Germanium Lenses

27Feb, 2018

A. Optical Components Ltd. has a diverse line of optics products that are specially customized based on clients’ requests. All manufacturing processes follow stringent specifications by legitimate authorities such as US Military Surface Quality Spec standards (MIL-0-13830A) and Deutsche Industrie (DIN) standards. Their manufacturing facilities are run by an experienced staff of engineers, technicians, production managers, and quality inspectors committed to superior quality.

One of the company’s premium products is its custom-made optical lenses. Lenses are made from various materials, but the material that will be thoroughly discussed in this article is Germanium. The lenses are made to perform various functions – either made to precision or of commercial quality. The company is capable of delivering a high-quality single, doublets, and triplets lenses, among many others. Single, doublets and triplets lenses all adhere to certain specifications which A. Optical follows. For instance, to achieve centration specification for a doublet, each element must be individually centered to a tighter specification and the two optical axes must be carefully aligned during the cementing process. For triplets, three optical axes must be aligned to result in a maximum angular deviation. The company also creates optical lenses of various intricate shapes. The lenses are available as cylinders and toroids.

Germanium Lenses – is a Chemical Element that is Grown Using the Czochralski Technique

One of the materials that A. Optical uses for its lenses is Germanium. Germanium is a chemical element that is grown using the Czochralski technique. There are only a few manufacturers around the world who do this.

Germanium (Ge) is a kind of material that is relatively hard and has a high density. Germanium, along with Silicon and Zinc Selenide (ZnSe) is all used in pyrometric applications. It is also an infrared-transmitting material that blocks ultraviolet (UV) and VIS wavelengths but allows IR from 2µm.

Among commonly available IR-transmitters, Germanium has the highest refractive index. The refractive index of Germanium changes very rapidly with temperature and the material becomes opaque at all wavelengths a little above 350K as the bandgap floods with thermal electrons. This means it has good thermal conductivity. It is subject to thermal runaway, meaning that the transmission decreases as temperature increases. Ge is also non-hygroscopic and non-toxic. It also has low optical dispersion, excellent surface hardness, and good strength. This means that it is an advantageous material in aspects of lens design where its refractive index allows otherwise impossible specifications to be built. With its very high refractive index, Anti-Reflective (AR) coating is recommended. With Germanium, there is a minimal chromatic aberration due to low dispersion.

Germanium transmits over 45% between 2-14μm up to 45⁰C but transmission degrades slowly at 100⁰C then more rapidly above 200⁰C. When Germanium is exposed to higher temperatures, it can lead to catastrophic failure in the material so it is actually not suitable for use in these particular conditions. Also, where weight is an issue, its relatively high density (5.33 g/cm3) should be put into consideration. Germanium has a Knoop hardness of HK780, slightly higher than Gallium Arsenide (GaAs), with which shares the same mechanical properties. This makes it ideal for IR applications requiring rugged optics.

Germanium is transparent in the infrared wavelengths. It is an essential optical material for Infrared (IR) because it can be readily cut and polished into lenses.

Germanium (Ge) Optics is applied in various Infrared (IR) systems. Its two most notable properties, which are its high index of refraction and its low optical dispersion make it very applicable for use in wide-angle camera lenses, microscopy, and in the optical fiber industry, which used up 60% of the annual germanium yield in 2002. It can also be used as a front optic in thermal imaging cameras with an 8-14 micron range for passive thermal imaging and for hot-spot detection. These are useful in the military, particularly for mobile night vision and fire-fighting. This element can also be used in the following areas: thermal imaging, spectroscopy, or monochromatic light sources such as quantum cascade lasers.

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