MgF2 Windows

MgF2 Windows: Uses and Optical Characteristics

An MgF2 window is an optical window crafted from crystalline Magnesium Fluoride. This robust and enduring optical material is well-suited for applications in demanding environments. It boasts exceptional resistance to chemical corrosion, as well as resistance to mechanical and thermal shocks. Additionally, it possesses a high threshold for laser damage.

MgF2 exhibits remarkable broadband transmission spanning from 120 nm to 8 μm, covering the deep ultraviolet to the mid-infrared spectrum. This property makes it an excellent choice for UV radiation sources and detectors, including applications involving the Hydrogen Lyman-alpha line. Frequently, it finds use as a UV viewing window, serving as an ideal candidate for UV polarizers and excimer laser applications. It maintains high transmittance between 120 nm and 8 µm, with a transmission rate exceeding 90% between 0.4-5.0 µm.

MgF2 has a melting point of 1255 degrees Celsius, a density of 3.177 g/cm3, and a tetragonal crystal structure. Typically, our optical windows are oriented with their circular surfaces perpendicular to the c-axis of the MgF2 crystal to minimize birefringence. Upon request, we can manufacture custom MgF2 windows with random cuts.

MgF2 stands alone among optical materials in its ability to combine a broad spectral transmission range with birefringence. Birefringence means that the refractive index depends on the polarization and direction of light propagation. Due to this property, a MgF2 window can exhibit double refraction, causing a beam of light to split into two rays following different paths.

The ray with a higher effective refractive index within the optical window is referred to as the “slow ray,” while the one with the lower effective refractive index is termed the “fast ray.” When a beam enters the MgF2 window from air, the slow ray will be refracted more toward the normal direction.

It’s important to handle MgF2 with care, as it is softer than fused silica, although it ranks as the hardest of the optical fluorides with a hardness rating of HK576.