MgF2 Windows

Optical windows are used to allow optical radiation to pass from one environment to another without allowing other elements of these environments to mix. And it does not change the wavelength distribution of the beam, the transmitted wavefront, nor does it scatter any of the light out of the beam.

MgF2 Window: Applications and Optical Properties

A MgF₂ window is an optical window manufactured from crystalline Magnesium Fluoride. This hard, durable optical material lends itself well to use under harsh conditions. It is highly resistant to chemical etching as well as mechanical and thermal shock. It also has a high laser damage threshold.

MgF₂ exhibits excellent broadband transmission from 120 nm to 8 μm , from the deep UV to the mid infrared. This makes them a good choice for UV radiation sources and receivers as well as for use at the Hydrogen Lyman-alpha line. They are often used as UV viewpoints, and are a good option for UV polarizers and excimer laser applications. It has a high transmittance between 120 nm and 8 µm, and between 0.4-5.0 µm transmits over 90%.

MgF₂ has a melting point of 1255 degrees Celsius. It has a density of 3.177 g/cm3, and a tetragonal crystal type. Our optical windows are typically oriented with the round surfaces perpendicular to the c-axis of the MgF₂ crystal to minimize birefringence.  Custom random cut MgF2 windows can be manufactured on request.

MgF₂ is the only optical material which combines a wide spectral transmission band with birefringence. This birefringence means that the refractive index depends on the polarization and propagation direction of light. Because of birefringence, a MgF2 window can exhibit double refraction, so that a ray of light will be split by polarization into two rays with different paths.

The ray component for which the optical window has a higher effective refractive index is called the slow ray, while the one with the lower effective refractive index is referred to as the fast ray. If a beam enters the MgF2 window from air, the slow ray will be refracted more towards normal.

Since MgF2 is softer than fused silica, care should be taken when handling. It is the hardest of the optical fluorides, however at HK576.

Factory Standards for Shanghai Optics MgF2 Windows

We offer Magnesium Fluoride Windows in a wide range of sizes, from 3.5 to 25.4 mm. Thickness is 1.0 to 3.0 mm.  The factory standard of our MgF2 windows dictates a diameter tolerance of +0.0, – 0.05mm and a thickness tolerance of  +/- 0.1mm. This is considered precision quality in the industry.

The clear aperture of our windows is greater than 90 percent, and the wavefront distortion no more than l/4 per 25 mm.

Parallelism of our windows refers to the sameness of orientation of the two planar surfaces. Our factory standard dictates a maximum deviation of 5 arc min.

The factory standard scratch dig number of our Magnesium Fluoride Windows is 40-20, which is precision quality. These numbers designate how scratch and dig size compare with a reference in MIL-PRF-13830B specifications. The number 40 means that any scratches on the surface of the window are no brighter tan those designated 40 in the specification. The sum of all 40-degree scratch lengths may not exceed ¼ of the diameter of the window.  The dig number, 20, means that the maximum allowable size of digs, or pits, in the surface of the optic is 0.2 mm. The total number of 0.2 mm digs may not exceed the diameter divided by twenty.

Factory Standard 

• Material: MgF2
• Irregularity (fringe): l/4
• Diameter Tolerance: +0.0, -0.05mm
• Thickness Tolerance: +/- 0.1mm
• Clear Aperture: >90%
• Parallelism: 5 arc min
• Surface Quality: 40-20
• Wavefront Distortion: l/4 per 25mm

Contact us for manufacturing limit or custom specifications.

Protective Bevel available