Infrared stray radiation analysis for antireflective film coated on an optical window

Antireflective films are extensively employed in optical detection systems to provide protection, increase signal transmittance, and suppress infrared (IR) stray radiation on optical windows. Drawing on thin film optical theory, several types of antireflective films are presented, and their optical properties are modeled. Additionally, directional spectral reflectivity at the interface between the film and the optical window is determined. Subsequently, an analysis of IR stray radiation in an optical system utilizes an equivalent model of optical windows coated with antireflective films, thoroughly investigating their corresponding effects. Results demonstrate that applying high-quality antireflective films can achieve a normal reflectance at the interface of less than 1.0%, effectively suppressing stray radiation originating from thermal emissions of the optical window itself. A contrast coefficient for each point on the entrance pupil surface is introduced to quantify the contribution of the target signal. The analysis reveals a significant increase in the contrast coefficient with the application of antireflective films, thereby substantially improving detection precision.