Germanium lenses are optical lenses made of polished germanium. These lenses are rugged and resistant to corrosion, and are ideal for harsh environments and applications where there is constant exposure to the elements.
At Shanghai Optics we manufacture a wide variety of germanium lenses with various anti reflection coatings. Spherical plano-concave, p-convex, concave-convex and aspheric lenses are all available in a wide variety of sizes. We are also able to accommodate special orders should you need a size, shape or AR coating.
Our germanium lenses have a high refractive index—the highest refractive index among readily available IR transmitters. It also exhibits minimal chromatic aberration due to low dispersion. Because of these properties, Ge lenses are ideal for use in infrared (FLIR and FTIR) field applications. Other applications include thermal imaging systems and precision analytic instruments which may be used in harsh environments.
It is the special hardness of germanium that gives it its unique ruggedness; Ge has a Knoop hardness of 780. It is a high density material, at 5.33 g/cm3, and allowances must be made for this weight if you are designing a weight sensitive system.
Germanium is also subject to thermal runaway. What this means is that the transmission will decrease as temperature increases, and the lens becomes opaque. Because of this thermal runaway effect, germanium lenses should only be used at temperatures below 100°C.
Germanium has optimal transmission (over 45%) in the 2-12 μm band, which makes it most useful for mid-infrared light. With anti-reflective coatings, transmission can be brought up to about 95%.
Types of Germanium Lenses
Shanghai Optics manufactures custom spherical plano-concave, p-convex, concave-convex and aspheric germanium lenses.
Our spherical plano-concave germanium lenses are primarily used to diverge a beam from a collimated light source, or to increase the focal length of an optical system. They may be used in beam expanders, and can also be used to balance out aberrations which were introduced by other lenses in an optical arrangement.
Plano-convex Ge lenses are flat on one side and convex on the other. These lenses have a positive focal length, and are often used for light collimation. They can also be used in focusing applications, and have widespread use in various fields, from science to industry to defense. We recommend these lenses be oriented so that the flat side faces the desired focal plane.
Our concave convex germanium lenses have one concave side (depressed inward) and one convex side (bulging outwards).
Our aspheric lenses have a more complex front. The curvature gradually changes as you move from the center of the lens out to the edge. Our aspheric Ge lenses are most often used to eliminate spherical aberration in an optical system. Adding an aspheric lens into an optical assembly has the potential to greatly simplify the system, and even the addition of relatively heavy germanium lens may actually decrease the systems weight.
Germanium Lens Factory Specifications
Shanghai Optics manufactures quality germanium lenses in a range of popular sizes, from 5m m to 350 mm in diameter. Our standard anti reflective coating is best suited for light transmissions between 3 and 12 μm. The focal length of our lenses is determined up to a +/-1% tolerance, and the surface flatness is l/4 @ 633nm.
The surface quality of our factory standard germanium lenses is 20-10 scratch dig, after coating. This is considered precision quality and is suitable for most laser applications.
Factory Standards
- Substrate Material: Ge (Germanium)
- Diameter: 5mm-350mm
- Shape: Spherical Plano-Concave, P-Convex, Concave-Convex or Aspheric
- Focal length: +/-1%
- Surface Quality: 20-10 (after coating)
- Surface figure: l/4 @ 633nm
- Clear Aperture: >85% of central dimension
- Antireflection Coating: @ 3-12 um
Contact us for manufacturing limit or custom specifications.
