Investigation into wide-angle bandpass filter for UV fluorescence imaging system

Filters are a critical component of ultraviolet fluorescence imaging systems, playing a significant role in the precise collection of signals. Designing a wide-angle bandpass filter that achieves ultraviolet transmission and cutoff within a specific angular range, while completely blocking the visible light spectrum, is a challenging work. Here, we systematically investigate the fabrication process, thin-film design, and film thickness monitoring methods based on the system's usage requirements, and develops a wide-angle bandpass filter for use in ultraviolet fluorescence imaging systems. Initially, the optimal ion source bias voltage for depositing HfO₂ films is determined to be 110 V, based on the analysis of its effects on the refractive index and surface shape of the films. Subsequently, a multilayer film design is developed using the splitting method to meet the spectral requirements of the ultraviolet fluorescence imaging system. Furthermore, a dual-wavelength film thickness monitoring method is proposed, which simulates and assesses the expected deviation of the film deposition process, matching more suitable monitoring wavelengths to monitor the film layers, thus reducing the impact of error accumulation on the film. Finally, the fabricated wide-angle bandpass filter meets the high transmission requirements within the 350–380 nm band at angles ranging from 0 to 18° and achieves cutoff in the 220–330 and 400–800 nm bands, satisfying the system requirements.