In a laser guidance system, filter devices extract specific laser signals from targets or lasers, suppress interference from background light, control the energy transmitted by the laser signals, and protect the detectors from contamination or damage. Therefore, the performance of light-filter devices has an important impact on the hit rate and anti-interference ability of laser-guided missiles. In recent years, in-depth research has been conducted on the central wavelength, transmittance, and bandwidth of filter devices at home and abroad, significantly improving their spectral performance. However, there have been few reports on the precise control of the energy of transmitted filter devices with thin films deposition. Consequently, a 1064 nm energy attenuation narrow band filter device was developed according to the filter requirements of the laser guidance system.

Based on the design theory of Fabry-Perot (F-P) filter films, Ta₂O₅ was selected as the high-refractive-index material, and SiO₂ was selected as the low-refractive-index material. A narrowband filter film and broadband interference cut-off film were designed and prepared on both sides of the quartz substrate using electron beams and ion-assisted deposition techniques. Cr was selected as the material for energy attenuation. Subsequently, the refractive index and extinction coefficient values corresponding to Cr with different thicknesses were determined through numerous experiments. Cr films of different thicknesses were deposited on samples with similar initial transmittances, and the relationship between the Cr film thickness and transmittance of the narrow-band light filter device was obtained, thus realizing precise attenuation of the transmission energy of the narrow-band light filter device.

During the preparation of the narrowband filter films, because of the large error in controlling the thickness of the film layers using the quartz crystal method, the transmittance of the prepared narrowband filter films decreased [Fig. 8(a)]. Through inversion analysis, the error compensation coefficients of quartz crystal method for Ta₂O₅ and SiO₂ were calculated as 1.15 and 1.21, respectively. After adjusting the error compensation coefficients, a narrowband filter film was prepared, and the final sample satisfied the design requirements (Fig. 9). When the transmission energy was the same, software analysis was used to deposit different metal films, among which Cr had the lowest reflectivity and the least impact on the receiving optical system (Fig. 7). Using an elliptical polarization instrument, the refractive index and extinction coefficient values corresponding to different thicknesses of Cr metal films were obtained (Fig. 10). The theoretical and actual transmittance values of Cr films with different thicknesses were deposited on narrowband filter devices with similar transmittance (Table 3), and the relationship between the actual transmittance and Cr film thickness was fitted (Fig. 12).

An energy attenuation narrowband filter device was developed for a laser guidance system. By adjusting the crystal control error coefficients, a high-transmittance narrowband filter with a transmittance of 99.034% at 1064 nm, an average cutoff depth of OD4, and a half-bandwidth of 8 nm was prepared. By depositing metal Cr films with different thicknesses on broadband cut-off films for energy attenuation, accurate control of the transmission energy of 1064 nm narrowband filter devices was achieved, reducing the decay from 99% to 10%?30%, with a control error of ±1%.