sensitivity calibration problems are encountered. Therefore, a compact optical path design with multiple probes incident on the same recording device is expected to be able to avoid these problems.

In response to the above needs, this paper proposes a compact polarization interferometer, which is capable of obtaining plasma interference, polarization, and shadowgraph images simultaneously on a single recording device and acquiring magnetic intensity with a single shot measurement. The polarized light enters the target chamber in parallel, and the lens system images the plasma region and relays the images to the target chamber. The prism separates two virtual images, and then the lens images the two virtual images to the CCD. A Nomarski interferometer with Wollaston prisms and polarizers is located before the CCD so that four images are obtained on a CCD, and the images involve the interference pattern containing the plasma electron density information and the polarization pattern containing the Faraday rotation angle information. The Faraday rotation angle obtained from the experimental diagnostics contains the information of the diagnostic light path integral, which cannot directly reflect the three-dimensional magnetic field structure. We calculate the plasma evolution by using magnetohydrodynamic simulation, design a ray-tracing program to simulate the behavior of diagnostic light passing through the plasma and compact polarization interferometer, and finally synthesize the line-integrated image on CCD. The reliability of the diagnostic instrumentation and numerical simulations is cross-validated by comparing the experimental diagnostic images with the numerically synthesized images.

After error calculation and parameter scanning, the compact polarization interferometer reaches the theoretically optimal sensitivity of 0.013°. In the solid target laser-ablation experiment, the instrument successfully diagnoses the signal of the self-generated magnetic field. The measured deflection angle is about 0.7°, and the self-generated magnetic field region is about long and wide. In addition, the electron density is about 1019 cm^-3, and the estimated magnetic field strength is about 0.9×10⁶ Gs. The intensity and spatial structure of the magnetic field are in good agreement with the numerical simulation, and the images synthesized by the simulation results show characteristics similar to the experimental diagnostic images.

The compact polarization interferometer has successfully diagnosed self-generated magnetic fields on the order of ten Tesla at a spatial scale of several hundred microns. Numerical simulations interpret the dynamic evolution and three-dimensional structure of the magnetic field. This compact polarization interferometer is expected to reduce the risks associated with imaging device variations and the complexity of diagnostic systems and improve the efficiency of magnetic field diagnosis.