Objective Spectral characterization testing is a key step in the thin film preparation process. Through this testing, the optical properties of the thin film can be determined, providing important foundations for optimizing and evaluating the performance of the thin film in applications. In narrowband filter testing, common spectroradiometers have a certain divergence angle. This divergence angle causes the incident light not to be perpendicular, resulting in wavelength-angle shift errors. These errors manifest as a shift towards the shortwave direction of the center wavelength, a decrease in peak transmittance within the passband, an increase in bandwidth, and a decrease in the steepness of the transition zone. These factors can lead to measurement errors during narrowband filter testing. To address this issue, a high-precision spectral characterization and metrology system has been developed in this study.
Methods By establishing a physical model of beam incidence, the divergence angle effect of beam incidence was analyzed, and the impact of angles on the center wavelength, peak transmittance, and full width at half maximum of narrowband filters was examined. A high-precision spectral characterization and metrology system (Fig.2) was set up using a laser beam with a small divergence angle as the light source. Furthermore, a comparison was conducted between the commonly used spectroradiometer test and the high-precision spectral characterization test system.
Results and Discussions Through the preparation and testing of a 532 nm narrowband filter, the spectral performance of the commonly used spectroradiometer test shows a shift of the center wavelength towards the shortwave direction, a decrease in peak transmittance within the passband, and a widening of the bandwidth, with a decreasing trend in the steepness of the transition region (Fig.7). The high-precision spectral characterization test results in a center wavelength of 532 nm, a peak transmittance of 87.2%, and a full width at half maximum of 0.79 nm (Tab.2), which are closer to the theoretical design curve. By comparing the spectral transmittance curves at different angles of 5° and 10°, the impact of the angle on the narrowband filter is validated (Fig.8).
Conclusions A high-precision spectral characterization and metrology system has been developed. Compared to traditional spectroradiometer testing, the high-precision spectral characterization test system can provide more precise test results. Spectral testing was conducted on a 532 nm narrowband filter to validate the practicality of the system. The high-precision spectral characterization and metrology system play a critical role in guiding the design and preparation of narrowband filters and are crucial in evaluating filter performance.
DownLoad: