Infrared nearly complete absorption in hexagonal boron nitride crystals based on guided mode resonance

The near-complete absorption effect in hexagonal boron nitride (hBN) crystals for mid-infrared spectra with guided mode resonance (GMR) is studied. It is achieved by placing an hBN film on a substrate, which is separated from a subwavelength grating by a dielectric film. Under normal incidence, the absorber demonstrates approximately 100% absorption in the reststrahlen upper-frequency band of light. The underlying physical mechanism responsible for this near-complete absorption effect is examined through visualization of electric field distributions at the resonant frequency. Additionally, to provide practical guidance for fabrication, the influence of structural dimensions on the absorption spectra is also explored. These findings reveal that guided mode resonance can be utilized to achieve perfect absorption in hBN films, thereby enhancing their potential applications in the mid-infrared range.