Driven by recent advancements in technology and a growing use of laser systems in aerospace, defense, and medical industries, the market is witnessing an increased demand for MgF2 crystals. The demand is specifically directed towards high quality MgF2 single crystals with distinct properties and performance characteristics. One of the sought after properties of MgF2 is its superior transmission range from IR to UV wavelengths, even extending to vacuum- UV region. The ability to transmit well in vacuum and in deep UV is of great importance to many emerging space applications and some already established applications, such as, UV detectors, excimer lasers, or projection lenses. Since, the transparency of MgF2’s in UV exceeds that of BaF2 and CaF2 and because MgF2 is hardest of all the fluorides the crystal lends itself to a special place in UV optics. To engineers that work on creating optical systems with the use of MgF2, the choice is often dictated by the fact that the material in addition to all the properties mentioned above is highly resistant to chemical and environmental effects. Our MgF2 optical parts in form of windows, blanks, prisms or any customized shapes are great option for high intensity lasers and spectroscopy systems.
Due to theoretically large long term laser durability and proven very high transmittance in the UV/VUV regions MgF2 bulk crystal is rapidly gaining
its status as a material of choice for optical lithography, taking precedence over traditionally used materials, such as crystalline quartz and fused silica.
Different forms of MgF2 and their unique optical properties
Single Crystal: Single crystal of MgF2 has a tetragonal structure. Mg 2+ is bonded to six equivalent F 1- atoms to form a mixture of corner and edge sharing MgF6 octahedra. The corner- sharing octahedral tilt angles are 500. There are two shorter (1.98A) and four
1.99A) Mg-F bond lengths. F1- is bonded in distorted trigonal planar geometry to three equivalent Mg2+ atoms.
That particular order of atoms gives MgF2 in a single crystal form a number of unique optical properties, such as: Birefringence: single crystal MgF2 exhibits birefringence, meaning it can split single ray of light into two polarized rays, due to different refractive indices along different crystal axes. MgF2 birefringence can be minimized or maximized by cutting the crystal in different orientations; C-axis cut for minimum and a-cut for maximum birefringence.
Refraction: (the bending of light as it enters a crystal, which is a measure of how much light slows down when entering the crystal). Single crystal of MgF2 has one of the lowest refractive indices among all common optical materials. That low refractive index is specially beneficial for minimizing reflections and maximizing transmission across wide spectrum.
Dispersion: ( the separation of white light into its constituents colors when
passing trough a crystal, caused by different wavelengths of light having slightly different refractive indices). In single crystal MgF2 the dispersion mechanism is based on electronic polarization of the ions within the crystal lattice; essentially, the displacement of the negatively charged fluoride ions relative to the positively charged magnesium ions when exposed to light, causes a refractive indices variations within wavelengths, leading to dispersion.
Polycrystalline: Polycrystalline solid of MgF2 consists of many individual grains or crystallites that are basically small single crystals of MgF2 separated by grain boundries. On a large scale , there is no periodicity across polycrystalline boule but there is periodicity within each grain that can measure up to several mm in diameter. Polycrystalline MgF2 exhibits somewhat different optical properties that still find to be useful depending on the type of the applications.
Birefringence of polycrystalline MgF2 varies depending on the grain orientation, potentially impacting polarization properties. Polycrystalline MgF2 presents more light scattering at the grain boundries, which can lead to image degradation and reduced clarity. However, in the infrared optics it is OK to use polycrystalline material, there scattering form grain boundries becomes less significant. Resistant to breakage: Grain boundries in the polycrystalline material impede the movement of dislocations in crystal thus provide better resistance to deformation and breakage, making crystal stronger. Powder: consists of micron to mm size crystallites of high purity. In powder form MgF2 is typically used as a coating material.
