Transmission of IR Wavelengths through Sapphire

Sapphire Al2O3 is a premium optical material valued for its exceptional hardness, thermal stability, and broad transmission spectrum. When designing optical systems, understanding how sapphire transmits infrared (IR) wavelengths across varying thicknesses is critical for optimizing performance. Generally, sapphire exhibits excellent, high-percentage transmission from the ultraviolet wavelengths well into the mid-infrared range, peaking up to approximately 5µm However, as the thickness of a sapphire window increases, its transmission profile shifts. Thicker windows introduce greater internal absorption, which noticeably accelerates the transmission drop-off (the “IR cutoff”) in the 4.5µm to 5.5µm band. This graphic illustrates the precise transmission percentages as a function of wavelength for several standard window thicknesses. By analyzing these curves, scientists and engineers can balance the mechanical strength required for high-pressure or harsh environments against the specific optical throughput needs of their IR sensors, thermal imaging systems, or spectroscopy applications.