One transparent material that allows almost 100% transmission of infrared, visible, and ultraviolet light is fused silica (also known as fused quartz). Fused silica is a high-purity form of glass that has excellent transparency across a broad range of wavelengths, including infrared (IR), visible, and ultraviolet (UV) regions.
Fused silica has low absorption and high transmission properties, making it suitable for applications where high optical clarity and minimal light loss are desired. It is commonly used in optical components, lenses, windows, and other optical systems that require transparency across a wide spectrum of light.
When placed above a black (light absorber) box, a fused silica window or cover would allow almost all the infrared, visible, and ultraviolet light to pass through to the box while minimizing any significant loss or absorption. This enables effective illumination and observation of the contents within the box.